Scott, I have had only two instances, in a five-year period, of a strange "data-like" signal showing up on one of the repeaters I manage. One was on the input, and the other was on the output.
The rogue signal on the input turned out to be an APRS modem that was transmitting in beacon mode. The owner had inadvertently bumped the channel selector knob on his mobile radio, and it was merrily chatting away on my repeater instead of on the APRS simplex channel. One of the local APRS buffs decoded the signal, and we contacted the owner who quickly reset his radio. The rogue signal on the output turned out to be a malfunctioning SCADA (Supervisory Control and Data Automation) base station owned by a petroleum company. Their oil fields were spread out over many miles, and a SCADA radio at each wellhead and valve box was polled by a base station at regular intervals. The base station was a low-tier commercial mobile radio that had developed a spurious signal at a subharmonic of its licensed carrier frequency. Unfortunately, that subharmonic and spurious signal was right on my repeater's output. Once the FCC got into the act, the malfunctioning radio was identified and replaced. The sudden appearance of your interfering signal is significant. I listened to the sound file, but I can't identify it. It may take a Doppler direction finder to track down the source. I tend to agree with the other posters that the signal is probably not malicious. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Scott Overstreet Sent: Tuesday, December 12, 2006 11:10 AM To: [email protected] Cc: Scott Overstreet; Dave Platt Subject: [Repeater-Builder] Mystery Signal Hello All An interfering mystery signal has suddenly appeared on the input (144.670 MHz) of our repeater. Using a five kHz-wide FM detector---The signal is approximately one second in duration----opens with 100 Hz PL (which continues throughout) and then three DTMF "zeros" follow in rapid succession and then possibly a short period of some sort of data. The signal repeats exactly two times an hour and the source is off in between transmissions. This goes on continuously without interruption or apparent change. Our area is between urban and big city and the signal is strong enough to be heard over a wide area using only an HT. A wave file of the mystery signal is at: http://www.radagast.org/~dplatt/hamradio/Signal_3.wav <http://www.radagast.org/~dplatt/hamradio/Signal_3.wav> using an FM detector with wide open squelch. We are obviously very interested in identifing this signal and its origin---- What is it ? Thanks-- Scott, N6NXI
