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questions about µBitX v4 power + spectral purity mods


Jonathan Washington
 

Hi all,

I have a few quick questions about a couple of the the µBitX mods listed at ubitx.net, and discussed in depth a couple years ago on this list.

1. Are Allison's suggestions for evening out power on the µBitX v4 still the recommended solution?  (Has there been anything else done on this front?)  I.e., is what's listed under "Answers so far" at

2. Does anyone have measurements of what the resulting output power across the bands is like?

3. Is there any reason these changes might be incompatible with the spurs (replacing L5 & L7) and harmonics (replacing the relays) fixes described here?  http://ubitx.net/spectral-purity/

I imagine it's in fact encouraged to address spectral purity issues before gaining more power on the upper bands.  But has anyone tested them together?  Are there some before/after measurements available?

I don't have the means to measure the efficacy of these mods myself, but I'm planning on doing all three, so I'm interested in hearing any results others have obtained.  In other words, I'd like to do them not because it says on the ubitx.net site "we think this works", but because someone(s) who's done it can share data or points of experience that demonstrate to me the extent to which it works.

--
Jonathan, KD5CFX


Ripley
 

Hello Jonathan,

When I built my v4 I did the mods to even out the power and improve the spectral purity documenting the results on QRZ. Click on this link. It has lots of before and after screen shots as I did each modification.  
https://forums.qrz.com/index.php?threads/ubitx-transceiver-semi-kit-build.624098/

Ripley
KD8UYQ


Don - KM4UDX
 

Jonathan, the uBITX is a delightful canvas -- it will carry and reflect your electrical and aesthetic paint.  [I just made that up.]

When I built my V4, I worried much about the same issues.  But, rather than spend effor on presumptive marginal signal compliance  issues, I put 24 volts to the finals, keep the audio drive in check, got the CEC software and a NEXTION screen install, hooked up my laptop, got Fldigi/WSJTX working, and had [have] a most rewarding experience on the air with voice and digital ops. 

Adding CEC/Nextion will make your radio experience dreamy.  Replacing SM inductors and relays will not. 

I've seen spurs on my V4 using a SDR to monitor the signal spectrum, but mostly when overdriving. And I can fix that without a solder iron. 

I've spent some time now looking a spectral purity of digital signals of fellow uBITXers and 7300ers and a thousand other rigs. The unavoidable observation: signal issues are caused by the device pushing the PTT or TX button. Hahahha

So, build that baby (any way you darn want) and get on the air. We need you.


_Dave_ AD0B
 

Have looked at ubitx.net but not for a couple of years. Didn't find it very helpful.

When I have put int the axiom relays I get about a half watt additional on most upper bands. Measured it on 4 different radios.
To my mind having that power released and not circulating around the filters has got to be a good thing as far as harmonics go.

I changed L5 and L7 as well.

Raj seemed to think that relays and the two inductors would give compliance so that is what I did. I respect him a lot. 

Before you change anything, verify that the stock radio worked properly

One thing that you will definitely want is more gain on the receiver. I started with a computer speakers/amp. Then added an internal amp in the case. The V4 in particular is pathetic. I use a large loop (1300') antenna and found that they are very quiet so more gain is a good thing.

On the v3 40m has more power than 20m and each band above that is less. 

The v4 that I have has more power on 20 than 40 and bands above 20 are stronger than they were on the v3, on 10 meters the v4 has close to 2x the power of the v3. Maybe 4 watts. 

I don't worry at all about having less power on the upper bands. Seems like a lot of work for very little gain. (pun?) Not sure if any uBITX is perfect that way. Have made continental contacts on the approx 3 watts that my v3 has on 15m Worked all over europe on the 5w on 20. Made one contact ssb phone to Australia on 20m  over 8000 miles. 

Have 90 DX countries with the uBITX The upper bands have been terrible so use 20-40-80 about 90% of the time.

Have made an air core 7 element 160 filter and hope to make more contacts on 160m this winter. 
-
73
Dave
ADOB
Raduino bracket and Ham_Made_Keys


Jonathan Washington
 

Thanks, Ripley, Don, and Dave.

I've had my µBitX for about 2 years, and have done pretty well with it driving a balanced 20m inverted-V dipole in my attic (tunable on 30m and 40m).  I have confirmed FT-8 contacts all over North America and a few in Western Europe with this configuration.

In fact, I've already done a number of easy mods, as documented here: http://wiki.firespeaker.org/%CE%9CBITX .  The radio is many times over tested and working.

