Keyboard Shortcuts
ctrl + shift + ? :
Показати всі комбінації клавіш
ctrl + g :
Не доступний для безкоштовних груп.
ctrl + shift + f :
Знайти
ctrl + / :
Сповіщення
esc to dismiss
Лайки
Пошук
QMX+ No transmit or receive
|
Hello again everyone and thanks to those who responded to my last emails. A few weeks later, many more late nights and still no further ahead, but i will disclose what i have found. First off, thanks for all the suggestions. The QMX is not in practice mode, not in protection mode and the Q507 mosfet is not lifted or broken that i can see. I have .3 ohms continuity between Q507 thru inductor L502, thru T501 and then to the drains of the finals. During transmit , i have .33 v from the drain of Q507 (i hope i have that right? It is the flat portion at the top of it just below L502). Source is 12v and the gate seems to drop only about 500mv or so during transmit. I had been told the threshold was -1.5 to -3v possibly on the gate? I just wish i understood it a little better, like the signal path through an old AA5, LOL. I installed my spectrum analyser at the jumper before the BNC and although no appreciable power out, ALL bands are delivering a almost perfect match with the signal being transmitted through the diagnostics mode. But...-20 to -30 db down in the mud. So very low. But it is there. I am lost for now. Does this make sense to anyone? Thanks for any and all help in advance! |
|
Joel, I would forget about Q507 for the moment, as if I understand correctly, you have no receive either. I would look at getting the receive working first. It is quite probable that you have multiple faults and are likely caused by a poor connections on the soldered joints. Have you checked for receive on each band? You say you have a spectrum analyser, does it have a built in signal generator? If so you can feed the output into a small coupling loop, say a couple of turns 10mm diameter and see if there is any life by holding it near to the band pass filters and work from there. When I built mine, I checked DC continuity for each of the toroids on the top side of the board as I fitted them and some of them were showing open on the first pass, so needed reworking with more flux. Hope this helps. Nick G0OQK |
|
Thank you Nick. My tiny SA has a SG. I will try it out. I spent so much time checking and double checking solder joints but I thought If I could do some well thought out testing, it would reveal the problem for sure. I will give it a try and let you know. Thank you! VY2KW
|
|
Hi Joel,
Have you used the terminal mode diagnostic screen? If so, can you post a screenshot of the result in both receive and transmit mode?
There are also some good hints on the troubleshooting page:
Note: Han's guide suggests getting the transmitter working first before the receiver. This is to verify that the LPF selection and circuits are correct before repairing the upstream receiver circuits.
73
Evan
AC9TU |
|
Hello Evan! I will try to post some screenshots this evening after i get home from work. it wont be for another 10 to 12 hours though. I have used the diagnostic function and verified that there is no Wattage and only .3v output during transmit on All bands. IMO, but humbly of course, the fact that i can see output at the bnc with my scope co-inciding with the frequency delivered in each band setting matching perfectly BUT -20 to -30 db under the noise floor, Makes me believe there is no drive? No appreciable voltage at the drains of the output transistors. .3v measured with DVOM. Thanks for the reply! VY2KW
|
|
You may be seeing a small amount of Rf on the BNC during transmit because CLK2, which drives the PA, is also connected to the output through R518. That bypasses the LPFs but does go through T507. Use your spectrum analyser to check the Tx frequency, it should be the same as the dial frequency.
As Evan says the diagnostics screen, both in Rx and when attempting to transmit may give useful information. The Hardware tests may also be useful, the Operation manual gives information about what they do and examples of what they should look like.
Do you hear any noise on the headphones? If so does it change as you change the volume? Do you hear a side tone when you key the transmitter?
