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I think I have a problem with my QDX: It seems to be hard of hearing. It's not quite deaf, as I can get, just barely, some signal on the lower bands (80, 40). With a dummy load on the QDX, if I transmit at 100mW on a separate TX into a dipole, I can see the signal being received on QDX quite strongly, so it looks like most things are working, but not well.
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It's a Rev 4 PCB, so it has the C71-C74 mod done prior to being shipped.
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Transmit seems fine.
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I've rewound L12 (first time had miscount on turns) and L2 (twisted the 3 wires tighter) and verified all the continuity tests noted in the assembly manual.
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The self-diagnostic tests seem fine, screenshots included below.
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But on WSJT-X, the waterfall stays empty. In fact, the noise level doesn't seem to change at all (all bands) with nothing connected to the BNC, vs. a 20m resonant dipole, vs. a 50ohm dummy load.
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If I put my finger on L12, the noise floor goes up and on occasion I will see a signal that wasn't there before.
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I'm not sure where to go next. It doesn't feel like the receiver should be this quiet, though.
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Lance,
Pardon my ignorance, but why do you have a dummy load connected while trying to receive signals??
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On Nov 9, 2022, at 13:42, Lance KJ5O < joe@...> wrote:
I think I have a problem with my QDX: It seems to be hard of hearing. It's not quite deaf, as I can get, just barely, some signal on the lower bands (80, 40). With a dummy load on the QDX, if I transmit at 100mW on a separate TX into a dipole, I can see the signal being received on QDX quite strongly, so it looks like most things are working, but not well.
?
It's a Rev 4 PCB, so it has the C71-C74 mod done prior to being shipped.
?
Transmit seems fine.
?
I've rewound L12 (first time had miscount on turns) and L2 (twisted the 3 wires tighter) and verified all the continuity tests noted in the assembly manual.
?
The self-diagnostic tests seem fine, screenshots included below.
?
But on WSJT-X, the waterfall stays empty. In fact, the noise level doesn't seem to change at all (all bands) with nothing connected to the BNC, vs. a 20m resonant dipole, vs. a 50ohm dummy load.
?
If I put my finger on L12, the noise floor goes up and on occasion I will see a signal that wasn't there before.
?
I'm not sure where to go next. It doesn't feel like the receiver should be this quiet, though.
?
<audiosweep_30.png><audiosweep_40.png><rfsweep_30.png><rfsweep_40.png><rfsweep_60.png><rfsweep_80.png><rfsweep_20.png><audiosweep_60.png><audiosweep_80.png><audiosweep_20.png><image_60.png><image_80.png><image_20.png><image_30.png><image_40.png>
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The dummy load is connected only while running the self-tests. Sorry to be unclear. It's connected to a 20m dipole when trying to actually receive signals - but I was noting that the noise level doesn't appear to change when I connect the dipole when compared to a dummy load (or even nothing) attached.
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No problem, partly my reading problem too.
It does sound like Rx isn't doing all it should. I would suggest reflowing the solder joints on L12, a full 10 seconds on each connection. I recently had another issue with another kit that turned out was just that. Joints looked good, but reflowed them and things began working. That enamel coating can be tough to get off.
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On Nov 11, 2022, at 08:22, Lance KJ5O < joe@...> wrote:
The dummy load is connected only while running the self-tests. Sorry to be unclear. It's connected to a 20m dipole when trying to actually receive signals - but I was noting that the noise level doesn't appear to change when I connect the dipole when compared to a dummy load (or even nothing) attached.
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Any of Hans kits with inductors I build I tend to tin the coil wires before I assemble them on the boards, this makes sure the enamel is gone and mostly eliminates this issue and you don’t risk damaging the PCB due to excessive heat
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Peter
M0PWX
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It does sound like Rx isn't doing all it should. I would suggest reflowing the solder joints on L12, a full 10 seconds on each connection. I recently had another issue with another kit that turned out was just that. Joints looked good,
but reflowed them and things began working. That enamel coating can be tough to get off.
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73,
Cliff, AE5ZA
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On Nov 11, 2022, at 08:22, Lance KJ5O < joe@...> wrote:
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The dummy load is connected only while running the self-tests. Sorry to be unclear. It's connected to a 20m dipole when trying to actually receive signals - but I was noting that the noise level doesn't appear to change when I connect the
dipole when compared to a dummy load (or even nothing) attached.
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I'm a pre-tinner also and see no reason to not do a DC continuity check before installing in a board.? Just seems like the sensible technique to me.? I pre-tin leads and braid on coax connectors as well and have had good success with that over the years.
Sent from my Verizon, Samsung Galaxy smartphone
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-------- Original message -------- From: M0PWX <M0PWX@...> Date: 11/11/22 9:50 AM (GMT-05:00) Subject: Re: [QRPLabs] #qdx Low RX levels, but not totally gone. Not sure where to look.
