How long has the pager been in operation? If it has been there for a long time either something changed in the pager setup or something changed on your end.
What you have is a case of RF overload. No other frequencies are involved, not even your own transmitter. 225 watts RF + how much antenna gain on the pager end or is that the total ERP of the pager? What is the difference in vertical height between the pager transmit antenna and your repeater antenna? What sort of filtering are you using? Duplexer? Dual antennas? The HP8924 in the Spectrum Analyser mode will show you the transmitted frequency shifting between the upper and lower limits. The deviation measurement will be useless since you are not measuring deviation of an analog signal. Setting up a digital paging transmitter usually involves activating a test mode which will place the unmodulated TX signal at the the limits. The adjustment is made to set the amount of shift from the center channel according to the enginnering for the system. When the incoming signal from the paging terminal is received it causes the transmitter to shift to one of the two limits which can be thought of as a 1 or a 0. Ironically the systems I saw usually used AFSK on the link from the paging terminal (modem to modem). If there is more than one transmitter involved measuring off the air cannot give you an accurate "deviation" measurement since any hetrodyne between the two or more carriers will also be seen by the service monitor and will distort the measurement. Milt N3LTQ Quoting Tim Sawyer <[email protected]>: > I have noticed the carrier appears to jump between +4 and -4 Khz of center. > > The transmitter is about 75 yards from me. It's running 225 watts > according to the tech. > > The interference is pretty strong. It competes with my base station > on low power. I'm 25 miles from the repeater. > -- > Tim > :wq > > On Aug 21, 2010, at 11:25 AM, [email protected] wrote: > >> Tim, >> >> Digital paging (mostly POCSAG coding these days) is FSK and will >> easily occupy 15KHz of bandwidth. >> >> On a Service Monitor deviation screen you will see a square wave >> pattern that looks like it is overdeviated unless you are very close >> to the transmitter in question. Read on and you will see why a >> deviation measurement is of little use. >> >> On a Spectrum Analyser you will see a single spike that jumps back and >> forth between a freq higher than the channel center and a freq lower >> than the channel center. The typical digital paging transmitter >> settings are +4KHz above the assigned freq and - 4KHz below the >> assigned freq. If the system uses multiple transmitters the + and - >> settings may be asymmetrical to allow for slight offsets between >> transmitters. As demodulated at the paging receiver the signal is a >> 1200 baud pattern of square waves. >> >> Newer systems such as FLEX may have two levels of + and - with >> settings of say +4K +2K -2K and -4K. >> >> If the problem is the digital paging transmitter you need to determine >> how close the transmitter is to your installation. Paging receivers >> represent a compromised antenna system and most paging transmitters >> compensate for the shortcomings of the receiver by sending at very >> high power levels. If the paging transmitter is close to you, it >> might be meeting spec but the low level grundge could be causing you >> problems. >> >> Milt >> N3LTQ >> >> Quoting Tim Sawyer <[email protected]>: >> >> > I'm looking at the pager freq with the SA. The dev looks wide to me. >> > I see about 15 Khz peak to peak. Is that normal? >> > >> > Also I see much bigger spikes. >> > >> > -- >> > Tim >> > :wq >> > >> > On Aug 21, 2010, at 6:59 AM, MCH wrote: >> > >> >> Again, just like a spur. >> >> >> >> Does it have a 'grungy' sound to it when you hear it on your input? >> >> >> >> Might also be worth putting the Spectrum Analyzer on your input to see >> >> if you can see it drifting through the frequency - or drifting onto it. >> >> >> >> Joe M. >> >> >> >> Tim Sawyer wrote: >> >> > Another tidbit about this problem is that it's clean in the >> >> mornings. The paging transmitter can be going off like crazy and >> >> the repeater will be totally clean in carrier squelch. As the day >> >> progresses it gets worse. >> >> > -- >> >> > Tim >> >> > :wq >> >> > >> >> > On Aug 20, 2010, at 7:51 PM, Chuck Kelsey wrote: >> >> > >> >> >> I agree, if you don't hear anything else in the mix, and it >> pretty much >> >> >> happens for the full length of the page, it's likely a spur >> on the paging >> >> >> transmitter, at least that's what I'd be looking at. >> >> >> >> >> >> Chuck >> >> >> WB2EDV >> >> >> >> >> >> >> >> >> >> >> >> ----- Original Message ----- >> >> >> From: "MCH" <[email protected]> >> >> >> To: <[email protected]> >> >> >> Sent: Friday, August 20, 2010 10:46 PM >> >> >> Subject: Re: [Repeater-Builder] Re: Intermod