Topics

RD16HHF1 power curve flattening...some

John <passionfruit88@...>
 

Having read with interest the information provided by Erhard Haertel (DF3FY) on ubitx.net regarding the changes to the finals circuit I decided to try to improve the flatness or lack thereof of the power curve over frequency on my uBitx unit.
 
I therefore performed his proposed changes (final's transformer, cap across drains, feedback resistors) with one exception: the feedback resistors between drain and source of the final was changed from 220 Ohms to 820 Ohms instead of 1K Ohms.
 
I got the following result at 13.8V, with idle current at 250mA per final, RV1 unchanged at approx 60% as before:
 
Freq.      Power     Total Current
 7Mhz        18W         2.8A
14Mhz        16W         2.7A
21Mhz         9W         1.5A
24Mhz        11W         1.9A
28Mhz        11W         2.2A
 
Hmmmm...not bad but still that dip at 21 and not that high on the high frequencies.
 
But the good news was that I would get power improvement all the way to the end of the RV1 pot and it looked like no compression was occurring. Good news as this means that I have spare power for frequency compensation.
 
Using the LTSpice simulation done by Jerry Gaffke (thanks Jerry) with a replacement of the finals with the RD16HHF1 model found on the internet and I got some interesting pointers (reality is always different, but I find this is a good starting point).
 
I simulated capacitors in parallel with the 22 Ohms emitter resistors in the pre-driver and driver stages alternatively. Since I had "free gain" left by turning RV1 this meant that none of the stages were limiting at 60%, therefore I could increase the gain anywhere in the chain, including at RV1 for that matter.

LTSpice gave me a flat curve with caps of 150-200pf in the pre-driver stages, and more importantly a rapid drop in power above 40Mhz which I hope may prevent V-UHF oscillations of the power train (linear amplifier specialists can comment on that point).
 
So I experimented with various caps values across the R87 and R88 resistors and found that I would not get more gain above 330pf.
 
Results as per above conditions (RV1 back at 60%):
 
Freq.      Power     Total Current
 7Mhz        18W         2.8A
14Mhz        16W         3.0A
21Mhz        10W         1.6A
24Mhz        11W         not recorded
28Mhz        14W         1.9A
 
Not perfect but at least now 10W on the high bands, and above 15W at and below 14 megs.
 
One minute key down then "finger heat test": the finals new transformer is a little warm but not much. The filters the same. The finals and the heat-sink (thermally coupled to the metal case) are fine.
 
So the question is: can the filters handle that kind of power over time? Short of doing and LTSpice simulation is there an easier way to calculate the current and therefore the flux density in the filters cores to check if we are getting to saturation or not? 
 
No instability and oscillation detected with a separate radio, but again I don't have a spectrum analyser. 
 
So in summary this is what I have in the circuit now: Finals as RD16HHF1s, feedback resistors R261/R262 as 820 Ohms, Tranformer 2T primary / 3T secondary on BN43-202, 33pF across the output transformer primary and 330pf across R87/R88.
 
I haven't tried capacitors across the driver stage emitter resistors (R941/942/911/96), nor from the high to the middle side of RV1 for the following reasons: I wanted to leave the drivers alone and not modify the way they drive the finals (impedance change), and at RV1 it meant that the capacitor value would need to change with the adjustment of RV1, although this could be the simplest way to correct the power curve. 
 
Interestingly enough for the units with the IRF510s, LTSpice reports a flat power curve with 800pf caps across these four drivers resistors....it could be just theory...and stability could be an issue as we reduce negative feedback. Is anyone game enough?
 
Happy hacking,
 
73, John (VK2ETA)

K9HZ <bill@...>
 

Here’s what I found... if you change R85 from 100 to 470 ohms (pre-driver stage bias), change R261 and R262 from 100 to 1K ohm (Although 820 ohms will work too… it’s not that critical), run RV1 wide open (full drive) and then use a compensating capacitor (your 33pf at 14 MHz) across T11 primary with a 1:4 transformer:

 

6M - 48pf

10M - 110pf

20M - 320pf

40M - 680pf

80M - 1,500pf

60M - 4,700pf

 

It shows at least 20 watts out on each band except for 6 meters... where it peaks at 12 watts.  My calculations show that the 3:2 is not optimal for this pair. You might want to have a look at:  http://www.tapr.org/pdf/PennyWhistleManual.pdf

 

 

 

 

Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

 

Owner – Operator

Villa Grand Piton – J68HZ

Soufriere, St. Lucia W.I.

