Jim Weir: RST-442 intercom query

Jim,
I have assembled and bench tested the RST-442 intercom and the audio quality
is excellent but I have a problem with the squelch.
Prior to reaching the squelch point when setting the squelch control all is
well with excellent audio but as soon as the squelch point is reached it
takes a loud voice to break the squelch though I have the mike close to my
lips.
I've checked the voltages mentioned on the instructions and looked at
waveforms with my oscilloscope but can't isolate the fault. There is a 1
volt P-P signal at pin 1 of U101A and 0.5 volts P-P at X116 and the squelch
circuit voltages appear to be as described in the Theory of Operation.
As things stand I can only use the intercom as a hot mike unit. Can you
suggest where the fault may be which is preventing the squelch being broken
with a normal voice or give me some troubleshooting tips to find it?
Thanks for your help,
Leo

On Wed, 20 Apr 2005 19:43:53 +1000, "Leo" LeoPowningatYahoo.com
wrote:

Jim,
I have assembled and bench tested the RST-442 intercom and the audio quality
is excellent but I have a problem with the squelch.
Prior to reaching the squelch point when setting the squelch control all is
well with excellent audio but as soon as the squelch point is reached it
takes a loud voice to break the squelch though I have the mike close to my
lips.
I've checked the voltages mentioned on the instructions and looked at
waveforms with my oscilloscope but can't isolate the fault. There is a 1
volt P-P signal at pin 1 of U101A and 0.5 volts P-P at X116 and the squelch
circuit voltages appear to be as described in the Theory of Operation.
As things stand I can only use the intercom as a hot mike unit. Can you
suggest where the fault may be which is preventing the squelch being broken
with a normal voice or give me some troubleshooting tips to find it?
Thanks for your help,
Leo


I had to take the sponge wind guard off my electret mike to correct
that. dont know why it mattered.
Stealth Pilot

Try this. Turn the intercom on and keep very quiet for about thirty seconds
to let the capacitors leak down their charge. THEN set the squelch to where
it is just barely squelching the background noise. Any voice or noise
during the leak-down period will reset the capacitors, so it is vital to
keep QUIET during this period.

In the aircraft, the ambient snarl will take care of this "problem" with a
constant level into the microphones.

Jim




"Leo" LeoPowningatYahoo.com wrote in message
...
Jim,
I have assembled and bench tested the RST-442 intercom and the audio
quality is excellent but I have a problem with the squelch.

Jim,
You say "just barely squelching the background noise" but there's no fine
adjustment on the squelch in my 442; there's a dull 'clunk' and the squelch
is on. The squelch is either Off or On like a switch at about 11 o'clock -
no fine adjustment, is that normal?
Thanks,
Leo
and thanks to Stealth for responding.

Leo LeoPowningatYahoo.com wrote:
Jim,
You say "just barely squelching the background noise" but there's no fine
adjustment on the squelch in my 442; there's a dull 'clunk' and the squelch
is on. The squelch is either Off or On like a switch at about 11 o'clock -
no fine adjustment, is that normal?
Thanks,
Leo
and thanks to Stealth for responding.

I removed the pot and installed a "10 turn" pot to give "fine control".
I've had my 442 intercom for over 25 years... and still LOVE IT!


Best regards,

Jer/ "Flight instruction and mountain flying are my vocation!" Eberhard

--
Jer/ (Slash) Eberhard, Mountain Flying Aviation, LTD, Ft Collins, CO
CELL 970 231-6325 EMAIL jer'at'frii.com WEB http://users.frii.com/jer/
C-206 N9513G, CFII Airplane&Glider, FAA-DEN Aviation Safety Counselor
CAP-CO Mission&Aircraft CheckPilot, BM218 HAM N0FZD, 227 Young Eagles!

Thanks Jer. I had considered doing the same and you've confirmed it.
73's,
Leo
VK3BSX
wrote in message ...

I removed the pot and installed a "10 turn" pot to give "fine control".
I've had my 442 intercom for over 25 years... and still LOVE IT!


Best regards,

Jer/ "Flight instruction and mountain flying are my vocation!" Eberhard

I've gotta figure out a way for my stuff to blow up after ten years so that
you have to buy another one. Twenty five years? Sheesh, that's less than
four bucks a year, or a penny a day. No wonder I'm an impoverished
engineer.

{;-)


Jim



I removed the pot and installed a "10 turn" pot to give "fine control".
I've had my 442 intercom for over 25 years... and still LOVE IT!

RST Engineering wrote:

I've gotta figure out a way for my stuff to blow up after ten years so that
you have to buy another one. Twenty five years? Sheesh, that's less than
four bucks a year, or a penny a day. No wonder I'm an impoverished
engineer.

{;-)

If you had stayed in school and got your PH.D., you would have learned
how to design things to blow up after a certain time period! :-)

Matt

"RST Engineering" wrote in message ...
I've gotta figure out a way for my stuff to blow up after ten years so that you have to buy another one. Twenty five
years? Sheesh, that's less than four bucks a year, or a penny a day. No wonder I'm an impoverished engineer.

{;-)


Jim


No more analog, make it all digital, then put a counter in it and POOF! gone after 10 years...

In article ,
RST Engineering wrote:
I've gotta figure out a way for my stuff to blow up after ten years so that
you have to buy another one. Twenty five years? Sheesh, that's less than
four bucks a year, or a penny a day. No wonder I'm an impoverished
engineer.


But just think, those were 1980 dollars.

Worth a lot more than the ones of today.


grin