Topics

boosting the power on 28 MHz #ubitx

Ashhar Farhan
 

peeps,

28 Mhz is unusually open for the last one week. I realized that our ubitx output is woefully low. Here is a fix that I made today, if some of you can try it out, let me know if it works as well.

Step #1 Increase the predriver gain towards the higher frequencies
The predriver Q90 has a emitter degeneration capacitor C81 (0.1uf) and and R83 (10 ohms). I replaced the C81 with a 470 pf and the R83 with 5 ohms. With this, the emitter reactance decreases with increasing frequency, yielding higher gain beyond 14 MHz.

Step #2 Take off the feedback from the IRF510s. 
Just remove the R261, R262 (both are 220 ohms) to open up the gain.

Let me know if this mod is replicable?

- f

docame12@...
 

How will this affect the lower freqs?

Ashhar Farhan
 

The power will level off around 13 watts.
- f

On Sat, 5 May 2018, 18:44 , <docame12@...> wrote:
How will this affect the lower freqs?

Skip Davis
 

Farhan what power out are you seeing with this modification at 28 MHz? 
I have installed Howard’s mods to the driver and in seeing 4 watts with RV1 at 2/3 ccw. 

Skip Davis, NC9O

On May 5, 2018, at 08:13, Ashhar Farhan <farhanbox@...> wrote:

peeps,

28 Mhz is unusually open for the last one week. I realized that our ubitx output is woefully low. Here is a fix that I made today, if some of you can try it out, let me know if it works as well.

Step #1 Increase the predriver gain towards the higher frequencies
The predriver Q90 has a emitter degeneration capacitor C81 (0.1uf) and and R83 (10 ohms). I replaced the C81 with a 470 pf and the R83 with 5 ohms. With this, the emitter reactance decreases with increasing frequency, yielding higher gain beyond 14 MHz.

Step #2 Take off the feedback from the IRF510s. 
Just remove the R261, R262 (both are 220 ohms) to open up the gain.

Let me know if this mod is replicable?

- f

Ashhar Farhan
 

4 watts, similar power as his mod.
- f

On Sat, 5 May 2018, 19:04 Skip Davis via Groups.Io, <skipnc9o=yahoo.com@groups.io> wrote:
Farhan what power out are you seeing with this modification at 28 MHz? 
I have installed Howard’s mods to the driver and in seeing 4 watts with RV1 at 2/3 ccw. 

Skip Davis, NC9O

On May 5, 2018, at 08:13, Ashhar Farhan <farhanbox@...> wrote:

peeps,

28 Mhz is unusually open for the last one week. I realized that our ubitx output is woefully low. Here is a fix that I made today, if some of you can try it out, let me know if it works as well.

Step #1 Increase the predriver gain towards the higher frequencies
The predriver Q90 has a emitter degeneration capacitor C81 (0.1uf) and and R83 (10 ohms). I replaced the C81 with a 470 pf and the R83 with 5 ohms. With this, the emitter reactance decreases with increasing frequency, yielding higher gain beyond 14 MHz.

Step #2 Take off the feedback from the IRF510s. 
Just remove the R261, R262 (both are 220 ohms) to open up the gain.

Let me know if this mod is replicable?

- f

Skip Davis
 

Thanks Farhan, this is a great design and has been a easy platform to modify both hardware and firmware. 
I might try part of your mod to see what results I get too. 

Skip Davis, NC9O

On May 5, 2018, at 09:35, Ashhar Farhan <farhanbox@...> wrote:

4 watts, similar power as his mod.
- f

On Sat, 5 May 2018, 19:04 Skip Davis via Groups.Io, <skipnc9o=yahoo.com@groups.io> wrote:
Farhan what power out are you seeing with this modification at 28 MHz? 
I have installed Howard’s mods to the driver and in seeing 4 watts with RV1 at 2/3 ccw. 

Skip Davis, NC9O

On May 5, 2018, at 08:13, Ashhar Farhan <farhanbox@...> wrote:

peeps,

28 Mhz is unusually open for the last one week. I realized that our ubitx output is woefully low. Here is a fix that I made today, if some of you can try it out, let me know if it works as well.

