VHF antenna

[Dear Prudence 2.0]

I seem to have poor VHF range on our 2018 Freedom 235. I am wondering if the antenna mast is too short. It is only a four footer (3db gain) and mounted on the gunwale. It barley reaches above the Bimini top. The radio works well if I am close to who I am calling. Should I change the mast to an 8‘ (6db gain)? Thanks

 

[Parthery]

Welcome to the forum.

Where do you use the boat?

Also - is your VHF on 25 Watt or 1 Watt. Make sure it's on 25.

 

[seasick]

VHF radio transmissions are line of sight. Therefore the higher the antenna, the farther the theoretical transmission distance.
Here is a calculator

VHF/UHF TV Line of Sight Calculator

Play around with different heights but the height has to change a lot to make a big difference. I ran a few calculations of the working distance for your situation and another vessel whose antenna was 12 feet high. I put yours in at 6 feet, 2 feet of freeboard and 4 feet of antenna. The distance is 8 miles. Changing you antenna mounting height to 12 feet makes the working distance increase to 10 miles.
If you have issues with boats you can see and not more than 8 miles away, the problem is not the antenna height. You could have a bad antenna, a bad connection, or even a bad radio.
I would check the connections first and those are OK, I suppose I would go for a new decent antenna.
One helpful clue determining if the sub par operation is both on send and receive. In other words, if the far end hears you fine but you don't hear them, then the radio is suspect also.

Find out if you have the automated radio check feature available in your area. That service enables you do make a radio check call and then hear what you said, transmitted back. It can be on several channels or not available at all. Ask around.
The usual channels are 24, 25, 26, 27, 28,

 

[Fishtales]

I like the 8' Digital antennas if you are replacing.

 

[Dear Prudence 2.0]

Welcome to the forum.

Where do you use the boat?

Also - is your VHF on 25 Watt or 1 Watt. Make sure it's on 25.

Thank you. Ocean coastal Maine. I’ll check the power setting. It was on 1w for all channels but 16. Manual states this is transmit power. I bumped up my local channel to high power (25 w). Will see how that works. Thanks for the feedback.

 

[seasick]

Note that if your issue is what you hear as opposed to how others hear you, the problem is not related to transmit power.

 

[Sparkdog118]

I use a 6db antenna 8 ft on my hard top. I get a 45 mile average range. One important thing is not to cut any of the wire that comes on the new antenna. It uses every inch of the wire to help the range. Just coil it up and store it under the dash if there is extra.

 

[wspitler]

One additional thought. The height of the receiving end is also a big factor. Some shore based antennas are quite high. Rescue 21 is the USCG Ch16 distress system and their antennas can be hundreds of feet high. There are predicted coverage plots for different USCG Sectors. St Pete FL for example: https://www.navcen.uscg.gov/images/marcomms/cgcomms/Rescue21/SecStPete.jpg The coverage plots are displaying predicted regional coverage area based on line of sight between the Regional Fixed Facility VHF receive antenna and an antenna six feet above water level. To fully understand line of sight you need to consider both ends of the connection. Atmospherics can also play a lesser role as can transmit power. As a retired USCG pilot. if we needed to get more communication range via VHF-FM we climbed in altitude. HF was our go to for OTH (over the horizon) comms back in the day. Now it's all about SATCOM for longer distances.

 

[SmokyMtnGrady]

I would add don't go cheap on the antenna. Drop the extra coin and get the Shakespeare models that are either Galaxy Series or Phase III models. They start to build the elements using silver plated brass. The fiberglass is beefier too and the mounting is stainless steel and not nylon or what ever cheap material a $59 antenna uses. All of these features mean better transmission and receiving.

 

[Blaugrana]

I agree with all of the above and plan to replace mine later this year when they go on sale.

Before replacing your current antenna have you tried troubleshooting? I was having issues with mine in which I wasn’t receiving transmissions not even the weather channels. When transmitting on the automated channels, I received no response.

Ended up checking the voltage at the unit, removed the antenna and just used a screwdriver and then redid the connection of the antenna.

I got more reception with the screwdriver than an 8ft or so Shakespeare Antenna. Once I redid the connector, it then started to work.

This Antenna is probably 20 years old but transmitted 25 miles to the automated channel very clearly. I would think your 2 yr old one should do a lot better assuming there have been advances with the materials and design.

 

[Meanwhile]

I would add don't go cheap on the antenna.

