Hey Jim I have a few thoughts that come to mind. Based on my experience with VHF and UHF repeaters colocated in cell sites I would say that you may want to consider the following. First the AC unit motors etc will not be a problem to the excellent FM rec you have there with the GE M2 even with the preamp. Plain electrical noise is not going to be your problem. It is an RF issue. And Multi RCC sites are very often a big mess as far as RF goes. Its too bad you have to go through all this but it is a fact of life in crowded sites that are also the best ones to be on.
The fact that your tests indicated the same actual values with the xmt on or off tells us that your duplexers are fine. And your rec tests direct connected are fine. Many cell sites are *real* bad with regard to rf on numerous freqs due to harmonics and mixing products/intermod. Some times you will only see your rf problem when 2 or more things occur at the same time aming it time consuming to pin it down. Sometimes the RF signal is slightly off your rcv freq but very strong and the skirts of the sweep are slightly coming into your channel. So you have to sweep the area with a good service monitor or Spectrum Analyzer to see what is going on. I use the IFR or R2200 plus the HP for this and it will show right up. It sounds like from the description you are in a very dirty site. You will have to consider 1. Moving to a new site even just a few hundred yards away on a new tower, or 2. Sweep with a spectrum analyzer to actually see if you can find the culprit(s) causing your problem and see if you can work with the equipment owner to clean it up. I doubt you will have much luck with this since if the techs at Verizon or Cell 1 ATT think their stuff is working fine they cant be bothered with your ham radio problems. They will tell you to take the site or leave it most of the time. 3. What I have had to do when the RF product was sitting just off our rcv freq and was fairly strong is install another cavity to clean it up. You may find it easier to use a pass type on your rcv channel unless you can definitely pin down the offending signal and reject it. Be aware that the preamp on your repeater can be a problem. GE and Moto reccomend those only for a base station and not a repeater unless you have a really clean site. They are notorious for intermod issues and most times are not worth the extra rvc gain in multi user sites. These suggestions are a start and may or may not do it for you but I would start with these basics. Keep an open mind to the fact that something at the site which is radiating some RF into your install may not be able to get fixed in practical terms and you may have to move either the frequency of your repeater or your site location, since I doubt you can get the cell guys/Paging RCCs to go away:) Let us know how this progresses 73 Glenn N1GBY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jim Brown Sent: Tuesday, September 25, 2007 8:20 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Duplexers Our local club recently installed a 2 meter repeater on a water tank adjacent to a cell site. Two cell towers are serviced by four buildings housing equipement, and we are having some desense due to noise pickup on the antenna. Running an iso-tee we found that our GE Mastr II receiver with GE preamp shows .6 uV for 12 dB SINAD using a dummy load in place of the antenna (.2 uV direct to the receiver bypassing the duplexer). With the antenna connected we see a 2 uV sensitivity for 12 dB SINAD. These readings are the same, with the repeater transmitter (40 watts) keyed or unkeyed. The noise floor is really decreasing the utility of the new repeater. The noise source seems to come and go as a quiet signal on the repeater input can become suddenly noisey, and vice versa - a noisey signal can become suddenly quiet. I hear the air conditioning units in the cell site buildings cycling and wonder if they might be the cause of the noise? Our antenna is only about 40 feet above the ground (at 7400 ft) while the cell antennas are at about 100 ft. So we are much closer to the cell site equipment buildings than the cell antennas. Two uV for the receiver sensitivity sure does limit the usefulness of the new repeater - Anyone have any thoughts? 73 - Jim W5ZIT [EMAIL PROTECTED] wrote: I am having some receive problems on my repeater and I am thinking that it might be desense. I am on 2M running a MASRII repeater with a Decibal Products band reject 6 can duplexer. While I can key the repeater from a pretty good distance the audio that makes it through the repeater drops off pretty quickly. I just had the duplexers tuned and they are tuned very well. So on to my question. If I were to take and seperate the recv cans from the xmit cans and run to 2 seperate antennas would that mess up the duplexer tuning? will 20' of vertical seperation plus the cans and the fact that I would be running through seperate cable, make a difference? Thanks, Vern KI4ONW ________________________________ Yahoo! oneSearch: Finally, mobile search that gives answers <http://us.rd.yahoo.com/evt=48252/*http://mobile.yahoo.com/mobileweb/onesear ch?refer=1ONXIC> , not web links. No virus found in this incoming message. Checked by AVG. Version: 7.5.488 / Virus Database: 269.13.30/1030 - Release Date: 9/25/2007 8:02 AM
