jobdone Posted March 15, 2014 Share Posted March 15, 2014 Ok for anyone looking for quick and dirty antennas a good starting place is a dipole. It has no gain (I'm talking DBd here as thats the only value that means anything - ahem dbi...). Firstly take your 300 (erm yeah close to the speed of light) divide it by the frequency in Mhz you want to RX. This gives you the wavelength in Meters. Divide this by 4 to get a quarter wave. Then multiply this by 0.95 (to allow for velocity factors of materials. make 2 lengths of this size in any conductive material - yes speaker wire is perfectly ok! then attach one piece to the inner of your coax and another to the outer of the coax. Puritans use a 1:1 balun at this point. A cheap choke (a few turns of the coax coiled) will work fine for TX - however this is just for RX you shouldn't need to worry. If the antenna is horizontal, it is horizontally polarised, Guess what happens if it's vertical?. Placing this as an inverted V is seen as vertically polarised too. The antenna legs might need to be 5% shorter for inverted V. Place this antenna as high up outside as you can get it for VHF and UHF! a low gain antenna very high will work better than a high gain antenna very low! as UHF and VHF are line of sight. The dipole should be about 60-70 Ohm. The inverted V is normally closer to 50 Ohm. For anyone wanting alot of gain on UHF always look into our old friend the biquad - it offers alot of gain and a wide angle. For VHF maybe look into a slim jim or a collinear (coax collinears are quite cheap to build). For anyone interested in a few different frequencies , dipoles can be placed together to make a 'cobweb' antenna.... Quote Link to comment Share on other sites More sharing options...
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