Date   
Surplus Case from Skycraft Parts #ubitx #bitx40

w4rjp
 

Last Saturday went to the Orlando, Fl Hamfest looking for a uBitx case.  Despite all the tailgaters/vendors none seem to have suitable cases. (Did snag an almost new Experimental Methods in RF Design book for $10, so not a total waste of time.)

My buddy and I decided to head over to Skycraft Parts & Surplus in the afternoon. While he made the rounds for parts for his next project, I headed for the surplus cases.  There on the top shelf were 5 aluminum cases. Pulled one down and said WOW, it is perfect for the BitX. They were made for transportation IP based video systems. The size is 8.2 X 8 X 3.5 inches and has separate panels for top, bottom, front and rear. As you can see from the pictures attached, the LCD hole is already cut as well as holes for a fan, BNC, and switch. Even included a circuit board with LCD, fan, BNC, etc.  Price $9.95.

If you are in the central Florida area (they will mail order) and are in need of an outstanding aluminum case for your uBitx or Bitx40/20 may want to check it out. Suspect they won't be on the shelf too long.

Re: New ideas for the Audio TX/RX pop and PA output stage improvements on ubitx.net

Rob Snow
 

I'm learning here.  I understand that a mica capacitor is the best type to use with RF from reading and they are the most stable.

What would the impact be of using a polystyrene or ceramic capacitor in place of the 33pf?  I'm assuming you would see distortion, but I don't know.

Re: Surplus Case from Skycraft Parts #ubitx #bitx40

Ross - VA1KAY
 

Here's a fun case I saw in Harbor Freight today.  Very handy if you want to keep your uBITX "safe" or if you just want to hide the fact that you are a uBITX owner!! 

Re: New ideas for the Audio TX/RX pop and PA output stage improvements on ubitx.net

Mike Woods
 

On 17/02/18 10:53 AM, John wrote:
I can't find reference to the ferrite balun BN43-201. Would it be BN43-202 instead by any chance?
John - I will ask Erhard DF3FY whether this was an error.  I suspect it was.

73 Mike

--
Mike Woods
mhwoods@...

Re: New ideas for the Audio TX/RX pop and PA output stage improvements on ubitx.net

M Garza <mgarza896@...>
 

Ceramic capacitors would work fine.  Just make sure it is rated for the voltage that will be present.  I use 500 or 1KV caps, personally.  Over kill, yes, but I have not had one fail yet.

Just my $0.02.

Marco - KG5PRT

On Sat, Feb 17, 2018 at 1:49 PM, Rob Snow <rsnow@...> wrote:
I'm learning here.  I understand that a mica capacitor is the best type to use with RF from reading and they are the most stable.

What would the impact be of using a polystyrene or ceramic capacitor in place of the 33pf?  I'm assuming you would see distortion, but I don't know.


Re: New ideas for the Audio TX/RX pop and PA output stage improvements on ubitx.net

Jerry Gaffke
 

Silver mica caps work fine, were state of the art when most hams learned how to build LPF's and such.
But that was 50 years ago.
Surface mount ceramic caps of type np0 or c0g are far cheaper and just as good.
I'd recommend something rated for at least 200 volts for a uBitx transmit filter, maybe even 500v.
Probably in a 1206 or 1210 size package.
Avoid other ceramic dielectrics such as x5r and x7r, fine for bypass caps but capacitance can vary wildly with applied voltage.
Polystyrene should be fine if that's what you got.

Through-hole caps are generally more expensive than surface mount,
as handling of surface mount parts is easier and sales volumes are much higher.

Jerry, KE7ER



On Sat, Feb 17, 2018 at 11:49 am, Rob Snow wrote:
I'm learning here.  I understand that a mica capacitor is the best type to use with RF from reading and they are the most stable.
 
What would the impact be of using a polystyrene or ceramic capacitor in place of the 33pf?  I'm assuming you would see distortion, but I don't know.

Re: New ideas for the Audio TX/RX pop and PA output stage improvements on ubitx.net

K9HZ <bill@...>
 

The mistake that most people make in RF circuits is not paying attention to the current rating of the part.  Make sure your capacitor can handle the current for its service.  The voltage, size, and rating (eg NPO) etc. are the easy parts.

 

 

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 Rob Snow
Sent: Saturday, February 17, 2018 1:49 PM
To: BITX20@groups.io
Subject: Re: [BITX20] New ideas for the Audio TX/RX pop and PA output stage improvements on ubitx.net

 

I'm learning here.  I understand that a mica capacitor is the best type to use with RF from reading and they are the most stable.

 

What would the impact be of using a polystyrene or ceramic capacitor in place of the 33pf?  I'm assuming you would see distortion, but I don't know.


Virus-free. www.avg.com

Re: top band ubitx

Michael Shreeve
 

Great work. Looks like the heat sinks are direct connect like the originals ? Sorry if you've already mentioned this.

I'm going for mica insulated types because then I can use a huge heat sink covering the entire back of the radio. We did it for years and no reason to not do it. I have one heat sink that came with a thermal electric cooler. Might use it, but I also have others.

Re: Micron? long, logical and hopefully both educational and amusing ...

dtruedog@...
 

That's great!!

Sent from my Verizon 4G LTE Droid

On Feb 17, 2018 12:07 AM, VE7WQ <v@...> wrote:

Hello Dexter,


Friday, February 16, 2018, you wrote among many words:


DNM> There was a young Curate of Kew

DNM> Kept a cat he found under a pew,

DNM> Tried to teach it to speak

DNM> alphabetical Greek,

DNM> But he never could get it past "mew".

