Please Recommend a Quality VHF Masthead Antenna

[goboatingnow]

Originally Posted by s/v Jedi

What you need is Silicone Rescue Tape, vinyl electra tape and a cable-tie.

First the Rescue tape: start with 1.5 straight wraps at the lowest end, then tension and stretch it and wrap towards the other end, overlapping by half. At the other end, finish with a straight wrap again while lowering tension.

Next, cover it with (good quality, like 3M that comes in a little round plastic box) black vinyl electra tape in much the same manner. Make sure all the rescue tape is covered. Now you have a loose end that sticks okay now but will come loose soon. Tie that down with the cable tie.

This is the standard telecom dressing that lasts until the vinyl tape falls off (1 years in the tropics, for ever in the UK ), after which you just put on new vinyl tape only.

I use self amalgamating tape followed by liquid tape. I've always found the PVC tape useless when exposed.

Dave

[goboatingnow]

Originally Posted by Scott Berg

Your point is well taken... please understand, I'm not challenging the ubiquity of the 259 conn, just their superiority in a hostile environment. In my 25 some years in the marine electronics industry more radio issues are caused by badly soldered 259s than I can count. That, RF grounds for MF/HF, and low voltage and you have 90% of my service calls.

A N conn is watertight by design and with the right tools much easier to install.

Like you I can solder a pl 259 connection in a bosun's chair but prefer the N conn for the antenna fitting... It comes down to preference and I'd still like to move beyond the traditional PL 259 UHF connectors... To each ones own.

FWIW the reports I get on my VHF radio ( LMR400 bury/N conns/whip (bridge-tester)) best any boat in the harbor and I hit 2m repeaters others next to me can't so my next system will be similar...

Scott
WA0LSS

I crimp all my 259s , never had a problem.

Dave

[goboatingnow]

Originally Posted by Dockhead

Mobile telephony is by far the single most important means of communications on board when cruising near coasts (which is the majority of the time even for circumnavigators).

It is by far the best Internet connection -- most consistently available and by far most economical, and in my experience usually more bandwidth and less latency than marina wifi connections. For that you need 3G (HSPDA, UMTS, etc.).

But it is also crucial for voice comms.

Seems to me that it is a possibly unwinnable technical challenge to greatly extend the range of 3G data comms.

But I can imagine a really killer 900mhz GSM voice comms system with a masthead mounted antenna and one of those obsolete high powered 8 watt fixed mount car phones which Motorola and Nokia used to make. Someone told me that there is an artificial limit to the range you can get for GSM as the towers detect the distance by measuring the echo time or something, and cut you off if you are too far away, even if you have a good signal. Need to research that I guess.

I'm starting to think something like that could be really valuable. I believe most European carriers use 900mhz for long range voice comms (and you can do GPRS or EDGE over that kind of channel in a pinch, too). For the occasional times when more range is needed for 3G, I could put that antenna out a hatch. Hmmmmm!

Gsm is limited by the timing advance issue in the base station.

[s/v Jedi]

Originally Posted by goboatingnow

I use self amalgamating tape followed by liquid tape. I've always found the PVC tape useless when exposed.

Dave

Lol. That self amalgamating tape, what is it made of? I.e. does it become a sticky mass or is it silicone?

[El Rubio]

I know this is older, but regarding sealing connectors, I use standard butyl, like the type that is supplied with Andrew/Commscope connectors, Scotch C130 self amalgamating tape - less mess, and have been trying out 3M- 70 silicone tape. The C130 and 3M tapes are very clean to remove. No residue at all is left and seals very well. I cover any sealant tape with standard electrical tape. This has lasted many years without failure. What our tower guys do is wrap with standard electrical tape, followed by a wrap with standard butyl, then another wrap of electrical tape. They call the first electric tape wrap "a courtesy wrap". It makes for no butyl mess when removing the connector in the future and is very effective seal. Someone posted N type connectors are weatherproof - don't believe that.

[Pete7]

So mulling over some ideas, what is the advantage of a centre fed antenna like the Shakespear Galaxy over say a quality base coil antenna like the Metz ?

Pete

[Dockhead]

Originally Posted by Pete7

So mulling over some ideas, what is the advantage of a centre fed antenna like the Shakespear Galaxy over say a quality base coil antenna like the Metz ?

Pete

Center fed dipole doesn't need a ground plane or radials. Any antenna has two electrical halves. A dipole has both of them as parts of the antenna; otherwise you need the masthead truck as a ground plane, or radials. Tends to work better. However, the Metz antennas are apparently quite good, too.

The base coil has nothing todo with the ground - it's to add inductance to increase the electrical length of the antenna, allowing the whip to be shorter.

[transmitterdan]

Originally Posted by Pete7

So mulling over some ideas, what is the advantage of a centre fed antenna like the Shakespear Galaxy over say a quality base coil antenna like the Metz ?

Pete

Pete,

The Galaxy isn't optimum for masthead mounting on a sailboat. It's very long and has the coax permanently attached. The Metz is designed for masthead mounting and won't break if you scrape under a bridge. It has a real screw on connector making it easier to run coax up the mast If you are going to mount the antenna on an arch or stern pole the Galaxy is fine. Coverage with either antenna will be about the same if mounted in the same location.

[Pete7]

Originally Posted by transmitterdan

Pete,

The Galaxy isn't optimum for masthead mounting on a sailboat. It's very long and has the coax permanently attached. The Metz is designed for masthead mounting and won't break if you scrape under a bridge. It has a real screw on connector making it easier to run coax up the mast If you are going to mount the antenna on an arch or stern pole the Galaxy is fine. Coverage with either antenna will be about the same if mounted in the same location.