Rent it: www.VillaGrandPiton.com

Like us on Facebook! facebook icon

 

Moderator – North American QRO Yahoo Group.

 

email:  bill@...

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of John
Sent: Sunday, February 25, 2018 7:59 PM
To: BITX20@groups.io
Subject: [BITX20] RD16HHF1 power curve flattening...some

 

Having read with interest the information provided by Erhard Haertel (DF3FY) on ubitx.net regarding the changes to the finals circuit I decided to try to improve the flatness or lack thereof of the power curve over frequency on my uBitx unit.

 

I therefore performed his proposed changes (final's transformer, cap across drains, feedback resistors) with one exception: the feedback resistors between drain and source of the final was changed from 220 Ohms to 820 Ohms instead of 1K Ohms.

 

I got the following result at 13.8V, with idle current at 250mA per final, RV1 unchanged at approx 60% as before:

 

Freq.      Power     Total Current

 7Mhz        18W         2.8A

14Mhz        16W         2.7A

21Mhz         9W         1.5A

24Mhz        11W         1.9A

28Mhz        11W         2.2A

 

Hmmmm...not bad but still that dip at 21 and not that high on the high frequencies.

 

But the good news was that I would get power improvement all the way to the end of the RV1 pot and it looked like no compression was occurring. Good news as this means that I have spare power for frequency compensation.

 

Using the LTSpice simulation done by Jerry Gaffke (thanks Jerry) with a replacement of the finals with the RD16HHF1 model found on the internet and I got some interesting pointers (reality is always different, but I find this is a good starting point).

 

I simulated capacitors in parallel with the 22 Ohms emitter resistors in the pre-driver and driver stages alternatively. Since I had "free gain" left by turning RV1 this meant that none of the stages were limiting at 60%, therefore I could increase the gain anywhere in the chain, including at RV1 for that matter.


LTSpice gave me a flat curve with caps of 150-200pf in the pre-driver stages, and more importantly a rapid drop in power above 40Mhz which I hope may prevent V-UHF oscillations of the power train (linear amplifier specialists can comment on that point).

 

So I experimented with various caps values across the R87 and R88 resistors and found that I would not get more gain above 330pf.

 

Results as per above conditions (RV1 back at 60%):

 

Freq.      Power     Total Current

 7Mhz        18W         2.8A

14Mhz        16W         3.0A

21Mhz        10W         1.6A

24Mhz        11W         not recorded

28Mhz        14W         1.9A

 

Not perfect but at least now 10W on the high bands, and above 15W at and below 14 megs.

 

One minute key down then "finger heat test": the finals new transformer is a little warm but not much. The filters the same. The finals and the heat-sink (thermally coupled to the metal case) are fine.

 

So the question is: can the filters handle that kind of power over time? Short of doing and LTSpice simulation is there an easier way to calculate the current and therefore the flux density in the filters cores to check if we are getting to saturation or not? 

 

No instability and oscillation detected with a separate radio, but again I don't have a spectrum analyser. 

 

So in summary this is what I have in the circuit now: Finals as RD16HHF1s, feedback resistors R261/R262 as 820 Ohms, Tranformer 2T primary / 3T secondary on BN43-202, 33pF across the output transformer primary and 330pf across R87/R88.

 

I haven't tried capacitors across the driver stage emitter resistors (R941/942/911/96), nor from the high to the middle side of RV1 for the following reasons: I wanted to leave the drivers alone and not modify the way they drive the finals (impedance change), and at RV1 it meant that the capacitor value would need to change with the adjustment of RV1, although this could be the simplest way to correct the power curve. 

 

Interestingly enough for the units with the IRF510s, LTSpice reports a flat power curve with 800pf caps across these four drivers resistors....it could be just theory...and stability could be an issue as we reduce negative feedback. Is anyone game enough?