DNM> 73 all

DNM> Dex, ZL2DEX


So, folks, I propose start calling the 'ubitx' the 'mewbitx'. :)


73! George

VE7WQ

Re: New ideas for the Audio TX/RX pop and PA output stage improvements on ubitx.net

Jerry Gaffke
 


On Sat, Feb 17, 2018 at 12:19 pm, K9HZ wrote:

The mistake that most people make in RF circuits is not paying attention to the current rating of the part.  Make sure your capacitor can handle the current for its service.  The voltage, size, and rating (eg NPO) etc. are the easy parts.

 

Re: New ideas for the Audio TX/RX pop and PA output stage improvements on ubitx.net

K9HZ <bill@...>
 

Yes that makes sense…

 

The current through a capacitor is given by I=C*dV/dt so the average current over time is I=C*int[dV/dt]/t… For your example: let’s use a 100pf capacitor in an 30 MHz circuit at 50 VRMS which is 140V P-P.  Iavg = 0.42 * 0.707 = 0.3 amps average.  Now the spec from that capacitor in your finding is 0.1% at 1 VRMS at 1MHZ which is 0.00028A * 0.707RMS *1000% = 0.2 Amps continuous at 30 MHz.  Yikes we are over by 50%!  Note that this DOES vary with capacitance… that’s why the larger the capacitor, the more current capacity is needed.

 

There are plenty of calculators on the internet to figure this out…. Google “capacitor Current Calculator”.

 

 

 

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 Jerry Gaffke via Groups.Io
Sent: Saturday, February 17, 2018 3:18 PM
To: BITX20@groups.io
Subject: Re: [BITX20] New ideas for the Audio TX/RX pop and PA output stage improvements on ubitx.net

 


This Vishay datasheet is fairly typical.
    

https://www.mouser.com/ds/2/427/vjcommercialseries-222796.pdf

Closest thing I see to a "current rating" for the c0g parts is the Dissipation Factor on page 1. 
Not quite enough information.
They spec a dissipation of 0.1% at 1.0 VRMS and 1 MHz,
but we might be using it at 50 VRMS and 30 MHz.

Any further advice on how to evaluate caps for use in a LPF?


Though note that this c0g spec is much better than the x7r spec,
which claims 2.5% dissipation at 1.0 VRMS and 1 KHz.

Jerry

On Sat, Feb 17, 2018 at 12:19 pm, K9HZ wrote:

The mistake that most people make in RF circuits is not paying attention to the current rating of the part.  Make sure your capacitor can handle the current for its service.  The voltage, size, and rating (eg NPO) etc. are the easy parts.

 


Virus-free. www.avg.com

Re: BITX40: Allard's Firmware with Rotary Encoder?

Don, ND6T
 

Although not Allard's sketch, this has worked for me: http://www.nd6t.com/bitx/documentation/encoder.htm I am also using polling (without the interrupts) on a replacement sketch for the uBITX although I haven't completed the menus and such, it still works much better than the original. Perhaps you can use portions. 73, ND6T

Re: RD16HHF1 in the uBITX #ubitx

K9HZ <bill@...>
 

I had a couple of hours of spare time today so I started off my measuring the gain of the pre-drivers in the uBITx.. and sure enough, there is a lot of variation from 1.8-54 MHz (where I want mine to work).  Substituting the RD15HVF1 (my choice of RF PA) into the circuit with no other changes gives results similar to what John saw.. but it is because of the pre-driver stages.  I contemplated ways of compensating the drive with frequency but there isn’t a really good solution using reactive components because it causes some other non-desirable behavior (like a peak in drive at 21 MHz that is too high for the PA).  I did land on a rather bruit force method that does work well… I removed RV1 (drive control) from the circuit board and replaced it with a tiny board with three small relays and four 100 ohm 10 turn pots.  The relays are controlled by the KT1, KT1, and KT3 drivers…  The short story is that now I have gain that is adjustable for essentially each of the bands (at least sets of bands that follow the LP filters).  I’ve adjusted the drive so that the PA puts out the same power (+/- about 2 watts) across the entire frequency spectrum.  I suppose this should have been an obvious answer, but I’m not fond of using relays for stuff like this even if they only draw milliwatts…

 

 

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: Thursday, February 15, 2018 7:39 AM
To: BITX20@groups.io
Subject: Re: [BITX20] RD16HHF1 in the uBITX #ubitx

 

I have done a strait replacement of the IRF510s with RD16HHF1s. 

 

Here are the before and after values I got.

 

All tests done with uBitx VR1 drive level in the same position of approx 60% of range.

 

1. IRF510s and main board at 12.1V. PA idle current checked at 0.20A total (factory setting) so assume 100mA in each final. 

(For info, Rx currents: 164mA no volume, about 209mA "normal" volume). 

- At 7.1Mhz:   10W, total current: 1.79A, of which PA current: 1.31A, therefore main board current 0.48A

- At 14.2Mhz: 5.5W, total current: 1.39A, of which PA current: 1.0A,  therefore main board current 0.39A

- At 21.2Mhz: 2.2W, total current: 0.95A, of which PA current: 0.53A, therefore main board current 0.42A

- At 28.1Mhz: 1.3W, total current: 0.95A, of which PA current: 0.53A, therefore main board current 0.42A

 

 

2. IRF510s with 16.5V, 13.8V for main board. PA total idle current checked at 0.21A. 

(For info, Rx currents: 188mA no volume, about 230mA "normal" volume). 

- At 7.1Mhz:  19W, total current: 2.65A, of which PA current: 2.09A, therefore main board current 0.56A

- At 14.2Mhz: 11W, total current: 2.20A, of which PA current: 1.80A, therefore main board current 0.40A

- At 21.2Mhz: 5.5W, total current: 1.40A, of which PA current: 1.00A, therefore main board current 0.40A

- At 28.1Mhz: 2.2W, total current: 1.02A, of which PA current: 0.60A, therefore main board current 0.42A

 

 

I haven't found a definitive reference for the safe and optimum values of the RD16HHF1s idle bias current but it seems to range from 200 to 500mA. So I would not recommend long term usage of the 500mA bias I used for these measurements.

