Radio corrections, and possible multi-path.

Jon Gramm

Member
Just out of curiosity, has anyone experienced radio issues near bodies of water?

I was surveying the other day. The base was on one side of a reservoir, I was on the other.
I was a little over one mile from the base. Base was transmitting at 35 watts. About one mile of water between us. Line of sight to the base.
When I got closer to the water, I would lose radio corrections. This was with both the internal, and external antenna.
When I went higher in elevation, or when a building would block my view of the water, I would receive corrections without issue.
It was a shallow angle from the base to the water, to the rover.
The only thing I could think of was multi-path, not much else happening in that area that could cause the loss of corrections.
 

Adam

Well-Known Member
5PLS
I don't know the answer. I wonder if the water acts a huge ground plane shooting the signals up. I have never worked around any bodies of water more than several hundred feet or so across.
 

Sean Joyce

Well-Known Member
I don't know the answer. I wonder if the water acts a huge ground plane shooting the signals up. I have never worked around any bodies of water more than several hundred feet or so across.

I am guessing that the water acts like a ground plane as Adam suggests and you just happen to be in a skip zone.
skipzone.JPG
 

Jon Gramm

Member
Thank you for your replies, and thoughts about this issue.
I have possibly seen this before with other equipment while working on a seismic gun boat, but I cannot say for certain.
Circumstances were very similar, shallow angle between the base, surface of the water, and the rover, radio transmitting at 35 watts.
 

Jon Gramm

Member
Thanks for the suggestion Matt!

I will remember that the next time.

I was too busy using profanities, and other magic words to do so at the time.
 

Matt Johnson

Well-Known Member
5PLS
Also I will mention that the link quality value displayed in the green box of the action screen has been broken for a long time but has recently been fixed in the version of J-Field that will be released with Linux. Currently it incorrectly always displays 100%.
 

Nate The Surveyor

Well-Known Member
Ideas:
I got into a spot, with no radio. Move 40', and it's got full strength. I believe it was a cell tower signal, sympathetic crossover.
Try 1/2 wave andenna.
Try removing the ground plane.
Try leaning the base tx pole.
Try a taller tx pole. I run around 16 to 20 foot base transmit mast. Elevate the transmit antenna. It's the number one "cure".

Nate
 

Matt Johnson

Well-Known Member
5PLS
The ground plane should not be removed with the 5 dB antenna. Removing it causes a big antenna impedance mismatch that reduces the radio range and overheats the radio because of returned power.
 

Jon Gramm

Member
Thanks Matt, and Nate!

Nate,
All of those things work, but this was a very strange thing.
No cell phone service in the area where this happened. A little over one mile away from the base, line of sight, I could see the base with my naked eye(s).
No ground plane on the antenna, do not use one. I had the antenna up about 12 feet using a Hixon 25' pole supported by a tripod. I didn't feel I needed any real elevation for the antenna given the distance to the base, line of sight, and transmitting at 35 watts. (Maybe a bit of overkill with the wattage, and that could possibly be part of the problem.)

Have worked in and around that area a lot lately without these issues, then only real difference is the amount of water between the base and the rover.

I am just going to chalk it up to the plate in my head creating the interference until I can determine the real cause.
 
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