Dual Transmitter hunting

Hello,
I am trying to find a way to track two simultaneous UHF pulses. approximately ever 2 seconds. Most of the time I know where one transmitter is and am trying to find a way to verify I have an unknown transmitter walking on my signal. Unfortunately all our transmitters are timed via gps so they transmit the same signal at the exact same time with almost the exact same data in the pulse. I have done some testing with two transmitters running at the same wattage approximately 500 foot away from each other and in spike I can not tell the difference between when one transmitter is running or two. Does anyone have any ideas what I am overlooking or the best way to go about verifying a second transmitter? Thanks.

[Justin Crooks]

Ethan,
This is a tricky problem. The first solution that springs to mind is that we are developing a phase coherent multi-channel system. This would be how this problem is generally solved (e.g. MUSIC algorithm, etc).
Short of that, if you had two systems, and arranged the antennas such that the signals arrived at different amplitude ratios or with different phase offsets, a little clever math could separate the signals.

• This reply was modified 1 year ago by Justin Crooks.

[Justin Crooks]

There are other methods as well. If you are able to lock and decode the stronger signal, you can sometimes digitally regenerate and “subtract” it then look at what’s left. But this might not work well if they are nearly identical signals.

• This reply was modified 1 year ago by Justin Crooks.

The problem with arranging the antennas is I don’t know where one of them is. The whole scenarios is a GPS based semi autonomous grade control. the base unit is in a fixed location transmitting data bursts at 2 second intervals to all the machine mounted receivers. the data burst is made up of timestamps and “correction data” The Base transmitter is also a GPS receiver and has to be in an exact spot without being moved with an integrated antenna. The issue I am having is, as GPS equipped machines become more common I run into jobsites with multiple contractors running individual base stations. The engineers set everything up and it is difficult to get information from a contractor I am not servicing. The location of the other transmitter is mostly unknown. In addition to this I have ran into issues previously with other contractors walking on my signal and massive interference from an electrical substation since the job was at a power plant.

Touching on the decoding bit of your suggestion, The signal may in fact be identical or very very close. The correction data is made up of a time stamp and some bits of information to allow for location correction due to ionospheric interference with the satellite signals (1.4, 1.8 and 1.1 GHz). The signal is similar enough that the receivers get confused and cant decide which transmitter to listen too.

I suppose if the problem is locating an interfering transmitter, a directional antenna and walking around your job site might do the trick. You can get a log periodic directional antenna for $70 or so from Digi Key. https://www.digikey.com/en/products/detail/te-connectivity-linx/ANT-DB1-LP-RM-01-N/2402472

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