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Re: QDX PTT to QRP LABS Amp

 

?The amp was previously adjusted for the correct bias and was in use with a QCX radio. I don¡¯t believe it should have needed adjusting just to use a different radio source, the QDX. Maybe I am wrong with this assumption.

I checked the finals, and both are shorted across all pins. Will order the parts needed to repair the amp, but still don¡¯t have a good reason for the QDX not trigging the amp, and/or causing the amp to fry.

The power supply used did clamp the current, but did not prevent the finals from blowing. I am not worried about repairing the amp, but how to have a QDX that works with an amp.

NT5AT - will

On Aug 13, 2022, at 8:09 PM, Adam via groups.io <qrp-labs@...> wrote:
?Wilson Little <wilsonlittle66@...> wrote:

Bad News is that trigger the amp immediately caused the amp to fry, and
also killed a power supply. Using another p/s, the amp immediately
pulls 10 amps, triggered or not. oops... Something went way wrong.
Did you adjust the bias voltage (R5)? Amp shouldn't be keyed without
setting it to minimum (counter-clockwise) first.

Fortunately most probably nothing drastic happened, you just killed the
final transistors (Q1 and Q2, IRF510). It happens, fortunately they're
cheap and you'll be able to replace them. I'd also replace R5 and IC1
just in case, because failing transistors could've damaged them too.

It's a good idea to add a fuse between the PSU and the amp anyway.
Re: Artwork for "Manual Days" Chinese Antenna Tuner

 

Turns out my 67 year old self isn't much better with decals than my 11 year old self! I think I need to not move them as much? and trust?the force.?I'm trying a bit more acrylic spray as well.?

[Insert pithy quote here]
Mark
Re: Qdx terminal tx test #qdx

 

KEN G4APB <lfoofui.nbz42@...> wrote:

But, pressing either p or t only gives me a brief transmission, not long
enough to actually do any measurements with. Am I doing something wrong
here? Would be nice if it stayed on transmit until The CAT timeout
occurred.
If you're connecting via VNC to raspi and can't just press and hold p or
t, try this:

1. Use PuTTY on the local machine to connect to the raspi via ssh
2. Install minicom on raspi
3. Use it to connect to QDX from the console (over ssh)

Or:

1. Install libhamlib-utils
2. Use rigctl to connect to QDX

rigctl commands:

- set frequency: f <freq in Hz>
- enable transmitting: t 1
- switch back to receiving: t 0
Re: QDX PTT to QRP LABS Amp

 

Ronald Taylor <wa7gil@...> wrote:

I really think you should trace this fault before lowering the value of
R10 in this case.
I agree. Looking at the schematic of the PA, I'd check Q5. It might have a
short-circuit (or near short-circuit) between it's gate and source.
Re: QDX PTT to QRP LABS Amp

 

Wilson Little <wilsonlittle66@...> wrote:

Bad News is that trigger the amp immediately caused the amp to fry, and
also killed a power supply. Using another p/s, the amp immediately
pulls 10 amps, triggered or not. oops... Something went way wrong.
Did you adjust the bias voltage (R5)? Amp shouldn't be keyed without
setting it to minimum (counter-clockwise) first.

Fortunately most probably nothing drastic happened, you just killed the
final transistors (Q1 and Q2, IRF510). It happens, fortunately they're
cheap and you'll be able to replace them. I'd also replace R5 and IC1
just in case, because failing transistors could've damaged them too.

It's a good idea to add a fuse between the PSU and the amp anyway.
Re: Artwork for "Manual Days" Chinese Antenna Tuner

 

Were you aware that you can get waterslide?decal paper that's printable with an inkjet printer?? There's both white background and clear background available.? So you can roll your own.


73
Jim N6OTQ

On Sat, Aug 13, 2022 at 7:40 PM Steve in Okinawa <sfab43@...> wrote:
I'm having terrible luck with the waterslide decals, but I've squeezed the tuner into a smaller box.

Re: Artwork for "Manual Days" Chinese Antenna Tuner

 

I'm having terrible luck with the waterslide decals, but I've squeezed the tuner into a smaller box.

