http://elecraft.85.s1.nabble.com/A-comment-about-Receiving-tp6216105p6219860.html
Note that many(most) tuners will not produce that pre-selector effect.
Only those with a resonant circuit will do that. Most common T-network
> I believe I understood all of your comment Ron.
> But as our noise floor at HF is limited by external noise (atmospheric,
> manmade and galactic) I don't understand how efficiency, within reason,
> comes into play for a receive antenna. Certainly, for signals above the
> noise floor, adding in 3 or 10 of attenuation makes no difference in the S/N
> ratio, and since the preselector cannot discriminate between signal and
> noise, I still don't understand the mechanism of how a preselector improves
> S/N unless its BW is better than the BW of the receiver- and I can't imagine
> that situation either.
> One of my best low band antennas is a rotatable half sized Flag whose gain
> runs around 30dB below my sloper.
>
> Dale W4OP
>
>> The antenna tuner acts as a pre-selector so to speak, by making the sytem
>> of
>> the antenna, the transmission line, and the radio, resonant, and matched
>> impedence.
>>
>> All of this adds up to minimize losses in a couple of ways. The impedence
>> matching means that the xmission line and antenna are as close to the
>> input
>> impedence of the radio (nominally 50 Ohms these days). If it is not at 50
>> Ohms then you do not get maximum power in to the rig based on simple
>> simple
>> Ohms law power.
>>
>> A highly simplified way of explaining resonance part of "a resonant
>> antenna"
>> is the act of making sure all of the current is in phase with the voltage
>> so
>> that when the power does get to the reciever, that it is in a useable form
>> to drive things. It is somewhat the reverse or inverse of a good spring
>> and
>> shock absorber system on a car....if you have things wrong, and drive
>> along
>> a rough road with bumps spaced jsut right relative to how fast, then all
>> heck breaks loose; maximim power transferred, and that is a resonant
>> system.
>> If things are not resonant, well, you get a smooth ride in your car, or in
>> the case of your radio, poor reception (and transmission).
>>
>> -ron WT5RZ
>>
>> --
>> View this message in context:
>>
http://elecraft.365791.n2.nabble.com/A-comment-about-Receiving-tp6216105p6217679.html>> Sent from the Elecraft mailing list archive at Nabble.com.
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