That is a good point, I hit a tree with the masthead this summer playing Swallows and Amazons up a river. I am also running out of space on the masthead, pretty certain that the existing antenna is both nothing special and mounted on a stand off bracket. Final thought is the Galaxy will be right next to the mast head lights and block some of the light to the stern were as the wire coat hanger Metz will be less of a problem.

Dockhead, thanks for the explanation and to all those who have contributed to this thread. Previously I had assumed a VHF antenna was just an antenna and didn't worry about fitting el cheapo version from the local chandlers. However, I am now considering an upgrade to antenna and perhaps more importantly coax, after all even a 31 ft boat has a 65ft run from masthead to VHF.

Pete

[Dockhead]

Originally Posted by Pete7

That is a good point, I hit a tree with the masthead this summer playing Swallows and Amazons up a river. I am also running out of space on the masthead, pretty certain that the existing antenna is both nothing special and mounted on a stand off bracket. Final thought is the Galaxy will be right next to the mast head lights and block some of the light to the stern were as the wire coat hanger Metz will be less of a problem.

Dockhead, thanks for the explanation and to all those who have contributed to this thread. Previously I had assumed a VHF antenna was just an antenna and didn't worry about fitting el cheapo version from the local chandlers. However, I am now considering an upgrade to antenna and perhaps more importantly coax, after all even a 31 ft boat has a 65ft run from masthead to VHF.

Pete

I agree with Transmitterdan -- if you have a chance of a close brush with a tree or bridge, then forget the Galaxy. It is long and rigid and there would be carnage at the masthead in such a case.

Antenna makes a huge difference -- more important than the radio itself. So choose carefully and avoid the El Cheapo types. If you go with a whip, I'm not sure I would go with a base coil loaded one. The coil shortens the radiating element for cases where you can't accommodate a longer antenna, but surely for you the main thing is flexibility, not length? The shorter radiating element won't be as efficient.

And yes -- the cable is also key. If you can fit it in your mast conduit, RG213 is a good bet. Some people like LMR400, which is still lower loss, but I've been warned too many times about problems with foam core coax in the marine environment to be willing to risk it, myself.


I'll be glad to help you pull the cable and get your connectors on if I'm in town when you do it. Just let me know. You will want the help as it takes more than two hands, and the learning curve is steep. I should be around the whole first half of January. I also have the crimp tools for putting on PL259's.

[El Rubio]

Just an FYI, Times Microwave LMR series cables are made with closed cell foam and do not wick moisture like some of the RG8 variants can. The braid on any cable, except possibly those impregnated with silicone will wick moisture if exposed to it. I wouldn't worry about moisture intrusion and just seal connectors properly.

[Greggegner]

What ever cable you use don't bend it hard or crush it during the installation. Get the lowest attenuation you can find and solder the connectors.

[Goudurix]

Originally Posted by Dockhead

Center fed dipole doesn't need a ground plane or radials. Any antenna has two electrical halves. A dipole has both of them as parts of the antenna; otherwise you need the masthead truck as a ground plane, or radials. Tends to work better. However, the Metz antennas are apparently quite good, too.

The base coil has nothing to do with ground - it's to add inductance to increase the electrical length of the antenna, allowing the whip to be shorter.

The base coil in typical (1/2 wave end-fed or 5/8 wave) VHF antennas (specified as "3dB" gain) is indeed there to match the antenna to 50 Ohm coax (impedance, reactance) and not meant to electrically lengthen the antenna. A half wave base fed antenna has very high impedance at its feedpoint.
Still it is a half wave antenna and comparable to 1/2 wave vertical dipole.

I use to Glomex marine (italian) vhf whip antennas. It shows good VSWR, not only at the end of the coax but also measured just below the antenna. "They work well" but this is only based on the range and radio reports I get on marine VHF.

Jan

[plebian99]

In the real world 5/8 wave antennas rarely achieve this 3bd gain. Considering that a 2 element yagi has 4 dbd, you can see why the gain claims of many manufacturers are very dubious.

What is often not discussed is that gain boost only occurs at certain peak take-off angles. ie the gain advantage is not uniform across the whole radiation lobe. 5/8th verticals on top of a very high mast is really a waste of effort for line of sight communications. The advantage over a simple antenna like 1/4 wave whip will never be realised practically in the real world, especially on a sailboat.

Another consideration is that when you study the radiation pattern of a 5/8th antenna high above the ground you will find that it introduces a lot of nulls in the radiation pattern. The 5/8th also has a very narrow main radiation lobe. This is the last thing you want on a pitching and yawing sailboat. It might be more acceptable on a low height powered vessel.

In the early 70's many communications companies did this very study on plotting signal strengths of vehicles with 5/8th antennas and 1/4 wave antennas in built up city areas. 5/8th antennas were found to be substantially weaker because of the lower angle of radiation. It was found that the more uniform radiation pattern of the 1/4 whip worked better between building and had a better chance of radiating signals out from high buildings because the more uniform radiation pattern. To this day you will rarely find 5/8th high gain whips on commercial communication service vehicles. Now if you on the high plains of Idaho it might be a different matter.

If It was me I would stick with a 1/4wave whip and use high quality cable like Andrew LDF450. There is a new version of this cable around now that does not absorb water. They also have an aluminum version which has more corrosion resistance. Using a high quality cable gives you gain on both RX and TX.

In VHF communications a mythical 3db gain is rarely going to make or break your VHF communications needs. This is especially so on a sailboat which has the antenna mounted at the best possible location. Changing to lower loss cable will buy you more and give you a better performing overall VHF system performance.

[s/v Jedi]

The Shakespeare Little Giant is 1/2 wave, not 5/8. It is a center fed dipole unlike the average grounded designs, which keeps the receiver S/N nice and clean.

Every user notices the big improvement this antenna makes and that is fact, not speculation