Batboard

Getting our ducks in a row and looking into the possibilty of going to a RTK setup for planting/spraying/tillage for farming. Basiclly you have a base station that knows where it is (stays on a fixed point, our repeater tower ) and it sends error correction signals to the field units. The tractors have 40 watt UHF radios transmitting on 456.***, the radio reciver for the gps will probaly be in the 460s or 470s (hasn't been licensed yet so I'm not sure). Will the two way radios in the tractors interfere with the radios that recieve the error correction signal? The antennas would both be mounted on the same cab roof, we could maybe put them up to 3 feet away at most, but they will all have the same ground if that matters. The other option is Trimble offers a 900mhz RTK base, but we really wanted to go with the 400mhz one. The main reason being we wanted to use the same UHF antenna our repeater uses on the tower without having to climb the damn thing and hang another antenna as well as buy all that coax that is bigger around than my thumb.
Do they make some type of filter that would block out a specific signal (say 456) and not let it into the GPS radio? One of the Field units I was looking at that goes in the tractor has the radio integrated into the computer that translates the error signal, if you fry that thing your out about twelve grand. That would be bad. So if you guys could let me know if we might have a problem having them both in the same band I would appreciate it.

Also, how would you keep the 35 watts from the RTK base radio from getting to the receiver in our repeater, could we add another duplexor that would keep that signal out? And that would keep the MiCORS high power out of the RTK radio as well. The RTK base only transmits, it doesn't recieve. Another thing about the gps transmitter they are over two grand used, I know they are continuous duty, but cmon, all it does is transmit a data packet, and not that often. Seems way over priced.

Let me know what you all think, no big hurry, won't put all the pieces together until next spring. But we should probably get started on the licensing, I have no Idea how long that takes.
Tyler

The potential exists for interference, but only when the mobile in the tractor is transmitting. How much talking do you do? We use radios on our farm, but there's not a lot of talking going on unless there is a breakdown or somebody needs something.

As far as keeping the RTK transmitter from interferring with your repeater, I would suggest vertical isolation. If you put your RTK antenna 50' or so directly below the receive antenna of your repeater then there shouldn't be a problem. If there is, you can always put notch filters on the transmitter of the RTK & the receiver of the repeater. You can always do the shotgun approach and spend a bunch of money on isolation equipment, or just try a few things first to see if you can make what you have work.

We are using stand-alone GPS receivers for our spray application guidance. Set the swath distance, make one pass for the unit to "find" itself and then go from there. Pretty accurate with very effective application of herbicides. The units are significantly cheaper than what you are talking about and require no additional infrustructure. What is your expected amortization to where what sounds like a very expensive system will start paying for itself?