[ARC5] Receiver input impedance.

[Kenneth G. Gordon]

On 30 Oct 2012 at 18:06, WA5CAB at cs.com wrote:

> Ken,
> 
> The 5 ohm source impedance was probably to mimic the expected antenna.
> The actual input impedance is quite high, being a parallel resonant
> coil and capacitor in parallel with a 2 meg resistor connected to the
> 12SK7 grid (through a DC blocking capacitor which you can ignore).
> This is why connecting coaxial cable to a Command Set antenna terminal
> detunes the input.

Yes. I knew this. Thanks, Robert.

> Neither BC-453-A nor BC-453-B ever had a Loop input. And the input is
> unbalanced, not balanced.

Again, I figured that out. I need to do some more research and figuring. I 
suppose one could use that 2 meg resistor as the limiting impedance.

In any case, it seems as though I could use a parallel-tuned circuit, coupled 
with a few turns round the "cold" end of the antenna coil, and a few turns 
around the center of the parallel-tuned circuit with both "ends" of the coil 
going to the twin-ax....maybe....

No. Probably not.

Ken W7EKB