Step #1 Increase the predriver gain towards the higher frequencies
The predriver Q90 has a emitter degeneration capacitor C81 (0.1uf) and and R83 (10 ohms). I replaced the C81 with a 470 pf and the R83 with 5 ohms. With this, the emitter reactance decreases with increasing frequency, yielding higher gain beyond 14 MHz.

Step #2 Take off the feedback from the IRF510s. 
Just remove the R261, R262 (both are 220 ohms) to open up the gain.

Let me know if this mod is replicable?

- f

Ashhar Farhan
 

I am keen to know how this works as it is an easy upgrade to give to the production guys
- f

On Sat, 5 May 2018, 19:14 Skip Davis via Groups.Io, <skipnc9o=yahoo.com@groups.io> wrote:
Thanks Farhan, this is a great design and has been a easy platform to modify both hardware and firmware. 
I might try part of your mod to see what results I get too. 

Skip Davis, NC9O

On May 5, 2018, at 09:35, Ashhar Farhan <farhanbox@...> wrote:

4 watts, similar power as his mod.
- f

On Sat, 5 May 2018, 19:04 Skip Davis via Groups.Io, <skipnc9o=yahoo.com@groups.io> wrote:
Farhan what power out are you seeing with this modification at 28 MHz? 
I have installed Howard’s mods to the driver and in seeing 4 watts with RV1 at 2/3 ccw. 

Skip Davis, NC9O

On May 5, 2018, at 08:13, Ashhar Farhan <farhanbox@...> wrote:

peeps,

28 Mhz is unusually open for the last one week. I realized that our ubitx output is woefully low. Here is a fix that I made today, if some of you can try it out, let me know if it works as well.

Step #1 Increase the predriver gain towards the higher frequencies
The predriver Q90 has a emitter degeneration capacitor C81 (0.1uf) and and R83 (10 ohms). I replaced the C81 with a 470 pf and the R83 with 5 ohms. With this, the emitter reactance decreases with increasing frequency, yielding higher gain beyond 14 MHz.

Step #2 Take off the feedback from the IRF510s. 
Just remove the R261, R262 (both are 220 ohms) to open up the gain.

Let me know if this mod is replicable?

- f

Skip Davis
 

I should have sometime this afternoon to try them out I’ll let you know my results. Also I have documented before and after mod readings at various test points in the TX driver stages so I can forward that to you too. 

Skip Davis, NC9O

On May 5, 2018, at 10:12, Ashhar Farhan <farhanbox@...> wrote:

I am keen to know how this works as it is an easy upgrade to give to the production guys
- f

On Sat, 5 May 2018, 19:14 Skip Davis via Groups.Io, <skipnc9o=yahoo.com@groups.io> wrote:
Thanks Farhan, this is a great design and has been a easy platform to modify both hardware and firmware. 
I might try part of your mod to see what results I get too. 

Skip Davis, NC9O

On May 5, 2018, at 09:35, Ashhar Farhan <farhanbox@...> wrote:

4 watts, similar power as his mod.
- f

On Sat, 5 May 2018, 19:04 Skip Davis via Groups.Io, <skipnc9o=yahoo.com@groups.io> wrote:
Farhan what power out are you seeing with this modification at 28 MHz? 
I have installed Howard’s mods to the driver and in seeing 4 watts with RV1 at 2/3 ccw. 

Skip Davis, NC9O

On May 5, 2018, at 08:13, Ashhar Farhan <farhanbox@...> wrote:

peeps,

28 Mhz is unusually open for the last one week. I realized that our ubitx output is woefully low. Here is a fix that I made today, if some of you can try it out, let me know if it works as well.

Step #1 Increase the predriver gain towards the higher frequencies
The predriver Q90 has a emitter degeneration capacitor C81 (0.1uf) and and R83 (10 ohms). I replaced the C81 with a 470 pf and the R83 with 5 ohms. With this, the emitter reactance decreases with increasing frequency, yielding higher gain beyond 14 MHz.

Step #2 Take off the feedback from the IRF510s. 
Just remove the R261, R262 (both are 220 ohms) to open up the gain.