I don't do SSB voice too often because some of the only time I get to be on the air is when my kids are sleeping, and the walls are fairly thin.  But when I do, headphones work okay.  AGC would be nice, and maybe when the kids get a bit older getting some additional gain for an external speaker would help get them interested in radio :)  But for now those are low-priority mods.

In any case, I'm finishing up an outdoor OCF multi-band dipole (just need some coax and some lightning protection), and with the more serious antenna setup I figured I should get around to worrying about compliance, and simultaneously getting better output power on more bands.

Ripley,

Your documentation is great!  What a service to the rest of us!

As far as I was able to tell, you had good success with the relay replacement and Allison's mods, but not much luck with several attempts at L5 & L7 replacement?

--
Jonathan, KD5CFX

On Thu, Aug 6, 2020 at 9:14 AM _Dave_ AD0B <davesters@...> wrote:
Have looked at ubitx.net but not for a couple of years. Didn't find it very helpful.

When I have put int the axiom relays I get about a half watt additional on most upper bands. Measured it on 4 different radios.
To my mind having that power released and not circulating around the filters has got to be a good thing as far as harmonics go.

I changed L5 and L7 as well.

Raj seemed to think that relays and the two inductors would give compliance so that is what I did. I respect him a lot. 

Before you change anything, verify that the stock radio worked properly

One thing that you will definitely want is more gain on the receiver. I started with a computer speakers/amp. Then added an internal amp in the case. The V4 in particular is pathetic. I use a large loop (1300') antenna and found that they are very quiet so more gain is a good thing.

On the v3 40m has more power than 20m and each band above that is less. 

The v4 that I have has more power on 20 than 40 and bands above 20 are stronger than they were on the v3, on 10 meters the v4 has close to 2x the power of the v3. Maybe 4 watts. 

I don't worry at all about having less power on the upper bands. Seems like a lot of work for very little gain. (pun?) Not sure if any uBITX is perfect that way. Have made continental contacts on the approx 3 watts that my v3 has on 15m Worked all over europe on the 5w on 20. Made one contact ssb phone to Australia on 20m  over 8000 miles. 

Have 90 DX countries with the uBITX The upper bands have been terrible so use 20-40-80 about 90% of the time.

Have made an air core 7 element 160 filter and hope to make more contacts on 160m this winter. 
-
73
Dave
ADOB
Raduino bracket and Ham_Made_Keys


 

You made my day Dave!

Raj


At 06/08/2020, you wrote:
Have looked at ubitx.net but not for a couple of years. Didn't find it very helpful.

When I have put int the axiom relays I get about a half watt additional on most upper bands. Measured it on 4 different radios.
To my mind having that power released and not circulating around the filters has got to be a good thing as far as harmonics go.

I changed L5 and L7 as well.

Raj seemed to think that relays and the two inductors would give compliance so that is what I did. I respect him a lot.

Before you change anything, verify that the stock radio worked properly

One thing that you will definitely want is more gain on the receiver. I started with a computer speakers/amp. Then added an internal amp in the case. The V4 in particular is pathetic. I use a large loop (1300') antenna and found that they are very quiet so more gain is a good thing.

On the v3 40m has more power than 20m and each band above that is less.

The v4 that I have has more power on 20 than 40 and bands above 20 are stronger than they were on the v3, on 10 meters the v4 has close to 2x the power of the v3. Maybe 4 watts.

I don't worry at all about having less power on the upper bands. Seems like a lot of work for very little gain. (pun?) Not sure if any uBITX is perfect that way. Have made continental contacts on the approx 3 watts that my v3 has on 15m Worked all over europe on the 5w on 20. Made one contact ssb phone to Australia on 20m  over 8000 miles.

Have 90 DX countries with the uBITX The upper bands have been terrible so use 20-40-80 about 90% of the time.

Have made an air core 7 element 160 filter and hope to make more contacts on 160m this winter.
-
73
Dave
ADOB
Raduino bracket and Ham_Made_Keys


Ripley
 

Hello Jonathan,

I tried two methods to reduce the spurs on the higher bands, the L5 & L7 replacement and a 45 MHz filter mod. Both by themselves helped to bring the spurs down in power but did not bring my v4 uBITX it into compliance. However, doing the L5 & L7 replacement together with the 45 MHz crystal filter mod made no additive improvement in spur reduction.

The bottom line for me was Allison’s modification to even out the power across the bands along with replacing the relays and adding the 45 MHz crystal filter or the L5 & L7 replacement were well worth the effort. I am totally comfortable operating this little radio in any mode and on any band without concern about FCC compliance issues floating around in the back of my mind.

Ripley


Jonathan Washington
 

Thank you, Ripley.  That summary of your thoughts helps.

