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#11
October 17th 18, 11:36 AM
posted to uk.radio.amateur,rec.radio.amateur.antenna
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4NEC2?
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" |
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