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Hello all,
I've been working away on my QMX build over the past few weeks and have something that *almost* works. It powers on, and there's no problem that I can see with the digital parts of the build or the power supplies, but unfortunately I have a short between the center pin on the BNC jack and ground. Even in this state, I was able to pick up some FT8 on 20m. After spending quite some time examining the soldering work on the BNC jack itself, I had a look at the T507 transformer.
This transformer ended up being the worst part of the build for me, I accidentally snapped my trifilar winding, and after I redid it, I didn't have enough of 0.33mm magnet wire to do the winding for the transformer. I borrowed some wire from a friend, which was thicker, difficult to wind, and as it turned out, not-enamelled, which I didn't realize until after I had soldered it into place. I had hoped the short would be because of the unenamelled wire, but when I removed the transformer, the short was still there.
It turns out that the (looking from the top) the left hand side for the "A" winding is tied to ground, and the right-hand side is connected to the pin on the BNC jack. I've checked with a continuity checker, and there doesn't appear to be any solder bridge immediately around the left-hand side, so I think the problem is further up the signal chain.
I'm having trouble figuring out how to proceed from the schematic. I was wondering if anyone had any advice for a good place to check next?
Thank you :)
Daniel
VE3NNE
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You should have DC continuity between those points. Check the
schematic. Remember this is designed for rf so that's why it's
working. Check your rf plots and if they are close to expected then
you are good to go.
-mike/w1mt
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Daniel, you WILL have a short between the center pin of the BNC and ground even if it is apparently working because the VSWR bridge transformer T507 has a winding directly across the output.? It you hear signals, it is working.? For those still building, carefully inspect the SMA footprint hot pad because it is very close to the ground of the BNC.? If it is really shorted to ground, that's likely where it would happen. It may be worth considering mounting the BNC first, then T107.? No doubt several people will make the same mistake.? I did.? See attached.
-Steve K1RF
------ Original Message ------
Date 9/15/2023 9:59:27 AM
Subject [QRPLabs] Mostly successful QMX build, but could use help tracking down short #qmx
Hello all,
I've been working away on my QMX build over the past few weeks and have something that *almost* works. It powers on, and there's no problem that I can see with the digital parts of the build or the power supplies, but unfortunately I have a short between the center pin on the BNC jack and ground. Even in this state, I was able to pick up some FT8 on 20m. After spending quite some time examining the soldering work on the BNC jack itself, I had a look at the T507 transformer.
This transformer ended up being the worst part of the build for me, I accidentally snapped my trifilar winding, and after I redid it, I didn't have enough of 0.33mm magnet wire to do the winding for the transformer. I borrowed some wire from a friend, which was thicker, difficult to wind, and as it turned out, not-enamelled, which I didn't realize until after I had soldered it into place. I had hoped the short would be because of the unenamelled wire, but when I removed the transformer, the short was still there.
It turns out that the (looking from the top) the left hand side for the "A" winding is tied to ground, and the right-hand side is connected to the pin on the BNC jack. I've checked with a continuity checker, and there doesn't appear to be any solder bridge immediately around the left-hand side, so I think the problem is further up the signal chain.
I'm having trouble figuring out how to proceed from the schematic. I was wondering if anyone had any advice for a good place to check next?
Thank you :)
Daniel
VE3NNE
|
Thank you!
My guess is that I had a solder bridge between the BNC and SMA pads, because I did see very high current when I tried to transmit, and once that was fixed, I kept looking for problems that weren't there :)
On Fri, Sep 15, 2023 at 11:08?AM Steven Dick, K1RF < sbdick@...> wrote: Daniel, you WILL have a short between the center pin of the BNC and ground even if it is apparently working because the VSWR bridge transformer T507 has a winding directly across the output.? It you hear signals, it is working.? For those still building, carefully inspect the SMA footprint hot pad because it is very close to the ground of the BNC.? If it is really shorted to ground, that's likely where it would happen. It may be worth considering mounting the BNC first, then T107.? No doubt several people will make the same mistake.? I did.? See attached.
-Steve K1RF
------ Original Message ------
Date 9/15/2023 9:59:27 AM
Subject [QRPLabs] Mostly successful QMX build, but could use help tracking down short #qmx
Hello all,
I've been working away on my QMX build over the past few weeks and have something that *almost* works. It powers on, and there's no problem that I can see with the digital parts of the build or the power supplies, but unfortunately I have a short between the center pin on the BNC jack and ground. Even in this state, I was able to pick up some FT8 on 20m. After spending quite some time examining the soldering work on the BNC jack itself, I had a look at the T507 transformer.
This transformer ended up being the worst part of the build for me, I accidentally snapped my trifilar winding, and after I redid it, I didn't have enough of 0.33mm magnet wire to do the winding for the transformer. I borrowed some wire from a friend, which was thicker, difficult to wind, and as it turned out, not-enamelled, which I didn't realize until after I had soldered it into place. I had hoped the short would be because of the unenamelled wire, but when I removed the transformer, the short was still there.
It turns out that the (looking from the top) the left hand side for the "A" winding is tied to ground, and the right-hand side is connected to the pin on the BNC jack. I've checked with a continuity checker, and there doesn't appear to be any solder bridge immediately around the left-hand side, so I think the problem is further up the signal chain.
I'm having trouble figuring out how to proceed from the schematic. I was wondering if anyone had any advice for a good place to check next?
Thank you :)
Daniel
VE3NNE
|
Hi Daniel,?
you will also need some enameled wire. ?If you can¡¯t find the proper wire please see my QRZ page and drop me an email. It won¡¯t work with bare wire.
73
Dick
W4PID
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All,?
Remember that CRT-style TVs and computer monitors have lots of easy-to-scavenge?enameled wire -- deflection yokes,?oscillator coils, and maybe even the degaussing coil if you get lucky and strike it rich with copper.? And while I haven't tried, the transformers inside wall wart supplies may have enameled wire you can strip.
I might try that as I watch the UTexas - Wyoming game this evening.? In the meantime, I have plenty of enameled wire because I don't throw away my e-waste the minute something goes bad.
73 Jim N6OTQ
On Sat, Sep 16, 2023 at 8:06?AM Richard Hattaway via <rhattaway= [email protected]> wrote: Hi Daniel,?
you will also need some enameled wire.? If you can¡¯t find the proper wire please see my QRZ page and drop me an email. It won¡¯t work with bare wire.
73
Dick
W4PID
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Do I need to rewind my T507 if I wound it the original way? It works this way, but what is the reason for twisting the windings?
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On Sat, Sep 16, 2023 at 01:49 PM, Chuck ke9uw wrote:
Do I need to rewind my T507 if I wound it the original way? It works this way, but what is the reason for twisting the windings?
T507 does not have twisted windings, perhaps you are confusing it with T401?
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Chuck,
The RWTST (12 volt) and WTST (9 volt) winding is for T501.? You do not need to use that method for the low-band (80-20) version of the QMX.? I would not rewind unless you have issues with transmitting and suspect the transformer has a short or was wound incorrectly.? The twisted winding is recommended (needed?) for the high-band (20-10 meter) version.? The improvements due to the winding method are most noticeable on the high-band versions, as explained in the document.? ?AFAIK there has not been a high band QMX yet offered.
Here is the link to the document:
73
Evan
AC9TU
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Oh yes, T501. Thankyou for the response. I'll leave mine for now.
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Richard Hattaway
Chuck ke9uw
K9NUD-Steve