Calculation >> >> >> >> >> >> >> >> >>> Could be a spur. Can you hear any other audio with the page? (ever) >> >> >>> >> >> >>> Joe M. >> >> >>> >> >> >>> Tim Sawyer wrote: >> >> >>>> >> >> >>>> It seems to pick up most of the page. Occasionally the beginning is >> >> >>>> missing or it will get just the very end. It always seems to >> >> drop at the >> >> >>>> same time as the page. >> >> >>>> >> >> >>>> -- >> >> >>>> Tim >> >> >>>> :wq >> >> >>>> >> >> >>>> On Aug 20, 2010, at 4:38 PM, Chuck Kelsey wrote: >> >> >>>> >> >> >>>>> >> >> >>>>> Does the entire page happen, or does it abruptly stop part >> way through >> >> >>>>> some >> >> >>>>> of the time? Partial page would indicate to me that another >> >> >>>>> transmitter is >> >> >>>>> in the mix and dropping before the pager does. >> >> >>>>> >> >> >>>>> However, I had a situation where there were four paging sites >> >> >>>>> scattered in >> >> >>>>> the county on the same frequency and one of the transmitters was >> >> >>>>> spurious >> >> >>>>> and getting into my receiver. In that case, I always heard >> the entire >> >> >>>>> page, >> >> >>>>> but only when that particular transmitter came up. >> >> >>>>> >> >> >>>>> Chuck >> >> >>>>> WB2EDV >> >> >>>>> >> >> >>>>> ----- Original Message ----- >> >> >>>>> From: "Tim - WD6AWP" <[email protected] >> >> <mailto:tisawyer%40gmail.com>> >> >> >>>>> To: <[email protected] >> >> >>>>> <mailto:Repeater-Builder%40yahoogroups.com>> >> >> >>>>> Sent: Friday, August 20, 2010 7:27 PM >> >> >>>>> Subject: [Repeater-Builder] Re: Intermod Calculation >> >> >>>>> >> >> >>>>>> It occurs whether or not the repeater transmitter is keyed. >> >> >>>>>> >> >> >>>>>> --- In [email protected] >> >> >>>>> <mailto:Repeater-Builder%40yahoogroups.com>, "Jeff DePolo" >> <j...@...> >> >> >>>>> wrote: >> >> >>>>>>> >> >> >>>>>>> Before we get into the math, an important question that >> needs to be >> >> >>>>>>> answered >> >> >>>>>>> is whether or not this mix occurs when your repeater >> transmitter is >> >> >>>>>>> unkeyed. >> >> >>>>>>> >> >> >>>>>>> >> >> >>>>>>> --- Jeff WN3A >> >> >>>>>>> >> >> >>>>>>>> -----Original Message----- >> >> >>>>>>>> From: [email protected] >> >> >>>>> <mailto:Repeater-Builder%40yahoogroups.com> >> >> >>>>>>>> [mailto:[email protected] >> >> >>>>> <mailto:Repeater-Builder%40yahoogroups.com>] On Behalf Of >> Tim Sawyer >> >> >>>>>>>> Sent: Friday, August 20, 2010 6:36 PM >> >> >>>>>>>> To: [email protected] >> >> >>>>> <mailto:Repeater-Builder%40yahoogroups.com> >> >> >>>>>>>> Subject: [Repeater-Builder] Intermod Calculation >> >> >>>>>>>> >> >> >>>>>>>> >> >> >>>>>>>> >> >> >>>>>>>> I have paging intermod from 157.740 Mhz. My receiver is on >> >> >>>>>>>> 144.540 Mhz. I'm 100% sure there is another transmitter >> >> >>>>>>>> involved in the mix because sometimes the pager is >> >> >>>>>>>> transmitting and I have no interference. >> >> >>>>>>>> >> >> >>>>>>>> I have an intermod calculator program but it wants all the >> >> >>>>>>>> known transmitters and the target receiver. But I need to >> >> >>>>>>>> solve for an unknown transmitter. Is there a way to calculate >> >> >>>>>>>> the other possible soruce(s)? >> >> >>>>>>>> -- >> >> >>>>>>>> Tim >> >> >>>>>>>> :wq >> >> >>>>>>>> >> >> >>>>>>>> >> >> >>>>>>>> >> >> >>>>>>>> >> >> >>>>>>>> >> >> >>>>>> >> >> >>>>>> >> >> >>>>>> >> >> >>>>>> ------------------------------------ >> >> >>>>>> >> >> >>>>>> >> >> >>>>>> >> >> >>>>>> Yahoo! Groups Links >> >> >>>>>> >> >> >>>>>> >> >> >>>>>> >> >> >>>>> ---------------------------------------------------------- >> >> >>>>> >> >> >>>>> No virus found in this incoming message. >> >> >>>>> Checked by AVG - www.avg.com <http://www.avg.com> >> >> >>>>> Version: 9.0.851 / Virus Database: 271.1.1/3084 - Release >> >> Date: 08/20/10 >> >> >>>>> 14:35:00 >> >> >>>>> >> >> >>>> >> >> >>>> >> >> >>>> >> >> >>> >> >> >>> ------------------------------------ >> >> >>> >> >> >>> >> >> >>> >> >> >>> Yahoo! Groups Links >> >> >>> >> >> >>> >> >> >>> >> >> >> >> >> >> ---------------------------------------------------------- >> >> >> >> >> >> >> >> >> >> >> >> No virus found in this incoming message. >> >> >> Checked by AVG - www.avg.com >> >> >> Version: 9.0.851 / Virus Database: 271.1.1/3084 - Release >> Date: 08/20/10 >> >> >> 14:35:00 >> >> >> >> >> >> >> >> >> >> >> >> ------------------------------------ >> >> >> >> >> >> >> >> >> >> >> >> Yahoo! Groups Links >> >> >> >> >> >> >> >> >> >> >> > >> >> > >> >> > >> >> > ------------------------------------ >> >> > >> >> > >> >> > >> >> > Yahoo! Groups Links >> >> > >> >> > >> >> > >> >> > >> >> > ---------------------------------------------------------- >> >> > >> >> > >> >> > Internal Virus Database is out of date. >> >> > Checked by AVG - www.avg.com >> >> > Version: 9.0.783 / Virus Database: 271.1.1/2746 - Release Date: >> >> 03/14/10 03:33:00 >> >> > >> >> >> > >> > >> >> > >
