Topics

uBitx TX performance with frequency

KD8CGH
 

I took some time to measure the actual performance of my uBitx with its original calibration against a dummy load. The instruments used are not lab calibrated. I did check my wattmeter against my recently factory calibrated K3 and found the power reported to be about 5% high. The power supply is rated as 25 amps and set at 13.7 volts. I tested by simply pressing the PTT (no audio input, power out 0) and keying CW.
Receive current: .25 A

  PTT CW CW
f kHz I amp I amp P watt
3,530 0.74 1.8 8
3,970 0.74 2.1 9
7,030 0.73 1.57 5
7,270 0.7 1.6 5
10,113 0.72 1.22 3
14,030 0.71 1.34 3
14,320 0.71 1.37 3
21,170 0.69 0.96 1
28,900 0.69 0.83 0.5

The results agreed in general with Dave's (WI6R) post https://groups.io/g/BITX20/message/39578, although his results start a bit higher and end even lower.
Although my current draw with PTT down agrees with the value specified on the Tune-up page, I never quite see 10 watts out. The 80 meter power isn't too bad, but the 14 MHz is half and 28 MHz is 1/4 of that mentioned on the uBitx web page.

What TX performance have others seen?
Any fixes for higher frequencies?

     Bob   KD8CGH

Ashhar Farhan
 

You can increase drive with the preset of the predriver.
- f

On 24 Jan 2018 6:24 pm, "KD8CGH" <rkayakr@...> wrote:
I took some time to measure the actual performance of my uBitx with its original calibration against a dummy load. The instruments used are not lab calibrated. I did check my wattmeter against my recently factory calibrated K3 and found the power reported to be about 5% high. The power supply is rated as 25 amps and set at 13.7 volts. I tested by simply pressing the PTT (no audio input, power out 0) and keying CW.
Receive current: .25 A

  PTT CW CW
f kHz I amp I amp P watt
3,530 0.74 1.8 8
3,970 0.74 2.1 9
7,030 0.73 1.57 5
7,270 0.7 1.6 5
10,113 0.72 1.22 3
14,030 0.71 1.34 3
14,320 0.71 1.37 3
21,170 0.69 0.96 1
28,900 0.69 0.83 0.5

The results agreed in general with Dave's (WI6R) post https://groups.io/g/BITX20/message/39578, although his results start a bit higher and end even lower.
Although my current draw with PTT down agrees with the value specified on the Tune-up page, I never quite see 10 watts out. The 80 meter power isn't too bad, but the 14 MHz is half and 28 MHz is 1/4 of that mentioned on the uBitx web page.

What TX performance have others seen?
Any fixes for higher frequencies?

     Bob   KD8CGH

Alex - PA1FOX
 

Bob,

Yes, I've seen similar behaviour on my homebrew uBitx. Increasing the drive will overload the PA at 80 meters but will hardly increase the power output at the high bands. I even made a change in the driver circuit that decreases the gain below 10MHZ so I could crank up the overall gain of the TX chain more trying to get more output at 14MHz and up. No success. After extensive experiments I've decided to replace the IRF510's with RD16HHF1 mosfets (not pin-compatible!).

I am now optimizing the output transformer and impedance levels but so far the TX power ranges from 10 watts at 80m to 8 watts at 17m. The 15m and up LPF is not finished yet, but reviewing the specs of the RF16HHF1 I don't expect much further power drop at 28 MHz.

Secondly I like the idea of the housing of these mosfets being the source, so a direct grounding to the case is easy. No insulation material needed and a better RF ground.

A slight disadvantage is that the bias current of the RD16HHF1 is a little higher, but that's ok for me.
If you should make such a change with the commercial PCB version, beware of the pin incompatibility.

