[Kenwood] Kenwood TS-930S Microphone Impedance Setting?

Sat, 12 Jan 2002 03:59:55 -0000

Early TS-930's allowed the user to switch between MCL and MCH.  The MCL
connection placed a 3.9K resistor in series with the mic line.  The MCH
connection placed a 47K resistor in series with the mic line.

Later TS-930's eliminated this option, always placing a 4.7K resistor in
series with the mic line.

73,
Steve London, N2IC

----- Original Message -----
From: Dr. Gerald N. Johnson, electrical engineer <[email protected]>
To: <[email protected]>
Cc: <[email protected]>
Sent: Tuesday, January 08, 2002 6:08 PM
Subject: Re: [Kenwood] Kenwood TS-930S Microphone Impedance Setting?

> Not surprising that the high impedance microphone output has more ALC
> action, getting to high impedance involves a transformer that steps up
> the voltage. So there's more voltage, but not more power from the
> microphone. And since the input of the radio has the same gain, probably
> the difference between MCL and MCH is a microphone load resistor
> (connected for MCL and not for MCH) the low impedance connection will
> always provide more audio for more ALC action at any give microphone
> gain control setting. Driving a 500 ohm radio with a 50K microphone will
> tend to give a poor frequency response, probably rolling of highs
> excessively though that depends on the microphone. That's the most
> likely result with a dynamic microphone and transformer. With a crystal
> microphone like the original D-104, the lows disappear when loaded with
> such a low impedance and its high frequency response peak gets
> drastically exaggerated. The microphone response will be flattest when
> the microphone impedance is lower or equal to that of the radio input.
> Going lower in microphone impedance won't affect the relative frequency
> response, but will demand more gain in the transmitter audio circuits to
> get full output.
>
> 73, Jerry, K0CQ
>
> --
> Entire content copyright Dr. Gerald N. Johnson. Reproduction by
> permission only.
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