Date   
Re: TIA amplifiers

ajparent1/KB1GMX
 

An alternate improvement is replace Q10/11/12 with mmbt2369 or BFr106
as the 3904 is not impressive at 45mhz.

Allison

80 Meters Harmonics Fix Proposal

Howard Fidel
 

I previously mentioned that I would try to reduce the harmonics by changing the output to 25 ohms and adding a step up transformer to go back to 50 ohms for the output. This would allow tripling the values of the capacitors at the input and output of the filters, reducing the effect of the stray relay and layout capacitance. I experimented some more with a simulator, and decided just to change the filter characteristics so I could stay with 50 ohms. I was able to come up with a filter that doubles the capacitance. The improvement is not as great, but at least on 80 meters, the harmonics don't exceed -45 dB in my tests. Not as much margin as I would like, but legal. I changed the 3 inductors to 1.6 uH by adding 2 turns on each. I added an extra 1000 PF cap in parallel with the input and output caps, bringing the total to 2000 pF, and I added a 620 pF cap in parallel with the one of the two paralleled 1000 pF caps in the middle two sections for a total of 2620 pF there. (750 pF would have been better, but I didn't have them). I attached the simulation for the design. 
If someone with good test equipment could validate what I have done, it would be great to get more data points. 
After validation of 80 I will try the 40 meter band. My test equipment is not good enough for the higher bands.(My analyzer only works to 30 MHz). 

Howard

PS my Arduino problems were probably a ground loop. They seem to have gone away by moving some cables.

Re: K5BCQ uBITX Relay Switched LPF/BPF board

 

Kees & Group:

 

Please Clarify: I thought I was told some time ago on this post that only passband filters would address the uBitix issues. If that earlier statement was correct, why are people working on solutions using lowpass filters???

 

David A Posthuma, WD8PUO

1 (616) 283-7703

 

From: BITX20@groups.io <BITX20@groups.io> On Behalf Of Kees T
Sent: Monday, September 03, 2018 10:23 AM
To: BITX20@groups.io
Subject: Re: [BITX20] K5BCQ uBITX Relay Switched LPF/BPF board

 

 W0PWE

Sep 2   

 

Kees - With 6 filters is the plan as follows?
LPF1 = 80M
LPF2 = 40M and 30M
LPF3 = 20M and 17M
LPF4 = 15M
LPF5 = 12M
LPF6 = 10M

Re: 80 Meters Harmonics Fix Proposal

Warren Allgyer <allgyer@...>
 

Howard

When I measured 80 meter harmonics the particularly troublesome ones were 5th at 18 MHz and 7th at 25 MHz. In both cases the attenuation of the stock uBitx at those frequencies was limited by the layout of the board and by the coupling of relays sharing both filter input and output in the same frame. In such cases the characteristics of the filters, both existing and any modifications are immaterial. The attenuation of the stock filter supplied is more than adequate. But the harmonics bypass the filter and go via I/O coupling straight to the output. Please measure the 5th and 7th harmonics on CW. I think you will find you have not done much to improve the stock situation.

WA8TOD

Re: K5BCQ uBITX Relay Switched LPF/BPF board

 

Kees:

 

Why manual band switching? Could not the code select the proper filter according to frequency the user selects on the uBitx? Could not the RF Switching be done using pin diodes or FET switching? I’m just trying to learn, thanks.

 

David A Posthuma, WD8PUO

1 (616) 283-7703

 

From: BITX20@groups.io <BITX20@groups.io> On Behalf Of Kees T
Sent: Monday, September 03, 2018 10:13 AM
To: BITX20@groups.io
Subject: Re: [BITX20] K5BCQ uBITX Relay Switched LPF/BPF board

 

Since most keep talking about the need for BPFs for certain bands, I "guess" the 80m-10m uBITX direction should be a board with 6 filter capability. How about a basic dual relay switched filter board (3-1/4" x 3-7/8") with up to 6 pluggable filters, all manually selected with a 6 position rotary switch --AND-- you can add a small mux board with 2N3904 relay drivers for the filters and a CD4028B mux to go from the 3 Raduino pins to the filters. Start with the existing 111,110,100,000 and add two others when you have the code modified.

73 Kees K5BCQ 

Re: K5BCQ uBITX Relay Switched LPF/BPF board

ajparent1/KB1GMX
 

On Mon, Sep 3, 2018 at 12:10 PM, David Posthuma wrote:

Why manual band switching? Could not the code select the proper filter according to frequency the user selects on the uBitx? Could not the RF Switching be done using pin diodes or FET switching? I’m just trying to learn, thanks.

