"MICHEL SAMSON" wrote to "MIKE ROSS" (03 Jul 03  17:32:00) 
 --- on the topic of "1/2 - 89.3 FM" 
 
 MS> About "89.3 FM" of June 26: 
 
 MR> ...UHF dx from Burlington Vt. to Montreal...  ...excellent in winter 
 MR> time but is very degraded in summer...  ...returns at night. 
 
 MS> I'll confess my expertise in fields like electromagnetic 
 MS> dispersion is rather limited, maybe my opinion that FM reception is 
 MS> better at night happens to be inaccurate and involves a more complex 
 MS> compound of factors as weather combined to interference from daytime 
 MS> activity. 
 MS> In the years when i had a simple amplified antenna installed 
 MS> on the 3rd floor balcony of a building at the corner of Henri-Bourrassa 
 MS> and St-Laurent, channel 3 seemed to propagate as differently from 97.7 
 MS> Mhz as the later FM channel could differ in behaviour compared to 
 MS> channel 57 (which hardly gave me an impression of being remote at all 
 MS> while snow usually buried channel 3). 
 MS> That's as much as i can share about dispersion!!! 
 
VHF FM band behaves quite differently from television UHF frequencies. 
The main difference is that the high UHF band approaches the low end of 
microwave radar frequencies and if you know how your microwave oven 
operates you will realize why there is substantial absorption of the 
high UHF wavefront energy by the water vapour in the air or in foliage. 
 
The VHF FM band is basically "line of sight" transmission but for many 
reasons it can extend to a couple hundred miles with fringe area 
reception conditions. High UHF however behaves even more like a light 
beam and the propagation effects which helps the VHF FM band can not 
usually be counted on and thus coverage is limited to just about 80 
miles as the crow flies. Coincidentally this is how far 57 is from us. 
 
This means that in ideal atmospheric conditions reception may be 
excellent but in my experience any weather deterioration will severely 
affect the signal quality due to the extreme length of the signal path. 
However, sometimes weather conditions conspire to improve reception 
beyond the normal. For instance when two weather fronts exist with a 
region of hot dry air between them which can form a tunnel wave guide 
effect. However alternatively if there is a solid sheet of rain from the 
transmitter to us then the signal will be very much weakened. 
 
Note that high UHF like ch.57 is more affected in these examples of 
weather conditions than the lower UHF like ch.22 and clearly shows the 
connection with the microwave oven or radar frequency analogy. 
 
 
 MS> - "Taming The Strong FM Station"/"TV Receiver
Overload", an 
 MS> unsigned 4 pages document... 
 
An excellent discussion of overloading and helical filters but it is 
slightly beyond the scope of a simple chicken fencing and baling wire 
kitchen table top solution. No doubt a very professional alternative and 
I thank you very much for the extremely detailed instructive content, 
and very educational! 
 
 
 MS> That's why i must agree when one argues that it's no exact science! 
 
No argument here but there is still wiggle room for a little science. 
 
 Mike 
 **** 
 
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