On 17/10/2018 10:00, Roger Hayter wrote:
Spike wrote:
On 16/10/2018 14:38, Ralph Mowery wrote:
In article , lid
says...
Very interesting, but I'd have to say that none of what you say refutes
my original contention that the distant station, which after all is the
one we are trying to communicate with, will notice any difference to the
received signal whether the sending station's antenna was tuned with a
20c torch bulb or a $300 VNA. You touched on the main vagaries of the
system when you said "What I've found is that such side by side
comparisons do not account for variations in propagation, path,
interference, local noise, time of day, position of the moon, and other
factors beyond the operators control".
Sometimes it is who is doing the adjusting and not how good the
equipment is.
That's very true, of course. Some good equipment is in the 'wrong hands'.
Almost 40 years ago I started keeping a repeater on the air that was
started by someone else. My test equipment at that time was a VTVM, a
$ 25 Heathkit signal generator, old Oscilloscope, swr meter, and
frequency counter.
To tune the receiver my best 'signal generator' was a ham near the edge
of the repeater coverage. I would have him just to key down for a
minute or two at a time while I adjusted the receiver. Over the years a
better receiver and transmitter was installed. Now I have some very
good test equipment, but can not say the coverage of the repeater is
very much better. What little improvement is made is probably because
the radio equipment is better.
Thanks! That's just the sort of thing I was on about - in this case you
actually used a distant station to help with the set-up, and it worked well.
At that time one thing I did not try to adjust or check was the duplexer
as I did not think I could with what I had to work with. Many years ago
the tuning instructions for duplexers was to tune for maximum signal on
the pass and best rejection. As test equipment became better and priced
in range, the pass tuning change to using a return loss bridge and
SA/TG. This seems to work much better. I found the pass was broad and
you could usually give the tuning rod a turn or two without much effect,
but he RLB shows up in less than 1/2 of a turn. Does it make a
difference ? Probably not in effective coverage (it may extend the
range a foot or two,hi), but at least I know it tuned the best it can be
with what I have to work with.
One thing that does come with better test equipment is knowing that the
equipment is tuned so it meets or exceeds the specifications. Before
it was just a guess as if the equipment did or did not meet
specifications.
Quite so. But 'specifications' are often written with other things in
mind - compatibility, spurii, stability, etc, and not necessarily
anything at all to do with how the distant station receives/perceives
one's signal.
ISTR it being a licence condition that one checked all the above
periodically - more honoured in the breach, perhaps, with commercial
kit.
That's the sort of road that Liebermann wanted to take the discussion
down; an interesting topic but not the issue under discussion.
--
Spike
"Nearly all men can stand adversity,
but if you want to test a man's character,
give him an internet group to manage"