 

David A Posthuma, WD8PUO

First there are two issues one being poor harmonic filtering and Kees is addressing that here.

The other is spurs from inadequate filtering above 17M,  That requires band pass filters before
the power amp.  The tail end low pass filter cannot fully try to address that.

I doubt the band pass filters he sells can stand 10W in that location.   Kees comment please?

Allison

Re: 80 Meters Harmonics Fix Proposal

Howard Fidel
 

Warren:
The fifth and the 7th are at -45dB now. You are missing my point. The design of the filter directly effects the level of the harmonics. Yes, the stray  capacitance creates a "sneak" path around the filter. However, the input and output capacitors of the filter act as a divider to that "sneak" signal. If you double the output capacitance, you 1/2 the sneak signals amplitude, reducing it 6 dB. If you create a model of each  of the filters in a simulator, and put 8 pF from input to output, you can clearly see the improvement in the attenuation of the filter for the higher output capacitance.
All the data I have seen shows that a 6 dB improvement would just make the uBitx legal.

Howard

On 9/3/2018 2:51 PM, Warren Allgyer wrote:
Howard

When I measured 80 meter harmonics the particularly troublesome ones were 5th at 18 MHz and 7th at 25 MHz. In both cases the attenuation of the stock uBitx at those frequencies was limited by the layout of the board and by the coupling of relays sharing both filter input and output in the same frame. In such cases the characteristics of the filters, both existing and any modifications are immaterial. The attenuation of the stock filter supplied is more than adequate. But the harmonics bypass the filter and go via I/O coupling straight to the output. Please measure the 5th and 7th harmonics on CW. I think you will find you have not done much to improve the stock situation.

WA8TOD


Re: 80 Meters Harmonics Fix Proposal

Gordon Gibby <ggibby@...>
 

Howard, I get your point. And a six DB improvement makes the device a much better transceiver per the regulations

With simple unshielded wiring to three external relays, in my tests I found the fifth harmonic of 80 meter CW was basically obliterated, but the seventh only went down by about six dB.  (I don’t have an explanation for the disparity ) I haven’t tried any shielded wiring to see if that would make any better — but it certainly might. 


In my case It might be simpler to add in a permanent low pass filter above 15 MHZ in my case.     Your idea of lowering the capacitance is interesting.  And it’s pretty simple also!   For many people that might be the easiest solution to the harmonic problem. 




On Sep 3, 2018, at 15:47, Howard Fidel <sonic1@...> wrote:

Warren:
The fifth and the 7th are at -45dB now. You are missing my point. The design of the filter directly effects the level of the harmonics. Yes, the stray  capacitance creates a "sneak" path around the filter. However, the input and output capacitors of the filter act as a divider to that "sneak" signal. If you double the output capacitance, you 1/2 the sneak signals amplitude, reducing it 6 dB. If you create a model of each  of the filters in a simulator, and put 8 pF from input to output, you can clearly see the improvement in the attenuation of the filter for the higher output capacitance.
All the data I have seen shows that a 6 dB improvement would just make the uBitx legal.

Howard

On 9/3/2018 2:51 PM, Warren Allgyer wrote:
Howard

When I measured 80 meter harmonics the particularly troublesome ones were 5th at 18 MHz and 7th at 25 MHz. In both cases the attenuation of the stock uBitx at those frequencies was limited by the layout of the board and by the coupling of relays sharing both filter input and output in the same frame. In such cases the characteristics of the filters, both existing and any modifications are immaterial. The attenuation of the stock filter supplied is more than adequate. But the harmonics bypass the filter and go via I/O coupling straight to the output. Please measure the 5th and 7th harmonics on CW. I think you will find you have not done much to improve the stock situation.

WA8TOD


Re: 80 Meters Harmonics Fix Proposal

Howard Fidel
 

Gordon:
Thanks for your concurrence. To prevent others from being confused,
I am raising not lowering the capacitance, which I am sure is what you meant.
And yes, I am trying to come up with an easy fix that all can implement including HF signals.

Howard

On 9/3/2018 4:05 PM, Gordon Gibby wrote:
Howard, I get your point. And a six DB improvement makes the device a much better transceiver per the regulations

With simple unshielded wiring to three external relays, in my tests I found the fifth harmonic of 80 meter CW was basically obliterated, but the seventh only went down by about six dB.  (I don’t have an explanation for the disparity ) I haven’t tried any shielded wiring to see if that would make any better — but it certainly might. 


In my case It might be simpler to add in a permanent low pass filter above 15 MHZ in my case.     Your idea of lowering the capacitance is interesting.  And it’s pretty simple also!   For many people that might be the easiest solution to the harmonic problem. 




