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V4 TX selective failure #ubitx-help #cat

Don - KM4UDX
 

Hello wise ones!
My V4 fails to push out RF when audio jack is driving -- voice or digital mode.
- Good news: when CW is key down: full power (yes!  So the back half of the TX chain works just fine.)
- When PPT on mic is pressed, rig goes into TX mode, but no RF output power regardless of mic drive level
- when pressing "tune" in WSJTX or Fldigi  the rig goes into TX mode, but no RF output juice regardless of audio (application) drive  level.  

So the problem seems to be early on in the audio chain?  The physical jack seems fine.

What/how do I do now to debug and fix?. 

Every day I'm off the air I lose WSPRnet ranking, and I feel so alone and isolated in the world. A quiet  uBITX is a sad uBITX...

Thank you thank you...

Evan Hand
 

First off, does it still receive as before?  That helps from the standpoint that the same clocks, mixers and filters are used for both receive and transmit.

The second question is how are the mic and audio from the digital interface connected?

Last question is what test equipment do you have?  For tests beyond static bias measurements, a scope or rf probe is required.   I have traced the signal through the TP's on the board using a 100 MHz scope and the power to the finals removed.  This would help in isolating the stage that is not amplifying, again IF the receiver still works as before.

Really need the answer to the first question before going forward with speculation.  

Take the above with a grain of salt and verify when possible.
73
Evan
AC9TU

Don - KM4UDX
 

First off, does it still receive as before?  That helps from the standpoint that the same clocks, mixers and filters are used for both receive and transmit.

Well that is interesting you asked that.  No.  Receive volume is way down.
 
The second question is how are the mic and audio from the digital interface connected?

Mic is wired per kit instructions with little PPT switch and plugs into std mic jack.  Digital interface is from external USB sound card and uses mini male/male plugs from the sound card into the ubitx mic/spk jacks. 
To switch from voice to digital, I pull out the mini plugs from the sound card and plug in the mic and speaker. Sort of primitive, but I do digital 80% of the time, so the jacks don't get a lot of in/out use. 

Nevertheless, I did buy some nice switchcraft mini jacks to replace the "value" jacks included with the kit at some point when I was either bored, or the "value" jacks gave up the ghost.
 
Last question is what test equipment do you have? 

Just a humble multimeter...

For tests beyond static bias measurements, a scope or rf probe is required.   I have traced the signal through the TP's on the board using a 100 MHz scope and the power to the finals removed.  This would help in isolating the stage that is not amplifying, again IF the receiver still works as before.
 

Don - KM4UDX
 

Evan & Co.

When I turn spkr volume full up, and I tap the top of the capacitors C52/62/64 near the beige jack (audio), I can hear each tap/scratch in the output. 

And on 14.073 I can hear the faintest tone signal at max volume.... Previously it blew me out of the room. (Minor hyperbole.) 

Don
km4udx

Evan Hand
 

So that means when connected to your antenna you are not receiving the other FT8 stations on the common frequencies that you use?  

What lead up to the issue?  what was the radio attempting to do?  Did you take it apart and reassemble or install a mod just before the failure?

Do you have access to another receiver that could possibly tune to the 32 Mhz or 12Mhz IF and BFO frequencies to see if the Raduino clocks are working?

With both receive and transmit being affected, it would point to one of the mixers or clocks, both are hard to troubleshoot with only a DMM.

Hopefully others can chime in here and give you better options.

Sorry can not be of more help.

73
Evan
AC9TU

Don - KM4UDX
 

So that means when connected to your antenna you are not receiving the other FT8 stations on the common frequencies that you use?  

Right, signal levels appear too low to decode now.

What lead up to the issue?  what was the radio attempting to do?  Did you take it apart and reassemble or install a mod just before the failure?

a:  I was using the ubitx in digital mode, adjusting the computer, and just the normal stuff....It has no mods and I learned long ago to leave well enough alone (but I frequently don't head that advice..hahah...tinker till it's broke is my normal moto...but in this case I promise that I didn't touch anything I shouldn't have...

  Do you have access to another receiver that could possibly tune to the 32 Mhz or 12Mhz IF and BFO frequencies to see if the Raduino clocks are working?

a: i do have a SDR (SDRuno) that I could use...

With both receive and transmit being affected, it would point to one of the mixers or clocks, both are hard to troubleshoot with only a DMM.

a: based on the block diagram, the SW sidetone works works, the CW Key works with RF. .. so the fault could be anything on the lower right...CLK#0 or #2, audio (de)mod, 2nd RF Mixer, the IF amps


Hopefully others can chime in here and give you better options.

Sorry can not be of more help.

Evan Hand
 

If you have one of the SDRPlay series of SDR, there is free software to turn the dongle into a spectrum analyzer that could be used to troubleshoot the radio. 


I am getting ready for a trip, so will not be available to help until tomorrow night. In the meantime I would look up analyzer software for your brand of SDR dongle and download it. 


73
Evan 
AC9TU

Don - KM4UDX
 

Rodger. 

_Dave_ AD0B
 

Don, How does your radio work when you have disconnected the sound card? When you are using a mic and regular headphones.
--
73
Dave
k0mbt
Raduino bracket and Ham_Made_Keys

Don - KM4UDX
 

Why does using this radio lead to so much humiliation?  Can you see where this is going?  Turns out I was trying to "adjust" master calibration and totally dorked it up. And wasn't smart or observant enough to catch my own stinky. 

Thank you Dave an Evan. You are the best. I am an idiot. 

Turns out when you wack your master calibration number (and why so many digits anyway?), you make your uBTIX operate just like mine did. CW RF and CW sidetone work great, but  audio and receive get whacked. 

Given it wasn't working anyway, so I had nothing to lose, I just hit reload factory defaults, and crossed my fingers.  Then I remembered that in Memory Manager I had a backup. So I fired up MM, reloaded the last save fine, and presto, I was back in business.

Proof that I am a very slow learner, I went right back into the tweaking calibration to reduce WSPRnet observed error to +/- 1 hz. 

A great site for tracking your 1 or 2 way WSPR beaconing  is http://wspr.vk7jj.com/


Evan Hand
 

The hart of this design is the hetrodyning up and down to provide the flexibility and selectivity.  That is why calibration is sooooo important.  There are two fixed points that need to be "hit" to make it work at all:
1 - the 45 MHz roofing filter
2 - the 11 or 12 Mhz (depending on version) "SSB" filter.  

This can only be done with calibration of the 3 clock signals.  The analogy that I think of is that 2 points define a line, and all three of the clocks need to be on that line.  Of course it is more like a snaking curve with the up and down signal manipulation.

I am glad you found your issue.  I would still recommend that you look at the SDR spectrum analyzer software for future use.  It is like using a finishing file where a rasp is needed for some applications but better than no tool at all.  It is also free with what you already have.  The best bet may be to ask Santa for 100 MHz,  or higher, oscilloscope for Christmas. 

73
Evan
AC9TU

Don - KM4UDX
 

Ha! A great analogy.  Thank you!!

Getting NanoNVA under my tree.  A scope would force me to learn sooo much more...

I'm going to focus on physically integrating my Atomic Pi SBC into my uBITX "case".  And I have a temperature switch and fans to add..and a TX/RX led, and...

Because the uBITX is working perfectly, I must get back to trying to break it.

Hahah

Don
KM4UDX

P.S. You people are the best!!!