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Harmonics measured by Warren. How bad?


Ashhar Farhan
 

Peeps,

Let me put some of the discussions on harmonic and spur purity of ubitx in context. This is going to be a long read, so bear with me as we plod through this. At the outset, I must thank Allison, Arv, Raj and Warren for their deep dives into these challenges.

Before I deep dive into these numbers, let me sum it up for those who just want the headline :

The ubitx put out harmonics less than 2 milliwatts on all the bands. That's well below what a 'commercially designed', well behaved, FCC compliant, 100 watt commerical set would spew out. There are some easy fixes. 

Now, onto the details:

Let's consider a no-name, standard issue, 100 watt HF transceiver with the harmonics below the required -43 dbc level. 100 watts is +50dbm. +50dbm - 43 dbc = +7dbm. That is about 5 milliwatts in harmonics. This is what we live with on air with all those factory built rigs. 5 milliwatts of harmonics. If you add a linear it can even get worse. An SB-220 after an Elecraft K2, will put out almost a watt of harmonics.

Now, consider our 10 watt ubitx. You can see the scans done by Warren. They are on https://groups.io/g/BITX20/album?id=65861. He has helpfully drawn a green line across the scans. The green line is the -43dbc line. Apart from the actual signal, everything else must stay below the green line as per the FCC guideline.

Let's sum up the report :

20 meters: SSB harmonics are higher by 4db, CW is good (https://groups.io/g/BITX20/photo/65861/4?p=Name,,,20,1,0,0).
30 meters: CW harmonics are 4db above the required level. SSB is not allowed anyway (https://groups.io/g/BITX20/photo/65861/5?p=Name,,,20,1,0,0)
40 meters: SSB is 3db above the green line, CW is even higher by 10 db (https://groups.io/g/BITX20/photo/65861/6?p=Name,,,20,1,0,0)
80 meters: SSB is within the spec, CW is out of spec by 5 db (https://groups.io/g/BITX20/photo/65861/8?p=Name,,,20,1,0,0)

To sum it up:
SSB: it is within the rulebook everywhere except on 20M & 40M by 3 db.
CW: it is within the rulebook except on  on 30M, 40M & 80 M.

So, what's the problem and how is it cured?

First: the trouble seems to be more with CW than SSB harmonics. We can reduce the CW level by decreasing the CW drive level. This is determined by the amount of current that flows into the front-end diode mixer by
changing the R105 to a higher value resistor. I guess one can also do this in software by reducing the CLOCK #2 current to 2 ma from 8 ma when in CW. This will clear CW for all the bands.

Second: the alignment as it comes out from HF signals will show far better harmonic suppression than being reported here. For instance, the -38 dbc on 20 meters and -30 db on 40 meters will almost disappear if you balanace it out with the bias on the IRF510s. The factory alignment works like this : First crank up both the IRF510s for 100 ma standing current on each, then tweak one of them to null out the harmonics. It is like balancing out the carrier on diode modulator.

Third: below 14 MHz, the IRF510s are distorting with too much drive. If you back off the drive to adjust to a leve of 7 watts, the harmonics will climb down to be within the spec. (Remember that the harmonics are not present at the output of the 45Mhz-to-HF mixer, they are generated in the power chain). This was also allison's suggestion.

Future revisions:
We use 3 section low pass filters made out of micrometals' toroids and  C0G caps from AVX. Most commercial sets use only 2 section low pass filters.  And yes, we can change the relays. I doubt if the problem is the relays. If it were so, it would be worse on the higher bands. The fact that the harmonics are climbing at the lower frequencies points to overdrive, not filter design. The filter layout etc is less critical on the lower bands as opposed to higher bands.

I guess that we we really need is a good transmit side ALC to cut the drive on lower bands. The gain varies by as more than 10 db across the spectrum from 3 Mhz to 30 MHz. Given that we want to keep the design to use what is available in a regular junkbox, this is a challenge to overcome with IRF510s and general purpose transistors. Allison has tried using 2N2222As with some success. 

So, in a nutshell, here is the summary:

The ubitx remains less polluting than a 100 watt commercial rig that works within the FCC requirements. The harmonics at 14 Mhz and below can be controlled by backing off the drive level. 

I would like to hear contrary views and figures. As I said before, unlike a commercially made radio, ubitx will thrive on critical feedback and design suggestions. This only gets better with time, like any good open source design.

Thanks all for the inputs,

- f


Jerry Gaffke
 

I mostly agree.

I'm OK with folks using this rig in those modes where it's maybe 2 or 3 dB off.
If 10dB, not so much.

The goal should be to meet standards on at some point, and to do so
without the aid of a spectrum analyzer or similar while tweaking it. 
I think this will require repeatable gains in some of the amps, the 45mhz IF comes to mind.

On the Bitx40, it was necessary for Allard to drive the modulator pretty hard to unbalance it
sufficiently on all rigs.  Could be we will need a pot at R104 to deal with rig variations.

Curious that Allison's spur at 45mhz - OperatingFreq does not show up in Warren's plots as an issue.

Would be nice to do everything with 2n2222's and 2n3904's,
but I think works and cheap and available from online distributors are the primary criteria.
Not many people have even half the parts for a uBitx in their junkbox.

Will be interesting to see what a few more rigs look like, and exactly
where and how much they are failing to meet spec. 

Jerry, KE7ER


On Thu, Aug 9, 2018 at 10:22 PM, Ashhar Farhan wrote:
Let me put some of the discussions on harmonic and spur purity of ubitx in context.


Warren Allgyer <allgyer@...>
 

Ashhar

I respectfully disagree with the main point of your premise, to paraphrase: "The uBitx is ok because it has less spurious emissions than are allowed for a commercial amateur transceiver operating at 100 watts or a transceiver/amplifier operating at 1500 watts". There are two things wrong with this premise, 1) Modern commercial transceivers are specified to have emissions at least 50 dB below carrier level; many are specified at 60 dB or more. Such transceivers have spurious emissions far below those of the uBitx even when operated at 100 or 200 watts. 2) Unfortunately that is not how the rules are written or applied by the respective governing bodies. The allowed level of emissions must be 43 dB below carrier level, 50 dB in most countries other than the USA, regardless what that carrier level may be. That may not seem logical but that is the rule that is a condition of our license and that we committed to uphold when we received it.

The compliance of my uBitx with these rules is summarized here:



You have addressed only the recently discovered harmonics issues. And my unit, as you have noted, is not disqualified by excessive harmonics on bands above 17 meters. Unfortunately, on those bands, it is disqualified by the previously discovered "45 MHz minus carrier" spurs.