Chris, G5CTH |
|
Yes indeed. I do hear background noise when listening with the headphones. When I key, I do hear a tone. When I transmitted and read the frequency with my spectrum analyzer, it was in diagnostic mode using putty. When in that mode, it transmits at whatever frequency is showing on the computer screen, IE, the band that I've selected. And it is almost exactly the same frequency as what's on the computer screen. As soon as I get a chance to collect some more data, I will respond again. Thanks again for all of your help! On Wed, Dec 11, 2024, 10:31 AM Chris via groups.io <chris.rowland=cherryfield.me.uk@groups.io> wrote:
|
|
Hello Nick. I tried that method this evening with my tiny SA. It does have a built-in signal generator and I rigged up a probe with an attached 10 mm diameter coil of copper wire at the end of it. I set my QMX to several different frequencies of several different bands and match those frequencies with my signal generator and with the headphones on my head, heard absolutely nothing. Interesting thing is, I have gone over my solder joints multiple times and made sure I had connection between the through hole and the actual wire. I have gone to Great lengths to make sure that all of my soldering is satisfactory, but I guess it's still possible to have a problem in that area. But absolutely no recieve at all. VY2KW
|
|
I’m sorry that didn’t work Joel, I had hoped that coupling into the band pass filters would bear fruit and give you a quick win. I quite understand why given the architecture of the transceiver, Hans suggests getting the TX working first. My normal approach would be to get the receiver working first, then worry about the transmitter. It’s good though that you have sidetone, display and noise out, at least the processor is working.
You mention having continuity from Q507 to the PA mosfets, have you checked continuity to ground? There shouldn’t be any. It is possible that there is a problem with the winding, or connection of T501, giving continuity between primary and secondary. When I checked continuity of my toroids after installation, I checked between the pads of the through plated holes on the opposite side of the board to that which was soldered. This eliminates any possible error, where you might touch the end of the winding wire with your probe and get a false reading. You do need fine tipped probes. I hope this helps. 73 Nick G0OQK |
|
Well Nick, all I can say is any advice is great advice! What I did with t501 is I originally built it installed it and after I doubted my own work, de soldered it and wound it again with new wire. And after I cleaned the wires where they go through the holes and get soldered, I checked for continuity before I even installed it I had no continuity between primary and secondary. You know what I actually need, and I hate starting up new threads for the exact same issue, but I really wish I had a couple of paragraphs explaining the signal path from the BNC all the way to the processor. I wasn't joking the other day when I said I wish I knew it as well as an old AA-5 tube radio. It took me a couple of years to understand how an AA-5 works but as long as I know how it works, I know how an AA-4 or an AA6 or any other old tube receiver works. It is the solid state gear that confuses me a bit. But that's okay because I am willing to learn. But if I had exactly what I mentioned, a description in paragraph form outlining all the different parts on the board where the signal path goes to be amplified and then either decoded or detected. But thanks very much for your help so far. I really appreciate it
|
|
Hi Joel,
A good place to start may be Hans's presentation in 2023. It covers more products than just the QMX; however, as Hans has stated many times, it has been a stepping-stone journey for him. Older products are the source of key learning that translates to the new product.
Here is the link from his web page:
Descriptions are scattered across the QRP-Labs web pages, some crossing over between prior kits and the new ones. One example is the tuning method for the shared low-pass filters.
The software has not been published and contains most of the magic. Some of the software blocks are described, but the details on the filters and other software-based modules are not very detailed.
I would also read the operations manual for the QMX, as some descriptions are included there.
As far as I know, no single source exists for all the blocks and modules used in the QMX. Maybe Hans will get time to write them after the massive workload with the firmware enhancements on his plate.
73
Evan
AC9TU |
|
On Thu, Dec 12, 2024 at 10:57 PM, Joel Macneill wrote:
I really wish I had a couple of paragraphs explaining the signal path from the BNC all the way to the processor.Joel, reading QMX Terminal Hardware Sweeps you will find some information about the RX path, also used for some of the sweeps. It's for the QMX but also usable for QMX+. For QMX+ the BNC is connected via a jumper to T507 and for QMX direct without a jumper. The other side of T507 is connected to the same point like R518 (test signal injection). The RX path of the QDX is very close to the one of the QMX. The assembly manual for the QDX section 3 delivers a lot of information about the design and the function.
Maybe this will help.
73 Ludwig
|
|
I'll try to describe the Rx path:
Starting on page 5 (of the schematic) the Rx goes through the power/SWR meter T507, then through C526 to the LPFs. The diodes select the appropriate LPF and the output from the LPF goes through C509 to the Rx switch Q508, it is now labelled RX_IN. The RX signal turns Q508 on and off.
The CLK2 RF TX signal generated by the MS5351 is also injected into the Rx path through R518, this is done for testing the Rx signal.
Then on Page 4 the RX_IN signal goes into the multiplexer switch IC408 (only on the QMX+) through the selected BPF and a second multiplexer IC402.
