On Aug 21, 2010, at 6:38 PM, men...@pa.net wrote: > 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. > > We've been having many problems at the site (including a broken tower cross arm, now fixed) for a while now and lots of things have been changing. I'm aware that it could be our problem as likely as theirs. We've been up there for 30 years, don't know how long they have been there, certianly longer than this problem.
> What you have is a case of RF overload. No other frequencies are > involved, not even your own transmitter. > > I'm thinking spurious pager TX , not our RX overload at this point. But I'm going to go have a look at things. > 225 watts RF + how much antenna gain on the pager end or is that the > total ERP of the pager? > > That's power out of the transmitter. I think they are allowed 999 watts ERP but I don't know what theirs is. > What is the difference in vertical height between the pager transmit > antenna and your repeater antenna? > > Our antenna is a little higher and about 75 yards away. > What sort of filtering are you using? Duplexer? Dual antennas? > > Split TX/RX antennas about 40 feet apart with near straight vertical separation. Six cavity BP/BR duplexer plus two bottle Wacom filter on the RX. TX has a 3 pole circulator and low pass filter. > 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). > > Yea, ok. I'm not that familiar with what these paging systems look like on the SA. It looked odd to me. But the consensus here seems to be that dev is ok. I did see another paging system with this same looking modulation. > 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. > > They do have more than 1 transmitter. I can't tell for sure if I can hear more than one. It's possible. >