You say "First: the trouble seems to be more with CW than SSB harmonics. We can reduce the CW level by decreasing the CW drive level."

Perhaps, but I think you will find that the harmonics on CW are far more a function of putting the harmonic rich square wave output of the Si5351 directly into the transmitter signal chain without filtering. The reason the CW versus SSB issue disappears in the high bands is because the circuitry itself acts as a filter "rounding" out the square waves at these higher frequencies. I don't think your proposed drive level change will affect CW harmonics but it is worth a try.

You have written "Second: the alignment as it comes out from HF signals will show far better harmonic suppression than being reported here. For instance, the -38 dbc on 20 meters and -30 db on 40 meters will almost disappear if you balanace it out with the bias on the IRF510s. The factory alignment works like this : First crank up both the IRF510s for 100 ma standing current on each, then tweak one of them to null out the harmonics. It is like balancing out the carrier on diode modulator."

The harmonics causing the problem in my screen shots are odd harmonics; 3rd, 5th, 7th, 9th etc. The alignment procedure you recommend only affects even harmonics due to the cancellation effect of the push-pull PA. It has no effect whatsoever on odd harmonics and, in fact, had been optimized just as you describe before my testing.

You say: "Third: below 14 MHz, the IRF510s are distorting with too much drive. If you back off the drive to adjust to a leve of 7 watts, the harmonics will climb down to be within the spec."

Sorry, but not so for my tests. As noted in my text, all harmonic screenshots were taken with drive reduced to result in a consistent power output for each band of +33 dBm, 2 watts. This was done precisely to avoid overdriving any stage of the transmission chain. At maximum drive, particularly on 80 and 40 meters the harmonics are considerably worse.

Your filter designs and components as supplied are adequate for the PA filtering application. Removed from the board and laid out in a linear fashion with no relays, the filters exhibit well over 55 dB of attenuation at the 3rd harmonic and higher for each band. The primary limiting factor is the strategy of running the input and output of each filter through at least one common relay; lower bands do this with two or all three of the relays. Input to output crosstalk within the relay becomes the first and most substantial contributor to the "blow-by" of harmonics bypassing the filters. The second factor is the "daisy chaining" of the low frequency signals through multiple relays. Finally, a high power PA harmonic filter must have extremely high overall isolation between the input and output of the assembly. The long traces and circuitous routing on the board to connect all of these relays contributes to lack of input/output isolation. When laid out on the board and routed through the relays the filters exhibit on the order of 25 dB attenuation at harmonic frequencies; far too little to be compliant.

The relays per se are not the problem.

It may be possible to make the uBitx compliant with only better PA filter layout: No sharing of relays between filter inputs and outputs, no daisy-chaining of relays, more straightforward PCB layout. However, due to the "45 MHz - carrier" spur issue such filters would need to be BPF rather than LPT. Alternatively, a 4-6 filter assembly, switched in conjunction with the PA filter and placed between the first mixer and the drive chain would likely clean up the signals to the point that the existing filter arrangement may work.

Based on the discussion here and a parallel one on the Facebook uBitx page, I do not believe my results are "sample of one" or the result of a defective unit. That, however, remains a possibility until someone publishes data assembled with similar care to refute them.

I love the concept of uBitx. I want it to work and work well. I sympathize with the pragmatic concept that "it makes less spur power than an high power commercial rig" but that is not the rule. And you can already see the number of people who connect the uBitx to linear amplifiers on the assumption they are starting out with a compliant radio but they are not. 

I cannot, in good conscience, put my unit on the air as it stands. Each amateur radio operator needs to be guided by his or her conscience in this matter. But if the decision is made to go ahead it should be made with the full knowledge that it is a violation to do so.

Thanks for soliciting responses and for listening.

WA8TOD 


Gordon Gibby <ggibby@...>
 

Thanks much for the great information.  I’ll be able to share it with those building this rig in our group.  

I think personally it’s important that this design become more than compliant, even without special special adjustments.   I suspect that will be coming.  

When I am able, I am going to try the little daughter board with relays on the far side of the filters so as to avoid the “blow by” in the single relay switching both sides of a filter.  There will still need to be a bit of daisychaining. If that gets me down 10 DB or so allowing more of the excellent filters to shine through, I’ll be quite happy.  

I would like to be able to run this rig into an amplifier for WINLINK or ALE service, on the lower bands, and that would be important to accomplish before running it through an amplifier.  

The spurs are a different issue, and don’t affect bands that I use very often. So I’ll let others fix those. 

Cheers, 

Gordon
 






On Aug 10, 2018, at 03:45, Warren Allgyer <allgyer@...> wrote:

Ashhar

I respectfully disagree with the main point of your premise, to paraphrase: "The uBitx is ok because it has less spurious emissions than are allowed for a commercial amateur transceiver operating at 100 watts or a transceiver/amplifier operating at 1500 watts". There are two things wrong with this premise, 1) Modern commercial transceivers are specified to have emissions at least 50 dB below carrier level; many are specified at 60 dB or more. Such transceivers have spurious emissions far below those of the uBitx even when operated at 100 or 200 watts. 2) Unfortunately that is not how the rules are written or applied by the respective governing bodies. The allowed level of emissions must be 43 dB below carrier level, 50 dB in most countries other than the USA, regardless what that carrier level may be. That may not seem logical but that is the rule that is a condition of our license and that we committed to uphold when we received it.

The compliance of my uBitx with these rules is summarized here:

<Screen Shot 2018_08_10 at 2.51.25 AM.jpg>

You have addressed only the recently discovered harmonics issues. And my unit, as you have noted, is not disqualified by excessive harmonics on bands above 17 meters. Unfortunately, on those bands, it is disqualified by the previously discovered "45 MHz minus carrier" spurs.

You say "First: the trouble seems to be more with CW than SSB harmonics. We can reduce the CW level by decreasing the CW drive level."

Perhaps, but I think you will find that the harmonics on CW are far more a function of putting the harmonic rich square wave output of the Si5351 directly into the transmitter signal chain without filtering. The reason the CW versus SSB issue disappears in the high bands is because the circuitry itself acts as a filter "rounding" out the square waves at these higher frequencies. I don't think your proposed drive level change will affect CW harmonics but it is worth a try.

You have written "Second: the alignment as it comes out from HF signals will show far better harmonic suppression than being reported here. For instance, the -38 dbc on 20 meters and -30 db on 40 meters will almost disappear if you balanace it out with the bias on the IRF510s. The factory alignment works like this : First crank up both the IRF510s for 100 ma standing current on each, then tweak one of them to null out the harmonics. It is like balancing out the carrier on diode modulator."

