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Author Topic: Help with QSK-5  (Read 3983 times)
K0YQ
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Posts: 1404




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« on: February 18, 2013, 11:48:28 AM »

Not sure whether to post this question here or in Elmers.  I have a bipolar external QSK-5 box that's been back to Ameritron twice in the past three months.  They swear all is okay, and it sometimes will work perfectly.  But then like today, I go QRO and the box doesn't pass the RF signal back to the rig until the 3-second bypass period clicks.  After each TX the receiver is deaf until the bypass period clicks.  A week ago when last used it was functioning perfectly and nothing has changed since.  Does this behavior sound like a spotty relay in the QSK-5?  The relay in the amp is fine.

I really like the QSK when it works but getting frustrated.  Thanks all for any suggestions.

 
« Last Edit: February 18, 2013, 12:43:42 PM by K0YQ » Logged
N4OI
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Posts: 398




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« Reply #1 on: February 19, 2013, 05:28:20 AM »

I assume the basic operation of your external QSK-5 is the same as the internal QSK-5PC.  If so, the switching between transmit and receive is achieved through changing the bias for the transmit and receive diode strings.  The key-in line from the radio triggers the bias voltage flip.  If you look at the schematic and read the description  http://www.ameritron.com/support.php?productid=QSK-5  , you will find there are just a few components in that biasing circuit, including transistors and op amps. 

Timing is critical!  From the radio, the key-in line MUST drop at least a few milliseconds before the transmit RF shows up, and then the transmit RF MUST drop a millisecond or so before the ken-in line is released.   Internally, timing is also important.  There are R-C components to control the bias switchover timing. 

Since the QSK-5 is external from your amplifier, I assume you have access to the internals when operating (unlike the internal card where there is lethal high voltage nearby).  If so, you could monitor the bias level at the receive diodes to see if it corresponds to the desensing you are experiencing.  Just walk the bias circuit back to find where the problem starts....  Since it is intermittent, check the pads around the R-C and op-amp components that control the receive diode bias timing.  In cases like these, I usually just reflow any connections that look like they could be cold solder joints; and for good measure, reflow the pads around the most likely suspects.  (Keep at it -- there is a rat in that woodpile somewhere!)    And of course, do all transmit testing into a big oil-filled dummy load!

I hope this helps.  Smooth QSK, combined with power, is a beautiful thing...

73 ES GOD BLESS U ES URS DE KEN N4OI  Grin   
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K0YQ
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Posts: 1404




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« Reply #2 on: February 19, 2013, 10:18:17 AM »

Thank you for the feedback Ken.  I pulled the boards and will check all the joints and connections and reflow where suspect, especially on the RX path. A cold joint would certainly explain the intermittent behavior that I'm seeing.

I'll follow up with the results and thanks again.

John
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K0YQ
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« Reply #3 on: February 20, 2013, 09:15:16 AM »

No luck and now officially moved into the sunk cost bucket.   Sad

Thanks again Ken.

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K9MRD
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Posts: 383




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« Reply #4 on: February 20, 2013, 09:34:32 AM »

Just a thought:

Does it work OK into a dummy load? If yes, it could be common mode/RFI problem.
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K0YQ
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Posts: 1404




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« Reply #5 on: February 20, 2013, 10:54:11 AM »

Just a thought:

Does it work OK into a dummy load? If yes, it could be common mode/RFI problem.

Yes I've been testing into the dummy load so not an RFI issue, unfortunately. 
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AD5X
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Posts: 1600




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« Reply #6 on: February 20, 2013, 12:07:23 PM »

What transceiver are you using?  Some Icom transceivers release the amp and QSK switch before RF goes away, resulting in hot-switching on unkey.

Phil - AD5X
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K0YQ
Member

Posts: 1404




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« Reply #7 on: February 20, 2013, 05:31:20 PM »

What transceiver are you using?  Some Icom transceivers release the amp and QSK switch before RF goes away, resulting in hot-switching on unkey.

Phil - AD5X

Hi Phil,

756Pro3 and Microham Microkeyer keying via the accessory jack on the rig.

