atms169 wrote: > Hey guys, I'm trying to find radiation patterns or a calculator to see > what would be the best possible coverage for our repeater.
There's a number of calculators on the web, and some good links in the RB website for Excel spreadsheets where you can see the math if you like. > We are in the very flat lands of Texas and our repeater is only up 50 > feet (total of 530 above sea level). With 120 watt output. 120 watts after the duplexer loss, or before? What kind of duplexer, feedline, etc. Assuming 50' for the transmitter and 8' (I'm being generous) for a mobile rig, the radio horizon between those two is approximately 14 miles, according to the popular calculators. Anything else isn't line of sight propagation. > Which do you think would work better? A dual folded dipole antenna > with low angle of radiation or a fiberglass vertical at 6db? Let's assume power doesn't matter for a moment, and just break it down into comparison of the antennas. Remember, altitude trumps all, antenna gain and feedline losses next, and the PA is *last* place you want to make up for a weak antenna system. The antenna is gain both directions, transmit and receive. The PA only helps people hear the repeater... it doesn't help them get into it. So... the important info is missing in your question... What band? Can't answer the antenna question without knowing what band you're looking at to compare different sized antennas. Makes a big difference. I will assume VHF for these answers for the moment. You say 6dB. Is that 6 dBd or 6 dBi? That also makes a big difference, since we're going from your numbers for the one antenna, and don't know which other antenna you're comparing to. What specific antennas are you looking at? Spec sheet on the web somewhere to reference? For both... the dipole array and the stick. Most dual-dipole-array antennas claim about 6 dBd gain when set up in an elliptical pattern. That assumes a 1/2 wave spaced (from the mast) dipole array, like this Sinclair: http://www.sinclairtechnologies.com/catalog/product.aspx?id=1680 There are different configurations for 1/4 wave spaced (from the mast) dipole arrays, the lowest gain being the purely omni-directional setup. The "offset" setup where you pick a direction to "push" your RF one way more than the others, gives you a little more gain that direction at the expense of the other side. http://www.sinclairtechnologies.com/catalog/product.aspx?id=326 Generically, there's no free lunch. The same sized antennas exhibit much the same gain, but you can do tricks with the dipoles a stick can't do... like offset the pattern a bit. You could always go for an enormous VHF corner-reflector! (Yep, they make 'em...) http://www.sinclairtechnologies.com/catalog/product.aspx?id=1403 It's ONLY 10' wide... hahaha... More info needed... the devil is in the details. Nate WY0X