The harmonics causing the problem in my screen shots are odd harmonics; 3rd, 5th, 7th, 9th etc. The alignment procedure you recommend only affects even harmonics due to the cancellation effect of the push-pull PA. It has no effect whatsoever on odd harmonics and, in fact, had been optimized just as you describe before my testing.

You say: "Third: below 14 MHz, the IRF510s are distorting with too much drive. If you back off the drive to adjust to a leve of 7 watts, the harmonics will climb down to be within the spec."

Sorry, but not so for my tests. As noted in my text, all harmonic screenshots were taken with drive reduced to result in a consistent power output for each band of +33 dBm, 2 watts. This was done precisely to avoid overdriving any stage of the transmission chain. At maximum drive, particularly on 80 and 40 meters the harmonics are considerably worse.

Your filter designs and components as supplied are adequate for the PA filtering application. Removed from the board and laid out in a linear fashion with no relays, the filters exhibit well over 55 dB of attenuation at the 3rd harmonic and higher for each band. The primary limiting factor is the strategy of running the input and output of each filter through at least one common relay; lower bands do this with two or all three of the relays. Input to output crosstalk within the relay becomes the first and most substantial contributor to the "blow-by" of harmonics bypassing the filters. The second factor is the "daisy chaining" of the low frequency signals through multiple relays. Finally, a high power PA harmonic filter must have extremely high overall isolation between the input and output of the assembly. The long traces and circuitous routing on the board to connect all of these relays contributes to lack of input/output isolation. When laid out on the board and routed through the relays the filters exhibit on the order of 25 dB attenuation at harmonic frequencies; far too little to be compliant.

The relays per se are not the problem.

It may be possible to make the uBitx compliant with only better PA filter layout: No sharing of relays between filter inputs and outputs, no daisy-chaining of relays, more straightforward PCB layout. However, due to the "45 MHz - carrier" spur issue such filters would need to be BPF rather than LPT. Alternatively, a 4-6 filter assembly, switched in conjunction with the PA filter and placed between the first mixer and the drive chain would likely clean up the signals to the point that the existing filter arrangement may work.

Based on the discussion here and a parallel one on the Facebook uBitx page, I do not believe my results are "sample of one" or the result of a defective unit. That, however, remains a possibility until someone publishes data assembled with similar care to refute them.

I love the concept of uBitx. I want it to work and work well. I sympathize with the pragmatic concept that "it makes less spur power than an high power commercial rig" but that is not the rule. And you can already see the number of people who connect the uBitx to linear amplifiers on the assumption they are starting out with a compliant radio but they are not. 

I cannot, in good conscience, put my unit on the air as it stands. Each amateur radio operator needs to be guided by his or her conscience in this matter. But if the decision is made to go ahead it should be made with the full knowledge that it is a violation to do so.

Thanks for soliciting responses and for listening.

WA8TOD 


iz oos
 

Gordon, you want to use the uBitx with an amplifier. Some people warn not to use it with an amplifier which would make things worse. Suppose you use the uBitx as is with a push pull amplifier that has 43db attenuation on the third harmonics and beyond. My question is, would such a setup be comply to FCC or ITU?


Il 10/ago/2018 12:13, "Gordon Gibby" <ggibby@...> ha scritto:
Thanks much for the great information.  I’ll be able to share it with those building this rig in our group.  

I think personally it’s important that this design become more than compliant, even without special special adjustments.   I suspect that will be coming.  

When I am able, I am going to try the little daughter board with relays on the far side of the filters so as to avoid the “blow by” in the single relay switching both sides of a filter.  There will still need to be a bit of daisychaining. If that gets me down 10 DB or so allowing more of the excellent filters to shine through, I’ll be quite happy.  

I would like to be able to run this rig into an amplifier for WINLINK or ALE service, on the lower bands, and that would be important to accomplish before running it through an amplifier.  

The spurs are a different issue, and don’t affect bands that I use very often. So I’ll let others fix those. 

Cheers, 

Gordon
 






On Aug 10, 2018, at 03:45, Warren Allgyer <allgyer@...> wrote:

Ashhar

I respectfully disagree with the main point of your premise, to paraphrase: "The uBitx is ok because it has less spurious emissions than are allowed for a commercial amateur transceiver operating at 100 watts or a transceiver/amplifier operating at 1500 watts". There are two things wrong with this premise, 1) Modern commercial transceivers are specified to have emissions at least 50 dB below carrier level; many are specified at 60 dB or more. Such transceivers have spurious emissions far below those of the uBitx even when operated at 100 or 200 watts. 2) Unfortunately that is not how the rules are written or applied by the respective governing bodies. The allowed level of emissions must be 43 dB below carrier level, 50 dB in most countries other than the USA, regardless what that carrier level may be. That may not seem logical but that is the rule that is a condition of our license and that we committed to uphold when we received it.

The compliance of my uBitx with these rules is summarized here:

<Screen Shot 2018_08_10 at 2.51.25 AM.jpg>

You have addressed only the recently discovered harmonics issues. And my unit, as you have noted, is not disqualified by excessive harmonics on bands above 17 meters. Unfortunately, on those bands, it is disqualified by the previously discovered "45 MHz minus carrier" spurs.

You say "First: the trouble seems to be more with CW than SSB harmonics. We can reduce the CW level by decreasing the CW drive level."

Perhaps, but I think you will find that the harmonics on CW are far more a function of putting the harmonic rich square wave output of the Si5351 directly into the transmitter signal chain without filtering. The reason the CW versus SSB issue disappears in the high bands is because the circuitry itself acts as a filter "rounding" out the square waves at these higher frequencies. I don't think your proposed drive level change will affect CW harmonics but it is worth a try.

You have written "Second: the alignment as it comes out from HF signals will show far better harmonic suppression than being reported here. For instance, the -38 dbc on 20 meters and -30 db on 40 meters will almost disappear if you balanace it out with the bias on the IRF510s. The factory alignment works like this : First crank up both the IRF510s for 100 ma standing current on each, then tweak one of them to null out the harmonics. It is like balancing out the carrier on diode modulator."

The harmonics causing the problem in my screen shots are odd harmonics; 3rd, 5th, 7th, 9th etc. The alignment procedure you recommend only affects even harmonics due to the cancellation effect of the push-pull PA. It has no effect whatsoever on odd harmonics and, in fact, had been optimized just as you describe before my testing.

