[ARC5] BC-453/Q5er Converter

[Henry Mei'l's]

Thanks for your response .

Actually, it was also my assumption that the Command receivers have hi-Z 
input  - based upon my experience with them, particularly when using very 
short antennas.
I just thought it to be an interesting issue considering the discussions 
some time ago on this thread, about the actual input Z of the MF and HF 
Command transmitters seeing as they were designed for use with relatively 
short end fed antennas, albeit with the aid of their internal  series 
roller-coil (and/or external coil-tapped inductors for lower frequencies).

Henry, Cph.

----- Original Message ----- 
From: "Ian Wilson" <ianmwilson73 at gmail.com>
To: "Discussion of AN/ARC-5 military radio equipment." 
<arc5 at mailman.qth.net>
Sent: Sunday, September 26, 2010 6:41 PM
Subject: Re: [ARC5] BC-453/Q5er Converter


> The general receiver schematic shows the antenna being connected to the 
> top
> of the input coil (L1) through a capacitor (C1). The grid of the RF
> amplifier tube
> is then tapped down on the coil.
>
> For the 190-550kc receivers, L1 is 285 turns with the tap at 198 turns; C1
> is
> 11pF. At 370kc (mid-frequency), the reactance presented by 11pF is 39k 
> ohm.
>
> At resonance, the impedance of the input tank circuit will be large and
> resistive,
> so the input will look like 11pF in series with a large resistance.
>
> This will match reasonably well to an electrically short antenna. Matching
> to
> 50 ohms wouldn't be easy (but there is probably no need anyway).
>
> 73, ian K3IMW
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