I agree. Except do Digital brand.

 

[seasick]

I use a 6db antenna 8 ft on my hard top. I get a 45 mile average range. One important thing is not to cut any of the wire that comes on the new antenna. It uses every inch of the wire to help the range. Just coil it up and store it under the dash if there is extra.

I believe most if not all of what you say until now
If you use the VHF calculator for line of sight distance and put your antenna height in as about 19 feet ( 8 ft antenna, on a 7 foot high hardtop, 4 feet off the water) the other antenna would have to be 850 feet tall! The horizon is only 6 miles away from your boat (at the tip of the antenna). I know that many CG stations have pretty tall antennas but pretty tall is 200 feet maybe.
How big was that last fish you caught

 

[SkunkBoat]

I believe most if not all of what you say until now
If you use the VHF calculator for line of sight distance and put your antenna height in as about 19 feet ( 8 ft antenna, on a 7 foot high hardtop, 4 feet off the water) the other antenna would have to be 850 feet tall! The horizon is only 6 miles away from your boat (at the tip of the antenna). I know that many CG stations have pretty tall antennas but pretty tall is 200 feet maybe.
How big was that last fish you caught

You can get skip with VHF. I routinely reach Triple wrecks from Toms Canyon.35 miles. A few nights ago I was talking with the west wall of the Hudson canyon from Toms canyon...32 miles

 

[Sparkdog118]

I do have a quality icom radio and a Shakespeare galaxy 5225XT model. When I fish 70 miles off the coast, I need all the range I can get.

 

[wspitler]

I believe most if not all of what you say until now
If you use the VHF calculator for line of sight distance and put your antenna height in as about 19 feet ( 8 ft antenna, on a 7 foot high hardtop, 4 feet off the water) the other antenna would have to be 850 feet tall! The horizon is only 6 miles away from your boat (at the tip of the antenna). I know that many CG stations have pretty tall antennas but pretty tall is 200 feet maybe.
How big was that last fish you caught

I believe the tallest Rescue 21 antenna is 300-400 feet. They often use existing towers, but most are shorter.

 

[wspitler]

You can get skip with VHF. I routinely reach Triple wrecks from Toms Canyon.35 miles. A few nights ago I was talking with the west wall of the Hudson canyon from Toms canyon...32 miles

Agree, you do get skip at times. I hear Sector Mobile Al pretty often from just north of Tampa Bay. Of course I can't transmit to them.

 

[seasick]

hmmmmm. My electrical skills are not so advanced for RF transmission. I am aware of atmospheric skip for other frequencies but this one is new to me. Back to the books

 

[seasick]

OK. I still believe most of what you say including your VHF transmission stories
I hate it when I have to admit I was w,,,, wro.... You know.

Here is what I found

1. At VHF and higher frequencies, small variations (turbulence) in the density of the atmosphere at a height of around 6 miles (9.7 km) can scatter some of the normally line-of-sight beam of radio frequency energy back toward the ground.
   
   

The article states that the phenomenon is not predictable and is not the same as reflections from the ionosphere.

 

[wspitler]

OK. I still believe most of what you say including your VHF transmission stories
I hate it when I have to admit I was w,,,, wro.... You know.

Here is what I found

1. At VHF and higher frequencies, small variations (turbulence) in the density of the atmosphere at a height of around 6 miles (9.7 km) can scatter some of the normally line-of-sight beam of radio frequency energy back toward the ground.
   

The article states that the phenomenon is not predictable and is not the same as reflections from the ionosphere.

Seasick, Thanks for the research. I assumed it was from the ionosphere like HF skip. There were times when I could keep an HF radio guard with CG Comsta Kodiak while operating in the Caribbean. I assume our 406 EPIRBs are not affected by ionospheric interference on the way to the satellites since they are UHF/low power or maybe their repetition makes up for any interference that might occur. Thanks!

 

[Sparkdog118]

I’ve never studied the mechanics of the vhf but I do have Thousands of miles of offshore hands on experience. I have a lot of buddy’s that are offshore guides. I took their recommendations years ago to get the best range for my radio. They say to get a radio with a quality final amp for transmitting (usually the expensive one lol) and use a quality 6db antenna for reception and transmission. Then raise it up as high as possible. They say the antenna needs to be in great shape to keep the range at its best. They also said that if you are using a weak antenna, it could damage the final amp in the radio when you transmit.