[Milsurplus] ARB Antenna capacitor

[Mike Feher]

What about simply, minimizing the effects of "suckout". 73 - Mike 

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 

-----Original Message-----
From: milsurplus-bounces at mailman.qth.net
[mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of Hue Miller
Sent: Monday, December 09, 2013 12:09 AM
To: milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] ARB Antenna capacitor

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.

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