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uBitx V6 20M band problem #antennas #ubitxv6

belthur@...
 

Added a 20m antenna to my Inverted V already having 40m. 
 
Now, I have 7150 in VFO:A and 14220 in VFO:B. 
 
When I give a TX, it will switch over to VFO:A in the middle of TX...
 
If I have 14220  in VFO:A, it just hangs. Not sure what's happening
 
Reloaded the Original firmware from github. No change. 

This happens only when I have my Linear Amplier switched on....
 
Anyone know why it's happening?

Evan Hand
 

My first guess would be RF back into the ubitx.  Especially since it is with the linear amp on.

Do you have the ubitx in a metal case, is it grounded, do you have a common mode choke on the coax to the antenna, and maybe a snap-on ferrite on the line to the amp?

Does CW have the same issue?  If not, then you could be overdriving the audio causing splatter which will feedback into the Nano control lines.

I would start by making sure the case of the ubitx is grounded.  Then I would do the CW test and verify that it is not overdriven audio.  If the problem is still there, then I would start looking for a common-mode current reduction on the coax lines.  For me at lower power snap-on ferrites around the coax have worked.  At the higher power, you may need to make an ugly current balun.
http://www.hamuniverse.com/balun.html

The above are just suggestions.  Your situation may not be the same as the ones that can cause the above, though it is most likely.
73
Evan
AC9TU

belthur@...
 

Thanks. No, my uBitx case isnt grounded. I will fix that. I will also try a Balun. 

Thanks.

belthur@...
 

Checked. CW is just fine. How do I avoid audio overdrive?

Evan Hand
 

Are you amplifying the mic at all?  Do you have another receiver that can be used to verify the output of the ubitx?

The only way to be sure is to measure the output.  What I have done is build a -50 db tap (My measurements were -45 db actual) to sample the output of the ubitx with an SDR (RSP1A) based spectrum analyzer.  If you have an SDR dongle of some sort, there are free SA software packages for them.  Here is the -50DB tap that I copied:
http://www.ad5x.com/images/Articles/Tap50dbRevA.pdf
I used a two-tone generator built from a kit to drive a BlueTooth speaker with the volume at about what I expected a person speaking to be, and then held the mic at about the expected distance from the speaker.  You may also need a step attenuator depending on the power of the amp.

Others have used another receiver with the ubitx connected to a dummy load and the receiver with little or no antenna to lower the input signal.  This works best if you have a waterfall display on the receiver.  Again, an inexpensive SDR dongle like an RTL-SDR can work.

I would first verify that you do not have any issues with the barefoot ubitx, then go on to the output of the amp.  When I did similar measurements for my rigs, I found that it was easy to overdrive both the audio and then the input to the amp.  I am currently waiting on a 7 element low pass filter for the amp, as the harmonic output was not within FCC requirements with an eBay 100watt LPF kit that was based on 5 element filters.  I also have a -6dp pad in the works to drop the output of the ubitx to below 5 watts.

FWIW
73
Evan
AC9TU

Evan Hand
 

belthur,

One other thought, The RF could be coming in through the mic cord.  A snap-on ferrite and 0.01 uF bypass caps on the input to the ubitx could help if that is the issue.

73
Evan
AC9TU