I haven't noticed anyone else offer this idea, so I'll jump in here. I often see low level signals all through the 2M band near digital equipment. This is especially true of devices equipped with RS-232 interfaces. The baud rates are often generated by dividing down a higher frequency crystal oscillator signal (4.9152 MHz is a common one) to generate the clock signals at the desired baud rate. These baud clocks are often generated with a lot of energy and are prone to leak out of the equipment. Sure, the significant energy is limited to perhaps a hundred or so harmonics away from the fundamental, but it's interesting to note that in your case, harmonics of 300, 1200, 2400, 4800, 9600, 14400, and 28800 baud (all common baud rates) fall exactly on 146.160000 MHz, and harmonics from others fall fairly close. Granted these are very high order harmonics (above 10K), however, with a sensitive receiver, I bet it's possible to be picking up that 10 thousandth or so harmonic of the original baud clock. With the proliferation of digital equipment that contains "throw away" serial ports and modems, it's not hard to see how you could have thousands of devices within close range, all hammering away at 146.16 MHz.
Steve McCarter, KB4OID Email: [EMAIL PROTECTED] Website: http://www.kb4oid.org Fort Walton Beach, FL, 32547 > -----Original Message----- > From: [email protected] [mailto:Repeater- > [EMAIL PROTECTED] On Behalf Of lpcoates > Sent: Friday, November 09, 2007 11:02 PM > To: [email protected] > 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 > > > > > > > > Yahoo! Groups Links > > >