 

Happy hacking,

 

73, John (VK2ETA)


Virus-free. www.avg.com

John <passionfruit88@...>
 

Thank you Bill.

I was intrigued by the low value of the capacitor value across T11. So that makes more sense.

I find interesting the size of the output transformer on the PennyWhistle compared to the BN43-202. It might explain the warm temperature of the T11 transformer at 18-15 Watts. I will try a BN43-3312 as it should still fit in the space between the finals.

I will definitely try your suggestions.

All the best,

73, John (VK2ETA)

K9HZ <bill@...>
 

Yes please publish your results when you update the circuits… as I’ve now gone away from working on that aspect of the radio in favor of designing a good RF-driven AGC, finishing the tuner, and working on a variable pass-band filter that is usable for CW AND SSB that is also cheap!  I already published to control circuit recently for saving the radio due to SWR, over power, etc.  

 

 

Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

 

Owner – Operator

Villa Grand Piton – J68HZ

Soufriere, St. Lucia W.I.

Rent it: www.VillaGrandPiton.com

Like us on Facebook! facebook icon

 

Moderator – North American QRO Yahoo Group.

 

email:  bill@...

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of John
Sent: Sunday, February 25, 2018 11:47 PM
To: BITX20@groups.io
Subject: Re: [BITX20] RD16HHF1 power curve flattening...some

 

Thank you Bill.

I was intrigued by the low value of the capacitor value across T11. So that makes more sense.

I find interesting the size of the output transformer on the PennyWhistle compared to the BN43-202. It might explain the warm temperature of the T11 transformer at 18-15 Watts. I will try a BN43-3312 as it should still fit in the space between the finals.

I will definitely try your suggestions.

All the best,

73, John (VK2ETA)


Virus-free. www.avg.com

Kelly Jack
 

Bill,

Does this mean that a different compensating capacitor is required for each band   ie. To get the 20w on each band?

Regards

Simon
VK3ELH

John <passionfruit88@...>
 

Hello Simon,

My understanding is that the value of the capacitor gives the peak of the very broad resonance. Therefore you choose where to increase the gain the most and select the capacitor accordingly.

73, John (VK2ETA) 

K9HZ <bill@...>
 

In order to be perfectly flat in response... yes.  Practical... no.  I would try 330pf and stick with that because you naturally have more gain  at lower frequency anyway. 


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

 

Owner – Operator

Villa Grand Piton - J68HZ

Soufriere, St. Lucia W.I.

Rent it: www.VillaGrandPiton.com


email:  bill@...

 


On Feb 26, 2018, at 12:47 AM, Kelly Jack <kellyjack1968@...> wrote:

Bill,

Does this mean that a different compensating capacitor is required for each band   ie. To get the 20w on each band?

Regards

Simon
VK3ELH

Nick VK4PP
 

Hi Group.
Anymore updates on this? I have received my components and plan to do the following:
RD16, BN43-3312 (4:1) with 330pf mica, 820ohm feedback, 330pf on R87/88, Re-bias 250-500ma?, 13.8v and play with RV1....

Thoughts?
73 VK4PLN

K9HZ <bill@...>
 

You are doing what I would…

 

 

Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

 

Owner – Operator

Villa Grand Piton – J68HZ

Soufriere, St. Lucia W.I.

Rent it: www.VillaGrandPiton.com

Like us on Facebook! facebook icon

 

Moderator – North American QRO Yahoo Group.

 

email:  bill@...

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Nik VK4PLN
Sent: Wednesday, March 7, 2018 6:17 PM
To: BITX20@groups.io
Subject: Re: [BITX20] RD16HHF1 power curve flattening...some

 

Hi Group.
Anymore updates on this? I have received my components and plan to do the following:
RD16, BN43-3312 (4:1) with 330pf mica, 820ohm feedback, 330pf on R87/88, Re-bias 250-500ma?, 13.8v and play with RV1....

Thoughts?
73 VK4PLN




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Nick VK4PP
 

Thanks Doc....
73

John <passionfruit88@...>
 

Hi Nik,

Not yet. I just received the BN43-3312 so I try that as soon as I finish the ATU (half way there). 