You say: "Third: below 14 MHz, the IRF510s are distorting with too much drive. If you back off the drive to adjust to a leve of 7 watts, the harmonics will climb down to be within the spec."

Sorry, but not so for my tests. As noted in my text, all harmonic screenshots were taken with drive reduced to result in a consistent power output for each band of +33 dBm, 2 watts. This was done precisely to avoid overdriving any stage of the transmission chain. At maximum drive, particularly on 80 and 40 meters the harmonics are considerably worse.

Your filter designs and components as supplied are adequate for the PA filtering application. Removed from the board and laid out in a linear fashion with no relays, the filters exhibit well over 55 dB of attenuation at the 3rd harmonic and higher for each band. The primary limiting factor is the strategy of running the input and output of each filter through at least one common relay; lower bands do this with two or all three of the relays. Input to output crosstalk within the relay becomes the first and most substantial contributor to the "blow-by" of harmonics bypassing the filters. The second factor is the "daisy chaining" of the low frequency signals through multiple relays. Finally, a high power PA harmonic filter must have extremely high overall isolation between the input and output of the assembly. The long traces and circuitous routing on the board to connect all of these relays contributes to lack of input/output isolation. When laid out on the board and routed through the relays the filters exhibit on the order of 25 dB attenuation at harmonic frequencies; far too little to be compliant.

The relays per se are not the problem.

It may be possible to make the uBitx compliant with only better PA filter layout: No sharing of relays between filter inputs and outputs, no daisy-chaining of relays, more straightforward PCB layout. However, due to the "45 MHz - carrier" spur issue such filters would need to be BPF rather than LPT. Alternatively, a 4-6 filter assembly, switched in conjunction with the PA filter and placed between the first mixer and the drive chain would likely clean up the signals to the point that the existing filter arrangement may work.

Based on the discussion here and a parallel one on the Facebook uBitx page, I do not believe my results are "sample of one" or the result of a defective unit. That, however, remains a possibility until someone publishes data assembled with similar care to refute them.

I love the concept of uBitx. I want it to work and work well. I sympathize with the pragmatic concept that "it makes less spur power than an high power commercial rig" but that is not the rule. And you can already see the number of people who connect the uBitx to linear amplifiers on the assumption they are starting out with a compliant radio but they are not. 

I cannot, in good conscience, put my unit on the air as it stands. Each amateur radio operator needs to be guided by his or her conscience in this matter. But if the decision is made to go ahead it should be made with the full knowledge that it is a violation to do so.

Thanks for soliciting responses and for listening.

WA8TOD 


Gordon Gibby <ggibby@...>
 

Hi iz—

Don’t know, but I wouldn’t recommend it. This is easy enough to fix, so why not fix it?  I would just use fixed bandpass output filters, but WINLINK & ALE both require fast electronic bandswitching. 

I picked up a little amp with a set of Lowpass  filters on eBay.   It will be sometime, but eventually I’ll add the extra relays and I think this will be a non-issue....  someone may easily beat me to it

Found a spectrum analyzer for $165, I may get that.   I’m getting old, and I don’t have forever.  

Gordon 



On Aug 10, 2018, at 06:56, iz oos <and2oosiz2@...> wrote:

Gordon, you want to use the uBitx with an amplifier. Some people warn not to use it with an amplifier which would make things worse. Suppose you use the uBitx as is with a push pull amplifier that has 43db attenuation on the third harmonics and beyond. My question is, would such a setup be comply to FCC or ITU?


Il 10/ago/2018 12:13, "Gordon Gibby" <ggibby@...> ha scritto:
Thanks much for the great information.  I’ll be able to share it with those building this rig in our group.  

I think personally it’s important that this design become more than compliant, even without special special adjustments.   I suspect that will be coming.  

When I am able, I am going to try the little daughter board with relays on the far side of the filters so as to avoid the “blow by” in the single relay switching both sides of a filter.  There will still need to be a bit of daisychaining. If that gets me down 10 DB or so allowing more of the excellent filters to shine through, I’ll be quite happy.  

I would like to be able to run this rig into an amplifier for WINLINK or ALE service, on the lower bands, and that would be important to accomplish before running it through an amplifier.  

The spurs are a different issue, and don’t affect bands that I use very often. So I’ll let others fix those. 

Cheers, 

Gordon
 






On Aug 10, 2018, at 03:45, Warren Allgyer <allgyer@...> wrote:

Ashhar

I respectfully disagree with the main point of your premise, to paraphrase: "The uBitx is ok because it has less spurious emissions than are allowed for a commercial amateur transceiver operating at 100 watts or a transceiver/amplifier operating at 1500 watts". There are two things wrong with this premise, 1) Modern commercial transceivers are specified to have emissions at least 50 dB below carrier level; many are specified at 60 dB or more. Such transceivers have spurious emissions far below those of the uBitx even when operated at 100 or 200 watts. 2) Unfortunately that is not how the rules are written or applied by the respective governing bodies. The allowed level of emissions must be 43 dB below carrier level, 50 dB in most countries other than the USA, regardless what that carrier level may be. That may not seem logical but that is the rule that is a condition of our license and that we committed to uphold when we received it.

The compliance of my uBitx with these rules is summarized here:

<Screen Shot 2018_08_10 at 2.51.25 AM.jpg>

You have addressed only the recently discovered harmonics issues. And my unit, as you have noted, is not disqualified by excessive harmonics on bands above 17 meters. Unfortunately, on those bands, it is disqualified by the previously discovered "45 MHz minus carrier" spurs.

You say "First: the trouble seems to be more with CW than SSB harmonics. We can reduce the CW level by decreasing the CW drive level."

Perhaps, but I think you will find that the harmonics on CW are far more a function of putting the harmonic rich square wave output of the Si5351 directly into the transmitter signal chain without filtering. The reason the CW versus SSB issue disappears in the high bands is because the circuitry itself acts as a filter "rounding" out the square waves at these higher frequencies. I don't think your proposed drive level change will affect CW harmonics but it is worth a try.

You have written "Second: the alignment as it comes out from HF signals will show far better harmonic suppression than being reported here. For instance, the -38 dbc on 20 meters and -30 db on 40 meters will almost disappear if you balanace it out with the bias on the IRF510s. The factory alignment works like this : First crank up both the IRF510s for 100 ma standing current on each, then tweak one of them to null out the harmonics. It is like balancing out the carrier on diode modulator."

