Cell Tower Interference / SDR Trunk
- Thread starter davejl2001
- Start date
OK, to be more precise: Dave is the only one that can provide that frequency or band of frequencies causing the issue. The answer to his problem is not going to fall in his lap; it is up to him to do the detective work and tests to discover the source. I can't do it for him, can you?
Agreed, the OP needs to provide more info. Perhaps backing off on gain in steps might find a balance between a usable signal and distortion vs. the 700 band noise floor. Perhaps a directional antenna might help, or moving his current one. If it were me, I'd invest in a custom high-pass filter. Filters are not a bad thing as system operators use them to attenuate troublesome interference.
davejl2001
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- Jan 16, 2003
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There is the frequency range. The site is about 8 miles away.
| 769.19375 | 769.45625 | 769.66875 | 769.96875 | 770.44375 | 770.66875 | 770.91875 | |||
| 773.34375 | 773.79375c | 774.31875c | 774.54375c | 774.78125c |
The OP is avoiding IDing the actual system; I'm not sure why. Without the name / location of the system, it's more difficult to check the FCC licensing for the system for any applications to change its parameters wrt transmit sites, antenna orientation, power changes, etc.
New Jersey Interoperability Communications System (NJICS) Site: West Orange Simulcast
New Jersey Interoperability Communications System (NJICS) Site: West Orange Simulcast Details
www.radioreference.com
Too bad it's a state license as it makes it more difficult to map potential changes without local knowledge - perhaps there is some relevant RPC correspondence. We'll have to assume the issue is interference from a new LTE site fairly close by, but not hideously close - I had a cell site 500' away that I could see out the window of my office but didn't suffer any ill effects (except possibly drowning out distant systems). Experiment with new antenna placement, a directional antenna, and / or buy a high pass filter. Or get a better receiver.
We had an issue with a Verizon LTE site (talk-out side) interfering with portables in a small town, with a secondary source from Axon body cameras (talk-in side). This will ultimately be resolved with a new system site in the area where the interference is being experienced. The FCC is aware of Band 13/14 LTE interference nationwide, but lots of finger-pointing going on. The carriers say their infrastructure sites are in spec and the system manufacturers need to design better radios, ignoring that their customers are not always using the best quality cell phones (or body cameras). We do need better receivers in general however.
We had an issue with a Verizon LTE site (talk-out side) interfering with portables in a small town, with a secondary source from Axon body cameras (talk-in side). This will ultimately be resolved with a new system site in the area where the interference is being experienced. The FCC is aware of Band 13/14 LTE interference nationwide, but lots of finger-pointing going on. The carriers say their infrastructure sites are in spec and the system manufacturers need to design better radios, ignoring that their customers are not always using the best quality cell phones (or body cameras). We do need better receivers in general however.
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You might derive some small relief for your reception of a 769mhz control channel by creating a “dummy“ system higher in frequency to shift the frequency window up; this has sometimes helped me.
Put simply, as far as I know, when you put your airspy on sdrtrunk to decode a system, you aren’t able to specify the desired center frequency; sdrsharp dynamically assigns this. One hack is to calculate your bandwidth for your receiver and program in a non-existent control channel a bit higher up, thereby keeping nothing on the left side of your receiver window below the lowest frequency you actually want. For example, if the lowest frequency you need to decode is 769.5, then make sure the left side of the spectrum view barely allows that to be visible. That may keep some of the “wall of noise” that is the cell network at 768 and below outside of your receiver. Also, when faced with this problem, use the minimum gain that works consistently.
Put simply, as far as I know, when you put your airspy on sdrtrunk to decode a system, you aren’t able to specify the desired center frequency; sdrsharp dynamically assigns this. One hack is to calculate your bandwidth for your receiver and program in a non-existent control channel a bit higher up, thereby keeping nothing on the left side of your receiver window below the lowest frequency you actually want. For example, if the lowest frequency you need to decode is 769.5, then make sure the left side of the spectrum view barely allows that to be visible. That may keep some of the “wall of noise” that is the cell network at 768 and below outside of your receiver. Also, when faced with this problem, use the minimum gain that works consistently.
The latest SDR Trunk release (0.6.1 final) has this in the release notes:
- Tuner minimum and maximum frequency now user adjustable so you can lock a tuner to a specific frequency range
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