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Too keep is short,?
QDX Rev 3 with the 1.04 firmware is providing 5 volts to the ring of the PTT cable, but not triggering the QRP Labs’ 50w Amp. ? What should I be checking?
more details:
- ?QDX wired for 12volts. ?
- ? QDX fully functional at low power. ?(Made numerous contacts on FT8 and RTTY)
- ?Using 2 different amps (40m and 20m) with same results, PTT voltage present, but amp not turning on.
- ?Amps turn on when QCX Mini or QCX+ is used to provide PTT signal
- ?Voltage from QCX Mini and QCX+ are approximately 4.98 volts
- ?Voltage from QDX is approximately 5.04 volts
- ?Voltage on tip from QCX radios has 5 volts present, QDX does not have that 5 volts (amp does not use tip, so should not be an issue)
- ?When checking QDX, identified Q7 was fried and shorts closed. ?Replaces with a diode, but results remains unchanged for amp not turning on.
- ?My assumption sitting here typing is that another component fails when Q7 failed. ?Thoughts?
I would like the option to use with amp on occasion. ? But, not sure where to go from here.
Any help would be appreciated. ?
NT5AT - Wil
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Hi Wil. It sounds like something might be loading down the 5 volts. You should find a way to measure that voltage while transmitting with the QDX PTT connected to the amplifier. I recall reading a thread on this group just a few days ago about something similar where a resistor was soldered across R10 to lower the resistance of this current limiting resistor and lessen the voltage drop to the amplifier PTT circuit but I can't think why that would be necessary since it is working?for most folks as designed. Anyway, there is no current limiting resistor in the PTT 5 volts coming from a QCX so that may explain why it works for one and not the other...
73 .. Ron
Too keep is short,?
QDX Rev 3 with the 1.04 firmware is providing 5 volts to the ring of the PTT cable, but not triggering the QRP Labs’ 50w Amp. ? What should I be checking?
more details:
- ?QDX wired for 12volts. ?
- ? QDX fully functional at low power. ?(Made numerous contacts on FT8 and RTTY)
- ?Using 2 different amps (40m and 20m) with same results, PTT voltage present, but amp not turning on.
- ?Amps turn on when QCX Mini or QCX+ is used to provide PTT signal
- ?Voltage from QCX Mini and QCX+ are approximately 4.98 volts
- ?Voltage from QDX is approximately 5.04 volts
- ?Voltage on tip from QCX radios has 5 volts present, QDX does not have that 5 volts (amp does not use tip, so should not be an issue)
- ?When checking QDX, identified Q7 was fried and shorts closed.? Replaces with a diode, but results remains unchanged for amp not turning on.
- ?My assumption sitting here typing is that another component fails when Q7 failed.? Thoughts?
I would like the option to use with amp on occasion. ? But, not sure where to go from here.
Any help would be appreciated. ?
NT5AT - Wil
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Will,
Note that the QCX+ rev 1 has the PTT signal on the TIP, and the others, including the QDX, have the PTT on the RING of the 3.5mm jack.? If you are using the same cable as a rev 1 QCX+, then it will not work.? Try a stereo extension cable.? That worked for me.
73
Evan
AC9TU
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Hi,?
I had to improve the QDX PTT +5V output line for that to work well:- 100R 0604 parallel to R10 470R,- 1k from Q12 drain to GND.This was necessary to come closer to the QCX PTT like output.
This is what I have done to get the reliable PTT trigering of a 50W PA from the QDX.? The reason is that the QCX's PTT is a direct logic output with either 0V or +5V level whereas the QDX PTT is "only" active +5V over 470R resistor.? In my case that was not enough.? Now it works.? And yes, it is a ring to ring 3.5mm connection.? 73 Bojan S53DZ
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... just to add...?
The reason for the 100R parallel to 470R is actually the PTT input in the 50W PA, which is over 470R and a red LED in series tied to the GND.? This way those +5V from the QDX is no more +5V but less.
73 Bojan S53DZ
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Sorry again, quicky fingers on a mobile phone... Hi.
Just wanted to conclude that's why I prefer an active 0 Ohm PTT (inactive = open circuit) instead of an active +5V PTT (inactive = 0V).? QDX is capable of doing that.??I will add one P-channel MOSFET to the 50W PA PTT input in the future.
73 Bojan S53DZ
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Hi Bojan. Interestingly, I breadboarded the keying circuit including the Red LED and resistors and there is still something like 3.3 volts available to the gates of the two BS-170 switches in the PTT circuit of the amplifier with the 470R current limiting resistor at R10 in the QDX. Since the Gate threshold?of these MOSFETS is around 2.5 volts, 3.3 volts should still be enough to turn them on I would think. The BS-170 I was testing saturated at something just greater than 2.5 volts on the gate.?100R in parallel with R10 increased that voltage going to the MOSFET Gates to 4.4 volts in my test setup. That won't hurt anything but your new short circuit current limiting/protection in the QDX is higher than before the mod. Did you do any before and after voltage measurements, especially at the gates of Q5 and Q6 in the?amplifier PTT circuit? Just curious as to what is causing the need for the modification.
Thanks ... Ron
Sorry again, quicky fingers on a mobile phone... Hi.
Just wanted to conclude that's why I prefer an active 0 Ohm PTT (inactive = open circuit) instead of an active +5V PTT (inactive = 0V).? QDX is capable of doing that.??I will add one P-channel MOSFET to the 50W PA PTT input in the future.
73 Bojan S53DZ
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I measured the voltage at the red TX led on the amp trigger by the QDX. ?It was only 0.89 volts.
The voltage on the red TX led on the amp triggered by the QCX Mini was 1.94 volts.
… ? Now, what is the best solution… ??
Regards, NT5AT - Will
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On Aug 13, 2022, at 2:22 PM, Ronald Taylor < wa7gil@...> wrote:
Hi Bojan. Interestingly, I breadboarded the keying circuit including the Red LED and resistors and there is still something like 3.3 volts available to the gates of the two BS-170 switches in the PTT circuit of the amplifier with the 470R current limiting resistor at R10 in the QDX. Since the Gate threshold?of these MOSFETS is around 2.5 volts, 3.3 volts should still be enough to turn them on I would think. The BS-170 I was testing saturated at something just greater than 2.5 volts on the gate.?100R in parallel with R10 increased that voltage going to the MOSFET Gates to 4.4 volts in my test setup. That won't hurt anything but your new short circuit current limiting/protection in the QDX is higher than before the mod. Did you do any before and after voltage measurements, especially at the gates of Q5 and Q6 in the?amplifier PTT circuit? Just curious as to what is causing the need for the modification.
Thanks ... Ron Sorry again, quicky fingers on a mobile phone... Hi.
Just wanted to conclude that's why I prefer an active 0 Ohm PTT (inactive = open circuit) instead of an active +5V PTT (inactive = 0V).? QDX is capable of doing that.??I will add one P-channel MOSFET to the 50W PA PTT input in the future.
73 Bojan S53DZ
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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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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
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And Will, have you measured the voltage over the series of 470R and the red LED?
? 73 Bojan S53DZ
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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
And Will, have you measured the voltage over the series of 470R and the red LED?
? 73 Bojan S53DZ
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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
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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.?
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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
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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
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
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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 ??
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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
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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
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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 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
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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.
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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.
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Ronald Taylor