There has been quite a lot lately about radios and antennas. Some
misinterpretations prompt the following;
The VHF (30-300MHz) in aviation around 120MHz is essentially
line-of-sight. Actually, much above that in freq is also - after hams talk
to others 8000 miles away because their satellites are up there 90 miles
looking down - and all this with 1/10 to 5 watts. So range is always the
same line-of-sight. What differs is what interferes with it. VHF will 'bend'
a bit around a corner refraction - but not much. Another reason is proximity
of a similar antenna or metal structure. A third is usually the radio. very
often, makers switch frequency-sensitive sections between transmitter and
receiver. SO, if the first two causes reveal nothing, the comparison of send
and receive bear investigating.
Line of sight between antennas is the formula:
Distance (stat miles) = SQRT[2 x height above horizon in feet]. As the good
book says, 100 foot tower sees 14.1 miles. A plane at 5000 above flat ground
'sees' 100 miles and two aircraft can hear each other 200 miles distant if
both are at 5000 feet. Complaints of distance are dependent on the
topography and the altitude. It's rare for an area authority not to have
full reception to the far corners of its responsibilty - so one should be
able to contact them outside their boundaries quite easily. This makes
another comparison simpler.
Good hunting
ferg
The vertical 1/2 wave antenna in the tail is a candidate for reduced
forward transmission because of both the engine and the width of two
occupants.
|