73, Alex
PA1FOX

chris gress <Chrisg0wfh@...>
 

Alex when you have your modifications all done can you please post it on here I am interested in doing mine when I get it chris

On 25 Jan 2018 07:37, "Alex Buurlage" <pa1fox@...> wrote:
Bob,

Yes, I've seen similar behaviour on my homebrew uBitx. Increasing the drive will overload the PA at 80 meters but will hardly increase the power output at the high bands. I even made a change in the driver circuit that decreases the gain below 10MHZ so I could crank up the overall gain of the TX chain more trying to get more output at 14MHz and up. No success. After extensive experiments I've decided to replace the IRF510's with RD16HHF1 mosfets (not pin-compatible!).

I am now optimizing the output transformer and impedance levels but so far the TX power ranges from 10 watts at 80m to 8 watts at 17m. The 15m and up LPF is not finished yet, but reviewing the specs of the RF16HHF1 I don't expect much further power drop at 28 MHz.

Secondly I like the idea of the housing of these mosfets being the source, so a direct grounding to the case is easy. No insulation material needed and a better RF ground.

A slight disadvantage is that the bias current of the RD16HHF1 is a little higher, but that's ok for me.
If you should make such a change with the commercial PCB version, beware of the pin incompatibility.

73, Alex
PA1FOX


Lawrence Galea
 

Farhan
I know it will increase the price, but how about switching over to the RD16HVF1 which would allow the rig to run from 12V doing away with those wanting more power to increase the voltage to the PA?
Would also do away with the PA heatsinks if the case is metal and it is used as the heatsink.
Regards
Lawrence

On Thu, Jan 25, 2018 at 6:23 AM, Ashhar Farhan <farhanbox@...> wrote:
You can increase drive with the preset of the predriver.
- f

On 24 Jan 2018 6:24 pm, "KD8CGH" <rkayakr@...> wrote:
I took some time to measure the actual performance of my uBitx with its original calibration against a dummy load. The instruments used are not lab calibrated. I did check my wattmeter against my recently factory calibrated K3 and found the power reported to be about 5% high. The power supply is rated as 25 amps and set at 13.7 volts. I tested by simply pressing the PTT (no audio input, power out 0) and keying CW.
Receive current: .25 A

  PTT CW CW
f kHz I amp I amp P watt
3,530 0.74 1.8 8
3,970 0.74 2.1 9
7,030 0.73 1.57 5
7,270 0.7 1.6 5
10,113 0.72 1.22 3
14,030 0.71 1.34 3
14,320 0.71 1.37 3
21,170 0.69 0.96 1
28,900 0.69 0.83 0.5

The results agreed in general with Dave's (WI6R) post https://groups.io/g/BITX20/message/39578, although his results start a bit higher and end even lower.
Although my current draw with PTT down agrees with the value specified on the Tune-up page, I never quite see 10 watts out. The 80 meter power isn't too bad, but the 14 MHz is half and 28 MHz is 1/4 of that mentioned on the uBitx web page.

What TX performance have others seen?
Any fixes for higher frequencies?

     Bob   KD8CGH


KD8CGH
 

Thanks all.
I'm not looking to stun pigeons, but it would be nice to have 5 watts on 30, 20 and higher if the solar activity ever picks up.
There is also a RD16HVF1 discussion in the "irf520 vs irf510" topic https://groups.io/g/BITX20/message/39265
It looks like that may be the best solution.

Alex - Thanks, please let the community know how the higher bands turn out.

    Bob   KD8CGH

K9HZ <bill@...>
 

This may be a futile attempt if the intermediate gain stages (pre-driver and drivers) fall off with frequency too.  I have not done this myself yet… still on my list… to actually publish a table showing the output at each stage with frequency to determine what needs attention BEFORE the PA.  Then a change to the PA makes full sense.

 

 

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

 

 

email:  bill@...