Let me know if this mod is replicable?

- f

Kees T
 

Are you able to measure compression for linear operation (SSB) ? Harmonic content and levels ?

73 Kees K5BCQ

Ashhar Farhan
 

So, here are the final mods, 
Replace C81 from 0.1uf to 470pf
Replace R83 from 10 ohms to 2.2 ohm
(you can short R83 as well) 
Replace 97, R98 from 47 ohms to 220 ohms
Remove C261, C262. 

So, what happens is that removing the C261 and C262 increases the gain of the finals. They are run open. Hence greater gain at 28 mhz. 
However, the gain is very high at lower frequencies. So, in order to reduce the gain at the lower frequencies, the 0.1 uf cap is replaced by the 470 pf. As the frequency of the signal drops, less and less RF flows through the 470 pf, decreasing the gain of the predriver. 470 pf is not a magical value, 220 pf works almost as well. 
Here are the pictures at 14 mhz. The two tone test reveals 20 db IMDR, which is alright. If you want to see better, buy yourself two RD16HHF1s. 

- f

On Sat, 5 May 2018, 22:02 Kees T, <windy10605@...> wrote:
Are you able to measure compression for linear operation (SSB) ? Harmonic content and levels ?

73 Kees K5BCQ

Ashhar Farhan
 

I forgot the picture of the experiment.
- f

On Sun, 6 May 2018, 09:58 Ashhar Farhan, <farhanbox@...> wrote:
So, here are the final mods, 
Replace C81 from 0.1uf to 470pf
Replace R83 from 10 ohms to 2.2 ohm
(you can short R83 as well) 
Replace 97, R98 from 47 ohms to 220 ohms
Remove C261, C262. 

So, what happens is that removing the C261 and C262 increases the gain of the finals. They are run open. Hence greater gain at 28 mhz. 
However, the gain is very high at lower frequencies. So, in order to reduce the gain at the lower frequencies, the 0.1 uf cap is replaced by the 470 pf. As the frequency of the signal drops, less and less RF flows through the 470 pf, decreasing the gain of the predriver. 470 pf is not a magical value, 220 pf works almost as well. 
Here are the pictures at 14 mhz. The two tone test reveals 20 db IMDR, which is alright. If you want to see better, buy yourself two RD16HHF1s. 

- f

On Sat, 5 May 2018, 22:02 Kees T, <windy10605@...> wrote:
Are you able to measure compression for linear operation (SSB) ? Harmonic content and levels ?

73 Kees K5BCQ

Jerry Gaffke
 

Very cool, thanks for digging into this.
I tried various schemes in LT-Spice, but improving the final is more
difficult than it seems going in. 
I could seldom correctly predict the results I got.
Need to re-read a few chapters of EMRFD. 
And of course, real hardware is likely quite different than the simulation.

So is this still the previously reported  4W at 30m, 13W on 80m?

Would raising the PA-PWR voltage to 24v improve that IMDR?
Perhaps if keeping power down to something reasonable with RV1,
we could get by without up-sizing the heatsinks.

Jerry


On Sat, May 5, 2018 at 09:28 pm, Ashhar Farhan wrote:
So, here are the final mods, 
Replace C81 from 0.1uf to 470pf
Replace R83 from 10 ohms to 2.2 ohm
(you can short R83 as well) 
Replace 97, R98 from 47 ohms to 220 ohms
Remove C261, C262. 
 
So, what happens is that removing the C261 and C262 increases the gain of the finals. They are run open. Hence greater gain at 28 mhz. 
However, the gain is very high at lower frequencies. So, in order to reduce the gain at the lower frequencies, the 0.1 uf cap is replaced by the 470 pf. As the frequency of the signal drops, less and less RF flows through the 470 pf, decreasing the gain of the predriver. 470 pf is not a magical value, 220 pf works almost as well. 
Here are the pictures at 14 mhz. The two tone test reveals 20 db IMDR, which is alright. If you want to see better, buy yourself two RD16HHF1s. 
 
