VHF antennas height vs DB

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
I suspect you have an abundance of experience trying to get your "opinion" across
 
I will let it go before it goes downhill.


For those buying radios and antennas and learning about cruising ....make sure you do your homework beyond simplistic, theoretical explanations.
 
Last edited:
I have less than .001% of ps experience.
But, even then many of us non rescue types have heard some pretty spectacular radio conversations.
Like the time off of Palm Beach a small boat was on fire with a family onboard. I listen to uscg trying desperately to train the radio operator how to get lat/long out of the gps. Meanwhile the husband is indisposed, trying to put out the flames. It seemed like an eternity.
 
diver dave said:
I have less than .001% of ps experience.
But, even then many of us non rescue types have heard some pretty spectacular radio conversations.
Like the time off of Palm Beach a small boat was on fire with a family onboard. I listen to uscg trying desperately to train the radio operator how to get lat/long out of the gps. Meanwhile the husband is indisposed, trying to put out the flames. It seemed like an eternity.
Click to expand...

Thats where the DSC sytem properly implemented could have transmitted their position. Easier and standardized connections to gps and incentives to do so.

Bud
 
PSNEELD,

I agree completely. Theoretical explanations are just that. They are a useful guide for selecting an antenna for your primary use. If I was running coastal waterways and rivers where I don't expect much rocking and rolling, I would opt for gain. If I had a sailboat offshore I would opt for lower gain and the height of the mast. Second thing is be sure it is installed properly. I just relocated a Morad VHF antenna I was using for AIS. A PO installed it about 3 feet from a 6 dB gain Digital antenna and six inches from an aluminum mast. On top of that there was an exposed connector in the transmission line. I relocated it to the front of the pilot house with an new transmission line and the range increased from 5 miles to about 12 miles on class b AIS transmissions.

Tom
 
Agree with ps on this one. Many haven’t programmed their dsc. Many don’t have the ten types of distress calls available. Usually because they haven’t read up on it and fooled around with it to be comfortable using it when needed. But also agree some form of backup not dependent upon the integrity of the ship is wise. If no electricity no ships battery dependent SSB or satphone will be available. Flooding is a not uncommon reason for distress. How this is addressed depends upon your program. At the least a ships epirb seems wise even if coastal. AIS like vhf is line of sight so limited in many settings. Texting is time consuming and maybe more difficult in a highly stressful setting. A Spot or GO! has its limitations as well. We carry ships vhf, ships satellite comm, SSB, personal and ships epirbs/AIS but also have several fully charged handheld vhfs. Once served as a communication relay between a sinking commercial fish boat and the CG. They had only a handheld vhf as their remaining functional comm to state the details of their situation and needs. That was done voice and relayed by us voice to the CG until their vessel showed up.
 
Last edited:
Feedline is part of the "Antenna System"

All good points and arguments. There is one (important) factor that I would like to add:

FEEDLINE selection (especially for longer runs).

From the antenna connector on the back of our radios, everything matters, and one can call it all an "antenna system". The quality of one's connectors, how well the connectors are connected to the coax, corrosion, water intrusion into coax or connectors, and of course the selection of which type of coax all matters. RG-58 (typical white or black 1/4" coax) is the most common on boats. Sellers and buyers like the low cost. But at VHF frequencies, the loss can be significant, especially for longer runs. All the advantages of a higher antenna can be lost in poor feedline conditions. Think of everything that comes after your radio's antenna connector as the "Antenna System".

This website has a good online calculator for different types of coax.
https://kv5r.com/ham-radio/coax-loss-calculator/ (Use SWR of 1.5 typical for a good Marine VHF antenna).

I input 25ft, RG-58 (2 types), at 25 watts and found 25% loss, so about 18.5 watts out. The feedline losses are also experienced on Receive, where the signal is measured in microvolts. ((Hams say, "If you can't hear him, you can't work him!"))

Then, I input RG-213, same conditions, there was only 15% feedline loss, so 21.2 watts out. RG-213 is 1/2" thick and easier to make solder connections to IMO. Admittedly, it won't fit through as many small holes on its way.

Your fundamental question is this: What to buy for an antenna?

I am not a fan of Marine VHF antennas that come with the [cheaper RG-58] coax connected to the antenna right out of the box. I much prefer to buy my feedline separately with PL-259 connectors on both ends, presumably done well with shrink tubing, etc. In contrast, I am a HUGE fan of the antennas that accept my coax feedline connection inside an aluminum or stainless steel tube, protected from the weather: e.g. Shakespeare Phase III 6225-R
A couple of regular s/s hose clamps will firmly attach this type of antenna to any vertical post or railing. Salt air and Water intrusion into coax is common in our boating world, a properly designed antenna protects this connection.