I will reset mine to probably the 400-450mA value I read from some articles.

 

3. RD16HHF1s and main board at 12.1VDC, 250mA idle bias each (Total 0.5A PA idle current). 

- At 7.1Mhz:  10W,  PA current: 1.20A

- At 14.2Mhz: 9W,   PA current: 1.21A

- At 21.2Mhz: 4.5W, PA current: 0.65A

- At 28.1Mhz: 5.5W, PA current: 0.95A

 

 

4. RD16HHF1s and main board at 12.1VDC, 500mA idle bias each (Total 1A PA idle current). 

- At 7.1Mhz: 10W, PA current: 1.18A

- At 14.2Mhz: 9W, PA current: 1.26A

- At 21.2Mhz: 5W, PA current: 0.71A

- At 28.1Mhz: 6W, PA current: 1.11A

 

 

5. RD16HHF1s and main board at 13.8VDC, 500mA idle bias each (Total 1A PA idle current). 

- At 7.1Mhz:  13.5W, PA current: 1.95A

- At 14.2Mhz: 13.5W, PA current: 1.93A

- At 21.2Mhz: 6W,    PA current: 1.38A

- At 28.1Mhz: 9.5W,  PA current: 1.79A

 

 

 

Interesting observations:

 

A. The RD16HHF1 produces a much flatter power curver over frequency (in my device), although it shows a dip somewhere near the 15m band.

 

B. The IRF510 can produce some nice power in the lower frequencies when increasing the PA supply voltage, but it comes at the price of a steep power drop at higher frequencies.

 

C. The bias does not seem to influence the efficiency of the finals at full power with RD16HHF1, since biasing at 250 and 500mA produces essentially the same output for the same DC power input. Assuming distortion reduces with higher bias, can we assume a higher bias (within limits) is preferable? Any risk of thermal runaway?

 

D. The board main current (which includes the current in the driving stages of the power amplifier) does not seem to change with frequency from 20m onwards. Is this because the gain is pretty constant? If so, most of the drop in power with increasing frequency seems to be in the IRF510s, supporting the results obtained with the RD16HHF1s.

 

E. With the current uBitx PA circuit the RD16HHF1 seems limited in output, although not having the proper test equipment I can't say where the limitation occurs.

 

F. When I increased the drive through VR1 I noticed that at around 40% for the lower frequencies and at around 60% for the top frequencies I get a compression effect and the output does not increase much more from there on. I left it at 60% and got a positive feedback on the voice quality on my first QSO on 40m. Therefore I assume that the compression/clipping is not significant at that level (but I can't measure the sprectral purity).

 

 

So since my target was around 10W on 10m and 10 to 15W on 40m minimum I can say I have reached my goal just by changing the finals to RD16HHF1s and supplying the board with 13.8VDC (below the 15.2/15V stated in the respective datasheets of the RD16HHF1 and TDA2822).

 

To replace the finals I simply cut the legs of the IRF510s about 3mm above the board and correspondingly cut and crossed over the drain and source pins of the RD16s to match, then soldered in place.

 

It would be interesting to compare these results with others who performed the finals swap on the stock uBitx.

 

Next is the installation of the TPA2016 audio amplifier with I2C controllable AGC.

This is a lot of fun.

 

All the best,

 

73, John (VK2ETA)

 




Virus-free. www.avg.com

Re: RD16HHF1 in the uBITX #ubitx

Gordon Gibby <ggibby@...>
 

​Dr. Schmidt -- no way to put some feedback into the circuit in some manner to stabilize the gain?    1000 pf across the 22 ohm emitter resistors to have a 3db break at 7 MHz?




From: BITX20@groups.io <BITX20@groups.io> on behalf of K9HZ <bill@...>
Sent: Saturday, February 17, 2018 6:51 PM
To: BITX20@groups.io
Subject: Re: [BITX20] RD16HHF1 in the uBITX #ubitx
 

I had a couple of hours of spare time today so I started off my measuring the gain of the pre-drivers in the uBITx.. and sure enough, there is a lot of variation from 1.8-54 MHz (where I want mine to work).  Substituting the RD15HVF1 (my choice of RF PA) into the circuit with no other changes gives results similar to what John saw.. but it is because of the pre-driver stages.  I contemplated ways of compensating the drive with frequency but there isn’t a really good solution using reactive components because it causes some other non-desirable behavior (like a peak in drive at 21 MHz that is too high for the PA).  I did land on a rather bruit force method that does work well… I removed RV1 (drive control) from the circuit board and replaced it with a tiny board with three small relays and four 100 ohm 10 turn pots.  The relays are controlled by the KT1, KT1, and KT3 drivers…  The short story is that now I have gain that is adjustable for essentially each of the bands (at least sets of bands that follow the LP filters).  I’ve adjusted the drive so that the PA puts out the same power (+/- about 2 watts) across the entire frequency spectrum.  I suppose this should have been an obvious answer, but I’m not fond of using relays for stuff like this even if they only draw milliwatts…

 

 

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: Thursday, February 15, 2018 7:39 AM
To: BITX20@groups.io
Subject: Re: [BITX20] RD16HHF1 in the uBITX #ubitx

 

I have done a strait replacement of the IRF510s with RD16HHF1s. 

 

Here are the before and after values I got.

 

All tests done with uBitx VR1 drive level in the same position of approx 60% of range.

 

1. IRF510s and main board at 12.1V. PA idle current checked at 0.20A total (factory setting) so assume 100mA in each final. 

(For info, Rx currents: 164mA no volume, about 209mA "normal" volume). 

