http://elecraft.85.s1.nabble.com/A-comment-about-Receiving-tp6216105p6219928.html
understand. That is one of the reasons we have passive filters up front in a
> Dale,
>
> The bandwidth can make a difference - the noise is broadband while the
> signal is narrowband.
> If the bandwidth of the receiver input is wide, then a preselector will
> make a difference because it decreases the total noise that the receiver
> is handling.
>
> 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
> of L-network tuners create either a high pass or a low pass filter.
>
> 73,
> Don W3FPR
>
> On 3/29/2011 9:55 AM, Dale Parfitt wrote:
>> 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:
>>>
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