Receiver gain does not work the same as transmitter power increase. A 10 db increase in transmitter power is not the equivalent of adding a 10 db preamp on the receiver. It would be if your receiver was very noisy (internally)(very poor receiver) to start with and the 10 db preamp overcame the receiver noise by that amount. But that rarely is the case. With a good receiver to start with you may gain only a couple of db realization on the receiver when adding 10 db or more gain ahead of it. You may not realize any increase in signal recovery if there is a high noise level at the site.
Also for every db of gain that you add in front of the receiver you decrease the intermod performance of the receiver by the same amount. 73 Gary K4FMX > -----Original Message----- > From: Repeater-Builder@yahoogroups.com [mailto:Repeater- > buil...@yahoogroups.com] On Behalf Of Kris Kirby > Sent: Wednesday, May 20, 2009 9:03 PM > To: Repeater-Builder@yahoogroups.com > Subject: Re: [Repeater-Builder] Re: Desense on High Power Linear Repeater? > > On Thu, 21 May 2009, atms169 wrote: > > Yes, 80 dB on the duplexers, 100 watts in, that's 10 dB and the preamp > > 18 dB, so I'm losing 8 dB ?? > > Assuming you're not experiencing front-end overload because of your > pre-amp. > > > The sensitivity I believe is 0.4 uV Dstar system. > > > > I live in Texas where it's flat. I'm adjusting my station to > > compensate for the height value. More power good receive. There is a > > 1000 foot commercial tower here which would have been perfect, but > > they want too much to let me use it. > > Yeah, they tend to charge quite a bit to get to the top of a 1kft tower. > > > I had thought of adding two more cans and purchasing a new phasing > > harness but, someone told me to stop and just add more filters. > > > > So I'm not sure which direction to go. > > > > I would like to push more power if possible. > > Transmit power does not equal recieve capability. You have to think > bi-directionally. If you have a 6dBd antenna, and a mobile has a 3dBd > antenna (unlikely these days), then transmitting 5W is equivalent to the > mobile transmitting 10W. However, reciever sensitivity plays an > important part as well. If you can't hear a station who is running 50W > into a 3dBd antenna, he likely is not in a position to hear your > repeater at 25W into a 6dBd antenna. > > Again, take out the pre-amp, insert a silver-plated teflon barrell. > > -- > Kris Kirby, KE4AHR > Disinformation Analyst > > > ------------------------------------ > > > > Yahoo! Groups Links > > >
