[Elecraft] Receiver impedance?

[Wayne Burdick]

All antenna-facing stages in our receivers are designed for a nominal 50 ohm input. All of the preamp stages incorporate feedback to ensure a predictable, constant input impedance.

73,
Wayne
N6KR


> On May 25, 2022, at 9:44 AM, John Oppenheimer <john at kn5l.net> wrote:
> 
> Hi Walter,
> 
> Elecraft receivers, I'm familar with (K2,K3,KX[23], use "Feedback
> Amplifiers" for their Pre Amp. The Feedback Amplifiers are designed for
> nominal 50 ohm input impedance. Fifty ohm input impedance is somewhat
> import for operation of the receiver bandpass filter.
> 
> I'll assume detector input impedance, preAmp bypass, is also nominal 50
> ohm impedance.
> 
> John KN5L
> 
> On 5/25/22 11:05 AM, Walter Underwood wrote:
>> What is a typical input impedance for modern receivers, or specifically Elecraft receivers? 
>> 
>> I’m asking because antenna tuners are a frequent question on an SWL group I follow and I’m pretty sure that they are not needed for most situations. If the receiver input impedance is not 50 Ω, that is a big data point.
>> 
>> My belief is that receivers are generally medium or high impedance, depending on whether the first RF preamp is bipolar or FET, but either way, mostly voltage-oriented.
>> 
>> And, yes, I know that antenna tuners can be a LPF or HPF, depending on their configuration.
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