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Alex Buurlage
Sent: Thursday, January 25, 2018 3:37 AM
To: BITX20@groups.io
Subject: Re: [BITX20] uBitx TX performance with frequency

 

Bob,

Yes, I've seen similar behaviour on my homebrew uBitx. Increasing the drive will overload the PA at 80 meters but will hardly increase the power output at the high bands. I even made a change in the driver circuit that decreases the gain below 10MHZ so I could crank up the overall gain of the TX chain more trying to get more output at 14MHz and up. No success. After extensive experiments I've decided to replace the IRF510's with RD16HHF1 mosfets (not pin-compatible!).

I am now optimizing the output transformer and impedance levels but so far the TX power ranges from 10 watts at 80m to 8 watts at 17m. The 15m and up LPF is not finished yet, but reviewing the specs of the RF16HHF1 I don't expect much further power drop at 28 MHz.

Secondly I like the idea of the housing of these mosfets being the source, so a direct grounding to the case is easy. No insulation material needed and a better RF ground.

A slight disadvantage is that the bias current of the RD16HHF1 is a little higher, but that's ok for me.
If you should make such a change with the commercial PCB version, beware of the pin incompatibility.

73, Alex
PA1FOX

K9HZ <bill@...>
 

The simple way to do this is to do what Hans did on the 5W PA he produces at QRP-Labs…. There is a second set of pads on the PCB that has the right pinout for the RDxx devices.  That way you can easily use either.  So if there is a V2 of the uBITx main board it is something to consider.

 

 

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

 

 

email:  bill@...

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Lawrence Galea
Sent: Thursday, January 25, 2018 4:01 AM
To: BITX20@groups.io
Subject: Re: [BITX20] uBitx TX performance with frequency

 

Farhan

I know it will increase the price, but how about switching over to the RD16HVF1 which would allow the rig to run from 12V doing away with those wanting more power to increase the voltage to the PA?

Would also do away with the PA heatsinks if the case is metal and it is used as the heatsink.

Regards

Lawrence

 

On Thu, Jan 25, 2018 at 6:23 AM, Ashhar Farhan <farhanbox@...> wrote:

You can increase drive with the preset of the predriver.

- f

 

On 24 Jan 2018 6:24 pm, "KD8CGH" <rkayakr@...> wrote:

I took some time to measure the actual performance of my uBitx with its original calibration against a dummy load. The instruments used are not lab calibrated. I did check my wattmeter against my recently factory calibrated K3 and found the power reported to be about 5% high. The power supply is rated as 25 amps and set at 13.7 volts. I tested by simply pressing the PTT (no audio input, power out 0) and keying CW.
Receive current: .25 A

 

PTT

CW

CW

f kHz

I amp

I amp

P watt

3,530

0.74

1.8

8

3,970

0.74

2.1

9

7,030

0.73

1.57

5

7,270

0.7

1.6

5

10,113

0.72

1.22

3

14,030

0.71

1.34

3

14,320

0.71

1.37

3

21,170

0.69

0.96

1

28,900

0.69

0.83

0.5


The results agreed in general with Dave's (WI6R) post https://groups.io/g/BITX20/message/39578, although his results start a bit higher and end even lower.
Although my current draw with PTT down agrees with the value specified on the Tune-up page, I never quite see 10 watts out. The 80 meter power isn't too bad, but the 14 MHz is half and 28 MHz is 1/4 of that mentioned on the uBitx web page.

What TX performance have others seen?
Any fixes for higher frequencies?

     Bob   KD8CGH

 

Xcott Craver
 

Hi,

I tried the uBITX with FT-8 on 20m, and I could easily hit 5W out and probably higher.  I've observed that typical SSB usage doesn't come close to CW output power, but the signals coming out of WSJT-X can outdo CW.

This is on a QRP wattmeter that also isn't precisely calibrated.  

Thanks, Xcott K2CAJ

Henning Weddig
 

All,

I guess that there are two design mistakes:

1. the supply voltage to the drains of the transistors is fed via individual chokes, not the "balancing" dual winding choke

2. the input cpacitance of the FET´s do a big harm

Please have a look on the often cited WA2EBY amp: he uses the choke (T2) on the output and in addition he is using inductances from the gate (L1, L2) to the bias feeding resistor (27 ohms). To my understanding the inductor forms a parallel resonator with the input capacitance of the FET thereby flattening the frequency response.