Re: QDX PTT to QRP LABS Amp

 

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Ronald,

Thank you very much for this communication. ? Unfortunately, I rush to the next step before receiving. ? You can see the results¡­. ? ?No so good. ? But, on a positive note, more things to play with and fix. ? :)

NT5AT
Will



On Aug 13, 2022, at 6:26 PM, Ronald Taylor <wa7gil@...> wrote:

Will, your measurements?were very thorough. Thank you for those. Those measurements are pointing to some other issue that we aren't yet seeing. You are showing almost the entire 5 volts dropped across R10. This should not be the case unless something is causing it to go to "almost" ground, i.e. very?low resistance, before going to the 50 watt amp. Please use your DVM, in current measuring mode, to measure the current going from the QDX to the amplifier on the PTT line. It should be only something in the neighborhood of 3 or 4 mA. I really think you should trace this fault before lowering the value of R10 in this case.

73 .. .Ron

On Sat, Aug 13, 2022 at 3:19 PM bojan.naglic <bojan.naglic@...> wrote:
The answer is yes.?
Because you said that with QCX the PTT switching works and because your measurements show that the voltage drop over the 470R in QDX is too much.?

73 Bojan S53DZ



Re: QDX PTT to QRP LABS Amp

 

¿ªÔÆÌåÓý

Good News / Bad News

Good news was I found a 100 ohm resistor to tack in parallel with the QDX R10 resistor, and it enabled the QRP Labs¡¯ 50w Amp to turn on. ? The red TX led might be a little less bright than when triggered through a QCX radio, but it clearly comes on.

Bad News is that trigger the amp immediately caused the amp to fry, and also killed a power supply. ?Using another p/s, the amp immediately pulls 10 amps, triggered or not. ?oops¡­ ? Something went way wrong. ?

Initial attempt with the modified QDX had the rf to a dummy load, and was triggered only for a second or two. ? The output from the QDX was just about 4.5 watts. ?I am unwilling to hook up the second amp to see if I get similar results.

It was a fun day playing and learning. ? Thanks for all the help.

Regards,?
NT5AT - Will ??


On Aug 13, 2022, at 5:19 PM, bojan.naglic <bojan.naglic@...> wrote:

The answer is yes.?
Because you said that with QCX the PTT switching works and because your measurements show that the voltage drop over the 470R in QDX is too much.?

73 Bojan S53DZ

Re: QDX PTT to QRP LABS Amp

 

Will, your measurements?were very thorough. Thank you for those. Those measurements are pointing to some other issue that we aren't yet seeing. You are showing almost the entire 5 volts dropped across R10. This should not be the case unless something is causing it to go to "almost" ground, i.e. very?low resistance, before going to the 50 watt amp. Please use your DVM, in current measuring mode, to measure the current going from the QDX to the amplifier on the PTT line. It should be only something in the neighborhood of 3 or 4 mA. I really think you should trace this fault before lowering the value of R10 in this case.

73 .. .Ron

On Sat, Aug 13, 2022 at 3:19 PM bojan.naglic <bojan.naglic@...> wrote:
The answer is yes.?
Because you said that with QCX the PTT switching works and because your measurements show that the voltage drop over the 470R in QDX is too much.?

73 Bojan S53DZ

Re: QDX: Receiving great but needs more audio output gain in order to xmit for more than 250 milliseconds.

 

¿ªÔÆÌåÓý

Oh, _that_ kind of dummy load, that everyone else in the known universe calls an attentuator. ?Makes me wonder if there's some other miscommunication going on here.

Which one of those 'dummy loads' do you use when your QDX is having this problem? ?Does it change if you use different ones?

73, Willie N1JBJ

On Aug 13, 2022, at 6:32 PM, n4qa <n4qa@...> wrote:

10-A-MFB-10,? ?-20,? ?and -30 dB ten watters.
Re: QDX: Receiving great but needs more audio output gain in order to xmit for more than 250 milliseconds.

n4qa at_hotmail.com
 

Please explain about the dummy load being an issue.
BTW, this dummy load requires no interconnecting coax- has bnc male on one end, female on the other.
My combination dummy load / attenuators consist of one each Bird model:
10-A-MFB-10,? ?-20,? ?and -30 dB ten watters. I use them for running QRPp and for attenuating xmtr output for direct connection to my Spectrum Analyzer.
Oh, and as a dummy load !
BTW, the XYL & I had a great time inside my old high school today !
73,
Bill, N4QA
Re: QDX PTT to QRP LABS Amp

 

The answer is yes.?
Because you said that with QCX the PTT switching works and because your measurements show that the voltage drop over the 470R in QDX is too much.?

