awall said:
The best thing you can do to improve your repeater operation is to put in a good quality reciever pre-amp.
I disagree. The best thing you can do is eliminate any desense so that the receiver performance is identical with the transmitter (all transmitters at the site, really) on or off. Adding a really hot preamp can make it impossible to fully eliminate desense.
awall said:
If you double your output power you will only see about 2 or 3 miles extended range and it will not do anything for the reciever.
That's a gross over simplification, and not necessarily true, depending on the power levels involved. It follows the inverse square law, where double/half the distance involves a 6 db change in power level. That applies in free space, so terrain is going to have an influence.
awall said:
Another trick that works real well is to get rid of the duplexer and run 2 antenna's and feed lines. Put your recieve antenna on top and hang the transmit antenna upside down about 20" or so below the recive antenna.
This is a useful technique, although the upside down antenna has some caveats. Not all antennas are "upside-down friendly", meaning there may be moisture/drainage problems. Or perhaps the radiation pattern is all wrong when it's upside down. But separate antennas are a useful technique in some, but not all , circumstances.
awall said:
Depending on the quality of your duplexer, you may have up to 2db loss of transmit signal so removing it would give you much better erp. By doing this (depending on terain) you could easilly double your range.
This is in contradiction to both your statement about doubling the power, and the inverse square law. 2 db of duplexer loss is not necessarily unreasonable, and being considerably less than 6 db doesn't come close to halving the usable range. The trick to dealing with this is to start with enough transmitter power so that after 2 db loss, you have a satisfactory amount at the antenna port. It's all part of the gain/loss budget you do when you design your repeater system.