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Old 06-10-2018, 14:03   #1
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What range should I expect from my VHF?

I have a 25W radio that has the whip antenna atop a 40ft mast. I had some issues with the connector when I first installed but recently pulled someone up to fix it. I am comparing it to my 5W handheld when making a test call and don’t know what to expect with the 25W radio. Is there a guideline or practical numbers I can follow to figure out if my radio is working fine?
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Old 06-10-2018, 14:35   #2
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Re: What range should I expect from my VHF?

In general, in the VHF band, the range is determined by the height of your antenna, not the power of the transmitter. Transmission is considered to be "line of sight". You need to consider the height of the receiving antenna. Google "radio horizon" and/or use an online calculator like this Radio Horizon calculator | converters and calculators

Assuming your 40' mast is atop a 5' deck, your antenna is 45' and if the receiving station is at sea level, your effective range is about 9.5 miles. If the receiving antenna is on a similar boat (i.e. 45'), then the range becomes 18 miles.
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Old 06-10-2018, 14:40   #3
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Re: What range should I expect from my VHF?

Power becomes important when range becomes large i.e. very high antennas. A 25 W radio might communicate with an aircraft at 20,000' as far as 200 miles while a 5 W radio might struggle at 100 -120 miles.
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Old 06-10-2018, 17:17   #4
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Re: What range should I expect from my VHF?

You get very slightly more than line of sight due to the way the vhf radio wave travels, but line of sight is a good reference, as vhf radio waves travel in an almost straight line, and penetrate the atmosphere, you can talk to the space station with VHF or it might be UHF, you have to be quick though, get them on 145 megahertz, range of 200 miles, course marine radio does not have that frequency, but it has same range, when you see space station you can talk to it, same with your radio, but to test all you need is someone with your handheld fifty yards away, if its loud and clear at that distance, it will be loud and clear at the twenty or so miles that you get from boat to boat.
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Old 06-10-2018, 17:25   #5
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Re: What range should I expect from my VHF?

Looks like maths is not my strong point
Corrected below
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.....................
Assuming your 40' mast is atop a 5' deck, your antenna is 45' and if the receiving station is at sea level, your effective range is about 9.5 miles. If the receiving antenna is on a similar boat (i.e. 45'), then the range becomes 18 19 miles.
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Old 07-10-2018, 10:03   #6
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Re: What range should I expect from my VHF?

Aircraft vhf range, as I was taught: 1.25(square root height transmitter in feet)+1.25(square root height receiver in feet)=range in NM. Fair winds!
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Old 07-10-2018, 10:29   #7
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Re: What range should I expect from my VHF?

The quality of the set also makes a difference. I had a variety of cheap ones over the years before fitting an Icom on my current boat. The cheap sets would struggle at anything over 10 miles with degraded speech and distortion. The icom has regularly given me 50m range to Coast Guard stations (with high aerials) that is as clear as a bell.
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Old 07-10-2018, 11:18   #8
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Re: What range should I expect from my VHF?

Quote:
Originally Posted by roland stockham View Post
The quality of the set also makes a difference. I had a variety of cheap ones over the years before fitting an Icom on my current boat. The cheap sets would struggle at anything over 10 miles with degraded speech and distortion. The icom has regularly given me 50m range to Coast Guard stations (with high aerials) that is as clear as a bell.
Also: according to a very informative previous post there may be issues with led lights aboard. Some may interfere with transmission and reception quality. It was suggested, to test any possible interference by using a handset and switching the led lights on and off whilst transmitting and the "noise" on the main set. Fair winds.
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Old 07-10-2018, 11:54   #9
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Re: What range should I expect from my VHF?

Power is also important for overcoming the loss in the antenna cable.
A 5w handheld is "at" the antenna, so it puts a full 5W into the antenna.
A 25W radio located below deck, with a 40' mast and maybe another 20' of cable snaking over to the mast, is 60' away from the mast.
There are a number of factors (especially the actual cable make and condition) that affect power loss in the cable and there are a number of online calculators for that:
Coax Loss Calculator | KV5R.COM
Indicates that even with a "good" quality cable, that 25W radio may only be putting 17W into the antenna. Yes, you can easily lose power in the cable. So...there's more than power ratings and line-of-sight to be considered. (And again, plenty of online line-of-sight range calculators out there.)

Also, marine VHF radios are FM radios, and all FM radios exhibit the "capture effect". That is, a receiver will lock into whatever is the strongest signal. If there are five people trying to use the same channel at once, the odds are pretty good that one strong signal will be received, if the other four are weaker they may not even create audible interference.
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Old 07-10-2018, 12:43   #10
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Re: What range should I expect from my VHF?

You have also to consider the height of the receiving antenna. Once Off Cape Fear a was able to communicate with the US Coast Gard at over 100 miles offshore. And at the time, my radio cable was in dubious state. I presumed that the Coast Gard ground station was equiped with powerfull radios and high placed antenna.
Some times when the sun is low on the horizon, strange things happens. I was able to talk clearly on ch 16 to cruisers about 500 miles away(Lake Champlain to Pointe au Pere in Gaspesia(Lower St-Laurence gulf) . It lasted for 15 minutes at least...
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Old 07-10-2018, 16:40   #11
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Re: What range should I expect from my VHF?

Lots of very good info posted here.

Now a short answer:

20 miles.
Or 10 miles at a dock.
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Old 07-10-2018, 16:55   #12
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Re: What range should I expect from my VHF?

Seems that atmospheric conditions can play a part.

We once heard VMR Bundaberg from 350 miles offshore. Quite clearly too.

No way could they hear us though.
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Old 07-10-2018, 17:21   #13
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What range should I expect from my VHF?

Skip can play tricks and have you both transmitting and receiving over stupid long distances, however of course that is an anomaly and you can’t count on it.
It seems skip rolls much better at night, and even moreso when there is fog, or it seems that way anyhow

I think but am not sure that AM skips far better than FM though
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Old 07-10-2018, 17:23   #14
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Re: What range should I expect from my VHF?

^^ for those interested https://en.wikipedia.org/wiki/Tropospheric_propagation
and
Tropospheric Ducting Forecast for VHF & UHF Radio & TV
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Old 07-10-2018, 22:47   #15
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Re: What range should I expect from my VHF?

[QUOTE=The icom has regularly given me 50m range to Coast Guard stations (with high aerials) that is as clear as a bell.[/QUOTE]

Hitting 50m with an Icom sounds a bit optimistic to me, however with repeaters in place, very realistic. I know in my cruising area - "Inside Passage, BC" - repeaters are abundant and so I can be in one area talking to the Coast Guard much further south. But it is the repeaters giving me the omph, not the radio.
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