eHam Forums => FoxHunting => Topic started by: WY3X on October 12, 2011, 02:28:19 PM

Title: How to locate...
Post by: WY3X on October 12, 2011, 02:28:19 PM
There is a nearby paging transmitter that is obliterating a local repeater on 145.350. It's seems centered on and is much stronger on 145.340.970. It's obviously malfunctioning. What frequency would you begin searching to see if you can discover the "actual" frequency of the paging transmitter? Is there a "table" of interfering frequencies that can be referred to?

Thanks, -WY3X

Title: RE: How to locate...
Post by: WB6BYU on October 12, 2011, 07:30:37 PM
The best solution might be to use a spectrum analyzer and look for the other spike that pops up at the
same time as the interfering one does.  The spectrum analyzer gives you the ability to monitor a wide
band of frequencies at one time.

Unfortunately there is no guarantee that there is any predictable relationship between the interfering
transmitter and your repeater frequency.  But sometimes you can work it out:  often transmitters
multiply by some convenient number like 6, 8, 12, 15, 16, 18 or 24 to reach their final frequency.
For example, a transmitter on 158.56 MHz that uses a multiple of 12 would have a fundamental at
158 / 12 = 13.213 MHz.  The 11th harmonic of this frequency comes out on 11 * 13.213 = 145.34.
Since most paging transmitters near the 2m band are in the 150 MHz range, try multiplying your
repeater frequency by 6/5, 8/7, 12/11, 15/14, 16/15, or 24/23 and see if there is anything close
to those frequencies.  You might also be hearing a sub-harmonic from a pager in the 450 band.

Otherwise, track down the signal and look up the site owner of wherever  you end up and explain
the situation.

Title: RE: How to locate...
Post by: KT4NR on December 05, 2011, 12:38:33 PM
Well we had a similar issue a couple years back. We triangulated the source of the noise and then had someone look up various pager transmitter licensees in the general area. Then it was a matter of getting near each site and listening and seeing what happened. Managed to narrow it to a hospital and when they were told what happened (it was jamming repeaters for at least 3 counties!) they quickly called to get it fixed. (Something about notifying the FCC of a problem may have helped too. :) )