VHF Transmission Distance

[FreeBeeTony]

How far can a VHF radio transmit?

I was ~ 20mi offshore last w/e.
I asked for a radio check on Ch 16 to see if I could reach the Coast Guard.......no replay.
I could hear them.............didn't seem like they could hear me.

I was communicating with other boats in the area so I know the radio was working.

 

[xtraham]

Re: VHF Transmission Distance

line of sight, depends on hight of antenna

 

[jurgenscraft]

Re: VHF Transmission Distance

Good evening, What antenna were you using, and how high on the boat is the antenna mounted I use a Icom radio and a Shakespeare 5525 Galaxy antenna mounted on the highest part of the boat and I get constant coms between ship and shore, Being 20 nautical miles + I always run my radios at their highest power setting, ie. 25 watts I see no purpose or reason to use the low power settings, Use a antenna with the maximum gain available , 6 db means 4 times your tx power as well as better reception compared with small no gain antennas.Regards William Wright

 

[FreeBeeTony]

Re: VHF Transmission Distance

I will have to check which ant I have.

It is installed on the radar arch.

 

[xtraham]

Re: VHF Transmission Distance

you my want to check swr with an inline swr meter to make sure standing wave ratio is okay, if not you will not be able to transmit very far and it will also damage the radio if the swr is high

 

[Boatist]

Re: VHF Transmission Distance

Just for your information the Coast Guard will never answer a radio check on Channel 16. It is actually against the rules and you can be cited for it.

On channel 22A they will sometimes answer but on a busy weekend not very likely.

In general a boat with a 8 foot antenna mounted 2 feet above the water will transmit about 5 miles. Talking with another boat with the same set up then boat to boat is about 10 miles.

For boats under 30 feet a 8 foot 6DB gain antenna is best choice. Mounting it on a higher pole will gain some distance but not as much as most think.

Talking to the Coast Guard distance really depends on how high the Coast Guard antenna is. In my area I have talked to the Coast Guard many times from over 80 miles away. The Coast Guard antenna in about 3000 feet high so with line of site that is a long way.

Another Coast Guard site I talk to from the ocean has a antenna on a 1000 foot high bluff on the Coast and up 200 feet on a tower, so it is 1200 feet high.

One thing I see a lot of boats do is to slant the antenna back at an angel. Since the 8 foot 6 db gain antennas transmit in a narrow horizontal band so foward it transmiting into space and to the stearn it transmiting into the sea. Both ways will greatly affect your distance. directly abeam of the boat would probably be normal.

I good antenna like Shakespeare's 5225 will receive and transmit better than the cheap flexable antennas. They have a brass or copper or silver radiator not a peice of tuned coax.

Comming into a Harbor, Fuel dock or Bait Dock use 1 watt of power it is more than you need to find a guest dock, get fuel or bait. This way other boats several miles away can still use the channel as well. They will not affect your comm and you will not affect theirs.

 

[Texasmark]

Re: VHF Transmission Distance

Well said Boatist.

Add to the slanted attitude of the antenna, the boat's attitude in the water, and they are really shooting the stars forward. Would think that they would slant it forward, if they were going to slant it at all.

We used to run VHF nav and com in aircraft and a couple hundred miles was not a problem; but at 30,000 ft, the horizon is a long ways off; especially if your receiver is also at 30,000, d

Nice comment about courtesy.

Mark

 

[xtraham]

Re: VHF Transmission Distance

a slanted antenna will only decrease operating range, transceiver antenna's must be mounted vertical when transmitting to other vertical mounted stations, and make sure to check the swr should be no more than 2 to 1 preferably 1.5 or less

 

[Texasmark]

Re: VHF Transmission Distance

Hey again xtra. Are your CB antenna's on your 18 wheeler tilted forward? d

Mark

 

[xtraham]

Re: VHF Transmission Distance

Hey again xtra. Are your CB antenna's on your 18 wheeler tilted forward? ">

Mark

18 wheeler ?

 

[Gone]

Re: VHF Transmission Distance

you my want to check swr with an inline swr meter to make sure standing wave ratio is okay, if not you will not be able to transmit very far and it will also damage the radio if the swr is high

The FCC truely frowns on (has laws against) people without a 1st or 2nd class FCC license installing/repairing/MAINTAINING marine/aircraft 2-way radios. It isn't a CB.
If you have a marine radio problem, go to the 2-way shop. Don't try to fix it yourself.

CD

 

[xtraham]

Re: VHF Transmission Distance

very crusty I did not sugest he repair his radio, simply check swr, it is not illegal in any way to place a meter in line to check the antenna and if defective replace it...in fact it is a requirement on a uscg inspected certified vessel to maintain a inline meter

Tom,

N3RIB Extra class amateur radio operator
look up my call on grz.com

 

[Texasmark]

Re: VHF Transmission Distance

I had a first class phone with radar endorsement when I was active in the business.

I never ran VHF on a boat, but since the antenna is 1/4 wave and the water is the other half, you'd think that tilting the antenna to compensate for the boat's usually nose high attitude would make the antenna perpindicular to the water and make for the best reception.


xtra.....18 wheeler refers to an over the roat truck having 18 wheels. Beins you are from Maryland I'm sure you have seen them with their antenna's all different directions.

The reason for tilting them forward, is that at highway speeds the wind blows them backwards so if you tilt them forward, when you do most of your yakin they will be vertical.

Mark

 

[xtraham]

Re: VHF Transmission Distance

hey tex, I thought, you thought I drove, I did for a couple years when I was younger, and yes I know why drivers tilt them foward , I was just trying to convey that vertical is the best over all way to install a mobile antenna and just fyi 18" would be 1/4 wave on vhf band and most cheap antennas are a diapole with a 50 ohm resister inline to insure a macth to the transmitter and the db gain is a selling factor, just a bit of info hope i am not taken to be sarcastic, not trying to be any way, but if you need any info on electronics i am here, and will help in any way i can...

ps when, god forbid you do happen to really need a vhf radio the bow of the boat prob. wont be up

Tom

 

[Gone]

Re: VHF Transmission Distance

Xtraham, I wasn't trying to make waves, here. I see too many cb'ers that tune, tweak,and modify antennas and radios that I just wanted to set the record straight.

CD

 

[xtraham]

Re: VHF Transmission Distance

no waves here, it's slick cam, most VHF radios are not used for thier intened purpose anyway, most around here use them as a fish finder.......