Yesterday evening I finished building my QDX and was quite proud of myself, for it was the first 'real' soldering project in ~8 years.
I already realized how old I have become when I needed a 20x microscope as an aid do scalpel away the Rev 3a ground short at C41, but it seamed to work.
Winding the toroids was kind of a challenge, but I photographed all the 0.3 mm wired once and double-checked the loops on the screen.
All the continuity checks in the manual where performed successful.
?
I used a lab PSU to power the QDX with 9V and limited the current, just in case.
All went well, LED stated flashing, then stayed on, as expected.
Voltage on the cheap PSU was fluctuating a bit around ~9.1 V to 9.3 V, current 160 mA.

I packet all and took it to my garden where I soldered before, hooked up the 20W dummy load and my Debian machine.
Connecting and upgrading the firmware worked flawless. I configured WSJT-X without problems as well, but I just tested sending on 40m.

This gave too much confidence, so without thinking much I connected my (maybe not perfect matched) portable backpack antenna, a 5:1 unun with a 2,7 m radiator.
Using WSJT-X I instantly received FT8 messages on 40?m, but my own CQ and replies where not answered. Current while transmitting ~ 0,5 A at 9,6 V (did not increase that on purpose).
Then I tried 20 m and during the first sending cycle I noticed a relay in my PSU clicking. In shock, I looked at the display, ~ 1,3 A and the voltage dropped.
I disconnected the PSU and inspected the PCB, no visible damage, but it now draws as much as I allow and the LED stays off.
The internal resistance on the power socket only 2,0 Ohm now.

I would really appreciate help to find some answers to the following questions.
- What did I fry and how to fix it? Voltage regulators? (I regret selling my thermal camera now)
- Any idea for the root cause? To my mind come:
??? - To high SWR on the antenna which was not matched at that location / position
??? - Current constrain in the PSU
??? - Mistakes I might made during assembly
??? - Errors on the PCB, possibly caused by the scalpel job

Pictures of the PCB are available, and I can investigate with a microscope if that helps.


73 Alexander DM8TE

Hi Bill,

In addition to what Hans stated, if you have the three flashes and the transmission stops, that could be an RF feedback problem.? Try transmitting into a dummy load using the terminal emulator, then using WSJT-X, and finally attaching the antenna.? If it works until you transmit with the antenna, you have RF feedback into the shack.? You can try snap-on ferrites on all the leads into and out of the QDX.? That has helped others, including myself, until you can adjust the antenna so there is no RF getting back down the transmission line.

73
Evan,
AC9TU

Did you turn off all audio processing and other special audio features in Windows? Things like echo cancellation will remove continuous tones like FT8, for instance.

73, Willie N1JBJ

I think the latest documents should be updated, to reflect this.

G7JUR

Joshua,
Windows 11 home.

Bill, what operating system are you using??

Joshua

Hey gang. Received my assembled QDX today...Thanks Mark !
OK, so the receiver is plenty hot...I'm playing on 40m first.
When I attempt to transmit - either by the 'Tune' button or by actually calling someone, the rig transmits for about 250 ms and then just stops xmitting. I found that I must operate the WSJT-X gain slider at 0dB to even achieve this truncated xmsn. The red LED blinks twice repetitively as it is indicating insufficient audio drive...I think ?!
I see in the ops manual where it suggests that the slider be operated at 0 dB and that there are audio gain commands which may be sent to QDX, such as AG21 etc. I think I need to send AG99 or so.
Exactly how do I do that ?
Please give me the step-by-step here !
WW2FLY is getting away and I really want to work them before the special event ends in a few days !
Many thanks for any help !
72 / 73,
Bill, N4QA

Putty works well in Linux as well.?
--
Colin Kaminski - K6JTH
https://www.qsl.net/k6jth/

Phil,

OK, now I have a clearer picture of what you are telling us.? You have a low current draw on transmit, so the power amplifier MOSFETs (BS170 Q8, 9, 10, and 11) are not drawing power.? That could be an L14 or T1 problem and other issues.? Verify that you have the input power (12, 9, or whatever you are supplying) on the 4 MOSFET drains.? If there is no power on all 4, try reflowing the connections for T1 and L14.? That is the most common problem.

Did you do the continuity check when you installed T1?

I should have started with the obvious.? Have you verified that the LED flashes 3 times, then pauses and repeats?? That would indicate that the audio level is not set high enough to measure the frequency.? This is not an issue if you use the Terminal Program Transmit test application.?

I suggest you set up a terminal emulator on your PC to help with the diagnostics.? For Windows, I use PuTTY.? Available here:

There are other options for other operating systems.? I have not used them.