- At 7.1Mhz:   10W, total current: 1.79A, of which PA current: 1.31A, therefore main board current 0.48A

- At 14.2Mhz: 5.5W, total current: 1.39A, of which PA current: 1.0A,  therefore main board current 0.39A

- At 21.2Mhz: 2.2W, total current: 0.95A, of which PA current: 0.53A, therefore main board current 0.42A

- At 28.1Mhz: 1.3W, total current: 0.95A, of which PA current: 0.53A, therefore main board current 0.42A

 

 

2. IRF510s with 16.5V, 13.8V for main board. PA total idle current checked at 0.21A. 

(For info, Rx currents: 188mA no volume, about 230mA "normal" volume). 

- At 7.1Mhz:  19W, total current: 2.65A, of which PA current: 2.09A, therefore main board current 0.56A

- At 14.2Mhz: 11W, total current: 2.20A, of which PA current: 1.80A, therefore main board current 0.40A

- At 21.2Mhz: 5.5W, total current: 1.40A, of which PA current: 1.00A, therefore main board current 0.40A

- At 28.1Mhz: 2.2W, total current: 1.02A, of which PA current: 0.60A, therefore main board current 0.42A

 

 

I haven't found a definitive reference for the safe and optimum values of the RD16HHF1s idle bias current but it seems to range from 200 to 500mA. So I would not recommend long term usage of the 500mA bias I used for these measurements.

I will reset mine to probably the 400-450mA value I read from some articles.

 

3. RD16HHF1s and main board at 12.1VDC, 250mA idle bias each (Total 0.5A PA idle current). 

- At 7.1Mhz:  10W,  PA current: 1.20A

- At 14.2Mhz: 9W,   PA current: 1.21A

- At 21.2Mhz: 4.5W, PA current: 0.65A

- At 28.1Mhz: 5.5W, PA current: 0.95A

 

 

4. RD16HHF1s and main board at 12.1VDC, 500mA idle bias each (Total 1A PA idle current). 

- At 7.1Mhz: 10W, PA current: 1.18A

- At 14.2Mhz: 9W, PA current: 1.26A

- At 21.2Mhz: 5W, PA current: 0.71A

- At 28.1Mhz: 6W, PA current: 1.11A

 

 

5. RD16HHF1s and main board at 13.8VDC, 500mA idle bias each (Total 1A PA idle current). 

- At 7.1Mhz:  13.5W, PA current: 1.95A

- At 14.2Mhz: 13.5W, PA current: 1.93A

- At 21.2Mhz: 6W,    PA current: 1.38A

- At 28.1Mhz: 9.5W,  PA current: 1.79A

 

 

 

Interesting observations:

 

A. The RD16HHF1 produces a much flatter power curver over frequency (in my device), although it shows a dip somewhere near the 15m band.

 

B. The IRF510 can produce some nice power in the lower frequencies when increasing the PA supply voltage, but it comes at the price of a steep power drop at higher frequencies.

 

C. The bias does not seem to influence the efficiency of the finals at full power with RD16HHF1, since biasing at 250 and 500mA produces essentially the same output for the same DC power input. Assuming distortion reduces with higher bias, can we assume a higher bias (within limits) is preferable? Any risk of thermal runaway?

 

D. The board main current (which includes the current in the driving stages of the power amplifier) does not seem to change with frequency from 20m onwards. Is this because the gain is pretty constant? If so, most of the drop in power with increasing frequency seems to be in the IRF510s, supporting the results obtained with the RD16HHF1s.

 

E. With the current uBitx PA circuit the RD16HHF1 seems limited in output, although not having the proper test equipment I can't say where the limitation occurs.

 

F. When I increased the drive through VR1 I noticed that at around 40% for the lower frequencies and at around 60% for the top frequencies I get a compression effect and the output does not increase much more from there on. I left it at 60% and got a positive feedback on the voice quality on my first QSO on 40m. Therefore I assume that the compression/clipping is not significant at that level (but I can't measure the sprectral purity).

 

 

So since my target was around 10W on 10m and 10 to 15W on 40m minimum I can say I have reached my goal just by changing the finals to RD16HHF1s and supplying the board with 13.8VDC (below the 15.2/15V stated in the respective datasheets of the RD16HHF1 and TDA2822).

 

To replace the finals I simply cut the legs of the IRF510s about 3mm above the board and correspondingly cut and crossed over the drain and source pins of the RD16s to match, then soldered in place.

 

It would be interesting to compare these results with others who performed the finals swap on the stock uBitx.

 

Next is the installation of the TPA2016 audio amplifier with I2C controllable AGC.

This is a lot of fun.

 

All the best,

 

73, John (VK2ETA)

 




Virus-free. www.avg.com

Re: RD16HHF1 in the uBITX #ubitx

K9HZ <bill@...>
 

Trouble is… it occurs at every stage so where do you put the gain equalization?  I made a couple of calculations and then swept the circuit and noticed that the PA ran away at 21 MHz so did not pursue that.  I’m sure there is a way to do it but I only had a couple of hours to work on it.

 

Another thing that one could do is use an AGC circuit fed back from the PA to the first driver stage to control the overall stage gain… but again that will take some simulating to get through.

 

BTW name is Bill…

 

 

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 Gordon Gibby
Sent: Saturday, February 17, 2018 6:54 PM
To: BITX20@groups.io
Subject: Re: [BITX20] RD16HHF1 in the uBITX #ubitx

 

​Dr. Schmidt -- no way to put some feedback into the circuit in some manner to stabilize the gain?    1000 pf across the 22 ohm emitter resistors to have a 3db break at 7 MHz?