I found in looking for the replacement inductors that someone in California, presumably on this list, is selling the EPCOS ones on eBay, so I placed an order for them the other day.  Last night I also ordered the other parts I needed for those fixes/mods (and a few other projects) from Digikey and Tayda.  So I'll see how it goes!

Now to get those last few antenna supplies while I wait for radio parts to arrive....  And maybe I should practice some SMD soldering while I'm at it....

--
Jonathan

On Fri, Aug 7, 2020 at 8:06 AM Ripley <bob.ripley@...> wrote:
Hello Jonathan,

I tried two methods to reduce the spurs on the higher bands, the L5 & L7 replacement and a 45 MHz filter mod. Both by themselves helped to bring the spurs down in power but did not bring my v4 uBITX it into compliance. However, doing the L5 & L7 replacement together with the 45 MHz crystal filter mod made no additive improvement in spur reduction.

The bottom line for me was Allison’s modification to even out the power across the bands along with replacing the relays and adding the 45 MHz crystal filter or the L5 & L7 replacement were well worth the effort. I am totally comfortable operating this little radio in any mode and on any band without concern about FCC compliance issues floating around in the back of my mind.

Ripley


Curt
 

Either axicom relays or an external relay board should bring cw into compliance. Ssb then will likely have spur issues at 15m and above. I have shielded L5 and L7 inductors mounted, no data yet as covid eliminated our club sessions where I get tested. I have not been able to get my v4 to behave with several versions tried of the second 45 mhz filter. At least one builder in our club got full compliance just changing to axicom relays, while others didn't. I don't sweat the power slope, we aren't true cw qrp on 80m but have enough RF on 10m as is.

73 curt


Slurm
 

Regarding Allison's mods, and Nick's mods (Nik ?) :: 

Someone should try and combine these two mods.  Nick was getting 14 watts as I recall on 10 meters and 22 or so on 80 and 40.  He pulled heavily from Erhart's mod using RD16HHF1 finals and a larger and specific output transformer and some other mods.   He didn't use Allison's mods.  

Allison picked more suitable transistors, etc, that are better suited for the drivers.

Here is a link to Nick's mods, it's a long thread.  What he's done is manage to greatly increase power out with a cool running output transformer.  That hopefully is limiting harmonics, but I'm still waiting for someone to report on his spectral purity.  Nick is using RD16HHF1's for his finals, with the crossed pins.   If QRP is 10 watts or less, lets get 10 watts or more.  If anyone wants less, the can easily turn the pot down to whatever they want.

long thread that eventually shows Nick's mods::::
https://groups.io/g/BITX20/topic/rd16hhf1_power_curve/12897964?p=Created,,,20,1,0,0::recentpostdate%2Fsticky,,,20,2,0,12897964

Sincerely,

Slurm


MadRadioModder
 

Where is this worry about harmonics coming from?  All of the issues with harmonics was problems with the design and placement of the OUTPUT FILTER NETWORK.  It has NOTHING to do with the transistors or associated circuitry…. Unless you figure out a way to get the devices to operate out of their linear region or saturate the transformers generating too much power.  Neither of these are probable.

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Slurm
Sent: Saturday, August 8, 2020 1:22 PM
To: BITX20@groups.io
Subject: Re: [BITX20] questions about µBitX v4 power + spectral purity mods

 

Regarding Allison's mods, and Nick's mods (Nik ?) :: 

Someone should try and combine these two mods.  Nick was getting 14 watts as I recall on 10 meters and 22 or so on 80 and 40.  He pulled heavily from Erhart's mod using RD16HHF1 finals and a larger and specific output transformer and some other mods.   He didn't use Allison's mods.  

Allison picked more suitable transistors, etc, that are better suited for the drivers.

Here is a link to Nick's mods, it's a long thread.  What he's done is manage to greatly increase power out with a cool running output transformer.  That hopefully is limiting harmonics, but I'm still waiting for someone to report on his spectral purity.  Nick is using RD16HHF1's for his finals, with the crossed pins.   If QRP is 10 watts or less, lets get 10 watts or more.  If anyone wants less, the can easily turn the pot down to whatever they want.

long thread that eventually shows Nick's mods::::
https://groups.io/g/BITX20/topic/rd16hhf1_power_curve/12897964?p=Created,,,20,1,0,0::recentpostdate%2Fsticky,,,20,2,0,12897964

Sincerely,

Slurm


Virus-free. www.avg.com

--

…_. _._


Slurm
 

MadRadioModder,

I recall you saying this before.  Has anyone fixed the filter bank and isolated it from the offending components?  Which core and winding are you using on the transformer?