Any of Hans kits with inductors I build I tend to tin the coil wires before I assemble them on the boards, this makes sure the enamel is gone and mostly eliminates this issue and you don’t risk damaging the PCB due to excessive heat
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Peter
M0PWX
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It does sound like Rx isn't doing all it should. I would suggest reflowing the solder joints on L12, a full 10 seconds on each connection. I recently had another issue with another kit that turned out was just that. Joints looked good,
but reflowed them and things began working. That enamel coating can be tough to get off.
?
73,
Cliff, AE5ZA
On Nov 11, 2022, at 08:22, Lance KJ5O <joe@...> wrote:
?
The dummy load is connected only while running the self-tests. Sorry to be unclear. It's connected to a 20m dipole when trying to actually receive signals - but I was noting that the noise level doesn't appear to change when I connect the
dipole when compared to a dummy load (or even nothing) attached.
?
?
?
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Thank you. I was able to crank up the temperature on the soldering iron to about 650°F and reflowed all the enameled wire. It looks better - the noise floor goes up when an antenna is connected vs nothing, so that's a good improvement.
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Lance
I don’t mean to hijack your thread - what scope are you using - looks Mac based?
thanks!
Michael
--
KD7PTZ
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Lance,
I may be old school but on my two Solomon soldering ?pencils (one with a fine tip and one with a larger broad tip) I turn them up as high as they will go. ?I then apply to the part being soldered quickly, apply fine 60/40 Kester solder, and remove as soon as I see a nice flow of molten solder. Get in there, get the job done, and get out. ?Too long on a part or connection on the board with too little heat causes problems, at least it did years ago for me. ?Hi heat. Short time. ?Good solder joints for 60 years. ?The only kits I ever sent back to Heathkit were found to have had cold solder joints. ?And the hotter the better. ?I love my Weller butane soldering pencil. ?Gets hot quickly and melts solder, even outside in cold weather. Never leave home without it. ?
My forte with new hams is antenna installation with my home brew high power pneumatic antenna launcher. ?Sounds like a shot gun when it goes off but almost hits the moon if necessary. And if I hit the tree instead of the crotch of the tree the pvc slug I shoot shatters….. lots of fun! Almost like 4th of July at times. ?But my success rate is greatly improved lately. ?I am now called One Shot MacGiver! ?I have even been written up in our club paper…… what a hoot! ?
Dave K8WPE? David J. Wilcox’s iPad
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On Nov 11, 2022, at 7:05 PM, Lance KJ5O <joe@...> wrote:
?Thank you. I was able to crank up the temperature on the soldering iron to about 650°F and reflowed all the enameled wire. It looks better - the noise floor goes up when an antenna is connected vs nothing, so that's a good improvement.
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Lance,
If the issue is still not resolved by reflowing enameled wire connections, have you tried checking continuity of the tip connection of the BNC/SMA connector to the PC board or to capacitor C2?
That's about all that's left between your antenna and the QDX. Your RF sweeps all look good.
Have you ruled out your antenna system, feed line and connectors? The assumption is that you have, but I have to check.
You might try bypassing C2 and capacitively coupling your antenna to the anode of D1 and see if that improves reception.
In the front-end portion of QDX's schematic below I've highlighted the path where the internal test signal is injected into the signal path. Also highlighted C2 just to show it's position in the circuit.??
Good luck!
--Al
WD4AH
? ^^ CLK2 test injected here at yellow highlight
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Thanks. Reflowing fixed it. I should have been more patient, but that enamel is tougher than I thought.?
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Just thought I'd jump in with similar issue here. Unit transmits admirably but all-but deaf on receive.
- Reheated all L12 leads set to 800 F;
- reheated and confirmed values for C28-31 also;
- confirmed continuity with IC3 3-4-5-6-9;
- confirmed continuity X1 - C2 - D1.
Passbands attached. 40 looks more like a high-pass filter; 30 looks just plain strange; 20 looks ok I guess. No change before/after the above attempts. More ideas welcome, thank you. Elwood, WB0OEW
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Elwood,
Are the RF sweeps done with a 50ohm dummy load connected and the case closed?? The response can be influenced by the antenna if connected, as we as noise from devices in the shack.
The low-pass filters are in the receive path, so try reflowing the toroids for them.? Also, verify that the 6 filter section diodes are working correctly.? The two selecting the LPF should read close to zero volts on the banded side.? All others should be close to the input voltage supplied to the QDX.
73
Evan
AC9TU
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Hi Evan,
Thanks for your help. We are making progress. Should have thought to use the dummy load, plot shapes are now sensible.
Reflowed all the filter toroids and confirmed voltages on selection diodes are correct for each band.
20 and 40 now look fine, but 30m is still pretty weak, -11 db, see attached.
I've also attached my band configuration. Since 20 and 30 share LPF 2 and 20 is fine, that suggests LPF 2 is ok. But BPF 2 is unique to 30 so I'm thinking L12 is still bad, but I've reflowed it, and C28-31, twice now. IC3? perhaps??
73
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Peter M0PWX
wa8yan.radio
David Wilcox K8WPE