The harmonics causing the problem in my screen shots are odd harmonics; 3rd, 5th, 7th, 9th etc. The alignment procedure you recommend only affects even harmonics due to the cancellation effect of the push-pull PA. It has no effect whatsoever on odd harmonics and, in fact, had been optimized just as you describe before my testing.

You say: "Third: below 14 MHz, the IRF510s are distorting with too much drive. If you back off the drive to adjust to a leve of 7 watts, the harmonics will climb down to be within the spec."

Sorry, but not so for my tests. As noted in my text, all harmonic screenshots were taken with drive reduced to result in a consistent power output for each band of +33 dBm, 2 watts. This was done precisely to avoid overdriving any stage of the transmission chain. At maximum drive, particularly on 80 and 40 meters the harmonics are considerably worse.

Your filter designs and components as supplied are adequate for the PA filtering application. Removed from the board and laid out in a linear fashion with no relays, the filters exhibit well over 55 dB of attenuation at the 3rd harmonic and higher for each band. The primary limiting factor is the strategy of running the input and output of each filter through at least one common relay; lower bands do this with two or all three of the relays. Input to output crosstalk within the relay becomes the first and most substantial contributor to the "blow-by" of harmonics bypassing the filters. The second factor is the "daisy chaining" of the low frequency signals through multiple relays. Finally, a high power PA harmonic filter must have extremely high overall isolation between the input and output of the assembly. The long traces and circuitous routing on the board to connect all of these relays contributes to lack of input/output isolation. When laid out on the board and routed through the relays the filters exhibit on the order of 25 dB attenuation at harmonic frequencies; far too little to be compliant.

The relays per se are not the problem.

It may be possible to make the uBitx compliant with only better PA filter layout: No sharing of relays between filter inputs and outputs, no daisy-chaining of relays, more straightforward PCB layout. However, due to the "45 MHz - carrier" spur issue such filters would need to be BPF rather than LPT. Alternatively, a 4-6 filter assembly, switched in conjunction with the PA filter and placed between the first mixer and the drive chain would likely clean up the signals to the point that the existing filter arrangement may work.

Based on the discussion here and a parallel one on the Facebook uBitx page, I do not believe my results are "sample of one" or the result of a defective unit. That, however, remains a possibility until someone publishes data assembled with similar care to refute them.

I love the concept of uBitx. I want it to work and work well. I sympathize with the pragmatic concept that "it makes less spur power than an high power commercial rig" but that is not the rule. And you can already see the number of people who connect the uBitx to linear amplifiers on the assumption they are starting out with a compliant radio but they are not. 

I cannot, in good conscience, put my unit on the air as it stands. Each amateur radio operator needs to be guided by his or her conscience in this matter. But if the decision is made to go ahead it should be made with the full knowledge that it is a violation to do so.

Thanks for soliciting responses and for listening.

WA8TOD 


Dennis Zabawa
 

If one puts this in the perspective of a simple, inexpensive, multi-band, SSB/CW, transceiver that is built from "junk box" parts, the  uBITX meets most criteria well.  The apparent cure for it's ills appears to be proper alignment and tuneup.  What many users are trying to do is to create the equivalent of a commercial radio, for peanuts, by driving it to the limits and amplifying it.  Don't blame the radio when it doesn't work well in that environment.


m5fra2@...
 

Good to see you have not been put off the rig Gordon. I have seen reports  on other channels of tests that do not confirm the current stuff that is flying around.

 

Colin – M5FRA

 

From: BITX20@groups.io <BITX20@groups.io> On Behalf Of Gordon Gibby
Sent: 10 August 2018 11:14
To: BITX20@groups.io
Subject: Re: [BITX20] Harmonics measured by Warren. How bad?

 

Thanks much for the great information.  I’ll be able to share it with those building this rig in our group.  

 

I think personally it’s important that this design become more than compliant, even without special special adjustments.   I suspect that will be coming.  

 

When I am able, I am going to try the little daughter board with relays on the far side of the filters so as to avoid the “blow by” in the single relay switching both sides of a filter.  There will still need to be a bit of daisychaining. If that gets me down 10 DB or so allowing more of the excellent filters to shine through, I’ll be quite happy.  

 

I would like to be able to run this rig into an amplifier for WINLINK or ALE service, on the lower bands, and that would be important to accomplish before running it through an amplifier.  

 

The spurs are a different issue, and don’t affect bands that I use very often. So I’ll let others fix those. 

 

Cheers, 

 

Gordon

 

 

 

 

 


On Aug 10, 2018, at 03:45, Warren Allgyer <allgyer@...> wrote:

Ashhar

I respectfully disagree with the main point of your premise, to paraphrase: "The uBitx is ok because it has less spurious emissions than are allowed for a commercial amateur transceiver operating at 100 watts or a transceiver/amplifier operating at 1500 watts". There are two things wrong with this premise, 1) Modern commercial transceivers are specified to have emissions at least 50 dB below carrier level; many are specified at 60 dB or more. Such transceivers have spurious emissions far below those of the uBitx even when operated at 100 or 200 watts. 2) Unfortunately that is not how the rules are written or applied by the respective governing bodies. The allowed level of emissions must be 43 dB below carrier level, 50 dB in most countries other than the USA, regardless what that carrier level may be. That may not seem logical but that is the rule that is a condition of our license and that we committed to uphold when we received it.

The compliance of my uBitx with these rules is summarized here:

<Screen Shot 2018_08_10 at 2.51.25 AM.jpg>

You have addressed only the recently discovered harmonics issues. And my unit, as you have noted, is not disqualified by excessive harmonics on bands above 17 meters. Unfortunately, on those bands, it is disqualified by the previously discovered "45 MHz minus carrier" spurs.

You say "First: the trouble seems to be more with CW than SSB harmonics. We can reduce the CW level by decreasing the CW drive level."

Perhaps, but I think you will find that the harmonics on CW are far more a function of putting the harmonic rich square wave output of the Si5351 directly into the transmitter signal chain without filtering. The reason the CW versus SSB issue disappears in the high bands is because the circuitry itself acts as a filter "rounding" out the square waves at these higher frequencies. I don't think your proposed drive level change will affect CW harmonics but it is worth a try.

You have written "Second: the alignment as it comes out from HF signals will show far better harmonic suppression than being reported here. For instance, the -38 dbc on 20 meters and -30 db on 40 meters will almost disappear if you balanace it out with the bias on the IRF510s. The factory alignment works like this : First crank up both the IRF510s for 100 ma standing current on each, then tweak one of them to null out the harmonics. It is like balancing out the carrier on diode modulator."

