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SWR Protection QMX mini

 

I’m traveling in GB and attempting to activate several POTA parks while I’m here. ?I’m away from my test equipment and I’m soliciting advice.
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I took my QMX low band and a 20m QCX for backup. I have a 12v Talent Cell power bank. ?Antennas are 20m and 40m EFHW that tested less than 1.5:1 SWR on 20m and 40m (also less than 1.5:1 on 20m with the 40m EFHW) both fed through 20 ft of RG-316 and a 1:9 UNUN.?
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My QMX is set to SWR protection ON at 1:2. ?When I start calling CQ, I can call off and on for about 10 minutes, then the SWR protection will shut down transmission. Rebooting the QMX will restore transmission for a bit. ?But after another 15 minutes or so, it’s shutting down about every 2-3 minutes. Today I reset the SWR Protection to 3:1. ?It took a bit longer, but it was still shutting down about every 5 minutes. ?I switched over to using the QCX.
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I know that an antenna’s tuning and SWR will vary from site to site according to the height, ground conductivity, etc,. ?But these antennas were fine at home. If the SWR is really above the set value, why does it take so long to trigger? ?
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Any idea what’s going on? And any suggestions? ?Shall I turn the SWR Protection OFF?
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Thanks.
Jack N8EU
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An end-fed half wave needs a 49:1 transformer, not a 9:1! So that's probably not helping you any!

9:1 is used with end-fed random wires.

However, assuming for the moment that was a typo, the main times I've seen SWR change on me with? an antenna that started out "good" was when it was overheating. It's unlikely 5 watts is overheating it (unless it is in fact a 9:1, in which case, the impedance mismatch means all bets are off). Is it in direct sunlight or something else that might be heating the transformer?

Michael WD0OM

On Thu, Sep 19, 2024, at 14:17, Jack Kibelbek via groups.io wrote:
I’m traveling in GB and attempting to activate several POTA parks while I’m here. ?I’m away from my test equipment and I’m soliciting advice.
?
I took my QMX low band and a 20m QCX for backup. I have a 12v Talent Cell power bank. ?Antennas are 20m and 40m EFHW that tested less than 1.5:1 SWR on 20m and 40m (also less than 1.5:1 on 20m with the 40m EFHW) both fed through 20 ft of RG-316 and a 1:9 UNUN.?
?
My QMX is set to SWR protection ON at 1:2. ?When I start calling CQ, I can call off and on for about 10 minutes, then the SWR protection will shut down transmission. Rebooting the QMX will restore transmission for a bit. ?But after another 15 minutes or so, it’s shutting down about every 2-3 minutes. Today I reset the SWR Protection to 3:1. ?It took a bit longer, but it was still shutting down about every 5 minutes. ?I switched over to using the QCX.
?
I know that an antenna’s tuning and SWR will vary from site to site according to the height, ground conductivity, etc,. ?But these antennas were fine at home. If the SWR is really above the set value, why does it take so long to trigger? ?
?
Any idea what’s going on? And any suggestions? ?Shall I turn the SWR Protection OFF?
?
Thanks.
Jack N8EU
?
?
 

If I were in your shoes I would leave the SWR protection enabled. 3:1 is a reasonable threshold.
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Maybe you could double check your antenna and coax performance by using the ‘Hardware Test’ > ‘SWR Tune’ mode and monitor the SWR while fiddling with the antenna and feedline and see if you can pinpoint some instability.
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I just repaired a QMX+ that, when on two different known good dummy loads, it tripped on SWR protection on some bands and not others. The problem was some remaining enamel on a couple of the wires ?on T507. Check yours on a good dummy load and if the internal SWR meter declares something wrong with it, recheck those wires.?
Good luck. …73…Ron

On Thu, Sep 19, 2024 at 12:17 Jack Kibelbek via <jack45458=[email protected]> wrote:
I’m traveling in GB and attempting to activate several POTA parks while I’m here.? I’m away from my test equipment and I’m soliciting advice.
?
I took my QMX low band and a 20m QCX for backup. I have a 12v Talent Cell power bank.? Antennas are 20m and 40m EFHW that tested less than 1.5:1 SWR on 20m and 40m (also less than 1.5:1 on 20m with the 40m EFHW) both fed through 20 ft of RG-316 and a 1:9 UNUN.?
?
My QMX is set to SWR protection ON at 1:2.? When I start calling CQ, I can call off and on for about 10 minutes, then the SWR protection will shut down transmission. Rebooting the QMX will restore transmission for a bit.? But after another 15 minutes or so, it’s shutting down about every 2-3 minutes. Today I reset the SWR Protection to 3:1.? It took a bit longer, but it was still shutting down about every 5 minutes.? I switched over to using the QCX.
?
I know that an antenna’s tuning and SWR will vary from site to site according to the height, ground conductivity, etc,.? But these antennas were fine at home. If the SWR is really above the set value, why does it take so long to trigger? ?
?
Any idea what’s going on? And any suggestions?? Shall I turn the SWR Protection OFF?
?
Thanks.
Jack N8EU
?
?
 

Good catch on the 9:1 issue, Michael.
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Thinking of some potentially field expedient solutions:
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If you have tuner with you, perhaps treat it like a “random” wire with the 9:1 unun.
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If no tuner, maybe take your EFHW and feed in the center as a half-wave dipole?
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If all else fails, and depending on where you’re traveling, maybe visit one of the ham radio stores for parts or a different antenna solution. I think ML&S is near London, Heathrow and Waters & Stanton is in the Milton Keynes area.
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73 de W6CSN
https://w6csn.blog/2024/06/19/uk-pota-rain-and-shine/
 

I've had windy conditions give me a variable SWR, depending on how the antenna was hung.
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But when SWR really started hassling me, I fixed it by using a different feedline. Later I diagnosed a flaky connector on my preferred cable.
 

That was a typo. It is a proper 49:1 UnUn.?
 

Then we're back to: is there any way the transformer could be overheating. It seems unlikely, but so far, it's the only thing I've personally seen in the wild that leads to the specific symptoms you describe.?

For example, using the Chameleon Hybrid Micro, if I forget that it's only rated for 20W continuous digital mode use, with a 100W radio where I forgot to dial back the drive. It'll work for a while, and then I can watch the SWR slide upward in the course of a 15 second FT8 cycle.

Again, it seems unlikely when we're only dealing with 5W max, but...

On Fri, Sep 20, 2024, at 10:28, Jack Kibelbek via groups.io wrote:
That was a typo. It is a proper 49:1 UnUn.?
 

Depending upon the core size and type, yeah, heating at 5w is a thing. Especially w/ EFHW antennas.
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Al, K2ZN
 

or bad coax and or connectors.

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