On the higher frequencies, >144 MHz, the noise received at the antenna is
usually (unless you have problems with QRM and QRN) close to or lower than the
thermal noise. Your possibility of receiving a signal is then limited by the
noise factor in the receiving system (your antenna, feeders and receiver). If
you don't have an antenna with good directivity (to get a good signal), a low
loss feeder (not to loose signal and add thermal noise) and a low noise
receiver (not to add noise to your signal) you will have problems receiving
weak signals. At HF the received signal already comes with a good amount of
noise (the noise temperature is high, to use a "professional" term). If you
loose some signal in your feeder you loose noise just the same so your
signal/noise figure stays about the same. Naturally, if you have plenty if
looses you will at some point loose too much signal to hear your station.
Think about it: You rarely hear about anyone putting a pre-amp at the antenna
when working HF but you find it frequently when working VHF/UHF such as
moon-bunch, TV reception etc. I don't think anybody would even think about
adding even a short coax between the antenna and receiver working 10 GHz.
Hans - N2JFS
To: firstname.lastname@example.org; email@example.com
Sent: Tue, Apr 13, 2010 1:58 pm
Subject: Re: [TowerTalk] TowerTalk Digest, Vol 88, Issue 45
In a message dated 4/13/2010 10:20:10 A.M. Pacific Daylight Time,
>>Some potential problems with the amp as already mentioned but you don't
>>get the real advantage for long coax runs with low loss coax which is
>>loss on the received signals. If you can't hear them - you can't work
>>no matter how much power you're running.
> Yes, BUT -- coax loss on RX only matters if the limitation is noise in
receiver. That is VERY RARE on the HF bands, where the major limitation is
either QRM or noise picked up on the antenna. In other words, on HF, coax
loss only affects TX.
I'm not splitting hairs about noise limitations of your rx.
Are you saying that the practical effect of a gain (less loss) of 3 dB
on the air due to lower loss coax is not heard on your receiver? So your
dipole, vertical, coat hanger, etc.is just as good on receive as your
multi-element yagi if it was all fed with the same coax? Isn't gain gain and
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