On Sep 3, 2018, at 15:47, Howard Fidel <sonic1@...> wrote:

Warren:
The fifth and the 7th are at -45dB now. You are missing my point. The design of the filter directly effects the level of the harmonics. Yes, the stray  capacitance creates a "sneak" path around the filter. However, the input and output capacitors of the filter act as a divider to that "sneak" signal. If you double the output capacitance, you 1/2 the sneak signals amplitude, reducing it 6 dB. If you create a model of each  of the filters in a simulator, and put 8 pF from input to output, you can clearly see the improvement in the attenuation of the filter for the higher output capacitance.
All the data I have seen shows that a 6 dB improvement would just make the uBitx legal.

Howard

On 9/3/2018 2:51 PM, Warren Allgyer wrote:
Howard

When I measured 80 meter harmonics the particularly troublesome ones were 5th at 18 MHz and 7th at 25 MHz. In both cases the attenuation of the stock uBitx at those frequencies was limited by the layout of the board and by the coupling of relays sharing both filter input and output in the same frame. In such cases the characteristics of the filters, both existing and any modifications are immaterial. The attenuation of the stock filter supplied is more than adequate. But the harmonics bypass the filter and go via I/O coupling straight to the output. Please measure the 5th and 7th harmonics on CW. I think you will find you have not done much to improve the stock situation.

WA8TOD



Re: K5BCQ uBITX Relay Switched LPF/BPF board

Kees T
 

The QRP Labs LPF filters are rated at 10W according to Hans Summers, the BPF filters he sells are not, probably because of the series current the capacitors have to handle or larger inductors required. No reason you can't make up BPFs which CAN handle 10W. The filters you see in the pictures are blank boards I made up and you add what components you need to add, and design your own. Could come out with a different BPF filter layout if needed. With those little 1.5" x 0.5" boards you can get 16 per 100mm x 100mm panel .....that's 160 boards per 10 prototype panel order for only $2 plus $5? for scoring plus shipping.

73 Kees K5BCQ  

Re: uBitx Unfiltered

ajparent1/KB1GMX
 

Start with 1V is adequate as the dive is Current not Voltage for transistors.

Altering the resistors make the previous stage a bit happier and lower the loss
to the resistors but the basic issue is crappy transistors, transformers, and layout.

For L8 and L9 the common practice is bifiler wind on a common core 
so the current balance out to zero flux in the core. I used 2t bufilar #26
on FB43-202 to get about the same result.   Then again anything
did help compared to existing.  The driver and predriver transformers are
not so good either.  While your at it the q90 transformer is not as good
as could be.  T11 rewind it as something reasonable for 10mhz and up.
try 2:3 or even 2:2.  For better IMD run about 150 to 200ma per transistor
on the finals.

Trying to get more than 1.8W on 10 with basically 10W at lower end is repeating
the work I did 2.5 months ago.  Ditch the 3904s put in 2222s tell me that is not
remarkable difference.  Or go straight to 3866s or 5109s.  FYI everyone found
the MPSH10s to be rather marginal improvement.

Then add RLC feedback to the driver and Predriver to keep the gain fade
with frequency a bit flatter.  With that you should be to 12W on 80 and 40
and about 5-6W on 10M.  The spur at 17mhz (10M) will now plague you.

Reset the bias to Q90, its a low level stage and even 10ma is high.
some of them are running at over 25ma for 1 milliwatt or RF.  BEst way
1K is series with a 2K with a parallel .01uf chip. The idea is 3K DC R
and 1K AC R.  Use a real transistor there too MMBR2369 is better
(flat to about 22mhz)  BFR106 (flat pas 30mhz)  work very well.
A mmbt5179 should work if kept under 10ma as well.

You will have to reduce the extremely high standing current of the
predriver and driver.  The 22ohm emitter resistors tend to cause voltage
limiting on the pre-driver and driver as well as much to great emitter
degeneration.  Using 8.2 to 10 ohms improved that.  Bypassing them with
220/330/470 pf helps get some upper frequency peaking.

Flattening the power was more or less doable.but spurs and harmonics made
it worthless.  Also if the gain gets to about 60db at 20mhz and up the amp is then
subject to oscillation from ground loops extending back to the 33mhz low pass filter.
the fix is slice the board and separate. There are secondary loops with DC power
lines having RF (TX-DC+) due to parallel paths under the relays and near the
power amp.   Look at Kees picture of the board without relays. 

 Allison

Re: 80 Meters Harmonics Fix Proposal

Gordon Gibby <ggibby@...>
 

Yep, sorry, you were lowering the impedance, raising the capacitance.   Slip of the tongue. (I use Siri)


You might tell us how you changed each value in those filters.   