The harmonics causing the problem in my screen shots are odd harmonics; 3rd, 5th, 7th, 9th etc. The alignment procedure you recommend only affects even harmonics due to the cancellation effect of the push-pull PA. It has no effect whatsoever on odd harmonics and, in fact, had been optimized just as you describe before my testing.

You say: "Third: below 14 MHz, the IRF510s are distorting with too much drive. If you back off the drive to adjust to a leve of 7 watts, the harmonics will climb down to be within the spec."

Sorry, but not so for my tests. As noted in my text, all harmonic screenshots were taken with drive reduced to result in a consistent power output for each band of +33 dBm, 2 watts. This was done precisely to avoid overdriving any stage of the transmission chain. At maximum drive, particularly on 80 and 40 meters the harmonics are considerably worse.

Your filter designs and components as supplied are adequate for the PA filtering application. Removed from the board and laid out in a linear fashion with no relays, the filters exhibit well over 55 dB of attenuation at the 3rd harmonic and higher for each band. The primary limiting factor is the strategy of running the input and output of each filter through at least one common relay; lower bands do this with two or all three of the relays. Input to output crosstalk within the relay becomes the first and most substantial contributor to the "blow-by" of harmonics bypassing the filters. The second factor is the "daisy chaining" of the low frequency signals through multiple relays. Finally, a high power PA harmonic filter must have extremely high overall isolation between the input and output of the assembly. The long traces and circuitous routing on the board to connect all of these relays contributes to lack of input/output isolation. When laid out on the board and routed through the relays the filters exhibit on the order of 25 dB attenuation at harmonic frequencies; far too little to be compliant.

The relays per se are not the problem.

It may be possible to make the uBitx compliant with only better PA filter layout: No sharing of relays between filter inputs and outputs, no daisy-chaining of relays, more straightforward PCB layout. However, due to the "45 MHz - carrier" spur issue such filters would need to be BPF rather than LPT. Alternatively, a 4-6 filter assembly, switched in conjunction with the PA filter and placed between the first mixer and the drive chain would likely clean up the signals to the point that the existing filter arrangement may work.

Based on the discussion here and a parallel one on the Facebook uBitx page, I do not believe my results are "sample of one" or the result of a defective unit. That, however, remains a possibility until someone publishes data assembled with similar care to refute them.

I love the concept of uBitx. I want it to work and work well. I sympathize with the pragmatic concept that "it makes less spur power than an high power commercial rig" but that is not the rule. And you can already see the number of people who connect the uBitx to linear amplifiers on the assumption they are starting out with a compliant radio but they are not. 

I cannot, in good conscience, put my unit on the air as it stands. Each amateur radio operator needs to be guided by his or her conscience in this matter. But if the decision is made to go ahead it should be made with the full knowledge that it is a violation to do so.

Thanks for soliciting responses and for listening.

WA8TOD 


m5fra2@...
 

  • Found a spectrum analyzer for $165

Beware, there can be lots of issues with old SAs

 

From: BITX20@groups.io <BITX20@groups.io> On Behalf Of Gordon Gibby
Sent: 10 August 2018 12:17
To: BITX20@groups.io
Subject: Re: [BITX20] Harmonics measured by Warren. How bad?

 

Hi iz—

 

Don’t know, but I wouldn’t recommend it. This is easy enough to fix, so why not fix it?  I would just use fixed bandpass output filters, but WINLINK & ALE both require fast electronic bandswitching. 

 

I picked up a little amp with a set of Lowpass  filters on eBay.   It will be sometime, but eventually I’ll add the extra relays and I think this will be a non-issue....  someone may easily beat me to it

 

Found a spectrum analyzer for $165, I may get that.   I’m getting old, and I don’t have forever.  

 

Gordon 

 

 


On Aug 10, 2018, at 06:56, iz oos <and2oosiz2@...> wrote:

Gordon, you want to use the uBitx with an amplifier. Some people warn not to use it with an amplifier which would make things worse. Suppose you use the uBitx as is with a push pull amplifier that has 43db attenuation on the third harmonics and beyond. My question is, would such a setup be comply to FCC or ITU?

 

Il 10/ago/2018 12:13, "Gordon Gibby" <ggibby@...> ha scritto:

Thanks much for the great information.  I’ll be able to share it with those building this rig in our group.  

 

I think personally it’s important that this design become more than compliant, even without special special adjustments.   I suspect that will be coming.  

 

When I am able, I am going to try the little daughter board with relays on the far side of the filters so as to avoid the “blow by” in the single relay switching both sides of a filter.  There will still need to be a bit of daisychaining. If that gets me down 10 DB or so allowing more of the excellent filters to shine through, I’ll be quite happy.  

 

I would like to be able to run this rig into an amplifier for WINLINK or ALE service, on the lower bands, and that would be important to accomplish before running it through an amplifier.  

 

The spurs are a different issue, and don’t affect bands that I use very often. So I’ll let others fix those. 

 

Cheers, 

 

Gordon

 

 

 

 

 


On Aug 10, 2018, at 03:45, Warren Allgyer <allgyer@...> wrote:

Ashhar

I respectfully disagree with the main point of your premise, to paraphrase: "The uBitx is ok because it has less spurious emissions than are allowed for a commercial amateur transceiver operating at 100 watts or a transceiver/amplifier operating at 1500 watts". There are two things wrong with this premise, 1) Modern commercial transceivers are specified to have emissions at least 50 dB below carrier level; many are specified at 60 dB or more. Such transceivers have spurious emissions far below those of the uBitx even when operated at 100 or 200 watts. 2) Unfortunately that is not how the rules are written or applied by the respective governing bodies. The allowed level of emissions must be 43 dB below carrier level, 50 dB in most countries other than the USA, regardless what that carrier level may be. That may not seem logical but that is the rule that is a condition of our license and that we committed to uphold when we received it.

The compliance of my uBitx with these rules is summarized here:

<Screen Shot 2018_08_10 at 2.51.25 AM.jpg>

You have addressed only the recently discovered harmonics issues. And my unit, as you have noted, is not disqualified by excessive harmonics on bands above 17 meters. Unfortunately, on those bands, it is disqualified by the previously discovered "45 MHz minus carrier" spurs.

You say "First: the trouble seems to be more with CW than SSB harmonics. We can reduce the CW level by decreasing the CW drive level."

Perhaps, but I think you will find that the harmonics on CW are far more a function of putting the harmonic rich square wave output of the Si5351 directly into the transmitter signal chain without filtering. The reason the CW versus SSB issue disappears in the high bands is because the circuitry itself acts as a filter "rounding" out the square waves at these higher frequencies. I don't think your proposed drive level change will affect CW harmonics but it is worth a try.

