GB3FM - GB3FN - GB3FX
|The coverage maps are taken from prediction programs.
The stylised map was drawn using them as basis but modified in the light of experience.
Coverage maps are always dependent on the parameters of the mobile. A 25W mobile with a high gain antenna will usually provide better coverage than a 5W mobile with a low gain antenna. The siting of the antenna on the vehicle can cause markedly different propagation in different directions. This is more pronounced at 50MHz than at 433MHz as the groundplane on 433MHz doesn't need to be so big to be effective (by a factor of nearly ten).
Finally, a lot depends on the perception of the users. Some users will give up using the repeater as soon as its signal falls off the end stop of the signal meter, and don't like any flutter. Others will carry on to the bitter end and try and get service if it's just above squelch. The coverage maps here are closer to the latter, i.e. coverage is shown as present if it is usable but weak.
The map has been plotted using the rather excellent
Radio Mobile program from VE2DBE. It shows expected mobile coverage.
GB3FXAs with GB3FN, the map has been plotted using the rather excellent Radio Mobile program from VE2DBE. It shows expected mobile coverage, with some dependency on local conditions and the abilities of the mobile installation.
Yellow shows a strong signal, and this area should be workable for most mobiles.
Varying antenna efficiency and background noise on 50MHz make the map a little less predictable than at higher frequencies. (Diesel engined cars without CD players do better than petrol engined cars with the CD going - 'FX's output seems to be close to a harmonic of a crystal used universally in CD players!) Many mobiles will achieve somewhere between the two - depending on which direction they are pointing in and so which direction their antenna works best in.
Some indications on how far the 'regulars' running up to 50W and quarter wave antennas have worked GB3FX:
M1 North - Luton
Coverage MapsClick on an image or the associated text for a full size map.
GB3FMCoverage predictions are likely to be more approximate at 23cm than for our other repeaters.
There are two maps plotted:
GB3FM mobile - whereas 23cm mobiles are few and far between, this gives an idea of where the repeater might be heard. The repeater should be audible over the yellow area with a simple setup, such as a portable inside a car (perhaps on the dashboard). The green and blue areas will probably need an external antenna, such as an Alford slot on top of the car; the blue area probably audible only when there are not local obstructions near the mobile.
GB3FM fixed - this is intended to give an idea where a fixed station with an outside aerial may be able to hear the repeater. The yellow area has a good probability of success and the green area should also be achievable for a fixed station with a reasonable aerial without too much local obstruction. The blue area may still be good to receive the repeater, but is likely to need a good aerial and possibly some careful location of the aerial to avoid local obstructions.
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