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QMX+ suddenly SWR sweep stops

 

Hello list,

yesterday I did a SWR sweep, to "let my tuner learn" - its an LDG AT-100Pro II.
On 10m & 12m everything worked fine with 5-6 Tunes.

Running it on 15m, the terminal-window got black after 3 Tunes.
Ctrl-Q changed nothing, pressing T did something (I heard the relais), pressing On/Off switch gave the message "Locked by Terminal" (or similar). I had to disconnect power.
Then I tried again, but the same things happened. So I did a factory reset, but the SWR sweep still stops working at some point.

Any ideas what could be wrong or broken?

Cheers,
Torsten

--
vy 73 de Torsten | DB2TE

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Where was this idea mentioned in the instructions ??

ATUs aren¡¯t very bright. ?They initially offer a wild range of match solutions to spot a good one some of which will look
like a horrible SWR at the transmitter
?
Along with the horrible SWR may be high CMC which can cause damage too?
?
Running such tests at the lowest TX output power the tuner will accept is a good plan- ? Doing it via a 3dB pad is good too?
?
 

I concur with Bruce.? The SWR sweep runs at full qmx power.? The fault you are getting arises from the high common mode currents and high swr that briefly appear when you tune into the load.? These will be different on each band - much worse on some than others.? These common mode RF currents come back on the coax shield and into your qmx, and then up the USB cable into your computer,? disrupting operation. The momentary high swr may also damage your finals.
?
A good CMC (common mode choke) on your antenna feedline (always use it), along with an attenuator (use while tuning) will avoid the problem.? ?Note that avoiding all this is why the internal HW SWR test on the qmx uses 1/4 output power (50% voltage).
?
Stan KC7XE?
 

Hi Stan,

does it run at full power?
I read the manual and thought it runs with 50%, according to the Tune setting ...

Seems I misread, or at least misunderstand it :-(

Cheers,
Torsten


Am 29. Januar 2025 17:33:21 MEZ schrieb "Stan Dye via groups.io" <standye@...>:

I concur with Bruce.? The SWR sweep runs at full qmx power.? The fault you are getting arises from the high common mode currents and high swr that briefly appear when you tune into the load.? These will be different on each band - much worse on some than others.? These common mode RF currents come back on the coax shield and into your qmx, and then up the USB cable into your computer,? disrupting operation. The momentary high swr may also damage your finals.
?
A good CMC (common mode choke) on your antenna feedline (always use it), along with an attenuator (use while tuning) will avoid the problem.? ?Note that avoiding all this is why the internal HW SWR test on the qmx uses 1/4 output power (50% voltage).
?
Stan KC7XE?
 

My bad. Sorry.
SWR sweep does run at the reduced power, as indicated in the upper right of the screen.

But it is bad idea to use this sweep into a tuner.? It sweeps over a wide frequency range, momentarily giving power to several different frequencies across that range.? Probably not enough time at any one of the frequencies for your ATU to properly tune.

The ATU is designed to auto tune at a single, stable frequency.? So it is much better to use the single-frequency HW tune function, which does that.? Do it for your favorite frequencies on each band, and the ATU memories will store it.

The SWR sweep is good to use into an antenna (bypassing the tuner) to see how its SWR matching curve looks, so you can adjust the antenna to perform well across your desired?frequency ranges.

Stan KC7XE


On Wed, Jan 29, 2025 at 10:59?AM hamradio@... via <hamradio=[email protected]> wrote:
Hi Stan,

does it run at full power?
I read the manual and thought it runs with 50%, according to the Tune setting ...

Seems I misread, or at least misunderstand it :-(

Cheers,
Torsten


Am 29. Januar 2025 17:33:21 MEZ schrieb "Stan Dye via " <standye=[email protected]>:
I concur with Bruce.? The SWR sweep runs at full qmx power.? The fault you are getting arises from the high common mode currents and high swr that briefly appear when you tune into the load.? These will be different on each band - much worse on some than others.? These common mode RF currents come back on the coax shield and into your qmx, and then up the USB cable into your computer,? disrupting operation. The momentary high swr may also damage your finals.
?
A good CMC (common mode choke) on your antenna feedline (always use it), along with an attenuator (use while tuning) will avoid the problem.? ?Note that avoiding all this is why the internal HW SWR test on the qmx uses 1/4 output power (50% voltage).
?
Stan KC7XE?
 

Hi Bruce,

sorry, I have seen your email just now.

It's not mentioned in any document!
Now, with your and Stan's describtion I fully agree that its a realy bad idea ...

Thanks a lot for explaining it! I'll change my setup, and won't do it again that way ;-)

Cheers,
Torsten

Am 29.01.2025 um 10:02 schrieb Bruce Akhurst:

Where was this idea mentioned in the instructions ?
ATUs aren¡¯t very bright. ?They initially offer a wild range of match solutions to spot a good one some of which will look
like a horrible SWR at the transmitter
Along with the horrible SWR may be high CMC which can cause damage too
Running such tests at the lowest TX output power the tuner will accept is a good plan- ? Doing it via a 3dB pad is good too
--
vy 73 de Torsten | DB2TE

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