Trying to find the perfect VHF antenna

[Brian.D]

The Glomex antennas look nice enough. However, I am not a fan of FME Connectors. With the pounding a boat can take in rough weather, there is a possibility (if remote) that the connector can work its way loose. I would say that PL-259 (UHF connectors) are time-proven to work. Just keep the whole connection water tight with dual wall heat shrink.

JMHO

[CarinaPDX]

The masthead VHF (my previous post) is a stainless whip with a PL-259 and I think pretty much ideal [it has a low SWR]. The AIS antenna is mounted on the radar pole aft and has the FME connector. The advantage is that the included cable can be routed through holes slightly larger than the cable, then connected in place without soldering/crimping a PL-259 (and the FME connector was installed at the factory). Given how badly so many people do making up a PL-259 this is a reasonable approach. I think it best to have an AIS antenna tuned to the AIS frequencies, and this was what was available at the time. Again, I would prefer a stainless whip, and for me the PL-259 would have been fine if it was available, but the AIS tuning was paramount. As it was I installed it while at anchor, standing on the pushpit and stretching up to assemble, so I was happy with it.

Many years ago the first generation of ethernet used coax cables and PL-259 terminals. My brother did a lot of networking and was often called in to troubleshoot; short answer: it was (almost) always the lousy install of the PL-259's that was to blame - even crimped ones. Unfortunately while it was easy to find - that was the first place to look - IT guys don't like to hear their problem was of their own making, with such an apparently simple task.

Greg

[barnakiel]

We use a short stub antenna. It has less dB but better angles.


b.

[psp2psp2]

I got fed up dealing with masthead antenna problems, so I mounted a 3 ft fibreglass GLOMEX VHF antenna on the stern railing. I'm not an engineer, but I figured the very short cable run would compensate for loss of height, and any issues with corrosion or dodgy connections would be easier to fix.

I use this antenna both for R/T and AIS reception, and haven't noticed any difference in range from having it mounted much lower down. In fact, I regularly receive AIS data from vessels over 50NM distant.

AGE OF SAIL - Home

[GTom]

Originally Posted by psp2psp2

I got fed up dealing with masthead antenna problems, so I mounted a 3 ft fibreglass GLOMEX VHF antenna on the stern railing. I'm not an engineer, but I figured the very short cable run would compensate for loss of height, and any issues with corrosion or dodgy connections would be easier to fix.

I use this antenna both for R/T and AIS reception, and haven't noticed any difference in range from having it mounted much lower down. In fact, I regularly receive AIS data from vessels over 50NM distant.

AGE OF SAIL - Home

If you use a decent cable (even r8x, shipped with many decent vhf antennas) you'll hardly loose anything. It's the broken connectors and wet foam dielectrics that kill your traffic.
AIS goes further (don't ask me why...), but voice is usually line of sight. That's why I'll put my separate AIS antenna on the stern, likely on the radar pole:

[powsmias]

home depot runnin a sale on this one now
https://www.homedepot.com/p/Tram-AIS...b2XGvlfwt-5IeI

[S/V Illusion]

Originally Posted by barnakiel

We use a short stub antenna. It has less dB but better angles.


b.

Line of sight is line of sight. No amount of additional power can compensate for the reduced line of sight which occurs with low antennas. And no stub antenna is an efficient radiator or affects radiation angle in any way. Marketing is so adorable.

[GTom]

BTW anyone selling antennas with N-type connector on the Northern hemisphere? The only one I saw so far was in New Zealand.

[barnakiel]

Originally Posted by S/V Illusion

Line of sight is line of sight. No amount of additional power can compensate for the reduced line of sight which occurs with low antennas. And no stub antenna is an efficient radiator or affects radiation angle in any way. Marketing is so adorable.

This:


SMALL/VHF - Banten


at 10m, matched with the fat cable.


What is my problem? Talk to me.



Or do you sail a cruise ship with stabilizers?


My boat will heel 25-30 degs on a regular basis. Think of a small and narrow double ender in trade winds.


Rx.


?


Cheers,

b.

[Wotname]

Originally Posted by psp2psp2

...... I'm not an engineer, but I figured the very short cable run would compensate for loss of height,

Height trumps power!
1 watt at 10 ft is way way way better than 10 watts at 1 ft etc. Obviously you need a bit of both though

Originally Posted by psp2psp2

.
and any issues with corrosion or dodgy connections would be easier to fix.
..........

This is very very true!

[stormalong]

Avoid LMR400. Not only because of the foam dielectric, because LMR400 uses aluminum conductors and the center wire is not stranded. The center wire in copper clad so it can be soldered but despite appearances it is aluminum. The shield cannot be soldered - a crimp connector must be used. A proper crimping tool is about $50. Apply that money towards rg-213.

A good source of tinned rg-213 is Davis RF. No affiliation, just a happy customer.

[TreblePlink]

Antenna brand or type doesn't matter much. Height is everything at VHF, so it belongs at the masthead if you want best range. As has been mentioned, most problems are connector and corrosion related. I use teflon rg58/u - I forget the exact nomenclature. 18 meters does introduce some loss, but in the overall scheme of things, not much. If you have range issues, and the antenna LOOKS ok, the first thing to check is standing wave ratio - "SWR." You do this by inserting the meter between the radio and the antenna transmission line. Meters can be had on ebay for $30, or can be borrowed. You should see less than 2:1 on channel 16.


I have spent my career doing communications and antenna work.

[Auspicious]

Nothing is perfect. I like the Metz Manta for many reasons.

Originally Posted by stormalong

Apply that money towards rg-213.

I like RG-214. Double shielding. Remember to isolate the antenna bracket from the mast to avoid ground loops.

Originally Posted by TreblePlink

Antenna brand or type doesn't matter much. Height is everything at VHF, so it belongs at the masthead if you want best range.

AND NOTHING ELSE UP THERE. Separate AIS antennas (recommended), cellular, satellite, WiFi - all belong somewhere else. Spreader, pole, backstay, where ever but not at the masthead.

I like the Daiwa CN-801 cross needle meter which works on both HF and VHF.

[CarinaPDX]

While we all agree that antenna height and line-of-sight is more important, I don't think we should dismiss the importance of reducing cable losses (or obsessing about it either). RG-58 has about a 6dB loss over 100ft at marine VHF frequencies, and RG-213 has less than 3dB loss. The 3dB difference is a halving of signal strength. So a 100ft run from radio to antenna with 25W output will result in roughly 12.5W for RG-213 and 6.3W for RG-58 (about what a handheld puts out). At the margins of the range this does make a difference, although less than it may appear, as it is stated in decibels because the radiated power is an inverse square of the distance, not a linear relationship. Having that little bit of extra range is what a good install is all about, and entails both height and low cable loss.

Greg

[TreblePlink]

Originally Posted by Auspicious

I like RG-214. Double shielding. Remember to isolate the antenna bracket from the mast to avoid ground loops.

RG-214 is certainly low loss.



But I have never heard of isolating the antenna bracket from the mast. Is there a reference advocating this? The mast and stays form part of the antenna and can't be ignored. Some "no ground plane required" antennas can work with just the coax outer conductor forming the "other half" of the dipole, but most mast top antennas need the stays and or mast connection. From a lightning protection standpoint (nearby, not direct mast strike where not much helps) bonding at the top and close to the base is best.


All metal near the antenna affects the pattern. In a previous post I showed a typical effect on the vertical field due to induced mast and stay currents:

http://www.cruisersforum.com/forums/...-193349-2.html