73 Bojan S53DZ
Re: QDX PTT to QRP LABS Amp

 

¿ªÔÆÌåÓý

Ok, confession time. ? I am not an electrical engineer. ? I am a mechanical engineer. ? This might be important in that my understanding may need corrected by folks who are much more knowledgable. ? :)

First set of measurements are using the QCX Mini to trigger the amp, which triggers the amp correctly.

On the QRP Labs¡¯ 50v AMP
- ?Voltage drop R16 (470 ohm) resistor is 2.13 volts.
- ?The incoming voltage at resistor R16 (470 ohms) referenced to ground is 4.07 volts.
- ?And, as expected the outgoing measured voltage at the resistor R16 referenced to ground is 1.94 volts.
? ? ? ? ?In - Drop = Out ?- - - ?4.07 v - 2.13v = 1.94 v?

Second set of measurements using QDX to trigger amp, which does not turn on the amp nor the red TX Led

On the QRP Labs¡¯ 50v AMP
- ?Voltage drop R16 (470 ohm) resistor is 0.00 volts.
- ?The incoming voltage at resistor R16 (470 ohms) referenced to ground is 0.82 volts.
- ?The outgoing measured voltage at the resistor R16 referenced to ground is 0.82 volts.
? ? ? ? ? In - Drop = Out ?- - - ? 0.82 v - 0.00v = 0.82 v

On the QRP Labs¡¯ QDX with the PTT disconnected
- ?Voltage input to R10 mesures 5.03 v ref to ground
- ?Voltage output of R10 measure 5.03 v ref to ground
- ?Voltage drop across R10 is 0.00 v
???
On the QRP Labs¡¯ QDX with the PTT connected
- ?Voltage input to R10 mesures 5.00 v ref to ground
- ?Voltage output of R10 measure 0.86 v ref to ground
- ?Voltage drop across R10 is 4.13 v
?
So is the answer still to add a parallel resistor to lower the voltage drop across the QDX R10 resistor? ??


Just for record keeping:

I made the comment that the QCX Mini and QCX+ both worked with the QRP Labs¡¯ 50w Amp. ? Another user commented that the two radios are configured differently, tip versus ring on the PTT cable to trigger the amp, which is accurate. ? However, I modified the QCX+ (per QRP Labs instruction manual) to swap to the ring configuration.?



On Aug 13, 2022, at 3:55 PM, bojan.naglic <bojan.naglic@...> wrote:

?Links:

You r
Re: QRP Labs VFO/Signal generator and Kenwood TS-520 VFO

 

Hi Charles,

Please see the U3S Assembly Manual what to add to the PCB and how to connect things and for the jumpers.
At least you will have to insert one BS170 to allow the signal CLK0 to come to the LPF.? The PCB is the same.

73 Bojan S53DZ
Re: QDX PTT to QRP LABS Amp

 

Ron, of course you are right about the current protection of a BSS84 in the QDX.? It is now about 61mA instead of about 11mA.? But this current limit is used only if one does a short to GND during the PTT high state.

73 Bojan S53DZ
Re: QDX PTT to QRP LABS Amp

 

Hi Will. Probably best to go ahead with Bojan's suggestion and parallel a 100R across R10 in the QDX to raise the PTT eying voltage. Hope that solves it for you .. .73 ... Ron


On Sat, Aug 13, 2022 at 1:55 PM bojan.naglic <bojan.naglic@...> wrote:
And Will, have you measured the voltage over the series of 470R and the red LED?
? 73 Bojan S53DZ

Re: QDX PTT to QRP LABS Amp

 

And Will, have you measured the voltage over the series of 470R and the red LED?
? 73 Bojan S53DZ
Re: QDX PTT to QRP LABS Amp

 

Hi Will,
generally I prefer using the active zero Ohm PTT line, as I said.? And I will do it in due time.

73 Bojan S53DZ
Re: QDX PTT to QRP LABS Amp

 

Hi Ron,
No I did not do those precise voltage measurements, however I did a simple test when I was first trying to use the QDX PTT to trigger the PA.? I noticed that in that case the power did not go to the expected level as it went when I provided full +5V to the PTT input.? So I decided to make the PTT active level high enough for the T/R switch to switch solid.? Probably the red LED in my PA is working at somewhat lover voltage?? And yes at the time of that first test my PTT cable was quite long.

73 Bojan S53DZ
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