You have written "Second: the alignment as it comes out from HF signals will show far better harmonic suppression than being reported here. For instance, the -38 dbc on 20 meters and -30 db on 40 meters will almost disappear if you balanace it out with the bias on the IRF510s. The factory alignment works like this : First crank up both the IRF510s for 100 ma standing current on each, then tweak one of them to null out the harmonics. It is like balancing out the carrier on diode modulator."

The harmonics causing the problem in my screen shots are odd harmonics; 3rd, 5th, 7th, 9th etc. The alignment procedure you recommend only affects even harmonics due to the cancellation effect of the push-pull PA. It has no effect whatsoever on odd harmonics and, in fact, had been optimized just as you describe before my testing.

You say: "Third: below 14 MHz, the IRF510s are distorting with too much drive. If you back off the drive to adjust to a leve of 7 watts, the harmonics will climb down to be within the spec."

Sorry, but not so for my tests. As noted in my text, all harmonic screenshots were taken with drive reduced to result in a consistent power output for each band of +33 dBm, 2 watts. This was done precisely to avoid overdriving any stage of the transmission chain. At maximum drive, particularly on 80 and 40 meters the harmonics are considerably worse.

Your filter designs and components as supplied are adequate for the PA filtering application. Removed from the board and laid out in a linear fashion with no relays, the filters exhibit well over 55 dB of attenuation at the 3rd harmonic and higher for each band. The primary limiting factor is the strategy of running the input and output of each filter through at least one common relay; lower bands do this with two or all three of the relays. Input to output crosstalk within the relay becomes the first and most substantial contributor to the "blow-by" of harmonics bypassing the filters. The second factor is the "daisy chaining" of the low frequency signals through multiple relays. Finally, a high power PA harmonic filter must have extremely high overall isolation between the input and output of the assembly. The long traces and circuitous routing on the board to connect all of these relays contributes to lack of input/output isolation. When laid out on the board and routed through the relays the filters exhibit on the order of 25 dB attenuation at harmonic frequencies; far too little to be compliant.

The relays per se are not the problem.

It may be possible to make the uBitx compliant with only better PA filter layout: No sharing of relays between filter inputs and outputs, no daisy-chaining of relays, more straightforward PCB layout. However, due to the "45 MHz - carrier" spur issue such filters would need to be BPF rather than LPT. Alternatively, a 4-6 filter assembly, switched in conjunction with the PA filter and placed between the first mixer and the drive chain would likely clean up the signals to the point that the existing filter arrangement may work.

Based on the discussion here and a parallel one on the Facebook uBitx page, I do not believe my results are "sample of one" or the result of a defective unit. That, however, remains a possibility until someone publishes data assembled with similar care to refute them.

I love the concept of uBitx. I want it to work and work well. I sympathize with the pragmatic concept that "it makes less spur power than an high power commercial rig" but that is not the rule. And you can already see the number of people who connect the uBitx to linear amplifiers on the assumption they are starting out with a compliant radio but they are not. 

I cannot, in good conscience, put my unit on the air as it stands. Each amateur radio operator needs to be guided by his or her conscience in this matter. But if the decision is made to go ahead it should be made with the full knowledge that it is a violation to do so.

Thanks for soliciting responses and for listening.

WA8TOD 


m5fra2@...
 

I plan to not exceed 5W output and cannot understand the desire to squeeze every last watt out of any rig. Try QRP you will be amazed, 5W is close to 2 stops down on 100W!

 

From: BITX20@groups.io <BITX20@groups.io> On Behalf Of Dennis Zabawa
Sent: 10 August 2018 13:02
To: BITX20@groups.io
Subject: Re: [BITX20] Harmonics measured by Warren. How bad?

 

If one puts this in the perspective of a simple, inexpensive, multi-band, SSB/CW, transceiver that is built from "junk box" parts, the  uBITX meets most criteria well.  The apparent cure for it's ills appears to be proper alignment and tuneup.  What many users are trying to do is to create the equivalent of a commercial radio, for peanuts, by driving it to the limits and amplifying it.  Don't blame the radio when it doesn't work well in that environment.


ajparent1/KB1GMX <kb1gmx@...>
 

Farhan,

Sorry, that comparison to a 100W radio does not pass.  

First its not a 100W radio, it is, a 10W, therefor the spec is -43dbc for FCC.  Its simple
and easy to measure and for our use close is fine.  However gross error of 10db is not.

For the harmonic issue:

The perspective I have is why is it that filters in isolation perform the job well but on the board fail
very badly.  The engineering of the filters was correct.  What is broken?  That is the problem to solve.

Myself and other have concluded the problem is a component, the board layout. The problem is
simple fixes are not effective enough and implementing better fixes is to say the least awkward and 
difficult for many.

The current solution and one that is known to work is external low pass filters.  

Allison


Ashhar Farhan
 

Allison,
I agree. What was your reading of harmonics on 40 meters? My own reading was that the harmonics were down by - 45dbc.
For the next set of pcbs, i will add another relay so that we dont snake around the LPFs. The PCB needs a revision. I am dead sure. 
- f

On Fri, 10 Aug 2018, 19:08 ajparent1/KB1GMX, <kb1gmx@...> wrote:
Farhan,

Sorry, that comparison to a 100W radio does not pass.  

First its not a 100W radio, it is, a 10W, therefor the spec is -43dbc for FCC.  Its simple
and easy to measure and for our use close is fine.  However gross error of 10db is not.

For the harmonic issue:

The perspective I have is why is it that filters in isolation perform the job well but on the board fail
very badly.  The engineering of the filters was correct.  What is broken?  That is the problem to solve.

Myself and other have concluded the problem is a component, the board layout. The problem is
simple fixes are not effective enough and implementing better fixes is to say the least awkward and 
difficult for many.

The current solution and one that is known to work is external low pass filters.  

Allison


Kees T
 

Farhan,

I disagree with using the comparison to 100W rigs for "actual effect". While it may make practical sense, that's not the rule, FCC or ITU.

There is a lot of opportunity for fixes, most have been covered by the various threads. The one I'm interested in is how to fix the existing V3/V4 boards and will continue to pursue that.

Thanks to all the guys with the really good Spectrum Analyzers and their efforts.

73 Kees K5BCQ


Doug W
 

On Fri, Aug 10, 2018 at 09:15 AM, Ashhar Farhan wrote:
For the next set of pcbs, i will add another relay so that we dont snake around the LPFs. The PCB needs a revision. I am dead sure. 
Probably not practical but would you ever consider a version of a new board that ships without components that could be scavenged and reused from a prior version board?  Would still make sense to have the factory do the cheap machine stuffed parts.
 