 

 


From: BITX20@groups.io <BITX20@groups.io> on behalf of K9HZ <bill@...>
Sent: Saturday, February 17, 2018 6:51 PM
To: BITX20@groups.io
Subject: Re: [BITX20] RD16HHF1 in the uBITX #ubitx

 

I had a couple of hours of spare time today so I started off my measuring the gain of the pre-drivers in the uBITx.. and sure enough, there is a lot of variation from 1.8-54 MHz (where I want mine to work).  Substituting the RD15HVF1 (my choice of RF PA) into the circuit with no other changes gives results similar to what John saw.. but it is because of the pre-driver stages.  I contemplated ways of compensating the drive with frequency but there isn’t a really good solution using reactive components because it causes some other non-desirable behavior (like a peak in drive at 21 MHz that is too high for the PA).  I did land on a rather bruit force method that does work well… I removed RV1 (drive control) from the circuit board and replaced it with a tiny board with three small relays and four 100 ohm 10 turn pots.  The relays are controlled by the KT1, KT1, and KT3 drivers…  The short story is that now I have gain that is adjustable for essentially each of the bands (at least sets of bands that follow the LP filters).  I’ve adjusted the drive so that the PA puts out the same power (+/- about 2 watts) across the entire frequency spectrum.  I suppose this should have been an obvious answer, but I’m not fond of using relays for stuff like this even if they only draw milliwatts…

 

 

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: Thursday, February 15, 2018 7:39 AM
To: BITX20@groups.io
Subject: Re: [BITX20] RD16HHF1 in the uBITX #ubitx

 

I have done a strait replacement of the IRF510s with RD16HHF1s. 

 

Here are the before and after values I got.

 

All tests done with uBitx VR1 drive level in the same position of approx 60% of range.

 

1. IRF510s and main board at 12.1V. PA idle current checked at 0.20A total (factory setting) so assume 100mA in each final. 

(For info, Rx currents: 164mA no volume, about 209mA "normal" volume). 

- At 7.1Mhz:   10W, total current: 1.79A, of which PA current: 1.31A, therefore main board current 0.48A

- At 14.2Mhz: 5.5W, total current: 1.39A, of which PA current: 1.0A,  therefore main board current 0.39A

- At 21.2Mhz: 2.2W, total current: 0.95A, of which PA current: 0.53A, therefore main board current 0.42A

- At 28.1Mhz: 1.3W, total current: 0.95A, of which PA current: 0.53A, therefore main board current 0.42A

 

 

2. IRF510s with 16.5V, 13.8V for main board. PA total idle current checked at 0.21A. 

(For info, Rx currents: 188mA no volume, about 230mA "normal" volume). 

- At 7.1Mhz:  19W, total current: 2.65A, of which PA current: 2.09A, therefore main board current 0.56A

- At 14.2Mhz: 11W, total current: 2.20A, of which PA current: 1.80A, therefore main board current 0.40A

- At 21.2Mhz: 5.5W, total current: 1.40A, of which PA current: 1.00A, therefore main board current 0.40A

- At 28.1Mhz: 2.2W, total current: 1.02A, of which PA current: 0.60A, therefore main board current 0.42A

 

 

I haven't found a definitive reference for the safe and optimum values of the RD16HHF1s idle bias current but it seems to range from 200 to 500mA. So I would not recommend long term usage of the 500mA bias I used for these measurements.

I will reset mine to probably the 400-450mA value I read from some articles.

 

3. RD16HHF1s and main board at 12.1VDC, 250mA idle bias each (Total 0.5A PA idle current). 

- At 7.1Mhz:  10W,  PA current: 1.20A

- At 14.2Mhz: 9W,   PA current: 1.21A

- At 21.2Mhz: 4.5W, PA current: 0.65A

- At 28.1Mhz: 5.5W, PA current: 0.95A

 

 

4. RD16HHF1s and main board at 12.1VDC, 500mA idle bias each (Total 1A PA idle current). 

- At 7.1Mhz: 10W, PA current: 1.18A

- At 14.2Mhz: 9W, PA current: 1.26A

- At 21.2Mhz: 5W, PA current: 0.71A

- At 28.1Mhz: 6W, PA current: 1.11A

 

 

5. RD16HHF1s and main board at 13.8VDC, 500mA idle bias each (Total 1A PA idle current). 

- At 7.1Mhz:  13.5W, PA current: 1.95A

- At 14.2Mhz: 13.5W, PA current: 1.93A

- At 21.2Mhz: 6W,    PA current: 1.38A

- At 28.1Mhz: 9.5W,  PA current: 1.79A

 

 

 

Interesting observations:

 

A. The RD16HHF1 produces a much flatter power curver over frequency (in my device), although it shows a dip somewhere near the 15m band.

 

B. The IRF510 can produce some nice power in the lower frequencies when increasing the PA supply voltage, but it comes at the price of a steep power drop at higher frequencies.

 

C. The bias does not seem to influence the efficiency of the finals at full power with RD16HHF1, since biasing at 250 and 500mA produces essentially the same output for the same DC power input. Assuming distortion reduces with higher bias, can we assume a higher bias (within limits) is preferable? Any risk of thermal runaway?

 

D. The board main current (which includes the current in the driving stages of the power amplifier) does not seem to change with frequency from 20m onwards. Is this because the gain is pretty constant? If so, most of the drop in power with increasing frequency seems to be in the IRF510s, supporting the results obtained with the RD16HHF1s.

 

E. With the current uBitx PA circuit the RD16HHF1 seems limited in output, although not having the proper test equipment I can't say where the limitation occurs.

 

F. When I increased the drive through VR1 I noticed that at around 40% for the lower frequencies and at around 60% for the top frequencies I get a compression effect and the output does not increase much more from there on. I left it at 60% and got a positive feedback on the voice quality on my first QSO on 40m. Therefore I assume that the compression/clipping is not significant at that level (but I can't measure the sprectral purity).

 

 

So since my target was around 10W on 10m and 10 to 15W on 40m minimum I can say I have reached my goal just by changing the finals to RD16HHF1s and supplying the board with 13.8VDC (below the 15.2/15V stated in the respective datasheets of the RD16HHF1 and TDA2822).