Then thr signal goes through the trifilar transformer T401, then through the Tayloe Detector, IC403. This is driven by IF signals from CLK0 and CLK1. Some frequency selection is done here.
The output is two differential signals, the I and Q phases, at the IF of about 12 kHz.
It is now amplified by the instrumentation amplifiers IC405 and IC406. This is the only amplification the RF (well now IF) signal gets, it then goes into the L and R channels of IC307 which is a stereo audio ADC. This has differential inputs and passes the signal to the processor.
The rest of the magic (filtering, demodulation, etc.,) happens in the processor. The audio is output to the stereo DAC, IC401 and is amplified by IC404 to appear on headphones. It is also sent to the USB Audio output.
This should help to give a number of points that a skilled RF engineer could probe, or inject a Rf level signal to see how far it's getting.
It might be possible to bypass the LPF and BPF circuits by connecting between the BNC output and IC401 pin7 and running the Rx tests, CAREFULLY. If the tests involve transmitting using the PA then the signal will be far too high, but for the Rx tests AIUI CLK2 generates the test signal which is attenuated by R518 and will, as well as going through the LPSFs will go through T507 to the BNC output. Any other Rf signal source that can be attenuated enough could also be used.
Hope this helps. Naturally any probing round the circuit at this level needs to be done with appropriate care for the device and your test kit, which may not appreciate large amounts or DC or Rf inadvertently applied.
Chris, G5CTH |
|
Just read your description Chris. I am going to follow this path the next time I am in the shack. I will be checking closely for any solder shorts although I don't think there is any. I have double and triple checked my soldering and have rewired T501 and T507 with no results. What I do know for sure is that there is the 5V ptp on the gates of the output transistors and grounded sources but only .33v on the drains which is traced all the way to the Q507 transistor. Thats during transmit. Because receive and transmit were both not working, i thought i might find a common failure. Thanks for all your help!!
|
|
On Sun, Dec 15, 2024 at 06:55 PM, Joel Macneill wrote:
only .33v on the drains which is traced all the way to the Q507 transistor.The question here is why. The gate of Q507 should be high (+12V) in receive and go a volt or two low on transmit to turn the power on. This is controlled by the quartet of transistors, Q13 to 16, there is feedback through R508 and R509 to the base of Q16 and the control signal from the microcontroller is DAC to the base of Q15. I think these should be low on receive and go high on transmit, maybe a volt or two. Chris |
|
Thank you to everyone in the group!! And hope you all have a merry christmas!! I just realized that farther back in this thread, I said that I would submit audio and RF sweeps and I still have not done it yet. Been very busy lately. I have reviewed this thread several times away from the shack and in solitude, lol when i get it, to absorb all the info i have been given. What I documented is this.... *****Low pass filter sweeps were good on the lower to mid HF bands (160m thru 20m), and not so good on higher bands like 6m***** Audio sweeps all bands -100db,**** RF sweeps all bands 90 to 120 db below with no detectable center frequency on any bands,***** Image sweep , no bands above -90db*****SWR sweep very chaotic due possibly to the low power output. As I previously promised, I will try to submit some actual screen shots of my sweeps. Just received my new QMX mini kit today from Hans and I want to wait to figure out my problem with the QMX+ before I start that project. I cannot handle multiple unfinished projects around the house. Again, I want to say thanks, Merry Christmas and a Happy new year!! Will be back again with the screenshots. 73s Joel MacNeill VY2KW
|
|
Hello all! I finally had a chance to get a few screenshots of my diagnostics . I picked one band to sample, the 80m band. I am having the same problem on all bands. I hope this may shed some light on my problem. In my opinion, the LPF screenshot looks okay but the others are of some concern. Can anyone tell me what they think of these? Thanks! On Wed, Dec 25, 2024 at 10:07 AM Joel Macneill <joelmacneill1977@...> wrote:
|
|
On your very first screen, the readout confirms what you first suspected in that Q507 is not turning on, hence one reason for no transmit. Might I suggest measuring Q507 VGS, the voltage between the gate and source and see how that compares with the voltage at the junction of R506 and R507. The voltage should be the same as on the gate, as they are connected together. Nick G0OQK |
Повідомлення
Більше
Додаткові параметри
Більше
to navigate to use esc to dismiss