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Snowandsail · 03-07-2023, 06:46

Hello, I have a new boat with a new Raymarine vhf radio. Antenna mounted at mast head 82ft hight, but the range of transmitting is less than 13 miles. I can receive and hear clearly but my transmit is unclear to the other person. I’m operating in the Bahamas, VHF is in USA mode. Please give me some feedback about what I can do to increase my transmit range. It seems it should be farther. Thank you.

Tin Tin · 03-07-2023, 07:08

Does your VHF have Low and high power setting?

What model antenna is it, there are different types and qualities that increase range.

See this too https://www.hamuniverse.com/lineofsightcalculator.html

S/V Illusion · 03-07-2023, 07:11

How much “less than 13 miles”? 12, 6, 2, …?

Is the boat, radio and coax new or just new to you? If actually new, 13 miles is a reasonable expectation of max range depending on the height of the receiver’s antenna.

Shrew · 03-07-2023, 07:16

The max distance to the horizon from 82 feet in the air IS 13 miles.

wholybee · 03-07-2023, 08:56

Since you can hear them clearly that would indicate that the line of sight path is good and they should hear you if are transmitting as well as them.

As mentioned, some radios will default to only 5 watts on some channels. So check that.

On a long run (82ft mast) the type of coax is critical. For example, the commonly used RG8x would have more than 60% signal loss at 100'.

Most VHF problems are a result of a connector problem. If the weatherproofing failed at the connector at the base of the antenna, that can cause the problem you are having.

river · 03-07-2023, 09:45

Apart from using low loss coax, and checking connectors, it could be an audio problem. Is there some plastic film over the microphone?

George_SD · 03-07-2023, 10:08

Seems to be working as expected at sea-level receiving station.
At 82ft mast (antenna height)
Line of Sight Distance: 17.85 km / 11.09 mi
Radio Horizon - Service Range: 20.60 km / 12.80 mi

The radio horizon / service range of an antenna will always be slightly further than the straight line-of-sight distance to the horizon. This is due to the refractive effect of the Earth's atmosphere, which causes RF signals to propagate in a slightly curved line over long distances, pushing out the effective horizon distance.

You may be able to hear them fine because they are transmitting at a higher power (normal for ground stations) or have a higher antenna placement.

wholybee · 03-07-2023, 10:28

Those doing LOS calculations. Don't forget to take into account the second antenna height. Assuming the second mast is a bit shorter, 50 ft, the combined LOS would be over 20 miles.

Ship to ship 25 miles is possible with both installations very good. Less than 10 is common because so many installations are not good.

chp · 03-07-2023, 12:21

The formula for VHF range is 1.23 X sq rt of the height of the antennae above ground.
sq rt of 82=9 X 1.23= 11.13 miles. Power has some influence, but mostly line of sight.

wholybee · 03-07-2023, 12:49

Quote:

Originally Posted by chp

The formula for VHF range is 1.23 X sq rt of the height of the antennae above ground.
sq rt of 82=9 X 1.23= 11.13 miles. Power has some influence, but mostly line of sight.

Plus the same for the height of the receiving antenna. So if both masts are at 82ft, then 22+ miles.

If the OP is communication with another sailboat (vs a high power land station) and at 13 miles he can clearly heat the other boat, and the other boat can't hear him, he is within LOS and probably does have some issue.

HankOnthewater · 03-07-2023, 17:03

I agree with with all comments that transmission range might be reduced by:
- poor connectors (as prove that receiving is OK, but transmission is impaired). BTW connectors of power supply, aerial and microphone could be involved
- poor quality of coax cable
- transmit is set to low level

I disagree that about 13 miles is about right for VHF comms. Yes, the formula shows the line of sight at 82 ft (25.4 meters) is around 10.6 NM (although most previous posts mentioned "miles" and therefore get slightly higher values).
I found that range of VHF on my Icom sets on previous and my current boat was around 20-35 NM. Both to shore and other sailing boats. And yes, the shore based aerials are usually elevated as were the aerials on most sailing boats.

For those who do most the calculations using the other system (=metric), the formula for line of sight is 2.1 x square root of height in metres, gives the distance in NM. And of course the same calculation is applied to the other aerial or light as well, then these two values added to get the distance/line of sight.

GILow · 04-07-2023, 18:21

I’ve been asked for help with poor vhf range on more boats than I can remember now.

And each time I bring my SWR meter and each time there is some kind of serious SWR issue.

Find someone with a meter and have them check for you. Simple job that can mostly be done from the radio end. Only need to go up the mast for really subtle issues.

FWIW, one guy I helped with this issue had factory fitted coax on his Sun Oddesy, and it was the crap thin stuff. He was pushing out less than one watt, about 0.8 from memory. He dragged in a new cable, the proper thick stuff, but managed to put a kink in it somewhere and ended up at about 2 watts. He decided to live with it. I argued he may well die with it too, but hey… horse… water…

**Jammer** · 05-07-2023, 08:50

Quote:

Originally Posted by Snowandsail

Hello, I have a new boat with a new Raymarine vhf radio. Antenna mounted at mast head 82ft hight, but the range of transmitting is less than 13 miles. I can receive and hear clearly but my transmit is unclear to the other person. I’m operating in the Bahamas, VHF is in USA mode. Please give me some feedback about what I can do to increase my transmit range. It seems it should be farther. Thank you.

Sure.

First of all, how far can you transmit? To who? You should be able to contact well-equipped sailing vessels that are 25 miles away. You may not be able to contact marinas, bridges, locks, etc., from these distances because they have will have their squelch turned up. You will not be able to contact, say, someone using a handheld in your dinghy, because the receive antenna is limiting.

If you genuinely have a problem, there are three things you will want to check, in order.

Connectors in the feedline from the radio to the antenna.
The antenna itself.
Other problems with the feedline, such as a poorly chosen type of coax, or corrosion or damage.

With a 90' feed line you may need to run some of the tests at the top of the mast to find the problem. The best way to check the feed line is with a VNA, with a temporary piece of coax from the mast top to the radio location, so you can see what the losses are.

team karst · 05-07-2023, 13:23

It must be noted that these various LOS charts and graphs simply indicate if the two antennas can see each other. That is just step one. Noise sources at both locations are also a factor. My victron MMPT’s for instance, spew out considerable vhf noise. If the received signal does not exceed this noise, you dont have a comm link.