On Sep 3, 2018, at 16:20, Howard Fidel <sonic1@...> wrote:

Gordon:
Thanks for your concurrence. To prevent others from being confused,
I am raising not lowering the capacitance, which I am sure is what you meant.
And yes, I am trying to come up with an easy fix that all can implement including HF signals.

Howard
On 9/3/2018 4:05 PM, Gordon Gibby wrote:
Howard, I get your point. And a six DB improvement makes the device a much better transceiver per the regulations

With simple unshielded wiring to three external relays, in my tests I found the fifth harmonic of 80 meter CW was basically obliterated, but the seventh only went down by about six dB.  (I don’t have an explanation for the disparity ) I haven’t tried any shielded wiring to see if that would make any better — but it certainly might. 


In my case It might be simpler to add in a permanent low pass filter above 15 MHZ in my case.     Your idea of lowering the capacitance is interesting.  And it’s pretty simple also!   For many people that might be the easiest solution to the harmonic problem. 




On Sep 3, 2018, at 15:47, Howard Fidel <sonic1@...> wrote:

Warren:
The fifth and the 7th are at -45dB now. You are missing my point. The design of the filter directly effects the level of the harmonics. Yes, the stray  capacitance creates a "sneak" path around the filter. However, the input and output capacitors of the filter act as a divider to that "sneak" signal. If you double the output capacitance, you 1/2 the sneak signals amplitude, reducing it 6 dB. If you create a model of each  of the filters in a simulator, and put 8 pF from input to output, you can clearly see the improvement in the attenuation of the filter for the higher output capacitance.
All the data I have seen shows that a 6 dB improvement would just make the uBitx legal.

Howard

On 9/3/2018 2:51 PM, Warren Allgyer wrote:
Howard

When I measured 80 meter harmonics the particularly troublesome ones were 5th at 18 MHz and 7th at 25 MHz. In both cases the attenuation of the stock uBitx at those frequencies was limited by the layout of the board and by the coupling of relays sharing both filter input and output in the same frame. In such cases the characteristics of the filters, both existing and any modifications are immaterial. The attenuation of the stock filter supplied is more than adequate. But the harmonics bypass the filter and go via I/O coupling straight to the output. Please measure the 5th and 7th harmonics on CW. I think you will find you have not done much to improve the stock situation.

WA8TOD



Re: uBitx Unfiltered

Gordon Gibby <ggibby@...>
 

Thank you, Alyson, for even more education

I’m just about finished building a UHF repeater for emergency work, and I’ll be able to turn back to this rig at some point.  I don’t need it to work past 20 m, so little bitty improvements will suffice for my needs.  I don’t have quite the needs that others have.


Gordon



On Sep 3, 2018, at 16:28, ajparent1/KB1GMX <kb1gmx@...> wrote:

Start with 1V is adequate as the dive is Current not Voltage for transistors.

Altering the resistors make the previous stage a bit happier and lower the loss
to the resistors but the basic issue is crappy transistors, transformers, and layout.

For L8 and L9 the common practice is bifiler wind on a common core 
so the current balance out to zero flux in the core. I used 2t bufilar #26
on FB43-202 to get about the same result.   Then again anything
did help compared to existing.  The driver and predriver transformers are
not so good either.  While your at it the q90 transformer is not as good
as could be.  T11 rewind it as something reasonable for 10mhz and up.
try 2:3 or even 2:2.  For better IMD run about 150 to 200ma per transistor
on the finals.

Trying to get more than 1.8W on 10 with basically 10W at lower end is repeating
the work I did 2.5 months ago.  Ditch the 3904s put in 2222s tell me that is not
remarkable difference.  Or go straight to 3866s or 5109s.  FYI everyone found
the MPSH10s to be rather marginal improvement.

Then add RLC feedback to the driver and Predriver to keep the gain fade
with frequency a bit flatter.  With that you should be to 12W on 80 and 40
and about 5-6W on 10M.  The spur at 17mhz (10M) will now plague you.

Reset the bias to Q90, its a low level stage and even 10ma is high.
some of them are running at over 25ma for 1 milliwatt or RF.  BEst way
1K is series with a 2K with a parallel .01uf chip. The idea is 3K DC R
and 1K AC R.  Use a real transistor there too MMBR2369 is better
(flat to about 22mhz)  BFR106 (flat pas 30mhz)  work very well.
A mmbt5179 should work if kept under 10ma as well.

You will have to reduce the extremely high standing current of the
predriver and driver.  The 22ohm emitter resistors tend to cause voltage
limiting on the pre-driver and driver as well as much to great emitter
degeneration.  Using 8.2 to 10 ohms improved that.  Bypassing them with
220/330/470 pf helps get some upper frequency peaking.