The boat I have today (Mainship 390) came with an old but good VHF radio, RG-58 coax run to a S/S whip on one of the arms atop of the radar mast. It does all the basics and it does it well. Did I replace it? No! I kept it as a second VHF to actively monitor a second channel. (Dual Watch is good, but a second VHF is much better! On more than one occasion, when approaching a friend to raft up together, he missed a key transmission of mine on our VHF-68 because of "dual watch" traffic he got on VHF-16, to give one example.)

I added a newer VHF (Raymarine 73) that had AIS receive, it talks with the boat's chart plotter, and of course I used the good feedline (20feet), and the Phase III antenna mentioned above. It beats the pants off the older VHF, but the combination of having both is great. ((Side note: I like the VHF radios with GPS built right in! In an emergency, it is nice to know the 'panic button' knows your MMSI as well as your position without relying on wired connections.))

I grew up on sailboats, and the obvious height v. gain question was discussed with my Dad on several occasions. Running the cheap coax the long distance up the mast, and not ensuring a weather-proof connection to the antenna is simply not worth it. "You need to be able to inspect and change out your coax." If you can run good quality 1/2" coax up the mast and ensure a weatherproof connection to the antenna, and be able to change the coax out every few years (clanging inside the mast), then a VHF antenna at the top of the mast can work very well. Don't let one advantage (high antenna) be lost to the disadvantage of a poor feedline as part of the overall antenna system.

So called "Direct Bury" coax is usually really good for U/V protection etc.
 
Last edited:
The bare copper in the 213. Is fixed with the Belden i referenced above.
Agree with the non weatherproof nature of pl259 hw too. Seal it with self fusing tape
 
Capt Ray said:
All good points and arguments. There is one (important) factor that I would like to add:

FEEDLINE selection (especially for longer runs).

From the antenna connector on the back of our radios, everything matters, and one can call it all an "antenna system". The quality of one's connectors, how well the connectors are connected to the coax, corrosion, water intrusion into coax or connectors, and of course the selection of which type of coax all matters. RG-58 (typical white or black 1/4" coax) is the most common on boats. Sellers and buyers like the low cost. But at VHF frequencies, the loss can be significant, especially for longer runs. All the advantages of a higher antenna can be lost in poor feedline conditions. Think of everything that comes after your radio's antenna connector as the "Antenna System".

This website has a good online calculator for different types of coax.
https://kv5r.com/ham-radio/coax-loss-calculator/ (Use SWR of 1.5 typical for a good Marine VHF antenna).

I input 25ft, RG-58 (2 types), at 25 watts and found 25% loss, so about 18.5 watts out. The feedline losses are also experienced on Receive, where the signal is measured in microvolts. ((Hams say, "If you can't hear him, you can't work him!"))

Then, I input RG-213, same conditions, there was only 15% feedline loss, so 21.2 watts out. RG-213 is 1/2" thick and easier to make solder connections to IMO. Admittedly, it won't fit through as many small holes on its way.

Your fundamental question is this: What to buy for an antenna?

I am not a fan of Marine VHF antennas that come with the [cheaper RG-58] coax connected to the antenna right out of the box. I much prefer to buy my feedline separately with PL-259 connectors on both ends, presumably done well with shrink tubing, etc. In contrast, I am a HUGE fan of the antennas that accept my coax feedline connection inside an aluminum or stainless steel tube, protected from the weather: e.g. Shakespeare Phase III 6225-R
A couple of regular s/s hose clamps will firmly attach this type of antenna to any vertical post or railing. Salt air and Water intrusion into coax is common in our boating world, a properly designed antenna protects this connection.

The boat I have today (Mainship 390) came with an old but good VHF radio, RG-58 coax run to a S/S whip on one of the arms atop of the radar mast. It does all the basics and it does it well. Did I replace it? No! I kept it as a second VHF to actively monitor a second channel. (Dual Watch is good, but a second VHF is much better! On more than one occasion, when approaching a friend to raft up together, he missed a key transmission of mine on our VHF-68 because of "dual watch" traffic he got on VHF-16, to give one example.)

I added a newer VHF (Raymarine 73) that had AIS receive, it talks with the boat's chart plotter, and of course I used the good feedline (20feet), and the Phase III antenna mentioned above. It beats the pants off the older VHF, but the combination of having both is great. ((Side note: I like the VHF radios with GPS built right in! In an emergency, it is nice to know the 'panic button' knows your MMSI as well as your position without relying on wired connections.))

I grew up on sailboats, and the obvious height v. gain question was discussed with my Dad on several occasions. Running the cheap coax the long distance up the mast, and not ensuring a weather-proof connection to the antenna is simply not worth it. "You need to be able to inspect and change out your coax." If you can run good quality 1/2" coax up the mast and ensure a weatherproof connection to the antenna, and be able to change the coax out every few years (clanging inside the mast), then a VHF antenna at the top of the mast can work very well. Don't let one advantage (high antenna) be lost to the disadvantage of a poor feedline as part of the overall antenna system.

