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QCX goes into practice mode

 

I'm in the process of integrating a 20 meter QCX, 50 watt amp, and DC-DC converter into one cabinet.? I've finished wiring and am testing, but have a problem that I'm finding difficult to solve.?

When I key down, The QCX goes into practice mode within a split second and there is no output power.? If I disconnect power to the 50 watt amplifier (and either turn off Practice Mode via the menu or power cycle the QCX), the QCX works as it should.? The QCX, amp, and DC-DC converter were working fine when they were in their separate enclosures.

Has anyone seen this problem, or have any suggestions?

Thanks,
Jim/ND6P
 

RF getting into QCX.? You will need to isolate amp.
 

Also, is this with a dummy load attached? If not, where and what sort of antenna are you using and where is the feedpoint?
This is definitely an RF problem.
 

Yes RF leakage from inductors in the PA are getting into the microcontroller. You will have to study your arrangement and experiment with shields. Until someone has done it, not easy to prescribe a certain solution.?

Curt
 

Yes, this is with a dummy load attached.?
EdMohrman
 

Yeah, no one has reported doing what you are attempting. But, there has been a sprinkling of people reporting their QCX did some bad thing, probably due to RF on the feedline or similar

Ed?
 

Hi Jim. I did the same thing once with a QCX, 50 watt amp and boost converter for the amp so I could drive the whole thing with 12 v and have 20 v for the amp. And I even made the thing for 5 bands with switched filters. I had lots of RF issues that were different for every band as you can imagine. It seemed to work best for me on the lower bands 80/40 and worst as far as RF issues on 20/17.? I agree with the first responder on this thread. The amplifier should probably be isolated from the QCX inside the cabinet. Maybe a metal shield all around the amplifier with coax connectors in and out of the shield for RF and even a feed through capacitor for power to the amplifier. Bypass everything. Shield the audio and keying lines to the QCX and the PTT line to the amp.?

It is not a project for the faint of heart. But it is a worthwhile effort. Good luck and please let us know how it goes.?

Ron

On Thu, Jun 9, 2022 at 18:58 ND6P <jpkellyburbank@...> wrote:
Yes, this is with a dummy load attached.?

 

On Fri, Jun 10, 2022 at 03:08 AM, EdMohrman wrote:
Yeah, no one has reported doing what you are attempting. But, there has been a sprinkling of people reporting their QCX did some bad thing, probably due to RF on the feedline or similar
Using 40, 30 and 20m QCX+ here with 50 watt amps. Only one I had a problem with was the 20m QCX+ and its 50 watt amp in separate case. It needed a bit of RF taming. If the amp was unenclosed and put in a box with the QCX boards then I guess there could be issues.

Reg????????????????????????? G4NFR
 

You were all correct.? I fully shielded the 50 watt PA and things are working as they should now.
To do that, I made up a new end-plate for the amp from a piece of single-sides PCB.? Then I soldered
the coax cable shields and mounted the feed through caps to that.? I also added a LC filter at pins 7 and 11 on
IC3 to isolate the QCX at the TX connection.? Worked like a charm.

Jim/ND6P
 

Nice clean presentation, great job.
Gary W0CKI


-----Original Message-----
From: ND6P <jpkellyburbank@...>
To: [email protected]
Sent: Sat, Jun 11, 2022 10:16 am
Subject: Re: [QRPLabs] QCX goes into practice mode

You were all correct.? I fully shielded the 50 watt PA and things are working as they should now.
To do that, I made up a new end-plate for the amp from a piece of single-sides PCB.? Then I soldered
the coax cable shields and mounted the feed through caps to that.? I also added a LC filter at pins 7 and 11 on
IC3 to isolate the QCX at the TX connection.? Worked like a charm.

Jim/ND6P
 

Nice set up! Curious if you can regulate voltage to PA so that you can adjust Pout?
Rich
kq9l
 

Rich,

I'm powering the amp with 20 volts and I feed the QCX output
directly into the amp, so my power level is fixed.? I did think about building
to allow the QCX to bypass the amp for a 5 watt option, but decided not to
that to in the end to keep things simple.

Jim/ND6P
 

Thanks Jim!
 

Hi Jim, Wow! A beautiful looking rig. Could you tell us where you got that blue/white project case?

Thanks and 73,

Brian G3ZOH
 

Brian,

I bought it from eBay:
?
sunillakhani


Unfortunately, I do not see any blank cabinets for sale today from them today, but perhaps they will have some more at some point.? Or you might contact them directly and ask.

Jim/ND6P

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