Note:? Sometimes when a PA BS170 goes bad it puts PA voltage onto the IC503 and damages it.??

On Wed, Jan 24, 2024 at 07:59 PM, Peter Li wrote:

Oh, and you probably already know but even with TN0110s you do still want the Zener protection diodes.

Good point! I was planning on a diode on L14 to suppress any TX end spike instead, as I added to my QDX 80-20 after blowing the BS170s. (No high SWR antenna there, either.)?


Peter Li wrote:

Looks good Nate, and it looks like you have your heatsink bolted down as well? The reason I kept my FETs standing up was to keep the leads short, but not clear how much this matters for heat transfer versus good case contact like you have.

Yes, I bought a small heatsink and drilled and threaded it directly, using the QRP-Labs supplied screw to hold it in place, and a bit of thermal paste.?

-Nate
N8BTR

An update for anyone interested: L507 inductor found to be faulty gone O/C would explain why weak reception on 40m & 60m, now need to locate a replacement.
I still need to investigate why no transmit on any channel, done all Hans QDX tests apart from checking for a 5V squarewave during transmit on BS170 transistors.
I suspect there may be a problem with the TX_BIAS which was indicated in the self tests.

On Wed, Jan 24, 2024 at 02:38 PM, Shirley Dulcey KE1L wrote:

I use the QRPometer from NM0S electronics. It was originally a 4SQRP kit; the designer now sells an updated version. He sells them through a store on eBay:?

?

I also built this QRPOmeter and it seems to work quite nicely. Fun build.
Dean - KC9REN

?

Peter_Li, I just thought I'd share what my QDX heat sinks look like also. I found the heat sinks for the TO-92 case of the TN0110 MOSFETS were a bit loose and what I did was put three wraps of copper foil tape onto the MOSFET and then used thermal paste before pushing the heat sink onto them. I also installed a couple of stick on type heat sinks onto the board to help remove the heat from there too. When transmitting into a dummy load, I do feel heat on my finger from all of them. This may or may not be overkill by using heat sinks in both locations but I thought it couldn't hurt.
?

Two more information:

1. All tests were made with turns spread over the whole toroid. So inductivity is lower than with turns pushed together.

2. Ref. to manual page 40 L508 should get only 11 turns and not 13. Calculate with 13 turns L should be 270 nH like shown in table (286 nH). I measured 270 nH when made with only 11 turns! So this points also to a higher AL than from the data sheet.

73 Ludwig

Thank you, Ron.

It was a very small hope because I understood that broken resistors due to electromagnetic interference is something very unusual.

But anyway, this is a good reason to order a few FST and 50PA from qrp-labs (always put off buying PA). Here in Poland it is hard to find genuine TI FST.

Again, thank you a lot.

According to the T30-17 data sheet tolerance for AL is +/- 5%.
From my L measurement the tolerance seems to be at least +25 %.
Any idea?

Here are some attenuation values (all in dB, LP for 12/10 m):
v1: Simulation with L values from manual
v2: Simulation with found L values for original winding
v3: measured attenuation values for original winding
v4: measured attenuation values for reduced winding

?? f/MHz? 24.9???? 28.5???? 49.8???? 57.0 ??? 74.7???? 85.5
v1??????? 0??????? 0??????? 23?????? 31.1???? 55.1???? 56.3
v2??????? 1??????? 4??????? 37.2???? 49.1???? 51.5???? 50.2
v3??????? 0.2????? 1.8????? 37.6???? 51.7???? 55.9???? 54.9
v4??????? 0??????? 0.2????? 25.4???? 36.2???? 63.0???? 55.5

There seems to be only one critical value for v3: 1.8 dB @ 28.5 MHz. It would reduce output to around 70 % compared to v4.

Especially for the first four frequencies the values from version 1 and 4 and from version 2 and 3 are similar.
So I guess my L measurement is not wrong.

73 Ludwig

Hans

Thank you so much for coming back to me so quickly.

I'm not aware of any differences or deficits in the 20-10m assembly or operating instructions.

These are really minor points. For example, there is only an inventory for the low band version (p.5 of the manual for rev. 5) and, e.g., the simulated response of the LPF only seem to be documented for the low band version. It is perfectly possible to build the high band version with the existing documentation, but debugging a transceiver that is malfunctioning is a bit more challenging (but again, totally possible). In fact one may just as well argue that I did not familiarize myself well enough to address problems on-site, or that this only shows because the low band version is documented particularly well...

The operating manual provides sample sweeps for all the bands

I'm super afraid to ask for those sample sweeps (where do I have to look?) but I guess I have to since failed to locate them when studying the operating manual. The only sample sweep I find is on p.28 of the 1.10 operating manual, and FWIW it looks quite different from those we observed. Furthermore, the documentation states that "ideally the peak of the response (line of yellow asterisks) should coincide with the center frequency of the band" which is not really the case for our sweeps. I understand that the BPF is shared with the 17 m band center frequency of the band, but it looks wrong still which prompted me to have a more detailed look at this.