So called "Direct Bury" coax is usually really good for U/V protection etc.
Click to expand...

Agreed, Cable loss and I will add reflected power is a real problem.

Shakespeare makes an antenna meter to measure forward and reflected power. That is the only way to be sure if your antenna system is operating properly. Usually 5% or less of reflected power is acceptable.

Bud
 
Hippocampus said:
Agree with ps on this one. Many haven’t programmed their dsc. Many don’t have the ten types of distress calls available. Usually because they haven’t read up on it and fooled around with it to be comfortable using it when needed. But also agree some form of backup not dependent upon the integrity of the ship is wise. If no electricity no ships battery dependent SSB or satphone will be available. Flooding is a not uncommon reason for distress. How this is addressed depends upon your program. At the least a ships epirb seems wise even if coastal. AIS like vhf is line of sight so limited in many settings. Texting is time consuming and maybe more difficult in a highly stressful setting. A Spot or GO! has its limitations as well. We carry ships vhf, ships satellite comm, SSB, personal and ships epirbs/AIS but also have several fully charged handheld vhfs. Once served as a communication relay between a sinking commercial fish boat and the CG. They had only a handheld vhf as their remaining functional comm to state the details of their situation and needs. That was done voice and relayed by us voice to the CG until their vessel showed up.
Click to expand...

I have a question for you. If you were leaving for a 90 day trip to the Bahamas and you could only bring 2 emerg communication devices, cell phone excluded, which two would you pick from VHF, 2nd VHF, portable VHF, epirb, satelite phone, spotX,

Bud
 
Another great way to check your radio is real world transmits and receives.

Unfortunately the Sea Tow automated radio check is being or has been discontinued.
 
Before marine I was a broadcast and 2/W tech with a FCC comm'l license - though I'm not an antenna expert, per se...

The stated height differences will be of insignificant effect compared to the gain figures. UHF might be a different story. The 9Db antenna will reach approximately twice as far as the 3Db, and that will be so in any atmospheric conditions. But if this is on a boat, sea conditions also need to be considered.

Antenna gain comes from flattening the radiation pattern. The 3Db antenna pattern is close to a donut shape and the 9Db more like a pancake. When a boat rolls or pitches the round cross-section of the donut pattern still sends about the same signal in the horizontal plane while the flattened pattern sends it's signal into the sky or sea. In rough conditions a high gain antenna may be completely ineffective for transmitting.
 
Bud said:
I have a question for you. If you were leaving for a 90 day trip to the Bahamas and you could only bring 2 emerg communication devices, cell phone excluded, which two would you pick from VHF, 2nd VHF, portable VHF, epirb, satelite phone, spotX,



Bud
Click to expand...



Easy one: Epirb and handheld vhf. And im doing a departure today for said place [emoji847]
Rationale; one lightning hit can take out anything on 12V, and anything with a connected wire over a few meters long. In reach or spot is close 3rd. All these are/could be portable, water resistant, and no ext wires.
 
Agree with DD. In anything to do with comm always best to have two different technologies and not be totally dependent on ships integrity. In South Florida and much of the Bahamas lighting strike is a concern. Hence, the faraday box of your stove a blessing. At present like the ICom handhelds but that’s personal preference.

In your list would prefer a Go to a Spot having used both. The basic Spot is great for breadcrumbs but Go is easier to use with better functionality c/w Spot X and globalstar is a PIA to interact with.

My thinking as been to avoid 9db high gain antennas on small boats even if stabilized. Wonder (getting back to the OP) if that’s the consensus opinion?

Open ocean much less concern about lightning but would still have a handheld vhf of good quality but think the list would be satphone, vhf and epirb at a minimum. If you set up a separate email and don’t give out your phone number/email address except to a very small number having voice is a big deal. Jump in cost is worth it. Several times had voice calls with techs while trying to fix things. Voice made a huge difference.
 
Last edited:
Hippocampus said:
My thinking as been to avoid 9db high gain antennas on small boats even if stabilized. Wonder (getting back to the OP) if that’s the consensus opinion?
Click to expand...


If the boat isn't excessively rolly, the 9db antennas should work fine. And if you're worried about it or operate in areas where they may need to be lowered a lot, put in a smaller 6db or 3db for each radio as well with a coax switch so you can just select the other antenna if needed.
 
Rs that’s exactly what we’ve done and it’s worked fine so far. What have you done yourself?
 
Hippocampus said:
Rs that’s exactly what we’ve done and it’s worked fine so far. What have you done yourself?
Click to expand...


