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nuckollsr(at)cox.net
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 Posted: Wed Sep 20, 2006 10:39 am Post subject: Transmitter Sidetone Adjustment |
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At 10:37 AM 9/20/2006 -0700, you wrote:
| Quote: |
I have a Garmin SL40 COM and a GM340 audio panel installed in
my RV-9. Got all the wiring finished this past weekend and
wheeled her out onto the ramp for a radio check.
When I keyed the Mic (actually I grounded the PTT wire - no
stick installed yet) and called out to my local airport's
pattern for a radio check, the sound of my own voice in the
headset was deafening. Folks in the pattern called out "loud
and clear" so I'm not worried about the functioning of the
radio per se. All other volumes in the headset -
intercom/chatter on the frequency - are just fine - its only
when I TX that I get deafened.
Is there an adjustment somewhere, or have I goofed up my wiring
somewhere ?
|
Back in WWII, radios were vacuum tube technology, and
not terribly robust. It was useful for many voice
communications situations for the talker to hear their
own voice in the headphones. This served two
purposes: (1) a ready check of transmitter operation
and (2) folks tend to enunciate more accurately when
they could hear themselves speak . . . difficult to
do in high noise environments like the cockpit of an
airplane. Transmitters were all amplitude modulation
and it was common practice to install a "crystal receiver"
on the antenna circuit. Detected audio was applied
to the intercom system for presentation at the speaker's
ears. If you can't hear yourself in the headphones,
you KNOW that nobody else is hearing you.
Nowadays, the "sidetone" audio is no longer sampled
from the transmitter's output signal and instead comes
from some point in a transmitter's audio system. As
such, the modern sidetone is useful only for purpose
(2) above . . . this means that there are cases where
you can hear yourself when in fact your transmitter is
not functioning properly.
Radios that offer the sidetone feature will also have
a sidetone level adjust potentiometer. The Microair
radios I used to sell had a plastic sticker over a
small hole that offered access to the adjustment
potentiometer. Someplace in the installation instructions
for your equipment you should be able to find
instructions for setting up sidetone levels.
Bob . . .
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gerf(at)gerf.com
Guest
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| Posted: Wed Sep 20, 2006 11:50 am Post subject: Transmitter Sidetone Adjustment |
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RTFM ... found it ... thx Bob 
g
| Quote: |
III" <nuckollsr(at)cox.net>
At 10:37 AM 9/20/2006 -0700, you wrote:
>
>
>
>I have a Garmin SL40 COM and a GM340 audio panel installed in
>my RV-9. Got all the wiring finished this past weekend and
>wheeled her out onto the ramp for a radio check.
>
>When I keyed the Mic (actually I grounded the PTT wire - no
>stick installed yet) and called out to my local airport's
>pattern for a radio check, the sound of my own voice in the
>headset was deafening. Folks in the pattern called out "loud
>and clear" so I'm not worried about the functioning of the
>radio per se. All other volumes in the headset -
>intercom/chatter on the frequency - are just fine - its only
>when I TX that I get deafened.
>
>Is there an adjustment somewhere, or have I goofed up my wiring
>somewhere ?
Back in WWII, radios were vacuum tube technology, and
not terribly robust. It was useful for many voice
communications situations for the talker to hear their
own voice in the headphones. This served two
purposes: (1) a ready check of transmitter operation
and (2) folks tend to enunciate more accurately when
they could hear themselves speak . . . difficult to
do in high noise environments like the cockpit of an
airplane. Transmitters were all amplitude modulation
and it was common practice to install a "crystal receiver"
on the antenna circuit. Detected audio was applied
to the intercom system for presentation at the speaker's
ears. If you can't hear yourself in the headphones,
you KNOW that nobody else is hearing you.
Nowadays, the "sidetone" audio is no longer sampled
from the transmitter's output signal and instead comes
from some point in a transmitter's audio system. As
such, the modern sidetone is useful only for purpose
(2) above . . . this means that there are cases where
you can hear yourself when in fact your transmitter is
not functioning properly.
Radios that offer the sidetone feature will also have
a sidetone level adjust potentiometer. The Microair
radios I used to sell had a plastic sticker over a
small hole that offered access to the adjustment
potentiometer. Someplace in the installation instructions
for your equipment you should be able to find
instructions for setting up sidetone levels.
Bob . . .
|
--
__g__
==========================================================
Gerry Filby gerf(at)gerf.com
----------------------------------------------------------
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