In Part 2 of Mike Krossors article (fig 4) the "bad" frequency response of "normal" IRF510 amps is clearly shown, so it seems that L1 and L2 togehter wit the series inductance of the input balun are upgrading the performance.

Please have alook on the Philips (NXP) app note NCO8701. In this app note they are also using inductors in the input and even from the drain to the balun on the output. Design formulas are also given there.

I am not sure if the drivers are "good" enough for driving the high capacitive input of the IRF510.

I recently read an article (EDN) about the 2N2219 als vidoe amps, they do not perform very well, althoug I remember that this transistor (two in parallel) was used in a 2 m AM transmitter (german company Semcoset, MBS22?, about 1969, the year I got my ham radio license). A 2N3866 is preferred even for video amps in the 50 MHz range!

What about a BFG135 or similar for the driver? Or: RD00HS ????

I am urgently waiting on my µBITX ordered on Dec 24 2017.

Henning Weddig

DK5LV


Am 25.01.2018 um 09:01 schrieb Lawrence Galea:

Farhan
I know it will increase the price, but how about switching over to the RD16HVF1 which would allow the rig to run from 12V doing away with those wanting more power to increase the voltage to the PA?
Would also do away with the PA heatsinks if the case is metal and it is used as the heatsink.
Regards
Lawrence

On Thu, Jan 25, 2018 at 6:23 AM, Ashhar Farhan <farhanbox@...> wrote:
You can increase drive with the preset of the predriver.
- f

On 24 Jan 2018 6:24 pm, "KD8CGH" <rkayakr@...> wrote:
I took some time to measure the actual performance of my uBitx with its original calibration against a dummy load. The instruments used are not lab calibrated. I did check my wattmeter against my recently factory calibrated K3 and found the power reported to be about 5% high. The power supply is rated as 25 amps and set at 13.7 volts. I tested by simply pressing the PTT (no audio input, power out 0) and keying CW.
Receive current: .25 A

  PTT CW CW
f kHz I amp I amp P watt
3,530 0.74 1.8 8
3,970 0.74 2.1 9
7,030 0.73 1.57 5
7,270 0.7 1.6 5
10,113 0.72 1.22 3
14,030 0.71 1.34 3
14,320 0.71 1.37 3
21,170 0.69 0.96 1
28,900 0.69 0.83 0.5

The results agreed in general with Dave's (WI6R) post https://groups.io/g/BITX20/message/39578, although his results start a bit higher and end even lower.
Although my current draw with PTT down agrees with the value specified on the Tune-up page, I never quite see 10 watts out. The 80 meter power isn't too bad, but the 14 MHz is half and 28 MHz is 1/4 of that mentioned on the uBitx web page.

What TX performance have others seen?
Any fixes for higher frequencies?

     Bob   KD8CGH


Rod Davis
 

Henning and all,

I am not sure the individual-chokes-method is a mistake: my understanding is that technique results in a substantial improvement in IMD.

Remember, every design decision is a tradeoff.

Rod KM6SN


On 01/25/2018 09:02 AM, Henning Weddig via Groups.Io wrote:

All,

I guess that there are two design mistakes:

1. the supply voltage to the drains of the transistors is fed via individual chokes, not the "balancing" dual winding choke

2. the input cpacitance of the FET´s do a big harm

Please have a look on the often cited WA2EBY amp: he uses the choke (T2) on the output and in addition he is using inductances from the gate (L1, L2) to the bias feeding resistor (27 ohms). To my understanding the inductor forms a parallel resonator with the input capacitance of the FET thereby flattening the frequency response.

In Part 2 of Mike Krossors article (fig 4) the "bad" frequency response of "normal" IRF510 amps is clearly shown, so it seems that L1 and L2 togehter wit the series inductance of the input balun are upgrading the performance.

