There is an additional factor that can cause deterioration of repeater coverage when PA power is significantly increased. It's broadband noise. Increasing PA power increases the intensity and coverage of the induction field which risks stimulating close aboard rusty joints and even dissimilar mental joints into behaving like broadband generators which will end up as noise on your own receiver channel. It doesn't help that it also ends up on every other receiver channel at the site. The potential consequence is to turn the repeater into an alligator. And adding additional cavities to the receiver and/or the transmitter is an exercise in futility because the junk you experience is dead on-channel. Sure, some sites may be well enough maintained to preclude this result, but the maintenance at my site has dropped to just about zero in recent years and cranking up power would produce a cure that's worse than the disease. Bruce K7IJ In a message dated 10/19/2007 12:34:58 P.M. Pacific Daylight Time, [EMAIL PROTECTED] writes:
Skipp, It is not just a cautious road to travel; it may also be an unnecessary one. Since repeater coverage is primarily limited by its ability to receive the low-powered distant stations, 250 watts of transmit power may be far in excess of what is needed for a balanced system. Even at sites where the noise floor is very low, that much power hardly seems necessary. Ironically, an increase to 250 watts from, say, 100 watts may result in reduced receive sensitivity if the duplexer must be improved to handle the higher power without desense. The power increase may allow the repeater to be heard full-quieting at a greater distance, perhaps a 20% increase, but may also reduce the ability of distant stations to be heard full-quieting by the repeater. In other words, an increase in power might result in a reduction in the coverage area. I'm not just making this stuff up- I have seen it happen more than once. At one Ham repeater site, the previous owner of a repeater had a TE Systems power amplifier set for about 150 watts hooked up to a Wacom 4-cavity duplexer. Even though the duplexer was perfectly tuned, it just couldn't handle that power level without some desense, and the coverage area was relatively small. When I took out the TE amplifier and fed the 15 watt driver directly to the duplexer, the coverage area ballooned to at least five times its previous distance. Some of the Hams who now were able to use the repeater from a considerable distance asked, "Wow! What did you do- triple the power output?" They were floored when I responded, "No, I cut it by a factor of ten!" I make no claim that my experience is typical, but I do assert that "More is not always better." YMMV... 73, Eric Lemmon WB6FLY ************************************** See what's new at http://www.aol.com
