Topics

Power Mic and uBITX 6

KB9WOO
 

I purchased and wired up the power mic that was mentioned in this thread https://groups.io/g/BITX20/message/79613?p=,,,20,0,0,0::relevance,,procom,20,2,0,71576826.  Starting a new thread specifically about this microphone.

Those who are using this microphone successfully, what level are you setting it at?  Setting mine around 4 or a little less doesn't seem to move the needle at all - same as the Baofeng mic.  Setting it higher than 4 seems to cause the radio to get stuck in TX and sometimes does a bunch of clicking.  I posted a video on another thread of my radio doing this and it was suggested that it may be common-mode current.  I changed my antenna setup and tried again.  I didn't notice "Fast Tune" blinking as it was before, but it still got stuck in TX once.  If I switch to CW and key the mic in order to check my SWR, it comes back good, below 1.5 on 20m.  Switch it back to ssb and key the mic gives me no needle movement unless I turn up the mic and then it gets stuck in TX.  Can't guarantee that is the pattern yet, but that's what I saw on my last test.

I'm trying to chase down where my problem is, so knowing what is working for other users of this microphone might help me rule it out.


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Mark, kb9woo
Milwaukee, WI uBITX v6

Evan Hand
 

Mark,
I am using this mike with both v4 and v5 uBITX.  I do not own a v6, however, it is mostly the same as the v5.  For all of them, a setting of 4 to 5 is enough to drive the needle to the same power out as CW with a constant tone or whistle into the mic.  For this test I had a 1000 Hz tone played through my laptop and held the mic about as far away as I would use it.  Lots of variables there, so not a true level adjustment process.  Used it to verify the mic worked.

I also had problems with RF getting into the rig and causing two things:
1 - Would lock up the display and stay in transmit mode until I power cycled the rig.
2 - Got reports of distorted audio when I got rid of the lock-up.

The tests I did were to transmit into a dummy load to verify that it was RF in the shack.  With that validation, I put a number of snap-on ferrites that fit around the coax at the entry to the shack, and at the connector to the rig.

To solve the RF-induced audio distortion I put snap-on ferrites on the mic cord just before the rig.

I also grounded the rig to the best ground that I have (a copper cold water pipe).

The above was before I bought an RSP1A SDR so that I could use the free spectrum analyzer software to verify the "Splatter" of the audio.  It turns out that on some bands you can drive the output higher than the CW power.  This is on 40 meters where the CW has a dip for some reason.  I now suspect it might be due to losses through the first mixer specific to 40 meters. 

To sum up the above, RF is the most likely problem in my opinion.  I would suggest testing with a dummy load to verify that even at high audio settings you do not have the lock-up problem.  After that add common mode current reduction devices (balun being the best) and be sure to ground everything.  Then add the snap-on ferrites to the mic cord.

FWIW and YMMV
73
Evan
AC9TU

Arv Evans
 

Mark, kb9woo

As you mentioned, others have experienced similar problems.  Several 
possibilities may be contributing to the problem.

1)  Coiled cords on microphones have rather high inductance, leading to 
TF entering the microphone input, or to RF being rectified in the microphone 
amplifier components.  Coiled cords can still be used if each end is bypassed 
for RF with a 0.001 or 0.01 mfc capacitor.  

2) Overdriving the microphone inputs can result in spurious RF getting into 
the IF filter and causing feedback loops.  

3)  Microphone amplifiers that are not designed for Ham Radio use may 
have internal design problems resulting in RF rectification and resultant 
feedback loops.

4) Power supplies that do not provide adequate current can be modulated 
by current peaks and result in audio feedback to the microphone circuitry.

If practical, a shorter non-coiled cord can be used to see if this changes 
the amount of RF feedback and improper operation.  If the power supply is 
not capable of sustained 3 amperes output this could be a problem (more 
amperes if an add-on amplifier is being used).  The power supply regulator 
may need RF bypassing to keep its voltage stable during RF peaks.

Arv K7HKL
_._


On Thu, Jul 2, 2020 at 12:51 PM KB9WOO <kb9woo@...> wrote:
I purchased and wired up the power mic that was mentioned in this thread https://groups.io/g/BITX20/message/79613?p=,,,20,0,0,0::relevance,,procom,20,2,0,71576826.  Starting a new thread specifically about this microphone.

Those who are using this microphone successfully, what level are you setting it at?  Setting mine around 4 or a little less doesn't seem to move the needle at all - same as the Baofeng mic.  Setting it higher than 4 seems to cause the radio to get stuck in TX and sometimes does a bunch of clicking.  I posted a video on another thread of my radio doing this and it was suggested that it may be common-mode current.  I changed my antenna setup and tried again.  I didn't notice "Fast Tune" blinking as it was before, but it still got stuck in TX once.  If I switch to CW and key the mic in order to check my SWR, it comes back good, below 1.5 on 20m.  Switch it back to ssb and key the mic gives me no needle movement unless I turn up the mic and then it gets stuck in TX.  Can't guarantee that is the pattern yet, but that's what I saw on my last test.

I'm trying to chase down where my problem is, so knowing what is working for other users of this microphone might help me rule it out.


--
Mark, kb9woo
Milwaukee, WI uBITX v6

KB9WOO
 

Evan,

Thanks for the quick response!  I am ordering a dummy load so I can do that test and was wondering if I should get a choke as well.  I suppose it wouldn't hurt to have one on hand and could try with and without.  I plan to operate portable so no water pipe to ground to.

Thanks!

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Mark, kb9woo
Milwaukee, WI uBITX v6

KB9WOO
 

Arv,

Thank you.  I am operating off a 7 amp hour battery.


--
Mark, kb9woo
Milwaukee, WI uBITX v6

Bob Lunsford
 

Simply connecting the radio to a dummy load with a single cable (not going through switches, etc.) may isolate the possibility of it being or not a common-mode problem. Just an idea...

Bob — KK5R

On Thursday, July 2, 2020, 2:51:51 PM EDT, KB9WOO <kb9woo@...> wrote:


I purchased and wired up the power mic that was mentioned in this thread https://groups.io/g/BITX20/message/79613?p=,,,20,0,0,0::relevance,,procom,20,2,0,71576826.  Starting a new thread specifically about this microphone.

Those who are using this microphone successfully, what level are you setting it at?  Setting mine around 4 or a little less doesn't seem to move the needle at all - same as the Baofeng mic.  Setting it higher than 4 seems to cause the radio to get stuck in TX and sometimes does a bunch of clicking.  I posted a video on another thread of my radio doing this and it was suggested that it may be common-mode current.  I changed my antenna setup and tried again.  I didn't notice "Fast Tune" blinking as it was before, but it still got stuck in TX once.  If I switch to CW and key the mic in order to check my SWR, it comes back good, below 1.5 on 20m.  Switch it back to ssb and key the mic gives me no needle movement unless I turn up the mic and then it gets stuck in TX.  Can't guarantee that is the pattern yet, but that's what I saw on my last test.

I'm trying to chase down where my problem is, so knowing what is working for other users of this microphone might help me rule it out.


--
Mark, kb9woo
Milwaukee, WI uBITX v6