[ARC5] Receiver input impedance.

[D C _Mac_ Macdonald]

Isn't all of this discussion a case of "straining at gnats?" 
 
Aren't all of the "command set" receivers meant to operate 
with what is basically a random length, i.e., relatively high 
impedance, single wire antenna? 
 
* * * * * * * * * * * 
* 73 - Mac, K2GKK/5 * 
* (Since 30 Nov 53) * 
* k2gkk at hotmail.com * 
* Oklahoma City, OK * 
* USAF & FAA (Ret.) * 
* * * * * * * * * * * 
 
 
 

 

> Date: Wed, 31 Oct 2012 09:47:11 -0700
> From: ianmwilson73 at gmail.com
> To: arc5 at mailman.qth.net
> Subject: Re: [ARC5] Receiver input impedance.
> 
> Robert is correct about the input trimmer: this is in parallel with the
> tuned circuit,
> and the antenna connects to that through a small fixed capacitor. My bad.
> The
> impedance of the input at resonance is not determined by the grid leak
> resistor
> of the first tube, but by the parallel effective parallel resistance of the
> coil, namely
> 2pi * L * Q. Guessing that the tuning capacitor is around 300pF at 500kHz,
> then
> the coil inductance will be on the order of 350uH. With a Q of 50 the
> equivalent
> parallel resistance will be around 55k ohm.
> 
> 73, ian K3IMW
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