- f

Ashhar Farhan
 

Jerry,
The outputs are as follows (from the log book):
3.5 MHz - 12W
7 MHz - 14W
10 MHz - 11W
14 MHz - 10W
21 MHz - 7.8W
28 MHz - 4.4W
(The preset was kept at maximum)

- f


On Sun, May 6, 2018 at 10:14 AM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
Very cool, thanks for digging into this.
I tried various schemes in LT-Spice, but improving the final is more
difficult than it seems going in. 
I could seldom correctly predict the results I got.
Need to re-read a few chapters of EMRFD. 
And of course, real hardware is likely quite different than the simulation.

So is this still the previously reported  4W at 30m, 13W on 80m?

Would raising the PA-PWR voltage to 24v improve that IMDR?
Perhaps if keeping power down to something reasonable with RV1,
we could get by without up-sizing the heatsinks.

Jerry


On Sat, May 5, 2018 at 09:28 pm, Ashhar Farhan wrote:
So, here are the final mods, 
Replace C81 from 0.1uf to 470pf
Replace R83 from 10 ohms to 2.2 ohm
(you can short R83 as well) 
Replace 97, R98 from 47 ohms to 220 ohms
Remove C261, C262. 
 
So, what happens is that removing the C261 and C262 increases the gain of the finals. They are run open. Hence greater gain at 28 mhz. 
However, the gain is very high at lower frequencies. So, in order to reduce the gain at the lower frequencies, the 0.1 uf cap is replaced by the 470 pf. As the frequency of the signal drops, less and less RF flows through the 470 pf, decreasing the gain of the predriver. 470 pf is not a magical value, 220 pf works almost as well. 
Here are the pictures at 14 mhz. The two tone test reveals 20 db IMDR, which is alright. If you want to see better, buy yourself two RD16HHF1s. 
 
- f


K9HZ <bill@...>
 

Thanks.  This confirms what we tried two months ago.

 

 

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 Group at Groups.IO.

 

email:  bill@...

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Ashhar Farhan
Sent: Saturday, May 5, 2018 11:29 PM
To: BITX20@groups.io
Subject: Re: [BITX20] boosting the power on 28 MHz #ubitx

 

So, here are the final mods, 

Replace C81 from 0.1uf to 470pf

Replace R83 from 10 ohms to 2.2 ohm

(you can short R83 as well) 

Replace 97, R98 from 47 ohms to 220 ohms

Remove C261, C262. 

 

So, what happens is that removing the C261 and C262 increases the gain of the finals. They are run open. Hence greater gain at 28 mhz. 

However, the gain is very high at lower frequencies. So, in order to reduce the gain at the lower frequencies, the 0.1 uf cap is replaced by the 470 pf. As the frequency of the signal drops, less and less RF flows through the 470 pf, decreasing the gain of the predriver. 470 pf is not a magical value, 220 pf works almost as well. 

Here are the pictures at 14 mhz. The two tone test reveals 20 db IMDR, which is alright. If you want to see better, buy yourself two RD16HHF1s. 

 

- f

 

On Sat, 5 May 2018, 22:02 Kees T, <windy10605@...> wrote:

Are you able to measure compression for linear operation (SSB) ? Harmonic content and levels ?

73 Kees K5BCQ


Virus-free. www.avg.com

G1KQH
 

Ashar,

Is this mod going to be implemented on new production?

Thanks!

73 Steve

G1KQH

Ashhar Farhan
 

Yes, the plan was to use an RD device for the new version. We ran into availability issues. The lead time from Mitsuibishi was 10 weeks. So, I took a call to continue with the IRF510s. However, the new PCB has pads for the RD16HHF1 as well as the IRF510s.
- f

On Sun, 6 May 2018, 16:05 G1KQH via Groups.Io, <g1kqh=yahoo.co.uk@groups.io> wrote:
Ashar,

Is this mod going to be implemented on new production?

Thanks!

73 Steve

G1KQH

K9HZ <bill@...>
 

“However, the new PCB has pads for the RD16HHF1”

 

Thank you !!!!!!

 

 

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 Group at Groups.IO.

 

email:  bill@...

