RadioBanter - View Single Post - Help identify a desk-type microphone?

Fred McKenzie · October 9th 07, 12:38 AM posted to rec.radio.amateur.equipment

In article , wrote:

While sorting through my "collection" of junque microphones,
I found a desk-type mic with
* a fairly thick and heavy base with
* a four-wire cable,
* an RCA logo on the front, below and to the left of
* a plastic horizontal TRANSMIT bar, and
* a sticker on the bottom which says (and sorta looks like):

SHURE BROTHERS INC.
Controlled magnetic microphone
Model #MI-559156-1
Made in Evanston, ILL., U.S.A.
U.S. Patent D-198,850

In addition to the expected switch, the base also hides a one-transistor
something (presumably an amplifier).

W0PBV-

RCA used to make VHF/UHF NBFM two-way radio systems. I would guess that
this microphone was used for dispatching with an older model base
station.

You might check the Shure web site and see if they have any information
on the model number. However, it may be a proprietary number for RCA.

The Shure Controlled Magnetic or Controlled Reluctance microphone
elements came in both high and low impedances. You might do a simple 1
KHz impedance test on the element to determine which yours is. It could
most likely be used without the transistor amplifier if it matched a
radio's requirements. For example, the low impedance elements are about
200 Ohms, and work OK with Kenwood radios such as the TS-450.

The transistor amplifier is most likely to use a relatively low-output
microphone element with a radio originally designed for use with a
high-output carbon microphone. You didn't mention what HF radio you
used it with, but some recent Icom transceivers use a similar
arrangement with an amplified electret element. The low sensitivity you
experienced may be due to the old amplifier requiring a higher bias
level than the modern transceiver can provide.

Fred
K4DII