EMRFD Message Archive 4449
Message Date From Subject 4449 2010-03-13 09:00:24 drmail377 NPO Capacitors, Lowest Microphonics in DC RX? I think I saw a post here about how NPO capacitors exhibit lower microphonics in direct conversion receivers (or in-general). Anyone care to expand on why? I suspect it might be due to their differential physical construction.
4452 2010-03-14 09:52:02 Tim Re: NPO Capacitors, Lowest Microphonics in DC RX? 4453 2010-03-14 10:40:11 Art Re: NPO Capacitors, Lowest Microphonics in DC RX? Not to long ago I remember reading a web article about using surface
mount caps as microphones. Apparently they work very nicely. Wish I
could remember where I saw the article, I didn't bookmark it at the
time, and now I can't locate it!!!
4456 2010-03-15 11:20:30 Glen Re: NPO Capacitors, Lowest Microphonics in DC RX? Thanks for the link to Kemet, Tim -
like you, have mostly experimental and not theoretical knowledge of
weird dielectric properties.
Haven't heard microphonics from NP0 caps. But not all small-value
caps are free from piezo effects....
Once tried to use a 10pf 6KV ceramic cap to neutralize a 3 KV DC
vacuum tube. Could get a superb balance, but at only one plate
voltage. As plate voltage changed, so did the capacitance, unbalancing
the neutralizing network. In this case, even an air-dielectric cap
would give a similar result. An example of electric field forces at
If you push ANY of our components hard enough, you'll find non-linear
effects. Just ask anyone setting up test equipment to measure high IP3
4457 2010-03-15 11:51:43 Tayloe Dan-P26412 Re: NPO Capacitors, Lowest Microphonics in DC RX? I have used high value ceramic caps in the front end of a DC receiver,
and I really do not find the microphonics to be all that bad. If you
tap the parts themselves, they are clearly microphonic, but in normal
use, they do not seem objectionable.
In addition, when I have found parts that have been microphonic (like
the toroids in the LO filter in the NC2030 DC transceiver), the secret
to removing the microphonic quality seemed to be to simply to dampen the
vibration of the part. This can be done with a bit of hot glue or wax to
bridge the part to the board, dampening the vibration. For the purposes
of dampening, a soft substance (hot glue, wax) would be preferred to a
hard substance (epoxy).
- Dan, N7VE
4458 2010-03-15 12:57:45 Neil Douglas Re: NPO Capacitors, Lowest Microphonics in DC RX? Glen,
Jack Smith, K8ZOA, has measured a number of capacitors with changing
Even the common 100n decoupling capacitors are reduced to 80% of their
capacitance at 5V and 60% at 12V.
I used a ceramic 10U as a microphone to trigger a laser pulse cartridge I
made for a friends shotgun a few years ago.
The noise of the hammer falling triggered a pulse of red laser light that
shone out of the gun barrel.
4495 2010-03-31 13:47:05 davidpnewkirk Re: NPO Capacitors, Lowest Microphonics in DC RX? 4496 2010-04-01 23:19:51 drmail377 Re: NPO Capacitors, Lowest Microphonics in DC RX? Thanks all for the replies & links. Great info. I have experienced microphonics with surface mount caps. It seems SMT parts are more mechanically coupled to the board compared with through-hole parts. Board vibrations stress the dielectric in SMT caps more than in through-hole parts. YMMV.
Best 73's, David