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QMX MB - Wonky SWR Sweep

 

I'm hoping someone can help point me in the right direction. Just completed a build of a mid-band QMX. Loaded firmware 19 just fine. No issues with the initial start up. RF sweeps can use some work but I think I need to address the SWR sweeps first. Into a dummy load (independently measured at 1.1:1 or better), none of the bands have sweeps with values below 3.0:1 and most are much higher. With the exception of 20 m, most are just a noisy mess. 20 m gradually slopes down to 3.0:1 from higher values as the freq climbs.?

I checked the continuity of the T507 windings before installing and again confirmed continuity between appropriate pads (not leads) after installing. But still...what else could it be? I'm not sure if the secondary windings are both wound in the same direction or not, or if they're supposed to be --perhaps someone could clarify that.?

I know it's been suggested that the sharp edges of the binocular core might abrade the wire enamel and cause a short between windings. Though I shaved the edges with a knife before starting (per Hans), who knows, maybe I still inadvertently stripped some enamel away and caused a short.?

So before I remove T507 and start over, I'm hoping one or more of you helpful souls would suggest some alternatives.?

Many thanks in advance.

Mitch NK3H
 

Mitch,

Can you post a photo of your T507?
JZ

On Thu, May 30, 2024, 1:04?AM Mitch NK3H via <mitch=[email protected]> wrote:
I'm hoping someone can help point me in the right direction. Just completed a build of a mid-band QMX. Loaded firmware 19 just fine. No issues with the initial start up. RF sweeps can use some work but I think I need to address the SWR sweeps first. Into a dummy load (independently measured at 1.1:1 or better), none of the bands have sweeps with values below 3.0:1 and most are much higher. With the exception of 20 m, most are just a noisy mess. 20 m gradually slopes down to 3.0:1 from higher values as the freq climbs.?

I checked the continuity of the T507 windings before installing and again confirmed continuity between appropriate pads (not leads) after installing. But still...what else could it be? I'm not sure if the secondary windings are both wound in the same direction or not, or if they're supposed to be --perhaps someone could clarify that.?

I know it's been suggested that the sharp edges of the binocular core might abrade the wire enamel and cause a short between windings. Though I shaved the edges with a knife before starting (per Hans), who knows, maybe I still inadvertently stripped some enamel away and caused a short.?

So before I remove T507 and start over, I'm hoping one or more of you helpful souls would suggest some alternatives.?

Many thanks in advance.

Mitch NK3H

 

Hi John,

Thanks for the reply. I've posted some pics of the area around T507 from 3 different angles. Apologies for the poor lighting. Please let me know your thoughts. Many thanks. Mitch NK3H
 

Mitch - I would try hitting all 6 joints with some heat as a first measure.

The sharp edges of the toroid abrading the #28 AWG wire is a secondary concern IMHO, given that mix 43 ferrite has a fairly large DC resistance. If two turns are shorted together, then simply pushing the turns apart with a toothpick should clear up the short...

As for number of turns, with 10 turns thru each hole, you should be able to count 9 turns hugging the outside of the binocular core.


GL de va3rr
 

Mitch,

T507 winding looks correct, assuming the secondary turns count is right. VA3RR's advice is good. Recheck those soldered connections!

JZ


On Thu, May 30, 2024, 9:56?AM va3rr via <va3rr=[email protected]> wrote:
Mitch - I would try hitting all 6 joints with some heat as a first measure.?

The sharp edges of the toroid abrading the #28 AWG wire is a secondary concern IMHO, given that mix 43 ferrite has a fairly large DC resistance.? If two turns are shorted together, then simply pushing the turns apart with a toothpick should clear up the short...

As for number of turns, with 10 turns thru each hole, you should be able to count 9 turns hugging the outside of the binocular core.


GL de va3rr
 

Mitch,

here is something about bad SWR values.

73, Ludwig
 

Thanks GL. Will do and get back. Mitch NK3H
 

Thanks Ludwig. Will follow up and get back. Mitch NK3H
 

Thanks John. Mitch NK3H
 

GL and others,

I'm embarrassed to report that heat took care of it--or mostly. 60, 40, 30 & 20 all have SWR sweeps below 1.3:1. Thank you!
Hitting 'T' in putty yields about 1.25 watts for each freq at 12V.?

17m and 15m are still a little weird--lots of unevenness on either side of the targeted (vert line) freq, which is coming in at about 2.5:1. No output hitting 'T', but a few hundred mA are triggered.?

Not sure why the two high freqs show high SWR--I'm assuming it's unlikely to be T507 since the other bands are good. Is that right? If you have any thoughts on this I'd appreciate it.

The low power output on the lower freqs I can probably address by adjusting the winds on the appropriate toroids, right?
But the 0 output on the high freqs--is that possibly due to the high SWR? Does the Putty application trigger output protection like the radio working autonomously does? All suggestions are welcome. Many thanks.

Mitch NK3H
 

On Thu, May 30, 2024 at 11:28 PM, Mitch NK3H wrote:
Not sure why the two high freqs show high SWR-
Mitch, did you read this and this?

But the 0 output on the high freqs--is that possibly due to the high SWR? Does the Putty application trigger output protection
No output hitting 'T', but a few hundred mA are triggered.?
It looks like the PA is working. Here you will find something about the LPF section and also ckecking the PIN switching. I read about broken chokes (here L509 for LPF 2). So it wasn't possible to activate the LPF. You may find this issue following the last link.

73, Ludwig
 

Try running the LPF sweeps for the two bands that are giving you problems, and see if they correspond to those in the Operating Manual. Having said that, many have noted that the SWR sweeps aren't great on the higher bands, but good enough for the intended purpose.

There's was a large discussion on the stockton bridge here that I'm just reading through now. Also doing some reading on Owen Duffy's website:

73 de Russ, va3rr

On Thu, May 30, 2024 at 05:28 PM, Mitch NK3H wrote:

Not sure why the two high freqs show high SWR--I'm assuming it's unlikely to
be T507 since the other bands are good. Is that right? If you have any
thoughts on this I'd appreciate it.
 

Thank you Russ, Ludwig and others. Reworking T507 with significant heat on all the joints took care of the SWR sweep issue. Thank you very much for your help. Mitch NK3H

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