 

To replace the finals I simply cut the legs of the IRF510s about 3mm above the board and correspondingly cut and crossed over the drain and source pins of the RD16s to match, then soldered in place.

 

It would be interesting to compare these results with others who performed the finals swap on the stock uBitx.

 

Next is the installation of the TPA2016 audio amplifier with I2C controllable AGC.

This is a lot of fun.

 

All the best,

 

73, John (VK2ETA)

 

 

Virus-free. www.avg.com

Re: RD16HHF1 in the uBITX #ubitx

Dave Bottom <ars.kd6az@...>
 

It is interesting that Chris M0NKA does this with his mcHF SDR kit.

It has a Max Pwr setting that is similar to uBITX on 80M (12W) but they have a calibrate setting for each band at 5W, and then can step it down to 2W, 1W, 0.5W (these are approximate based on 5W setting of drive level.)

When I get back home (Orlando then Yuma Hamfest)  I’ll make some notes on how he’s done this, as I was already contemplating doing this on the uBITX when I go to the RD16HHF1’s.

Dave WI6R


On Feb 17, 2018, at 4:51 PM, K9HZ <bill@...> wrote:

I had a couple of hours of spare time today so I started off my measuring the gain of the pre-drivers in the uBITx.. and sure enough, there is a lot of variation from 1.8-54 MHz (where I want mine to work).  Substituting the RD15HVF1 (my choice of RF PA) into the circuit with no other changes gives results similar to what John saw.. but it is because of the pre-driver stages.  I contemplated ways of compensating the drive with frequency but there isn’t a really good solution using reactive components because it causes some other non-desirable behavior (like a peak in drive at 21 MHz that is too high for the PA).  I did land on a rather bruit force method that does work well… I removed RV1 (drive control) from the circuit board and replaced it with a tiny board with three small relays and four 100 ohm 10 turn pots.  The relays are controlled by the KT1, KT1, and KT3 drivers…  The short story is that now I have gain that is adjustable for essentially each of the bands (at least sets of bands that follow the LP filters).  I’ve adjusted the drive so that the PA puts out the same power (+/- about 2 watts) across the entire frequency spectrum.  I suppose this should have been an obvious answer, but I’m not fond of using relays for stuff like this even if they only draw milliwatts…

 

 

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! <image002.png>

 

Moderator – North American QRO Yahoo Group.

 

email:  bill@...

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of John
Sent: Thursday, February 15, 2018 7:39 AM
To: BITX20@groups.io
Subject: Re: [BITX20] RD16HHF1 in the uBITX #ubitx

 

I have done a strait replacement of the IRF510s with RD16HHF1s. 

 

Here are the before and after values I got.

 

All tests done with uBitx VR1 drive level in the same position of approx 60% of range.

 

1. IRF510s and main board at 12.1V. PA idle current checked at 0.20A total (factory setting) so assume 100mA in each final. 

(For info, Rx currents: 164mA no volume, about 209mA "normal" volume). 

- At 7.1Mhz:   10W, total current: 1.79A, of which PA current: 1.31A, therefore main board current 0.48A

- At 14.2Mhz: 5.5W, total current: 1.39A, of which PA current: 1.0A,  therefore main board current 0.39A

- At 21.2Mhz: 2.2W, total current: 0.95A, of which PA current: 0.53A, therefore main board current 0.42A

- At 28.1Mhz: 1.3W, total current: 0.95A, of which PA current: 0.53A, therefore main board current 0.42A

 

 

2. IRF510s with 16.5V, 13.8V for main board. PA total idle current checked at 0.21A. 

(For info, Rx currents: 188mA no volume, about 230mA "normal" volume). 

- At 7.1Mhz:  19W, total current: 2.65A, of which PA current: 2.09A, therefore main board current 0.56A

- At 14.2Mhz: 11W, total current: 2.20A, of which PA current: 1.80A, therefore main board current 0.40A

- At 21.2Mhz: 5.5W, total current: 1.40A, of which PA current: 1.00A, therefore main board current 0.40A

- At 28.1Mhz: 2.2W, total current: 1.02A, of which PA current: 0.60A, therefore main board current 0.42A

 

 

I haven't found a definitive reference for the safe and optimum values of the RD16HHF1s idle bias current but it seems to range from 200 to 500mA. So I would not recommend long term usage of the 500mA bias I used for these measurements.

I will reset mine to probably the 400-450mA value I read from some articles.

 

3. RD16HHF1s and main board at 12.1VDC, 250mA idle bias each (Total 0.5A PA idle current). 

- At 7.1Mhz:  10W,  PA current: 1.20A

- At 14.2Mhz: 9W,   PA current: 1.21A

- At 21.2Mhz: 4.5W, PA current: 0.65A

- At 28.1Mhz: 5.5W, PA current: 0.95A

 

 

4. RD16HHF1s and main board at 12.1VDC, 500mA idle bias each (Total 1A PA idle current). 

- At 7.1Mhz: 10W, PA current: 1.18A

- At 14.2Mhz: 9W, PA current: 1.26A

- At 21.2Mhz: 5W, PA current: 0.71A

- At 28.1Mhz: 6W, PA current: 1.11A

 

 

5. RD16HHF1s and main board at 13.8VDC, 500mA idle bias each (Total 1A PA idle current). 

- At 7.1Mhz:  13.5W, PA current: 1.95A

- At 14.2Mhz: 13.5W, PA current: 1.93A

- At 21.2Mhz: 6W,    PA current: 1.38A

- At 28.1Mhz: 9.5W,  PA current: 1.79A

 

 

 

Interesting observations:

 

A. The RD16HHF1 produces a much flatter power curver over frequency (in my device), although it shows a dip somewhere near the 15m band.

 

B. The IRF510 can produce some nice power in the lower frequencies when increasing the PA supply voltage, but it comes at the price of a steep power drop at higher frequencies.

