This is interesting. Today while using my Locus receivers I approached one of them I had left out running for a while to see how it was doing, as I was about to end the particular session. On my belt I had one of my Motorola Radius SP10 radios, it is a VHF "green" dot frequency, and it was on. Not transmitting, not receiving, just on.
As I approached the Locus, I noticed I was logging 6 green and 1 red. As I got to within about 10' south of it, the satellite indicator went to solid red. Hmmm. So I look at the quick reference card, nothing listed for this phenomenon. So I turned the receiver off and went about moving elsewhere.
As the employee and I discussed what happened, he brought up the fact that I had my radio with me. Next session, receiver worked fine. That is until I turned on my radio within 10 feet of it. Satellite indicator solid red again. Turn the radio off, and everything back to normal.
Further investigation shows my DIP switches in the radio to be set at (from top) RT, RT, LT, RT which the radio repair/supply place tells me is frequency 151.835.....this anamoly is similar to what JD, myself and perhaps a few others have seen happen with the satellite indicator.
Any takes on this?

Dave,

I suspect this phenomenon may be traceable to the "shielding" in your hand-held radio.

Back in the early dayz of GPS, I was always advised not to transmitt with hand-held radio's in close proximity to the GPS receiver. It could possibly cause interference with the reception of the GPS signal.

How did your data process ?
If your Locus Data processed OK, then I wouldn't worry about it.

If the Data from this session (Hand-Held
Radio interference) caused some problems, we can further investigate.

Bob LeMoine
Ashtech Precision Products

Bob,

Thanks for the reply. All the data, including the sessions where it appeared we had some interference processed just fine.
We are currently chugging along with a low PDOP yet only about 6 SV's in view most of the daylight hours here in central MS right now; things are a quite a bit slower than when we have 8, but still very good production.
The control ties are excellent, and I'm not upside down money wise in an outdated RTK system. When you consider they use the same SV's, thats a win-win in my book!

Dave,

You did say in your original post that you were NOT transmitting on the radio, right? This whole interference thing is still a big mystery to me. We hear that it's impossible to disrupt incoming gps signals from a whole bunch of folks, then hear that maybe it is possible from another team. I, for one, would really like to know if your two-way, just being on and not transmitting could disrupt gps signals as you seem to have actually demonstrated.

J.D. Billings

This is driving me up the wall. Back when I was flying helicoptors('92-95)for the Army we were given a list of 4-6 UHF/VHF frequencies that can, and have wreaked havoc with incoming GPS signals. Remember we got the good signals and we were warned about it. Imagin what it's doing with the civilian frequencies. Now if I can only find that blasted paper.

JD,

The motorola radio was clipped to my back pocket, I approached the receiver from the South when it happened. Not only this receiver but another as well. The radio was just "on", so even though I was not transmitting, I imagine it was receiving.
The particular setting of the DIP switches in the radio were a matter of coincidence, since a while back we had changed them to get rid of the "unknown survey crew" in our vicinity that had the I man saying "back up....12.67549883 feet" (!) you gotta love guys like that!
For what it is worth, this particular switch setting causes a static/squelch noise when near the Topcon 602 as it is working with a TDS data collector. We'll probably change the switch settings, but will be very far away from the GPS receiver when we use them; normally I stay at least about 75.35921' away.

Also, we have to live with the fact that the FCC requires us to be susceptible to interference, now if we can just narrow down the sources!
Modified By Dave Huff on 3/19/2001 at 9:53 PM

Every time that I stand at my set4E, I hear interference. I just turn my radio down. It is a Motorola also. I think it is the SP10 model. I don't know if the interference that you are reciving on your radio is related or not. The interference doesn't affect my gun, but I can see where it would affect your GPS. I have another set of radios that we use as a backup set. It is a couple of the small Talkabout Radios. Never had a problem with these. maybe something you could try.
Doug Kwater

I'm definately no radio expert, nor did I play one on TV, but back in the 70's, like most folks around here, got into the cb radio thing. As in every other endeavor of mine, I totally immersed myself in all aspects of cb radio technology. To the point I found an old ham radio handbook dedicated to nothing but antenna design and construction. I then changed to formulae to fit the cb radio frequencies and constructed a couple of setS of 3 bay horizontal directional antennas from bamboo poles and aluminum wire. This led me to understand, in a very basic "redneck" way, resonance. Case in point - the old "haunted house". We had one in the woods about a half mile from my growing up spot. On a cool clear autumn night, if your were really quiet, you could hear strange musical sounds eminating from the walls. Scared the girls silly. One night I was especially quiet and made out the sounds of the Beatles playing "Hard Days Night". Seems like the old wires stretched in the walls between the ceremic insulators were tuned to the exact wave length of the local radio station. I didn't understand that at age 12, but did after the cb radio thing. Also lots of strange stories circulated about old "so and so's cb chattering" coming outa the neighbors regrigerator, etc. Sounds like resonance to me.
To make a long story even longer, I still have to wonder if something in our Locus units, maybe not the micro strip antenna but some other component, could be subject to occassional resonance type interference.

Just musing

J.D.

Dave,

I'm leaning towards Bob's suggestion that the problem is caused by lack of shielding in the radio. Your reported frequency of 151.835 Mhz may be a clue. The GPS L1 frequency is 1575.72 Mhz. I don't know a great deal about RF interference but I do know that when we design a receiver, especially one to used with an internal UHF radio, we need to be very careful to shield any RF source that is a multiple of the GPS frequency. Your 151.835 is close to a 0.1 multiple of 1575.72. Even though you were not transmitting, the radio could be emitting RF noise at the 151.835 frequency causing the interference with the receiver.

Bill Martin
Ashtech Precision Products

Good answer, Bill. A radio doesn't need to be transmitting to cause interference with other elecronic gadgets. All electronics emit RF, often throughout a wide spectrum. Computers are a great example. We try to shield GPS receivers adequately, but cannot anticipate all possible RF emitters. J.D., I've even had RF engineers tell me it's half engineering and half witchcraft. :-}