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Taps and Scratchs on PCB heard on RX

PostPosted: Mon Apr 27, 2015 3:03 pm
by Sanath
Hello All,
I used small wire sleeves on each leg of every transformer and inductor to provide mechanical stress relief. It was my opinion that direct soldering of these inductors may break the magnet wire if its constantly bent and unbent . The manual doesnt call for this however.

Anyway, with no antenna connected i hear the mechanical scratches and taps on the PCB through the receiver; akin to the classic LC VFO issues when the coils were loose. However its only the bandpass filters and transformers that have inductors and wonder why i was hearing these?

Request you guys to test out ur rigs and let me know if hearing the taps and scratches is normal or not please.

listed are the conditions i tested it
With no antenna connected the default uncalibrated scope on 20m shows a noise floor of~ -125db and raises to ~ -110 with a bad(indoor 20m dipole touching floors and walls) antenna connected. The builds is for 30/20/17/15
Any thoughts on the mechanical stability of transformers and inductors and its effects? advise on "glue on top" when all seems fine tuned or the sleeves are entirely to be blamed?

With the antenna connected i don't hear these mechanical noise any more.



Cheers
Sanath
AD0BK

Re: Taps and Scratchs on PCB heard on RX

PostPosted: Mon Apr 27, 2015 3:42 pm
by W4MMP
Hi,
Yes, this has been reported before. It appears to be fact of life with some if not all of the Peaberry builds. I don't know if my Peaberrys have the issue. I have not tried the tap test.

Re: Taps and Scratchs on PCB heard on RX

PostPosted: Mon Apr 27, 2015 4:11 pm
by kz1x
The four 0.01 microfarad capacitors on the outputs of U6 are microphonic.

These are C15 - C18.

Another type capacitor might be less so, but I have not worked out that detail yet.

Re: Taps and Scratchs on PCB heard on RX

PostPosted: Tue Apr 28, 2015 3:00 am
by KC8UD
I've noticed the microphonics as well early on in my testing while looking for a possible cold solder joint. I used a plastic stick to tap several of the parts to see which one might be most reactive (this helped me find the culprit and allowed me to dab another touch of solder to fix my issues). I've noticed that I hear the microphonics the loudest while tapping near the oscillator (si570), not so much near the filters.

Re: Taps and Scratchs on PCB heard on RX

PostPosted: Tue Apr 28, 2015 12:57 pm
by kz1x
Please see this thread

http://ae9rb.com/forum/viewtopic.php?f=6&t=501&p=2719&hilit=microphonic#p2719

including the comments from AE9RB on the topic

Re: Taps and Scratchs on PCB heard on RX

PostPosted: Tue Apr 28, 2015 2:12 pm
by Sanath
Thanks for posting that link. Apologies for posting an answered Q, I thought i had searched the forum but apparently I didnt search "microphonic" !
Cheers
Sanath
AD0BK