[TowerTalk] Consequences of line loss??? Was: Power x RG58
Mon, 9 Nov 1998 08:07:06 -1000
Aloha to all,
I have rcvd a few responses to my assertion that the loss of
RG58 coax, in longer runs, could cause one to miss the
weakest signals in the rcv mode.
Well, these two responses in particular point out this error
1. >Jim, with respect, this isn't so! Losses work the same on transmit and
>receive, only you can't hear a dB or two on any HF band. All it does is
>raise the noise floor slightly.
2. >> Transmit loss concerns yes, receive loss concerns, no problem on HF.
>> As long as you can hear atmospheric noise in the receiver, gain loss
>> ahead of the receiver is NOT a problem.
>From this I have learned that any signal that you can
"hear" with whatever antenna set up you happen to have, you will hear
on the HF bands, at least 40 on up to 10 meters, without regard to the
loss/mismatch vswr of your transmission system on down to the rig
rcvr. On the low bands, special low noise pick up antennas, Beverages,
which actually have loss to the RF, can still improve the signal to noise
ratio you recv.
I will have to think about this for awhile. If you can hear the band
noise/QRN, then you are hearing the lowest level energy available
for the given conditions, including pass bandwidth or your IF
strip using filters, which reduct the noise and do increase signal
to noise ratio.
Perhaps I have put too much energy into worrying about antenna
system losses and impedance mismatches. I can get all the
xmtr power radiated (less line I-squared-R loss) using a tuner,
and the fact that the built in ATU of my transceiver does nothing
to improve the match of the rcvr to whatever impedance is seen
does not matter, as long as I can hear the band noise. I understand
that built-in ATU units operate only on the transmit side.
If I feel the other guy is not hearing me, I'll just flip the linear on,
perhaps, warm up the transmission line a bit with several tenths,
or maybe even a dB or two of the xmtr power, as DX can't hear
the difference caused by the line loss/mismatch on the other end
anyway. The shack antenna tuner does nothing to change the
mismatch of the transmission system beyond the tuner; just
matches that system to the xmtr output so all the power will
be coupled into the transmission system.
Now, do I have this correct??
73, Jim, KH7M
On the Garden Island of Kauai
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