[ARC5] [Milsurplus] ATD + R4

[David Stinson]

Thanks for writing, Bruce.

 

From:  Bruce Gentry

Subject: Re: [Milsurplus] ATD + R4

 

>. Did you add or modify an existing preamp in the
microphone base so you could use the original mic
input on the transmitter? 

 

It's an amplified-base D-104 mic.  I can't say
what the original owner

did as I've never examined another, just checked
that 

it had a DC-blocking cap on the output, which it
did.

Unlike many WWII Aircraft sets, the ATD has a mic
amplifier.

When the ATD audio input is selected for
"MAGNETIC," 

it places 300 Ohms from the audio input buss to
ground.

That's fine for the Lo-Z elements used then, but
kills the

output of Hi-Z mics most common today.  Lifting
one end

of the 300-Ohm resistor is all that's needed to
use a Hi-Z mic.

I haven't tried a non-amplified mic yet.  

 

>Does the transmitter have a built in T/R relay
and some sort of muting output for the receiver?

 

It does have a TR relay, but no muting contacts.
I put a small relay

across the keying relay coil (glued- no holes) and
ran two contacts

out via a small cable through the side vents- a NC
for receiver muting

and a NO for external amplifier keying.  I could
do all that with

an RF sensing circuit like they do for Chicken
Band amps, but

that takes a lot of fiddling to get the coupling
cap right.

Once I get everything mounted the cable won't be
noticeable.

 

73 Dave AB5S

 

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