Distance between VHF radio and antenna?

[Roamad]

I’ve read in various places that your VHF antenna should be mounted at least 6 ft. from the radio itself. On my C-Dory the radio is mounted next to the helm and the antenna is right outside the window, only about 12” from the radio. I’m asking because the antenna is damaged and I’ll soon be installing a new one. So, does the 6 ft. matter, and why does that seem to be the general advice?

[gulfcoast john]

We’ve run 13 trailer boats over the past 40 years we’ve been boating together and never once had an interference or other issue regarding a VHF radio vs antenna position.

Granted, I would not complete a permanent install of the antenna until an ops check. I found at least one net reference that advises the VHF radio should be AT LEAST 30 FEET from the antenna. Perhaps Marconi said that.

My Garmin VHF 200 manual has NO advice on any distance limit.

I took out all my handheld VHF radios and measured the distance between the radio and it’s rubber antenna and guess what I found?

I believe the ‘advice’ we’re seeing regards radios and antennas of several generations ago when both were not as well designed and more ‘leaky’ than current models.

That said, what I’ve come to believe:

DO NOT mount a GPS sensor in the radar beam. It will get fried.

DO NOT mount a magnetron (non-digital) radar so you or yours are in the beam, it can damage the eyes etc.

Standard advice is to mount any VHF antenna over 48 inches from the radar beam. I and you can’t do that, no problems to date, but mount the VHF antenna as far from the radar beam as you practically can and do an ops check before making it permanent.

VHF antenna transmissions are harmless to humans. Don’t worry about how close a modern VHF is to its antenna, but it does make sense to do an ops check first.

I'll defer to Bob re any specifics.

Hope this is helpful.

Happy Mounting!

John

[Roamad]

Thanks John, very helpful!

[hardee]

Ahemmm, John, You are right about the 30 feet thing. I tried to do that but I ran out of boat. My banker said I didn't need to buy a bigger boat, so I just used my 22 Cruiser, and You are right. It Works. and the banker didn't fire me. (Maybe Marconi meant 30 feet UP

Actually, there are some guidelines about how close you can install one VHF antenna to another VHF antenna. Hummm, I ran out of boat going those directions too. (Too many radios, not enough roof acreage I guess

Seriously, I have not heard about any particular distance radio to antenna. BUT you do not want to cut the Coax cord too short. I think it has a specific minimum length which I believe is 6 feet.

As you can see, I have 3 VHF's all side by side, and 3 VHF antennas on the top, plus there is an AIS active transceiver running full time as well. (The AIS shares one VHF antenna with one of the VHFs.) Yup, some folks think it is too many radio's, I just think the roof is too small, but the boat is just the right size.



What makes some difference is where the antenna is mounted. Height is you friend there, so as high as you can get it is good. The higher the better, so for me, that means mount on the top. The side mounts are too low and they will get in your way when you are on the walk-around.



If I had a radar arch they would be up there. Still hard to get 4 feet between, (which is HIGHLY recommended), but so far, after a dozen years, no issues.

Harvey
SleepyC

[colbysmith]

Right from the operating manual of my newest radio, the Standard Horizon GX-1600.

Antenna Installation:
The antenna must be located at least 3 feet (1 m) away from passengers in order to comply with the FCC RF exposure requirements.
6.2 LOCATION
The radio can be mounted at any angle. Choose a mounting location that:
• is far enough from any compass to avoid any deviation in compass
reading due to the speaker magnet
• provides accessibility to the front panel controls
• allows connection to a power source and an antenna
• has nearby space for installation of a microphone hanger
• is at least 3 feet (1 m) away from the radio’s antenna.
• the signal from the GPS satellite can receive sufficiently (GX1700).
Note: To insure the radio does not affect the compass or radios performance
is not affected by the antenna location, temporarily connect the radio in the desired location and:
a. Examine the compass to see if the radio causes any deviation
b. Connect the antenna and key the radio. Check to ensure the radio is
operating correctly by requesting a radio check

I've got two radios, thus two antenna's. I believe I've read somewhere there should be 6' between them. I probably only have 4', and a radome in between them. I haven't experienced any problems. Colby

[Hunkydory]

Our new Standard Horizon GX2400B had the same instructions as Colby’s. I’ve always disliked where the antenna was mounted just forward & outside the helm side window as it interfered with vision & forward video & photos, so with the new radio decided to move it to the cabin rear starboard side. It is now higher & should get better transmission & reception & out of the way when lowered for on the road & putting up & taking off the dingy from the cabin top.

Don’t think the close mount to me over the 19 years was any real health hazard, but sure like the present mount location better.

Jay

[Roamad]

Thanks for all the feedback. I think I will mount the new antenna on the roof somewhere.