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Ashhar Farhan
Sent: Sunday, May 6, 2018 6:14 AM
To: BITX20@groups.io
Subject: Re: [BITX20] boosting the power on 28 MHz #ubitx

 

Yes, the plan was to use an RD device for the new version. We ran into availability issues. The lead time from Mitsuibishi was 10 weeks. So, I took a call to continue with the IRF510s. However, the new PCB has pads for the RD16HHF1 as well as the IRF510s.

- f

 

On Sun, 6 May 2018, 16:05 G1KQH via Groups.Io, <g1kqh=yahoo.co.uk@groups.io> wrote:

Ashar,

Is this mod going to be implemented on new production?

Thanks!

73 Steve

G1KQH


Virus-free. www.avg.com

Tim Gorman
 

Jerry,

I tried raising the voltage on my final to 24v. It didn't help the 3rd
order IMD at all. I suspect most of the IMD is coming from crossover
distortion, not flat-topping.

tim ab0wr

On Sat, 05 May 2018 21:44:28 -0700
"Jerry Gaffke via Groups.Io" <jgaffke=yahoo.com@groups.io> wrote:

Very cool, thanks for digging into this.
I tried various schemes in LT-Spice, but improving the final is more
difficult than it seems going in. 
I could seldom correctly predict the results I got.
Need to re-read a few chapters of EMRFD. 
And of course, real hardware is likely quite different than the
simulation.

So is this still the previously reported  4W at 30m, 13W on 80m?

Would raising the PA-PWR voltage to 24v improve that IMDR?
Perhaps if keeping power down to something reasonable with RV1,
we could get by without up-sizing the heatsinks.

Jerry

On Sat, May 5, 2018 at 09:28 pm, Ashhar Farhan wrote:


So, here are the final mods, 
Replace C81 from 0.1uf to 470pf
Replace R83 from 10 ohms to 2.2 ohm
(you can short R83 as well) 
Replace 97, R98 from 47 ohms to 220 ohms
Remove C261, C262. 
 
So, what happens is that removing the C261 and C262 increases the
gain of the finals. They are run open. Hence greater gain at 28
mhz. However, the gain is very high at lower frequencies. So, in
order to reduce the gain at the lower frequencies, the 0.1 uf cap
is replaced by the 470 pf. As the frequency of the signal drops,
less and less RF flows through the 470 pf, decreasing the gain of
the predriver. 470 pf is not a magical value, 220 pf works almost
as well. Here are the pictures at 14 mhz. The two tone test reveals
20 db IMDR, which is alright. If you want to see better, buy
yourself two RD16HHF1s.
- f

Jerry Gaffke
 

That's interesting.
Perhaps the bias wants to be higher than 100ma.
Though as I recall, wa2eby was recommending 10ma of bias, and is quite competent.
As is Allison.

Perhaps there's IMD contributions from earlier stages?
Perhaps a fault in the uBitx design, I'm starting to suspect the use of the two chokes to feed the drains.

Jerry



On Sun, May 6, 2018 at 07:53 am, Tim Gorman wrote:
I tried raising the voltage on my final to 24v. It didn't help the 3rd
order IMD at all. I suspect most of the IMD is coming from crossover
distortion, not flat-topping.

Ashhar Farhan
 

The IMD from the driver stage is well below -30 dbc. It is close to -40dbc. I don't have access to my lab notes at the moment. The IMD is from the IRF510s alone. Changing to RD16HHF1 reduces the IMD products by another 10 db.

- f

On Sun, May 6, 2018 at 8:33 PM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
That's interesting.
Perhaps the bias wants to be higher than 100ma.
Though as I recall, wa2eby was recommending 10ma of bias, and is quite competent.
As is Allison.

Perhaps there's IMD contributions from earlier stages?
Perhaps a fault in the uBitx design, I'm starting to suspect the use of the two chokes to feed the drains.

Jerry



On Sun, May 6, 2018 at 07:53 am, Tim Gorman wrote:
I tried raising the voltage on my final to 24v. It didn't help the 3rd
order IMD at all. I suspect most of the IMD is coming from crossover
distortion, not flat-topping.