 

C. The bias does not seem to influence the efficiency of the finals at full power with RD16HHF1, since biasing at 250 and 500mA produces essentially the same output for the same DC power input. Assuming distortion reduces with higher bias, can we assume a higher bias (within limits) is preferable? Any risk of thermal runaway?

 

D. The board main current (which includes the current in the driving stages of the power amplifier) does not seem to change with frequency from 20m onwards. Is this because the gain is pretty constant? If so, most of the drop in power with increasing frequency seems to be in the IRF510s, supporting the results obtained with the RD16HHF1s.

 

E. With the current uBitx PA circuit the RD16HHF1 seems limited in output, although not having the proper test equipment I can't say where the limitation occurs.

 

F. When I increased the drive through VR1 I noticed that at around 40% for the lower frequencies and at around 60% for the top frequencies I get a compression effect and the output does not increase much more from there on. I left it at 60% and got a positive feedback on the voice quality on my first QSO on 40m. Therefore I assume that the compression/clipping is not significant at that level (but I can't measure the sprectral purity).

 

 

So since my target was around 10W on 10m and 10 to 15W on 40m minimum I can say I have reached my goal just by changing the finals to RD16HHF1s and supplying the board with 13.8VDC (below the 15.2/15V stated in the respective datasheets of the RD16HHF1 and TDA2822).

 

To replace the finals I simply cut the legs of the IRF510s about 3mm above the board and correspondingly cut and crossed over the drain and source pins of the RD16s to match, then soldered in place.

 

It would be interesting to compare these results with others who performed the finals swap on the stock uBitx.

 

Next is the installation of the TPA2016 audio amplifier with I2C controllable AGC.

This is a lot of fun.

 

All the best,

 

73, John (VK2ETA)

 

<image003.jpg>


Virus-free. www.avg.com

Re: RD16HHF1 in the uBITX #ubitx

Karl Heinz Kremer, K5KHK
 

How about using an I2C DAC, and then letting the Raduino setting the bias based on what band and what output power is desired? 
--
Karl Heinz - K5KHK

Re: RD16HHF1 in the uBITX #ubitx

K9HZ <bill@...>
 

It’s not the bias… it’s the drive level.

 

 

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 Karl Heinz Kremer, K5KHK
Sent: Saturday, February 17, 2018 8:07 PM
To: BITX20@groups.io
Subject: Re: [BITX20] RD16HHF1 in the uBITX #ubitx

 

How about using an I2C DAC, and then letting the Raduino setting the bias based on what band and what output power is desired? 
--
Karl Heinz - K5KHK


Virus-free. www.avg.com

Re: RD16HHF1 in the uBITX #ubitx

K9HZ <bill@...>
 

Well this is gonna be important when it comes to activating the tuner I’m designing.  You won’t want to tune under full power so this turns out to be a great way to decrease the power for tuning.

 

 

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 Dave Bottom
Sent: Saturday, February 17, 2018 7:32 PM
To: BITX20@groups.io
Subject: Re: [BITX20] RD16HHF1 in the uBITX #ubitx

 

It is interesting that Chris M0NKA does this with his mcHF SDR kit.

 

It has a Max Pwr setting that is similar to uBITX on 80M (12W) but they have a calibrate setting for each band at 5W, and then can step it down to 2W, 1W, 0.5W (these are approximate based on 5W setting of drive level.)

 

When I get back home (Orlando then Yuma Hamfest)  I’ll make some notes on how he’s done this, as I was already contemplating doing this on the uBITX when I go to the RD16HHF1’s.

 

Dave WI6R


On Feb 17, 2018, at 4:51 PM, K9HZ <bill@...> wrote:

I had a couple of hours of spare time today so I started off my measuring the gain of the pre-drivers in the uBITx.. and sure enough, there is a lot of variation from 1.8-54 MHz (where I want mine to work).  Substituting the RD15HVF1 (my choice of RF PA) into the circuit with no other changes gives results similar to what John saw.. but it is because of the pre-driver stages.  I contemplated ways of compensating the drive with frequency but there isn’t a really good solution using reactive components because it causes some other non-desirable behavior (like a peak in drive at 21 MHz that is too high for the PA).  I did land on a rather bruit force method that does work well… I removed RV1 (drive control) from the circuit board and replaced it with a tiny board with three small relays and four 100 ohm 10 turn pots.  The relays are controlled by the KT1, KT1, and KT3 drivers…  The short story is that now I have gain that is adjustable for essentially each of the bands (at least sets of bands that follow the LP filters).  I’ve adjusted the drive so that the PA puts out the same power (+/- about 2 watts) across the entire frequency spectrum.  I suppose this should have been an obvious answer, but I’m not fond of using relays for stuff like this even if they only draw milliwatts…

 

 

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! <image002.png>

 

Moderator – North American QRO Yahoo Group.

 

email:  bill@...

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of John
Sent: Thursday, February 15, 2018 7:39 AM
To: BITX20@groups.io
Subject: Re: [BITX20] RD16HHF1 in the uBITX #ubitx

 

I have done a strait replacement of the IRF510s with RD16HHF1s. 

 

Here are the before and after values I got.

 

All tests done with uBitx VR1 drive level in the same position of approx 60% of range.

 

1. IRF510s and main board at 12.1V. PA idle current checked at 0.20A total (factory setting) so assume 100mA in each final. 

(For info, Rx currents: 164mA no volume, about 209mA "normal" volume). 

- At 7.1Mhz:   10W, total current: 1.79A, of which PA current: 1.31A, therefore main board current 0.48A

- At 14.2Mhz: 5.5W, total current: 1.39A, of which PA current: 1.0A,  therefore main board current 0.39A

- At 21.2Mhz: 2.2W, total current: 0.95A, of which PA current: 0.53A, therefore main board current 0.42A

- At 28.1Mhz: 1.3W, total current: 0.95A, of which PA current: 0.53A, therefore main board current 0.42A

 

 

2. IRF510s with 16.5V, 13.8V for main board. PA total idle current checked at 0.21A. 

(For info, Rx currents: 188mA no volume, about 230mA "normal" volume). 