We can start here and see what you find.? As stated in my prior post, always have a dummy load or resonate antenna connected when the QDX is power.? This is especially true when testing for problems—transmitter test I always do with a dummy load first.
73
Evan
AC9TU

OOps I forgot how to write a message. Is there a way to correct things?

On Fri, Aug 12, 2022 at 12:01 PM, Evan Hand wrote:

I am not sure I understand what you are reporting.? When you say the VSWR meter doesn't budge, do you mean when in setting the forward power mode??

Sorry, I misspoke, I was using a?Thruline Wattmeter, set up to measure forward power.? The QDX was connected to a dummy load through the wattmeter, and I was clicking on the 'tune' button in wsjtx to key up the radio.?

It also helps to know the firmware installed on the QDX.? You can get this using the terminal program on the startup page or reading the file names when the QDX is in update mode.

I'll update with that info later this evening.

It would help if you could tell us what the input to the QDX current readings are on receive and transmit.?

If memory serves, the radio was drawing about 0.12 amps in receive and about 0.25 amps on transmit.?

I suggest you have a dummy load connected to your QDX when doing any testing, as it is easy to damage the BS170 MOSFET finals.

While testing I was using the dummy load kit from Hans

Since PSKReporter has spotted you, you are putting out some power.

I haven't tested it with an antenna since before I connected the wattmeter, maybe it worked briefly and then stopped because it was damaged.? I suppose it's possible I'm not using the wattmeter correctly.

Thanks,?
Phil KC2WAN

I bought one Chinese antenna tuner and soon found out that I could not install the variable capacitors and their knobs. But in my collection of ancient radio parts I found suitable ersatz.? So I built the circuit and found that losses were quite high. Using a toroid from Amidon improved things. Then I decided to change the circuit from T to L with a series inductance because I do not like that small parallel inductance of the T-network. So the only things that remained from the original tuner were the pretty case and the SWR meter which I supplemented with a moving coil meter to make it more sensitive and usable in bright sunlight.

The 500pF variable capacitor C1 in series with the coil compensates an adjustable part of the coil inductance. So the inductance is not limited to 12 discrete values. When tuning for lowest SWR one begins with C1=500pF.

Greetings all,

?

I've no wish to stir up the debate about which supply voltage QDXs should be built for, but in reading the manual, I saw where it says that the power slider in WSJT-X has no effect on the QDX and that any RF output reduction should be accomplished by lowering the supply voltage. So...

?

1) For those who have done the 12V build and adjust the supply voltage to change the RF output, what problems (if any) have you had?

?

2) Is the QDX tolerant of supply voltage change while powered up or do I need to turn it off before I make a change?

?

An example of why I would want to reduce the RF output is that I normally run ~1W when operating as a WSPR beacon, yet I usually operate FT8 at 2.5-3W, sometimes going up to 5W.

?

I appreciate the information!

?

Charles Johnson

KF4AYT

I am not sure I understand what you are reporting.? When you say the VSWR meter doesn't budge, do you mean when in setting the forward power mode??

It also helps to know the firmware installed on the QDX.? You can get this using the terminal program on the startup page or reading the file names when the QDX is in update mode.

It would help if you could tell us what the input to the QDX current readings are on receive and transmit.?

I suggest you have a dummy load connected to your QDX when doing any testing, as it is easy to damage the BS170 MOSFET finals.

Since PSKReporter has spotted you, you are putting out some power.

73
Evan
AC9TU

开云体育

That's not USB over Ethernet, it's USB over TIA-568 (CAT-{5,6,7}) _cable_

I have the QDX from last December (rev 2 I think?).? Somehow I managed to show up on PSK reporter for the nearest monitoring stations on my first try, but nobody was responding to my CQ or acknowledging my replies.? Hooked it up to a VSWR meter and the needle doesn't budge when I hit the 'tune' button in wsjtx, tested in both 20m and 40m.? Receive seems to work fine, I'm decoding ft8 just fine, but all I can do is listen.? Any recommendations for where to start with troubleshooting??

Tim,

Your doing great.

When I built my 50w amp I needed help with the troubleshooting before initial startup. Mistakes are expensive both in terms of time and replacement parts.

I found a great Youtube video for troubleshooting the 50w amp. What I found were simple mistakes that I repeatedly overlooked. Sometimes it takes a second set of eyes. Not having more than two, I switched gears and approached from another perspective. I found a very nice youtube video by NA5Y for troubleshooting or as in my case just making the final check before first power-up, which is what I did. It was a good thing I did to. I found several simple mistakes I made as a result of watching the video and following the tutorial. I don't know if the mistakes would have been catastrophic or not. What I did learn is to approach the challenge from a different perspective than what I was already doing. The video goes through a methodical approach with excellent explanations along the way so that I learned something in the process.?

I believe you will appreciate this video:?

--
KE4LJH
Steve,?
Florida