--
www.bitxmap.com


Gordon Gibby <ggibby@...>
 

​I just ordered relays, capacitors, and inductors....when I get a chance I'll lay out a simple board, or else build first prototype on perf board.   

Gordon




From: BITX20@groups.io <BITX20@groups.io> on behalf of Kees T <windy10605@...>
Sent: Friday, August 10, 2018 11:06 AM
To: BITX20@groups.io
Subject: Re: [BITX20] Harmonics measured by Warren. How bad?
 
Farhan,

I disagree with using the comparison to 100W rigs for "actual effect". While it may make practical sense, that's not the rule, FCC or ITU.

There is a lot of opportunity for fixes, most have been covered by the various threads. The one I'm interested in is how to fix the existing V3/V4 boards and will continue to pursue that.

Thanks to all the guys with the really good Spectrum Analyzers and their efforts.

73 Kees K5BCQ


berlenbach@...
 

Ashhar,

Thanks for responding to the issue. It's never fun.

As an alternative to Doug's suggestion, perhaps you could make a new retrofit filter section (board only or populated board). Something that less experienced builders could handle competently.

Bill VE7EAF


ajparent1/KB1GMX <kb1gmx@...>
 

Farhan,

I got -38 with reduced power (8w).  Turned up to 10W it was getting worse.  
Going to max (about 12W) was in the over drive region and less than -20DB.
I also noted that CW had about 3db more drive on two units.  That would
make it worse if the power is greater than 8W.

One if the locals who is not much for on line observed harmonics on his other
radio (7300)  asked me about it and I gave the situation.  He bypassed the all
but the T/R relay and uses an external manally switched filter built dead bug
using the parts off the board and worst band (80m) was -48DBC measured. 
Still has the 28mhz spur.   He plans to build a board to replace the 30mhz 9
element filter with band specific.   For that I suggested 3 low pass for 80-17
and band pass as that requires to no tuning.

For a re-spin of the board look at the carrier problem its not modulator leakage
as that checks out generally very good in isolation.  Also testing with T7
removed completely with D5 shows the same carrier level.  The filter works
though you get 3-5 db more carrier suppression and nearly 15db more stopband
if the crystal cans are grounded. The carrier leak is ground path coupled
and degrades the carrier suppression by a significant amount as a few
barely hit -29dbc.   I suspect being close to the mechanical edge of the
ground plane and the 12mhz IF amp being close are contributors.

Allison


Gordon Gibby <ggibby@...>
 

​Wow, allison --- great detective work!

This is going to be an awesome transceiver in the end.

gordon



From: BITX20@groups.io <BITX20@groups.io> on behalf of ajparent1/KB1GMX <kb1gmx@...>
Sent: Friday, August 10, 2018 12:08 PM
To: BITX20@groups.io
Subject: Re: [BITX20] Harmonics measured by Warren. How bad?
 

Farhan,

I got -38 with reduced power (8w).  Turned up to 10W it was getting worse.  
Going to max (about 12W) was in the over drive region and less than -20DB.
I also noted that CW had about 3db more drive on two units.  That would
make it worse if the power is greater than 8W.

One if the locals who is not much for on line observed harmonics on his other
radio (7300)  asked me about it and I gave the situation.  He bypassed the all
but the T/R relay and uses an external manally switched filter built dead bug
using the parts off the board and worst band (80m) was -48DBC measured. 
Still has the 28mhz spur.   He plans to build a board to replace the 30mhz 9
element filter with band specific.   For that I suggested 3 low pass for 80-17
and band pass as that requires to no tuning.

For a re-spin of the board look at the carrier problem its not modulator leakage
as that checks out generally very good in isolation.  Also testing with T7
removed completely with D5 shows the same carrier level.  The filter works
though you get 3-5 db more carrier suppression and nearly 15db more stopband
if the crystal cans are grounded. The carrier leak is ground path coupled
and degrades the carrier suppression by a significant amount as a few
barely hit -29dbc.   I suspect being close to the mechanical edge of the
ground plane and the 12mhz IF amp being close are contributors.

Allison


ajparent1/KB1GMX <kb1gmx@...>
 

On Thu, Aug 9, 2018 at 10:22 PM, Ashhar Farhan wrote:
Third: below 14 MHz, the IRF510s are distorting with too much drive. If you back off the drive to adjust to a leve of 7 watts, the harmonics will climb down to be within the spec. (Remember that the harmonics are not present at the output of the 45Mhz-to-HF mixer, they are generated in the power chain). This was also allison's suggestion.
This is true for SSB.  For CW your presenting a raw square  wave to the amplifier and most cases I've see about
3db stronger as well. this really shows below 10mhz (80 60 and 40m). Once your over 11mhz the 30mhz 9element filter
does a fair job of taming the square wave (third harmonic of 11 is 33mhz the cutoff frequency) so 20M tends to be cleanest.

Blaming the IRF510 for issues, its IMD is not great but OK.  Its harmonic production s a consequence of 
Load impedance, bias, and drive, issues all colliding.  BY that lack of fairly even gain at 20M its about 6db
down at the driver and if you push that it starts to distort so the IRF5100 are just amplifying that.  The load
impedance fo the IRF510s is about ideal at 80m but by 20M its way to high so they are in current starving (limiting)
and distortion is expected and it happens at more than about 5-6W.

A highly modified amp with much different transformers (all) with the IRF510s running comfortably
at 200ma each did not have issues with power out or distortion (harmonics and lowered IMD)
with a power level of 12W at 80m and 7W at 10M.  Also the third (strongest) harmonic was -30dbc
without any filters as I'd tapped in at the output of the amp to get around a board level feedback issue
(instability at about 16mhz).  So a reasonable filter would clean that up easily.

Allison


Bo Barry <bobarr@...>
 

Until some DISTANCE measurements are shown my only recommendation is that amplifiers should not be used! PERIOD!

During Field Day I heard our commercial Yaseu and Kenwood on at least THREE frequencies in my tent 100 yards away, so strong I had to avoid the areas of the band where they were!  The manufacturers did not provide filters, the club had to buy them!

I think the ubitx should be left at it is!  Until PSK reporter starts reporting harmonics!

Hey, unwanted emissions are everywhere. I made a QSO using a 100 watt light bulb when took poor to buy a dummy load!
Long live ubitx v4 at its CURRENT PRICE!