Hello Bruce Not sure of where you are trying to install this equipment but my reaction here is to step back a few steps and evaluate the sites.
Here in Chicago we are running some VHF equipment in the downtown area and for many years have worked with this band in high RF enviornments. My first reaction is that althought you have put together a very good receiver system when you get to the site is appears to be getting QRM. I usually find the noise floor to be the first probelm followed closely by adjacent channel desense, followed by un-natureal occurances such as in building equipment, electrical stuff, computers etc. Then you have to consider the RF mixing issues associate dwith co-users of the facility. Oh yes - do not forget about TV channel 7 - This also plays in t the equation in some cases. Usually this ends up with a test first scenario - Often a certain Type of receiver say a GE Mastr III versus a Motorola GR12225 ( any number of things will effect one versus the other when you get down to grabbing at straws ) will m ake a diffference, and of course addition of selectivity e.g. cavitiy filters, or a crystal filter - all of which will degrade the overall sensitivity. I have used different product ( not anything specific as mentioned above ) with some degree of variance in the results. You may end up with an effective sensitivity of 1 uV but that is better in some cases than operating a 0.25 uV at a less desirable site. The trade off is the time you desire to invest in getting this to fly to your satisfaction. Some food for thought Ed Folta K9QPJ Com/Rad Inc Des Plaines IL ----- Original Message ----- From: lpcoates To: [email protected] Sent: Friday, November 09, 2007 11:01 PM Subject: [Repeater-Builder] Possible interference on 146.160 Hi Our radio club has a portable repeater on 146.760 (-). Each time we install it on a commercial building we find what appears to be interference on or very near the input frequncy of 146.160. This repeater was installed at two private homes for several weeks each and worked flawlessley. Tonight it began to act up after just a few minutes. Another repeater was tried at one of these commercial sites and it also appeared to be receiving interference on 146.160. Tonight I tried a simple test of tuning my hand held to 146.160 and found several "hot spots" in the room where I picked up something as well as picking up something radiating from the electrical conduit. Both of the commercial sites have elevator equipment, one quite old and one very modern. One site hosts several other radio systems from 400 MHz to 10 GHz and the other site has not other radio equipment. Both buildings are 12 story office buildings. My question is, have other people found that this frequency is especially prone to interference from nearby electrical and electronic equipment? I know that the output frequency of 146.760 can be a problem because it's very close to the 41nd harmonic of the colorburst crystal, but I haven't been able to find any mention of problems on the input frequency of 146.160. Thanks Bruce - VE5BNC
