Buck wrote:
I have been reading the Inverted Vee thread about the differences in
receive and s/n.

My process of using the tuner is to find the highest noise level,
then, turn on the carrier and fine tune to the lowest SWR. Often I
find that the signal strength isn't as good as it was before tuning.

Assuming the SWR is acceptable when tuned to the best signal, even
though it is not at its lowest, would it be better to leave the tuner
at the best received signal and use the radio with a bit higher SWR?

I am talking about SWR below 2:1, (not 10:1) as measured by the meter
or radio at time of tuning. For me, acceptable SWR for my solid state
rigs is 1.7:1 as 1.8:1 often causes protective circuits to kick in and
reduce power.

Comments?

Buck
N4PGW

It would be really neat if we had a tuner that would selectively tune
the signal and noise. But alas, we don't. At HF, the signal and noise
are both coming from outside the antenna, so anything we do at the tuner
-- or anywhere between the antenna and receiver -- affects both equally.
The tuner won't affect the received s/n ratio unless you get it so badly
mistuned that you start hearing receiver noise, which isn't likely at
HF. So tune it any way you want.

For transmitting, you're always best off getting as much power to the
antenna as you can. (I mean actual power, not "forward power".) What
you're trying to do is make the best s/n ratio at the other guy's
receiver. You can't do anything about his noise, but for every dB you
increase your signal, you get a one dB improvement in the s/n ratio at
his end. This means having an SWR low enough that your rig doesn't shut
down. Unless you have an extraordinarily lossy transmission line, any
SWR below the shutdown point will get the same amount of power to the
antenna for practical purposes.

At VHF and above, receiver noise is usually greater than atmospheric
noise, so the rules change for receiving antennas. There, you do want to
get as much signal from your antenna as you can in order to get the best
s/n ratio. The rule for transmitting is still the same, though.

Roy Lewallen, W7EL