Antenna extensions

[Rooster 27509]

Ok I got some good feed back on the antenna question and hope others were able to glean a little info for themselves.

I have the 12 inch extension to put the GPS antenna above the radar but would like to go higher. This would be in the hopes of not cooking the GPS antenna again. I know how stupid is this guy anyways. Will somethings I excel at ( damage to antennas ) others have the rating of fair to poor.

thanks again
Jim

[Dreamer]

I always wondered why folks put the GPS antenna up that high. Now I know. With the cover off my 4kw Raymarine Radar, I laid out the path of it's transmission from the rotating element. Mounting the GPS on the shortest, stubby mount, the Radar beam passes several inches above it. This seems to work well and I always have about 8 satellites hooked up. What were the circumstances of your GPS antenna failing?

[Papillon]

I assume that you are aware that by putting your GPS antenna higher in the air above your boat, the more unstable your reception will be in a rocking sea. I would put it as low as possable on the roof or even bring it down to the fore deck. I have had them installed inside on other cabin boats and have had great reception.

[Falco]

For what it's worth, I have mine mounted about 1" above the roof railing on a stndard 1" swivel attached to the rail. I positioned the antennea below the radar beam. You can determine where this is if you know the angle of output for your radome. Mine was 11% (as I recall) and my Dad and I calculated the distance behind the radome where the GPS antenna would be below the beam. Never had a problem with either unit/reception.

[Rooster 27509]

Reply to Roger on the Dreamer.

From what I can gather the GPS antenna degrades over time if the radar beam passes over it and that must be what was taking place. ??

The new GPS antenna is now placed where it can't get struck with radar beam.
Another stupid question from me but -- nothing takes place when the radar beam passes over the VHS antenna (right)?

Jim

[Papillon]

Jim,
Short of sterilization, I can't think of a thing.

[Falco]

Here's an article that will give you a headache re: (high intensity) radar and GPS antennae:
http://mg.gpsworld.com/gpsmg/article/articleDetail.jsp?id=320030&pageID=1.

Interesting to note that getting within 1000 feet of a military vessel can fry commercial GPS antenna. The effect on recreational units must be intense. The effects on other parts must be present as well. Yet another reason to give these ships a wide berth.

As to radar beams and VHF antennae, I have never had a problem with my set up in which this is the case. I believe both emit the same VHF radiation as well.

[thataway]

I feel that it would be highly unlikely that a civilian radar of the output which we use on C Dories, would be likely to degrade a GPS antenna.
The study cited above used power levels which are vastly higher than what we use, used longer pulse wave duration, and were concerned only with active antennas. Many civilian antennas are passive (basically a wire antenna). A VHF antenna is also just a wire--and the radar will not harm it. I have run many years with both VHF and SSB antennas (both marine and ham) as well as at least one radar whose beam was hitting a passive antenna, with no ill effect.

I have lost GPS signal on occasion where passing near a Navy base or operating navy ship--and figured that was due to the EMF from the ship.
It is certainly fairly easy to jam a GPS reciever, and enough EMF can ruin an active antenna.

I currently keep my GPS antennas near to the cabin house (about 3") and the bottom of the Radar about 10" off the cabin house. I am not concerned about damage to the antenna, or loss of GPS. Both VHF antennas, and both ham antennas will be partly in the beam of the radar, and I am not concerned about damage.