I'm going to take the QSK5 box apart and start over once I get my taxes done.  Sad
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N4OI
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Posts: 398




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« Reply #8 on: February 21, 2013, 04:05:59 AM »

No luck and now officially moved into the sunk cost bucket.   Sad

Cheer up!  Just move the cost to "training and education."  Find the root cause by always asking, "Why doesn't it do [this or that]?"  Keep testing likely causes until you get the problem cornered -- then replace the component, repair the connection, or whatever it takes. 

You will learn something useful, feel good, and -- oh yes -- enjoy nice QSK again... 

73 ES GOD BLESS U ES URS DE KEN N4OI  Grin
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AD5X
Member

Posts: 1600




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« Reply #9 on: February 21, 2013, 04:56:17 AM »

What transceiver are you using?  Some Icom transceivers release the amp and QSK switch before RF goes away, resulting in hot-switching on unkey.

Phil - AD5X

Hi Phil,

756Pro3 and Microham Microkeyer keying via the accessory jack on the rig.

I'm going to take the QSK5 box apart and start over once I get my taxes done.  Sad

If you have a 'scope, look at the PRO3's amp-key/unkey timing with respect to RF output.  I've never looked at a PRO3, but I have looked at an IC-7000 and IC-706MKIIG and they both have the unkey problem.  I also have a 'scope trace of this problem on an IC-7600, though I've been told that has now been fixed.

If you have the unkey problem (which can result in hot-switching), running semi-break-in should resolve the problem.  Then you can experiment with the hang-time to minimize it for close-to-QSK operation.  We're talking 5-10ms of problem in the transceivers I referenced above, so even minimal hang-time would resolve hot switching (if that is the problem).

Phil - AD5X
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K0YQ
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Posts: 1404




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« Reply #10 on: February 22, 2013, 08:17:07 AM »

Unfortunately no access to 'scope or test equipment beyond my multimeter.  I really don't believe that it's a hot switching problem. 

It is not a very easy board(s) to disassemble or work with.  Q5 is the FET that gates the RX/TX and based on what I'm seeing could be the culprit.  The last time I tested the RX path was permanently disabled and TX diodes were always biased.  I don't want to blow up the front end of my rig, so must remain cognizant of my limitations as I work. No way the auditor would justify a new rig under "training and education".   Smiley

I'll have to look in more detail when time allows.  Thanks again for all the help and suggestions.

 
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K0YQ
Member

Posts: 1404




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« Reply #11 on: February 22, 2013, 08:19:47 AM »

Also want to be clear and fair that this box was bought used and not new from Ameritron.
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N4OI
Member

Posts: 398




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« Reply #12 on: February 23, 2013, 06:19:52 AM »

Unfortunately no access to 'scope or test equipment beyond my multimeter.  I really don't believe that it's a hot switching problem. 

It is not a very easy board(s) to disassemble or work with.  Q5 is the FET that gates the RX/TX and based on what I'm seeing could be the culprit.  The last time I tested the RX path was permanently disabled and TX diodes were always biased.  I don't want to blow up the front end of my rig, so must remain cognizant of my limitations as I work. No way the auditor would justify a new rig under "training and education".   Smiley

I'll have to look in more detail when time allows.  Thanks again for all the help and suggestions.

 

I think any danger to your radio would be from a sudden change in SWR between it and the QSK-5 while transmitting, which could take out your finals -- not the front end.  Therefore, I would suggest testing at the lowest power out possible.   If your symptom is intermittently desensed receive until the RF relay drops, then I would suspect:

(a) Burnt RF relay input pole, normally open (NO) contact - (this could be caused by a previous "hot switching event")
     Test/Remedy: DeOxit contact cleaner (from Radio Shack) on relay contacts
(b) Intermittent hot switching, including QSK-5 circuitry and radio key out/RF timing
     Test: Observe the fuse lamps/fuses in darkened room while transmitting - if flashing, then intermittent hot switching is happening
     Remedy: Troubleshoot key out to RF timing from radio; troubleshoot marginal bias circuit (Q5, RC timing, op amps, transistors, etc.)

 If the receive desense becomes constant and not just intermittent, then the lamp/fuses have opened (inexpensive from Ameritron and easy to replace) ... 

I hope this helps.  The Ameritron QSK-5 is a great device -- it easily keeps up with my K3's fine QSK at 30+ wpm.

73 ES GOD BLESS DE KEN N4OI  Grin   
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