A while back in time, I worked 20 miles south of Chapel Hill, NC. During the late morning and afternoon our vhf fire, low band EM, and a UHF carrier squelch sheriff mutual aid channels starting getting garbage that was noisy but occurred on the various channels from 47 mhs to 453 mhz.
A paging transmitter on 152 mhz at the UNC Hospital was the cause. An additional transmitter had been put in an equipment room on the top floor of the hospital,. When the roof heated up, along with the extra heat from the added transmitter, the older paging transmitter started sending spurs all over the place. Cooling the equipment room caused the problem to go away. Marv, WA4NC Glenn Little WB4UIV wrote: > > > Locally, years ago, we had a military transmitter that had a > wandering spur. I am near Charleston, SC. The spur was strong enough > to key up amateur radio repeaters in the two meter band from > Wilmington, NC to Savannah, Ga. > The offender turned out to be a 250 Watt base station used to cover > approximately 10 Acres. > The radio was a Motorola MICOR. > The service shop could not fix the problem, so, they replaced the > transmitter. > > This may be a spur from a transmitter. > The spur that we experienced wandered up the band, then, down the band. > The wander was slow enough that you could hear it approaching the > repeater input frequency as a weak off frequency signal. > It would wander through the passband of the repeater in about 30-45 > seconds and again sound like a weak off frequency signal as the > squelch closed. > The repeater was either in the 148 or the 150 MHz range and > interfered with a 146.79, 146.82, 146.88 and a 149.94 MHz repeater. > It took about a week to get the problem taken care of. > The military had tried to classify the frequency of the repeater on > this base due to the type of traffic that they handled. > > Kind of hard to hide what you are doing when transmitting in the > clear with that much power and having a spur keying up repeaters over > the distance that this one did. > > There is some software that allows finger printing of a transmission > base on the lockup signature and oscillator stability as seen on the > transmitted signal. > You could possibly compare the known probable offender with the > offender through one of the interfered with repeaters or it's input > frequency. > > Wish you well with resolving the problem. > > 73 > Glenn > WB4UIV > > At 11:51 PM 10/28/2009, you wrote: > >I have to wonder how he can say his stuff is clean when this just > >started a couple weeks ago. Did he perform a PM check within the last > >two weeks? Unlikely. > > > >Stuff can go south in a minute, and seldom just before you check it. > > > >Joe M. > > > >Paul Plack wrote: > > > > > > > > > Mike, > > > > > > If it moves around based on time of day, my first guess is a PA that's > > > gone bad, and has a parasitic that's temperature-related. > > > > > > If you've tracked an individual spur drifting 70 kHz up the band > during > > > a single transmission, this is not some (intentional) oscillator > > > drifting, but some combination of failed components or tuning > which has > > > produced a parasitic. > > > > > > Sorry to say, but a paging transmitter owner swearing his stuff is > clean > > > is pretty meaningless. The assumption in his industry is the > > > professionals who maintain his stuff are not the problem, it's "those > > > damn hams." Sadly, it may more often be the other way around these > days, > > > as companies maintaining paging equipment have transitioned to > > > underpaid, under-trained card-swappers instead of component-level > > > technicians with a clue about RF systems. > > > > > > 73, > > > Paul, AE4KR > > > > > > > > > ----- Original Message ----- > > > *From:* Mike <mailto:mwbese...@cox.net <mailto:mwbesemer%40cox.net>> > > > *To:* Repeater-Builder@yahoogroups.com > <mailto:Repeater-Builder%40yahoogroups.com> > > > <mailto:Repeater-Builder@yahoogroups.com > <mailto:Repeater-Builder%40yahoogroups.com>> > > > *Sent:* Wednesday, October 28, 2009 12:28 PM > > > *Subject:* [Repeater-Builder] Pager Interference to 2-meter & VHF > > > Public Service Band > > > > > > > > > > > > A couple of weeks ago, our repeater system started to experience > > > interference from a paging system... > > > > > > > > > ...one evening I tracked it from about 145.120 to 145.190 as it > > > swept through each transmission... > > > > > > > > > > > > . > > > > > > > > > > > > > > > > > > > > > ---------------------------------------------------------- > > > > > > > > > Internal Virus Database is out of date. > > > Checked by AVG - www.avg.com > > > Version: 8.5.387 / Virus Database: 270.13.38/2274 - Release Date: > > 07/31/09 05:58:00 > > > > > > > > >------------------------------------ > > > > > > > >Yahoo! Groups Links > > > > > > > >
