http://elecraft.85.s1.nabble.com/A-comment-about-Receiving-tp6216105p6219959.html
bandwidth IS NOT affected at all by input matching. At VHF this is
to contain the limiting noise. At this point the matching and
bandwidth issues become prime. There is no general statement that
> 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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