[ARC5] Receiver input impedance...

[Richard Knoppow]

----- Original Message ----- 
From: "Fuqua, Bill L" <wlfuqu00 at uky.edu>
To: <kgordon2006 at frontier.com>; "ARC5" 
<arc5 at mailman.qth.net>
Sent: Monday, October 20, 2014 10:10 AM
Subject: Re: [ARC5] Receiver input impedance...


>  Generally, impedance matching is not very useful at below 
> 30 MHz, especially below 10 MHz due to the atmospheric 
> noise. Any signal you can receive must be above the 
> atmospheric noise.
> That is why ferrite antennas are just fine for AM 
> broadcast receivers, but useless for transmission of 
> signals. Reciprocity still applies it is just that you 
> don't need much sensitivity at low frequencies.
> 73
> Bill wa4lav

   Well again the important thing at the receiver is to 
maximize the ratio of signal _voltage_ to noise voltage. 
Power transfer is of little importance so impedance matching 
is not very critical. Generally, if the receiver impedance 
is higher than the source impedance of the antenna and 
feeder it will be good for SNR. However its not a simple 
relationship because part of the receiver noise is the 
equivalent noise resistance. This is mostly generated in the 
input device whether its a tube or solid state. This becomes 
very important at frequencies much beyond about 30 mhz and 
maybe below that too.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com