question about radio sidetone

[Gary R.]

i have an old Stinson with a Cessna 300 nav-com in it.

surprisingly, the radio works OK, but i can't hear myself talk
on 2 different headsets.

but, i can transmit and hear others calling me OK.

what gives? is it a function of this early radio that it has no
sidetone---or a wiring problem?

thanks for any input.

email me pls?

[mikem]

On Apr 8, 3:20 pm, (Gary R.) wrote:
>... is it a function of this early radio that it has no
> sidetone---or a wiring problem?

I have flown older Cessnas that had the 300 series NavComs, and they
had sidetone.
Sidetone is generated inside the COM by sampling the audio from the
transmitter modulator
and routing it out through the "headphone" output pin, so you should
hear it when you transmit.
Either the radio has an internal problem, or possibly the "sidetone
level adjust" pot got turned down.
Most COMs have a "sidetone level adjustment", usually visible only
when the radio is out of its tray...

[Travis Marlatte]

Does an intercom interfer with this? If I shut my intercom off, I get no
sidetone. I've got an old Collins. That leads me to believe that the radio
is not providing any - whether blocked by the intercom or by design or
failure of the radio, I'm not sure. With the intercom on, I get sidetone
which I presume is being generated by the intercom.

When you use the handheld mic and speaker, clearly there shouldn't be any
feedback. I could believe that the headset output doesn't provide sidetone.
Why bother with the expense and extra parts?

--
-------------------------------
Travis
Lake N3094P
PWK
"mikem" > wrote in message
oups.com...
> On Apr 8, 3:20 pm, (Gary R.) wrote:
>>... is it a function of this early radio that it has no
>> sidetone---or a wiring problem?
>
> I have flown older Cessnas that had the 300 series NavComs, and they
> had sidetone.
> Sidetone is generated inside the COM by sampling the audio from the
> transmitter modulator
> and routing it out through the "headphone" output pin, so you should
> hear it when you transmit.
> Either the radio has an internal problem, or possibly the "sidetone
> level adjust" pot got turned down.
> Most COMs have a "sidetone level adjustment", usually visible only
> when the radio is out of its tray...
>
>

[mikem]

On Apr 9, 9:07 pm, "Travis Marlatte" >
wrote:
> Does an intercom interfer with this? If I shut my intercom off, I get no
> sidetone. I've got an old Collins. That leads me to believe that the radio
> is not providing any - whether blocked by the intercom or by design or
> failure of the radio, I'm not sure. With the intercom on, I get sidetone
> which I presume is being generated by the intercom.
>
> When you use the handheld mic and speaker, clearly there shouldn't be any
> feedback. I could believe that the headset output doesn't provide sidetone.

On older radios, I'm not sure if it is the radio, or the audio
switching panel which generates the sidetone. On the other hand, I've
worked on old 90 channel tube-type radios which did generate sidetone
internally. I know for a fact that Narco Mark12D, King/Bendix/
Honywell radios like a KX170 & KX155, Garmin SL30/40, ICOM 200, &
ValCom all generate headphone sidetone internal to the radio,
regardless of what the audio switching panel or intercom does. Most
intercoms have a strapable option which enables/disables the
generation of sidetone inside the intercom... I agree that you do not
want sidetone through the cabin speaker, only through the headsets.