[Milsurplus] ARB Antenna capacitor

[Hue Miller]

My thinking was that this condenser would have minimal effect in attenuating
stray oscillator inputs. I was thinking that the overall antenna capacity as 
seen
by the ARB with multiple receivers connected plus the circuit through the 
ATC
might be deemed ?too? far off the design "standard" capacity.  A condenser
of 36pF would pretty well define that antenna capacity, since it is a 
multiple
lower than would be seen by the rest of the outboard wiring. Would a high
capacity at the ARB antenna post detune the antenna's resonant circuit? I
do not know. More wisdom (more inputs from others) is required.
The impedance of the 36pF at 4495 kcs (for example :) is about 1000 ohms.
Yes, that would make for a filter effect, considering the low impedance of 
the
ARB input circuit to off-resonance frequencies. However for stray oscillator
inputs at the same frequency the ARB is receiving, 1000 ohms, I think, is
like, forgettable, considering the ARB input impedance.
It was worth the question for me to learn that this was not a hammy mod.
I believe I first saw it in a surplus store where most of the avionics of 
some
plane had showed up, ARB, ATC, and who knows what else.
-Hue

-----Original Message----- 
From: Mike Hanz
Sent: Sunday, December 08, 2013 8:34 PM
To: Hue Miller ; milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] ARB Antenna capacitor

On 12/8/2013 7:02 PM, Hue Miller wrote:
> So the series capacitor was to somehow discriminate against, how? ( Not 
> getting it. )
> And not to diminish the total antenna capacity, nor to somehow protect the 
> receiver?

Why would one want to decrease the antenna capacity seen from an ARB's
perspective, Hue?  I haven't found the mica transmitting cap on the ARB
antenna input used in any other system other than where multiple
receivers were attached to a common receive antenna.  That should tell
you something about its deployment.  What we do know is that it is
possible to reduce interaction through de facto bandpass filters, using
inherent set antenna input capacities and inductances.  What we do not
know at the moment is whether the intent was to diminish interference
from the ARB or the command sets.  Further research is needed.