So far I'm just running a 6db antenna on each VHF for my boat, as we're mostly in an area of low radio traffic and those antennas are good enough to talk to the USCG or CCG from anywhere on Lake Ontario. However, at some point I will add a pair of taller 9db antennas and add a coax switch next to each VHF. I just have to figure out the mounting, as well as where to place them for adequate spacing from other antennas.

The other thought for my boat is to change the existing mounts and antennas for a setup that can accommodate the taller antennas, but has a cable connector rather than built in cabling. Then when we head into the NY canals or somewhere with bridge clearance concerns, we can simply switch out the tall antennas for the shorter 6db ones.
 
For bridges, I have the big ones lowered. Some of the time they still transmit and receive fine for the bridges and close boats. If not, I just use my handheld.
 
diver dave said:
Easy one: Epirb and handheld vhf. And im doing a departure today for said place [emoji847]
Rationale; one lightning hit can take out anything on 12V, and anything with a connected wire over a few meters long. In reach or spot is close 3rd. All these are/could be portable, water resistant, and no ext wires.
Click to expand...

Agreed
 
Hippocampus said:
Agree with DD. In anything to do with comm always best to have two different technologies and not be totally dependent on ships integrity. In South Florida and much of the Bahamas lighting strike is a concern. Hence, the faraday box of your stove a blessing. At present like the ICom handhelds but that’s personal preference.

In your list would prefer a Go to a Spot having used both. The basic Spot is great for breadcrumbs but Go is easier to use with better functionality c/w Spot X and globalstar is a PIA to interact with.

My thinking as been to avoid 9db high gain antennas on small boats even if stabilized. Wonder (getting back to the OP) if that’s the consensus opinion?

Open ocean much less concern about lightning but would still have a handheld vhf of good quality but think the list would be satphone, vhf and epirb at a minimum. If you set up a separate email and don’t give out your phone number/email address except to a very small number having voice is a big deal. Jump in cost is worth it. Several times had voice calls with techs while trying to fix things. Voice made a huge difference.
Click to expand...

Agreed
 
This is maybe overkill, but this is my departure list today, just comm:

Gps/DSC enabled VHF marine with a 55’ high, apparently 4’ long fiberglass antenna of unknown make/model because I have yet to get close enough to it [emoji848] SWR is very low, no doubt due to loss in small coax. Its on the list…

AIS class B

HH VHF with a scattering of ham and marine freqs. And, its type accepted, but it wont float.

Icom airband 10 Watt vhf/am. I could call for help to a transatlantic aircraft via 121.5 directly.

In reach, newly commissioned

Island wifi / cell router

Cell with a 242 area code

HF/SSB with 23’ whip and auto tuner, 150 Watts

New EPIRB, registered, mounted on a life cell.

This way, lightning only takes out half my gear in the first strike. On that topic, i have rigged a heavy copper conductor from shroud to ocean when anchored. However, my expectations are low.

FCC ships license and oper. Permit

But I’m keeping all the valuable comm stuff at home. [emoji41]

Do weapons count as COMM devices [emoji41][emoji41]
 
Last edited:
is it possible that a 9DB antenna mounted lower on the vessel would be better performing than one mounted higher in light rolly seas.
 
hey Dave do you have room for one more. i got my slings ready
 
ofer said:
is it possible that a 9DB antenna mounted lower on the vessel would be better performing than one mounted higher in light rolly seas.
Click to expand...

Not sure that helps much as the angle off horizontal remains the same.

My experience...rarely in my professional experience was it so rough the 9db antennas still weren't superior communicators over 3/6 db.

And if terribly rough and an emergency....most situations I would be setting off my EPIRB, hitting the VHF DSC distress button that keeps transmitting till acknowledged by a SAR unit (as I understand it) and then using my hand held VHF when the resources were close and preparing assist.
 
Have had difficulties with both AIS and VHF when the other vessel is real close. Admittedly this was a sailboat with the antennas way up high. So as ps implies switched to the handhelds. Of course only an issue in dense fog, snow or sleet.
Would suspect that’s more of an issue and the other vessel could be farther away and run into similar troubles with a 9 than a 3 or 6. Is that true?
 
Last edited:
You must log in or register to reply here.

Similar threads

R
VHF Antenna Upgrades
Replies
18
Views
877
rslifkin
R
Pat T
New VHF & antenna questions
Replies
22
Views
4K
psneeld
psneeld
thead
Kadey Krogen 42PH
Replies
0
Views
1K
thead
thead
PhilPB
FOR SALE: 1983 Mainship 34' MKlll - $32,000 - Palm Beach County, Fl
Replies
20
Views
2K
PhilPB
PhilPB
A
FS: 1988 Albin 27 Family Cruiser $30k
Replies
6
Views
5K
AFC27
A

Latest posts

Back
Top Bottom