The Island Way: I used my IC-28H..(mobile) .which has "led bars" on rx signal strength. I drove around the island and map out receptions on strategic points. Clients are satisfied that a 15-watts tx at repeater site covered the whole island (32 square miles). Repeater located at center (highest point) of the island about 1700 ft. above sea level...coverage of 20+miles easy. All system powered by solar power. my 2-cents. Chris Mariana Islands
Nate Duehr <[EMAIL PROTECTED]> wrote: Mike Besemer (WM4B) wrote: > Whats the most accurate down-and-dirty method of measuring the > footprint of a repeaters receiver coverage? > > I know the whole question sounds like an oxymoron, but inquiring minds > want to know. > > de WM4B > > Mike Down-and-dirty: Drive around and see where it covers. Write on napkin from fast-food joint. (GRIN) Really-Fancy Down-and-Dirty: Find some software to plot received signal strength from a connected radio at regular intervals that also logs GPS data. "Coverage" for a repeater is reall a function of two things, the transmitter coverage and receiver usable sensitivity. You can build a system that transmits well but can't hear anything (alligator), and vice-versa (elephant). With that said, assuming your system is relatively "balanced" and youre engineering is right for both... Transmitter coverage is the above "drive around" method (well, if you can't key the repeater from where you can hear it, you might find out you're not as balanced as you thought you were). Receiver usable sensitivity (not just raw sensitivity, but sensitivity while hooked to the antenna system including noise and any interference present) is measured at the site. There's a nice article on the RB website about how to do that measurement, I believe. You can only extrapolate from there, because you don't know what the mobile rig's RF output, feedline, antenna, and height will be... so you just take something "average" and do the math from there to see where the repeater will "hear". (The most often used "method" here is just to go for the maximum usable receiver sensitivity that you can possibly squeeze out of your system and not worry about where it will theoretically hear. Push the number as low as you can without getting into the noise floor of the site or the noise figure of the radio -- since you're probably adding a pre-amp to get there on most receivers, even modern ones.) A another more "engineering" method would be to get a theoretical coverage pattern would be to use RF coverage prediction software and with good measurements of power output and the manufacturer's specifications for the antenna gain, you could build maps like this one: http://www.colcon.org/fig/thorodin_coverage.gif But you still have to go compare the map to the real world with real radios at some point. How much of that you do, all depends on how precise you want to be about it and how much time you can dedicate to the process. (GRIN) Free software is available for predication that does a "decent" job for the prediction part of it, and commercial software ($$$) will be marginally better at the analysis, and perhaps easier to use. (I don't know -- I don't use commercial software. http://www.cplus.org/rmw/english1.html - RadioMobile Software The free stuff is "good enough" almost all of the time for your personal use. If doing reports for others, the liability issues might drive you into the arms of a commercial piece of software. Many 2-way shops will do this type of thing for a fee, also -- if you're not the "do-it-yourself" type and don't have any friends in the biz. Of course all of the above also has other "real-world" realities that affect it... multi-path, interference sources off-site that don't bother the repeater but bother the end-users, adjacent channel interference/problems, etc etc etc. Just shoot for the best receiver sensitivity you can muster, engineer that in from the very start, and do it right (proper bandpass or other filtering, and pre-amp with the right amount of gain for the Noise Figure of your chosen repeater's receiver) and the transmitter at something "reasonable"... 50W out the duplexer (after duplexer loss, isolator, etc.) to the antenna is very similar to what the mobiles are going to push back toward the repeater... HT's 5W... So you can see it's really easy to build an "alligator". There are solid engineering reasons to build an alligator at times (remote receiver sites, need for building penetration for listening to the machine on HT's while someone will talk back on a fixed mobile in the building, etc.)... but mostly a balanced to "slightly alligator" system works best for the users. They can listen to the repeater to get a feel for how well they'll be into it... a major alligator never gives that kind of "user feedback loop" to the end-user... they hear it well everywhere and can't figure out why they can't get into it reliably. Nate WY0X Yahoo! Groups Links --------------------------------- Looking for last minute shopping deals? Find them fast with Yahoo! Search.