All that said, I am attaching a screenshot of the 20 m sweep as reported by the software and, for comparison, a sweep done with a SpecAn connected to the antenna port (TG) and to the pins of the single-ended side of T2, with the wire of T2 that connects to the IC3 output removed. I did not enable the marker table unfortunately, but to me, this sweep is quite different from the one in the terminal screenshot. I understand that the are not directly comparable as T2, the commutator and the amplifiers are removed but I would not have expected that kind of difference still. These are measurements from the unit I have access to right now, but most units were similar to those reported in this forum thread and thus even worse... I also understand that the audio-level dB should be divided by 2 for comparison with those reported by the SpecAn, but even then, it doesn't really add up, the shape looks different and the SpecAn sweep is also confirmed by the remaining measurements outlined in my previous post...

I guess the best way forward for me would be to first understand whether my results are in line with what is to be expected or not. I'm happy for any advice on this!

Regards and thanks again

Matt

Hello OGs, YLs,
Question, actually it could be a feature request.. The stm32 chip has an internal real time clock. Wouldn't it be nice to make usable? Currently the clock may be shown on the display ant it starts counting - starting from zero on power-on. Two things would be needed:
?- software - a settigs menu where the user would be able to set current time without a need of playing with gps
?- hardware... the diagram shows that cpu's vbat leg is connected right to the gnd... adding small battery there would be required to persist the time on power off. And since stm32's rtc draws some microAmps, some small button battery should suffice.
What do you think?

1) My display has one (top) row of solid black rectangles with no text.? If I turn the contrast pot, it just washes out to background colour.? ? Should I see 2 rows - or just 1 row.

2) I'm still having difficulty having the QMX show up as a Device on my Windows computer ..? I would expect it to show up alongside my Local Disk C: and my installed SDXC E: under the section "This PC . . . "? ? ? ? It DOES however show up as an item labeled "QMX Transcieiver " under the Devices and Printers tab of my Control Panel.

Its been a slow crawl to get things back on track.? It was working on 1 band two months ago - but was never able to do any diagnostics since my USB-C cable connection has been unworkable.? ?I opted for the install of the 2 10.1KOhm resistors on the QMX USB as proposed.? They pepper-flake-sized SMD resistors were successfully installed, yet I still have trouble getting my PC to acknowledge the QMX properly.??

I have disabled Bluetooth devices on the PC, so that would not be an issue - Phantom Com ports.??

When I turn the system on, I get the two audible pops, the audio volume controls work up and down, and the VFO dial rotates past a number of birdies.

I'm REALLY open to some assistance with diagnosing the problems.? ? Is it possible that a faulty factory-installed USB port could be the problem??? I'd really rather just do a rebuild than wander in the wilderness.

Input would be greatly appreciated.
Kevin / VE7KHI

?

开云体育

Both the QDX and QMX have a conf setting to adjust the frequency, but it is usually only necessary to adjust a few hz. Since the TX freq is correct then I'm pretty sure the QMX is ok. 1500 seems like you have something off in the software you are using. Not a likely number for the QMX itself it seems to me.

I have built the 80-20m qmx. Had few minor problems with toroid enamel making contact but now seems to receive and transmit well. I noticed my receive frequency was about 1.5khz off across all bands. It is transmitting on displayed frequency but am having to use rit to make contacts. Looking for some advice where to start troubleshooting.
Have not seen any info with same problem, may be overlooking something simple.?
Dan ka9toz

Hello there. Finished building my QMX a couple of weeks ago, and just wanted to share my experiences in case of any interest.
As others have mentioned, I did find it very challenging, with the very fine soldering work, especially with my 70 year old eyesight!
I was concerned about downloading the firmware, because I'm not exactly computer savvy, so I was delighted when the radio 'flashed up' without any smoke:)
However, although apparently receiving very well, there was no transmission. After resoldering every dodgy looking joint I could see, and there were a few, I found a broken SMD 5.1k resistor
R504, and after studying the circuit, decided this may be the cause of no transmit. I replaced it with a 5.6k SMD resistor off a junk box pcb, and Lo and Behold, we are up and running!!
After my initial joy and delight, and first qso, I had a couple of problems pop up.
1. Very erratic audio, randomly going very high and being un-controllable with encoder rotation.
2. Frequency jumping in large increments, and sometimes action of encoder reversing ie cw rotation of encoder, frequency decreasing and ccw increasing.
I tried a factory re-set, just in case, but this made no difference. As both encoders seemed to be 'playing up', I thought I would check all soldering of encoders to control pcb, and headers on both control and main pcb. All resoldered,
Fitted diode between L503 and C508 as per Hans' mod instructions. All now seems ok - fingers crossed. I have had numerous qso's now, on 7Mhz ,10Mhz and 14Mhz, all cw and have had great success. Congratulations Hans on a great little radio! I will buy you a coffee when I find out how the machine works:)
I have spotted a couple of glitches, but these are well written about already, so I wont repeat.
Going on holiday to Texas USA in a week, so will take the radio with me and see how I get on.
73's Martin G0ILZ

Try another USB port. ?Sometimes Windows refuses to work on a particular port …
--
73, Bernie, VE3FWF

Cliff, maybe the Groups page will not let an email address completely show. Please try this: email me with it. My info is good on QRZ. I would imagine you could not get my address because of the showing email address issue here on the page. 73, Gil KS4YX