Been busy with mic compressor SSM2167 (done), S-Meter (hardware and software done), SWR/POWER meter (hardware done, basic display), Arduino pro mini linked by I2C to Raduino to measure power, swr, final's current (hall effect sensor) and control the ATU plus shutdown the final's bias if required.

ATU is L-Network with 2 servos controlling a variable capacitor and a two wafers rotary switch to get 6 coil positions on high impedance and 6 on low impedance.

Too much fun.

If you get the mods for the final in, please let us know the results.

Thanks and 73, John (VK2ETA)

Kelly Jack
 

John,

How did you implement the ssm2167?

I have one in my bitx40.

Regards


Simon
VK3ELH

John <passionfruit88@...>
 

Hello Simon,

I used the small circuit board as found on eBay. A search of "SSM2167 Microphone Preamplifier Board Preamp COMP Compression Module DC 3V-5V" will show you the module I used.

I simply connected the input to the mic, added a 4.7Kohms resistor between the mic input and the 5VDC (taken from the Raduino) for biasing the electret and put a 10Kohms potentiometer in the output to adjust the power level to the mic preamp stage. 

So I didn't modify the uBitx board, simply inserted in the circuit. There is most likely too much gain which is reduced back with the output potentiometer , but I haven't received any negative feedback about the compressor except when I pushed the output potentiometer too high.

I have since removed the "R1" resistor and replaced it with a 51K Ohms resistor to get a 4/1 compression factor, up from the 2/1 as delivered. I haven't tested that on air yet.

On your Bitx40 what values resistors do you have for compression and noise gating?

Picture attached.

All the best,

73, John (VK2ETA)

Kelly Jack
 

Thanks John. 

I used the same board and similarly power from the regulated 5v line on the raduino. It also offboard and just inline with the mic line.

75k for compression and 1k for gating and 100k pot on output. At full output my audio was readable but distored based on the one audio check qso I had before I turned it down a bit.

I put a larger heatsink on the irf510 too to cater for the higher average output as the stock one was getting warm where previously it didnt.

A sideeffect of the mic being on all the time is that there is leakage through to the speaker and it causes some feedback if the mic is within 2 inches or so of the speaker. Not a big problem.

Sorry all for the off topic content!

Regards


Simon VK3ELH 

John <passionfruit88@...>
 

No worries, thank you Simon for the information.

I haven't noticed the feedback issue on mine.

Not sure where it coming from since Q6 is in-powered in RX. 

Worse case we can put an emitter follower npn on the supply side of the SSM2167 and extract the T/R line from the raduino (I have done that on mine) or bring the TX supply and regulate to 5V.

I will check that issue here.

73, John (VK2ETA)

Nick VK4PP
 

Mods so far, in tested. 

K9HZ <bill@...>
 

Nice… any power to it yet?

 

 

Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

 

Owner – Operator

Villa Grand Piton – J68HZ

Soufriere, St. Lucia W.I.

Rent it: www.VillaGrandPiton.com

Like us on Facebook! facebook icon

 

Moderator – North American QRO Yahoo Group.

 

email:  bill@...

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Nik VK4PLN
Sent: Friday, March 9, 2018 2:35 PM
To: BITX20@groups.io
Subject: Re: [BITX20] RD16HHF1 power curve flattening...some

 

Mods so far, in tested. 


Virus-free. www.avg.com

Nick VK4PP
 

Not yet, I have decided to re-model the case, and install my RaduinoI2C board... Also mounted a swr bridge... Gonna be a nice little rig if I get reasonable results from the PA mod..
73..

John <passionfruit88@...>
 

Nice job Nik. Eagerly awaiting your results.

73, John (VK2ETA)

Glenn
 

I have been experimenting on a different tack. Imnproving the response of the PA driver stages.

I used MPSH10's in my test board build and FT37-43 toroids wound as either trifilar or bifilar according to stage needs, of 10 turns.

Comparing the original uBITX driver which has a ~7db less gain at 10M end, this version has ~2dB drop.

I don't have any spare output FETS or I would check that out also, driven by the this test board.

glenn
vk3pe