UPDATE – 11/13/2018
KT7WW sent me the following message today:
Looks like we have a quiet vhf satellite band again thanks to some repairs today. I would appreciate having some people monitor that frequency range for a bit for verification
Thanks to everyone who put in time to help locate the source
Radio Direction Finding Assistance Needed
Stephen Nipper (N7DJX) and Amos Kirk (KT7WW) have identified a signal radiating from the downtown Boise area around 145.72 MHz. This signal is interfering with satellite operators in the area.
They need as much help as possible trying to pinpoint the exact source of this noise to work with the owner and possibly the FCC to resolve this issue and remove this source of interference.
The following information has been compiled from various sources including the Idaho Ham Radio Operators facebook page and email from the affected parties.
Issue Description from KT7WW
Over the last several months, there has been a strong but intermittent signal radiating from the direction of downtown Boise in the range of 145.660 to 145.760. KT7WW, N7DJX and others have been working to compile an understanding of the characteristics and source of the signal in order to eliminate it and the interference caused by the signal in the satellite portion of the 2 meter amateur radio band. The signal can has been observed at all hours of the day, and all days of the week, but has not yet been observed to have a consistent time interval that it is transmitted. Below are some recent observations.
Best results have been with an SDR where the signal can be observed as it changes frequency. An attenuator has also been very useful in areas where the signal strength is high to get a more accurate reading on direction. 2 or more radios tuned across the range of the transmitted signal have also been useful for a reference point.
On 11/5/2018 with a 3 element beam and an SDR receiver, KT7WW and N7DJX were able to get an approximate heading of 310 degrees from the Armory on Reserve Street. KT7WW and N7DJX also observed in the downtown Boise area several places that the signal required over 30 dB of attenuation before it would stop breaking the squelch on a handheld radio.
Other recent observations of signal strength from different locations around Boise indicate also that the downtown area appears to be the most likely location of the source.
On 11/6/Tom WA9WSJ observed that on his vertical, the signal strength was full scale from his home in Garden City. Tom’s best estimate of a heading from his location was 97 degrees, and it took 26 dB of attenuation to bring his S meter down to an S2 level.
On the evening of 11/7/2018 Rob KW2E observed the signal on his SDR near St. Luke’s Hospital using a small vertical antenna. Rob was able to observe on his SDR a carrier starting around 145.660 and drifting up in frequency slightly that was sustained for about 20 seconds. Then, the carrier would pause, then skip up to a higher frequency, and then sweep back to the lower frequency over 5 seconds. The sweep from low to high happened twice, and then he observed that the pattern started again as described above from the beginning.
How you can help
If you have direction finding gear, please try to find the heading of the strongest signal from your location. You will probably need to attenuate the signal to get a good heading. Document everything the best you can. KT7WW is consolidating all provided information from all operators on a map to try to locate the source.
Due to urgency of this issue they would like to reduce the amount of time spent following up on wild goose chases. Please collect information as accurately as possible.
Please include date and time, GPS coordinates, the heading of the strongest signal you measured, and the frequency or frequencies of the signal.
This information can be submitted directly to Amos and Stephen at the following email addresses
KT7WW – email@example.com
N7DJX – firstname.lastname@example.org
Why this needs to be cleared (from W4IMT)
There is some urgency associated with clearing this problem because in about 10+ days there will be a launch of Fox-1C, the fourth in the very successful AMSAT series of cubesats. Because N7DJX is the westernmost location of continental US ground stations, satellite control operators depend upon us for particularly vital vital satellite data during the early stages of operation over the Pacific Ocean region.
The OSCAR sub bands as listed in ARRL band plans are dedicated to satellite use only. Please limit use of these frequency allocations to satellite operation only. If you are operating a digital hotspot, or sending any other transmission in these frequency ranges, you may be causing interference to satellite communication without knowing it.
The allocations are
|2 meter||144.300 MHz -144.500 MHz (except APRS on 144.390 MHz)|
|2 meter||145.800 MHz – 146.000 MHz|
|70 centimeter||435.000 MHz – 438.000 MHz|