Please have alook on the Philips (NXP) app note NCO8701. In this app note they are also using inductors in the input and even from the drain to the balun on the output. Design formulas are also given there.

I am not sure if the drivers are "good" enough for driving the high capacitive input of the IRF510.

I recently read an article (EDN) about the 2N2219 als vidoe amps, they do not perform very well, althoug I remember that this transistor (two in parallel) was used in a 2 m AM transmitter (german company Semcoset, MBS22?, about 1969, the year I got my ham radio license). A 2N3866 is preferred even for video amps in the 50 MHz range!

What about a BFG135 or similar for the driver? Or: RD00HS ????

I am urgently waiting on my µBITX ordered on Dec 24 2017.

Henning Weddig

DK5LV


Am 25.01.2018 um 09:01 schrieb Lawrence Galea:
Farhan
I know it will increase the price, but how about switching over to the RD16HVF1 which would allow the rig to run from 12V doing away with those wanting more power to increase the voltage to the PA?
Would also do away with the PA heatsinks if the case is metal and it is used as the heatsink.
Regards
Lawrence

On Thu, Jan 25, 2018 at 6:23 AM, Ashhar Farhan <farhanbox@...> wrote:
You can increase drive with the preset of the predriver.
- f

On 24 Jan 2018 6:24 pm, "KD8CGH" <rkayakr@...> wrote:
I took some time to measure the actual performance of my uBitx with its original calibration against a dummy load. The instruments used are not lab calibrated. I did check my wattmeter against my recently factory calibrated K3 and found the power reported to be about 5% high. The power supply is rated as 25 amps and set at 13.7 volts. I tested by simply pressing the PTT (no audio input, power out 0) and keying CW.
Receive current: .25 A

  PTT CW CW
f kHz I amp I amp P watt
3,530 0.74 1.8 8
3,970 0.74 2.1 9
7,030 0.73 1.57 5
7,270 0.7 1.6 5
10,113 0.72 1.22 3
14,030 0.71 1.34 3
14,320 0.71 1.37 3
21,170 0.69 0.96 1
28,900 0.69 0.83 0.5

The results agreed in general with Dave's (WI6R) post https://groups.io/g/BITX20/message/39578, although his results start a bit higher and end even lower.
Although my current draw with PTT down agrees with the value specified on the Tune-up page, I never quite see 10 watts out. The 80 meter power isn't too bad, but the 14 MHz is half and 28 MHz is 1/4 of that mentioned on the uBitx web page.

What TX performance have others seen?
Any fixes for higher frequencies?

     Bob   KD8CGH



Alex - PA1FOX
 

This may be a futile attempt if the intermediate gain stages (pre-driver and drivers) fall off with frequency too.  I have not done this myself yet… still on my list… to actually publish a table showing the output at each stage with frequency to determine what needs attention BEFORE the PA.  Then a change to the PA makes full sense.

William, I made some measurements on the TX chain without the PA. In my case this is up to the 2N2219's as I use the original schematic. The overall gain dropped 6dB from 3.5 up to 30Mhz. This should have some influence but is not a huge problem. With the power drive input which the 2N2219's generate for the IRF's it was clear that the IRF's were hardly doing anything at the high frequencies. I've played around with bias inductors and different impedance levels at the gates of the IRF's but apart from increasing or decreasing the overall gain for all frequencies, there was not much change in frequency gain curve.
What influences most is the output transformer of the IRF's. The trifilair setup is a good starting point but I could optimize the PA efficiency by adding and removing a winding at the primary side of the transformer. (So one winding ends up bifilair.) It's not ideal though.

With the change to RD16HHF1 (not the HVF1) I have kept the FT43-37 output coil. It could be a bit small for this, so I ordered binocular coils with a slightly larger size (BN43-202) to use as an output transformer. Yes, it also helps that the RD16 series is desigined for 12 volts. The IRF's lose their lazyness at 24 volts.

