radio frequencies ( MHz )

[skid]

quick question

will an aerial designed for 156-163 MHz work with our commonly used PRS radios which say 477 MHz

also the aerial in question is supposedly for VHF, where our PRS radios are UHF

I know the question seems dumb, but I was having a blonde moment or possibly a CM and felt the need to ask

[meatc]

Na

You may be able to get it retuned, but will be crappy like it is.

Just had big conversation with the radio tech at work (hes a HAM radio nut, like won competitions and stuff) trying to ensure our radios for Taupo are as good as they are gonna get. Upshot is real science to tuning a radio including the wire length, and no real way to know if it needs shortening or lengthening unless built from scratch.

His advice but the dearest, and probably longest aerial you can afford/fit. For the most of what we do the mid length ones are sweet. Oh and if it ground dependant centre it in a big ground plain (middle of roof) round independent no so important.

opps more than you asked , but since I had nice fresh expert opinion I thought I would share.

[T-mo]

Quick answer: No. Antennae length is very important to good communications, reducing interference and standing waves.

PRS radios run from 476.4250MHz to 477.4125MHz at 12.5kHz channel spacing. Making the center frequency 477.4125MHz.

The simplest and most effective antenna design is a half wave antenna or dipole. The ideal antenna length is formulated off center frequency (above) the formula is wavelength = speed of light / frequency. Therefore wavelength = 299,792,458 (m/s) / 477,412,500 (Hz) = 0.62795268 (8 s.f.). Halved = 0.31397634.

Due to the fact elections move slower in antennae than free space and "Ground effect" the calculated ideal antenna length is actually too long and creates VSW issues so the practical length of a half wavelength antenna is about 95% of its calculated length.

So, a PRS UHF radio antenna length should be 95% of 0.31397634m = 0.298277523m = 298.3mm. A commercially made UHF antenna may well be longer than this as it will be a factor of its half or quarter wavelength.

Mounting location will affect antenna performance too. The vehicle acts as a ground plain and it. Bull bars are almost the worst place to mount them. Mounting them higher will help with wave propagation, remember VHF and UHF radios are line of sight only. Without the use of repeaters.