Flattening the power was more or less doable.but spurs and harmonics made
it worthless.  Also if the gain gets to about 60db at 20mhz and up the amp is then
subject to oscillation from ground loops extending back to the 33mhz low pass filter.
the fix is slice the board and separate. There are secondary loops with DC power
lines having RF (TX-DC+) due to parallel paths under the relays and near the
power amp.   Look at Kees picture of the board without relays. 

 Allison

Re: K5BCQ uBITX Relay Switched LPF/BPF board

Kees T
 

David,

Manual switching is only one of the options. There is also a small board you can add which can mux the 3 bits from the Raduino to all 6 sets of relays......but it would require a small code change. I was suggesting to use the codes 111,110,100, and 000 which the existing Raduino code supplies via TxA, TxB, TxC to select the 4 LPFs as today and add the remaining 2 when you get around to it. There is also no magic to 6x filters....it could be 5x or 8x filters or 12x filters if you add another select bit. 6x happens to fit readily on a 100mm x100mm panel.

The 4x LPF board version decodes the existing TxA,TxB, and TxC drivers just like the uBITX does today (and I have to reinstall K3). Those boards should be here next week.

73 kees K5BCQ

Re: K5BCQ uBITX Relay Switched LPF/BPF board

Kees T
 

You can also see, in the picture with the uBITX board, that the 2N3904's have already been pulled, waiting for the 2N2222A's ..............and other incremental improvements.  

73 Kees K5BCQ

Re: K5BCQ uBITX Relay Switched LPF/BPF board

Kees T
 

You can also  modify the existing filter for a faster roll-off which MAY catch enough of the 15m spur .....for instance. The plot labeled "1" is the original LPF, the other plot is the modified LPF.

73 Kees K5BCQ

Re: 80 Meters Harmonics Fix Proposal

Warren Allgyer <allgyer@...>
 

Got it Howard. And I agree with both the strategy and the necessary amount of improvement. On mine, a six dB improvement would make all bands legal for CW harmonics. That would be a nice solution for a CW only radio. Of course you must not use it on SSB for 20 meters and above but perhaps that is not your objective. Good work!

 

WA8TOD

Re: K5BCQ uBITX Relay Switched LPF/BPF board

MadRadioModder
 

Let’s do it…

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Kees T
Sent: Monday, September 3, 2018 3:26 PM
To: BITX20@groups.io
Subject: Re: [BITX20] K5BCQ uBITX Relay Switched LPF/BPF board

 

The QRP Labs LPF filters are rated at 10W according to Hans Summers, the BPF filters he sells are not, probably because of the series current the capacitors have to handle or larger inductors required. No reason you can't make up BPFs which CAN handle 10W. The filters you see in the pictures are blank boards I made up and you add what components you need to add, and design your own. Could come out with a different BPF filter layout if needed. With those little 1.5" x 0.5" boards you can get 16 per 100mm x 100mm panel .....that's 160 boards per 10 prototype panel order for only $2 plus $5? for scoring plus shipping.

73 Kees K5BCQ  


Virus-free. www.avg.com

--

…_. _._

Re: uBitx Unfiltered

ajparent1/KB1GMX
 

On Mon, Sep 3, 2018 at 07:25 AM, Michael Babineau wrote:
This got me thinking that for another $20 I could just order the QRP Labs 5W PA kit and build a separate 160m to 10m CW TX with raised cosine wave shaping.
I do mostly CW anyway so giving up SSB wouldn't be a big loss for me.
Why use linear amp with lower efficiency for CW?  Class C can be shaped for keying and offer much mroe power with far less consumed.  However binding the two ubitx to a QSX amp is not easy.

>>Has anyone else thought  of just designing  a separate  TX board  for use with the V3/V4 ubitx? I know that this sounds like giving up ... but in many ways this could be a simpler solution than attempting major surgery on the existing ubitx.

Basically to do that you need to build a replacement fo the rear half of the board.  The problem is fourfold.
No input filtering for the amplifier,
The amplifiers inability to product power at 10M
low pass filter layout (filters would work otherwise)
Board layout.

Allison
We want a magik pill to fix is all.

Re: K5BCQ uBITX Relay Switched LPF/BPF board

Guy WB7SZI
 

Forgive me if this is way over simplified. I’m not an RF designer, 
but couldn’t you manually just insert an appropriate LPF from your ant. connection to the antenna to reduce harmonics on that specific band? I agree that a six band LPF system would be great but I for one only use one or two bands most of the time. Is that doable? 
73,
Guy WB7SZI