[AMRadio] Microphone recomendation


bbruhns at erols.com bbruhns at erols.com
Tue Sep 22 11:16:23 EDT 2009


I used about 15 megs of grid-leak with a D-104 in the early 70s, and I was picking up a strong 9 Hz rumble that was probably from a nearby main road.  The D-104 is a good choice for super-high Z inputs because it has a strong response peak around 3 KHz.   This makes brighter, clearer audio, which improves things - especially with people listening on selective receivers.

   Bacon (the old Bacon), WA3WDR
Sent from my Verizon Wireless BlackBerry

-----Original Message-----
From: "Jim Tonne" <tonne at comcast.net>

Date: Tue, 22 Sep 2009 11:07:19 
To: Discussion of AM Radio in the Amateur Service<amradio at mailman.qth.net>
Subject: Re: [AMRadio] Microphone recomendation



I have been lurking here and reading the discussion
which seems to me to have reduced itself down to a
kind of "my daddy is better than your daddy" kind of
thing.

The person who said the D104 microphone could be
thought of as a voltage generator in series with a
500 pF capacitor hit the nail on the head!  Exactly
correct (although I thought it might be a  *slightly*
higher capacitance value).

I have spent a few minutes with LTspice and made
a plot which clearly shows what happens when you
change the value of the load on the D104 microphone.
With a 10 megohm load the -3 dB point will be right
at 30 Hz.  

Please, fellows, take a quick peek at this plot:
http://tonnesoftware.com/appnotes/D104loadTest.gif

The bottom line of this note is that going higher than
10 megohms for a load is nonsense.   Pure nonsense.

- Jim W4ENE


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