- At 7.1Mhz:  19W, total current: 2.65A, of which PA current: 2.09A, therefore main board current 0.56A

- At 14.2Mhz: 11W, total current: 2.20A, of which PA current: 1.80A, therefore main board current 0.40A

- At 21.2Mhz: 5.5W, total current: 1.40A, of which PA current: 1.00A, therefore main board current 0.40A

- At 28.1Mhz: 2.2W, total current: 1.02A, of which PA current: 0.60A, therefore main board current 0.42A

 

 

I haven't found a definitive reference for the safe and optimum values of the RD16HHF1s idle bias current but it seems to range from 200 to 500mA. So I would not recommend long term usage of the 500mA bias I used for these measurements.

I will reset mine to probably the 400-450mA value I read from some articles.

 

3. RD16HHF1s and main board at 12.1VDC, 250mA idle bias each (Total 0.5A PA idle current). 

- At 7.1Mhz:  10W,  PA current: 1.20A

- At 14.2Mhz: 9W,   PA current: 1.21A

- At 21.2Mhz: 4.5W, PA current: 0.65A

- At 28.1Mhz: 5.5W, PA current: 0.95A

 

 

4. RD16HHF1s and main board at 12.1VDC, 500mA idle bias each (Total 1A PA idle current). 

- At 7.1Mhz: 10W, PA current: 1.18A

- At 14.2Mhz: 9W, PA current: 1.26A

- At 21.2Mhz: 5W, PA current: 0.71A

- At 28.1Mhz: 6W, PA current: 1.11A

 

 

5. RD16HHF1s and main board at 13.8VDC, 500mA idle bias each (Total 1A PA idle current). 

- At 7.1Mhz:  13.5W, PA current: 1.95A

- At 14.2Mhz: 13.5W, PA current: 1.93A

- At 21.2Mhz: 6W,    PA current: 1.38A

- At 28.1Mhz: 9.5W,  PA current: 1.79A

 

 

 

Interesting observations:

 

A. The RD16HHF1 produces a much flatter power curver over frequency (in my device), although it shows a dip somewhere near the 15m band.

 

B. The IRF510 can produce some nice power in the lower frequencies when increasing the PA supply voltage, but it comes at the price of a steep power drop at higher frequencies.

 

C. The bias does not seem to influence the efficiency of the finals at full power with RD16HHF1, since biasing at 250 and 500mA produces essentially the same output for the same DC power input. Assuming distortion reduces with higher bias, can we assume a higher bias (within limits) is preferable? Any risk of thermal runaway?

 

D. The board main current (which includes the current in the driving stages of the power amplifier) does not seem to change with frequency from 20m onwards. Is this because the gain is pretty constant? If so, most of the drop in power with increasing frequency seems to be in the IRF510s, supporting the results obtained with the RD16HHF1s.

 

E. With the current uBitx PA circuit the RD16HHF1 seems limited in output, although not having the proper test equipment I can't say where the limitation occurs.

 

F. When I increased the drive through VR1 I noticed that at around 40% for the lower frequencies and at around 60% for the top frequencies I get a compression effect and the output does not increase much more from there on. I left it at 60% and got a positive feedback on the voice quality on my first QSO on 40m. Therefore I assume that the compression/clipping is not significant at that level (but I can't measure the sprectral purity).

 

 

So since my target was around 10W on 10m and 10 to 15W on 40m minimum I can say I have reached my goal just by changing the finals to RD16HHF1s and supplying the board with 13.8VDC (below the 15.2/15V stated in the respective datasheets of the RD16HHF1 and TDA2822).

 

To replace the finals I simply cut the legs of the IRF510s about 3mm above the board and correspondingly cut and crossed over the drain and source pins of the RD16s to match, then soldered in place.

 

It would be interesting to compare these results with others who performed the finals swap on the stock uBitx.

 

Next is the installation of the TPA2016 audio amplifier with I2C controllable AGC.

This is a lot of fun.

 

All the best,

 

73, John (VK2ETA)

 

<image003.jpg>


 

Virus-free. www.avg.com

Re: RD16HHF1 in the uBITX #ubitx

 

Bill,

We can make a power sense and feed the DC say 0-5V to an analog pin of the raduino and depending on the power level
change the drive current of the VFO, I think we can do a crude(ish) power control. Keeping the drive pot at the
max setting.

I understand that Allison has implemented an AGC/ALC that works on RX/TX.

Raj


At 18/02/2018, you wrote:
I had a couple of hours of spare time today so I started off my measuring the gain of the pre-drivers in the uBITx.. and sure enough, there is a lot of variation from 1.8-54 MHz (where I want mine to work).  Substituting the RD15HVF1 (my choice of RF PA) into the circuit with no other changes gives results similar to what John saw.. but it is because of the pre-driver stages.  I contemplated ways of compensating the drive with frequency but there isn’t a really good solution using reactive components because it causes some other non-desirable behavior (like a peak in drive at 21 MHz that is too high for the PA).  I did land on a rather bruit force method that does work well… I removed RV1 (drive control) from the cirrcuit board and replaced it with a tiny board with three small relays and four 100 ohm 10 turn pots.  The relays are controlled by the KT1, KT1, and KT3 drivers…  The short story is that now I have gain that is adjustable for essentially each of the bands (at least sets of bands that follow the LP filters).  I’ve adjusted the drive so that the PA puts out the same power (+/- about 2 watts) across the entire frequency spectrum.  I suppose this should have been an obvious answer, but I’m not fond of using relays for stuff like this even if they only draw milliwatts…
 
 
Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