I'll post the results of the experiments for those who said to be interested. I find it very interesting myself as well.

73, Alex
PA1FOX

Lawrence Galea
 

Agree.
Mine hasn't arrived yet so cannot check anything yet.Regards
Lawrence


On Thu, Jan 25, 2018 at 3:15 PM, K9HZ <bill@...> wrote:

This may be a futile attempt if the intermediate gain stages (pre-driver and drivers) fall off with frequency too.  I have not done this myself yet… still on my list… to actually publish a table showing the output at each stage with frequency to determine what needs attention BEFORE the PA.  Then a change to the PA makes full sense.

 

 

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

 

 

email:  bill@...

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Alex Buurlage
Sent: Thursday, January 25, 2018 3:37 AM
To: BITX20@groups.io
Subject: Re: [BITX20] uBitx TX performance with frequency

 

Bob,

Yes, I've seen similar behaviour on my homebrew uBitx. Increasing the drive will overload the PA at 80 meters but will hardly increase the power output at the high bands. I even made a change in the driver circuit that decreases the gain below 10MHZ so I could crank up the overall gain of the TX chain more trying to get more output at 14MHz and up. No success. After extensive experiments I've decided to replace the IRF510's with RD16HHF1 mosfets (not pin-compatible!).

I am now optimizing the output transformer and impedance levels but so far the TX power ranges from 10 watts at 80m to 8 watts at 17m. The 15m and up LPF is not finished yet, but reviewing the specs of the RF16HHF1 I don't expect much further power drop at 28 MHz.

Secondly I like the idea of the housing of these mosfets being the source, so a direct grounding to the case is easy. No insulation material needed and a better RF ground.

A slight disadvantage is that the bias current of the RD16HHF1 is a little higher, but that's ok for me.
If you should make such a change with the commercial PCB version, beware of the pin incompatibility.

73, Alex
PA1FOX


K9HZ <bill@...>
 

“The overall gain dropped 6dB from 3.5 up to 30Mhz”  That’s a factor of FOUR.  So Let’s say the drive is 1 watt at 3.5 MHz… tailing off to 0.25 watt at 30 MHz  That’s an enormous difference.  I would expect 1 dB or less over the entire range and that can be accomplished a lot of different ways… either using good design parameters or at least an AGC.

 

 

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

 

 

email:  bill@...

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Alex Buurlage
Sent: Friday, January 26, 2018 3:34 AM
To: BITX20@groups.io
Subject: Re: [BITX20] uBitx TX performance with frequency

 

This may be a futile attempt if the intermediate gain stages (pre-driver and drivers) fall off with frequency too.  I have not done this myself yet… still on my list… to actually publish a table showing the output at each stage with frequency to determine what needs attention BEFORE the PA.  Then a change to the PA makes full sense.

William, I made some measurements on the TX chain without the PA. In my case this is up to the 2N2219's as I use the original schematic. The overall gain dropped 6dB from 3.5 up to 30Mhz. This should have some influence but is not a huge problem. With the power drive input which the 2N2219's generate for the IRF's it was clear that the IRF's were hardly doing anything at the high frequencies. I've played around with bias inductors and different impedance levels at the gates of the IRF's but apart from increasing or decreasing the overall gain for all frequencies, there was not much change in frequency gain curve.
What influences most is the output transformer of the IRF's. The trifilair setup is a good starting point but I could optimize the PA efficiency by adding and removing a winding at the primary side of the transformer. (So one winding ends up bifilair.) It's not ideal though.

With the change to RD16HHF1 (not the HVF1) I have kept the FT43-37 output coil. It could be a bit small for this, so I ordered binocular coils with a slightly larger size (BN43-202) to use as an output transformer. Yes, it also helps that the RD16 series is desigined for 12 volts. The IRF's lose their lazyness at 24 volts.

I'll post the results of the experiments for those who said to be interested. I find it very interesting myself as well.

73, Alex
PA1FOX