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Old 19-03-2013, 21:22   #106
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Exactly what we use
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Old 20-03-2013, 03:34   #107
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Re: Please Recommend a Quality VHF Masthead Antenna

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Exactly what we use
Thanks! You've had no water absorption problems? How long have you had it up?
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Old 21-03-2013, 15:11   #108
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Re: Please Recommend a Quality VHF Masthead Antenna

Dockhead,
I have years of experience with foam-dielectric coax (> 30 years)...
Some Times LMR (and older "FM-8"), some Davis Bury-Flex, some Belden, and lots of Andrew Heliax....And, have not had any major "moisture" / "water-intrusion" issues.....
The only problem I've ever personally seen with foam-dielectric cables was some cheap generic "RG-8 foam" and "RG-213" (falsely-labeled) stuff with poorly installed connectors....of course RG-213 is supposed to be a solid PE dielectric cable, but I've actually seen foam-dielectric coax labeled RG-213!!!
{RG-213 is technically a "mil-spec" cable, but I've seen lots of true crap over the years that isn't good enough for a CB radio, let alone a marine VHF installation.....)
Please, whatever cable you decide on, do NOT buy "generic" or "no-name" cable....no matter what the spec sheet says if it ain't a respected name brand, I'd steer clear....




On-board my current boat, I have 2 runs of LMR-240 in the mast, and two runs of LMR-400uf from the mast compression post base (in the bilge) to the Nav Station....
Quote:
Originally Posted by Dockhead View Post
Thanks! You've had no water absorption problems? How long have you had it up?
I installed both of these in Nov/Dec 2004 (last time my mast was out)....that's over 8 years ago...and have had NO noticeable signal degradation (neither on transmit nor receive), nor any changes in VSWR (I have a vhf "cross-needle" power/swr meter permanently mounted at the Nav Station, right next to the one for my HF station)....

I haven't peeled back the heat-shrink or rescue tape on the top of the mast, but I HAVE done so to the junctions (using Amphenol PL-258 barrels) in the bilge, just last summer and all was clean, and shinny.....and no noticeable moisture issues with the cables....

I also have a short run of LMR-400uf from the Nav Station, back aft to the stern rail, for a separate AIS antenna....this cable is new (about one year old) and no issues there either....



On-shore, I have a couple runs of Davis Bury-Flex at my home in Florida, that have been up and working for 12-15 years....and also have a run of Andrew LDF 7/8" Foam dielectric Heliax on my tower for almost 30 years now for use on vhf (144mhz) and all is well!!!
Further I have 2 runs of about 1200' each (yes that's about a 1/2 mile) or Andrew LDF 7/8" foam dielectric Heliax, running my vhf and uhf repeaters....it's been up >20 years and all is well (I just swept the whole run last fall....)


I understand that if moisture gets into the cable, foam dielectric cable losses will increase faster than a solid dielectric cable, ruining the cable for most uses....but the solid dielectric cable is also ruined, it just takes a bit longer....

Remember that almost all the big coax runs you see on cellular / mobile phone towers is foam dielectric cable....and are being used at mid-high uhf freqs (700/800/900mhz and 1800/1900/2100mhz).....
All non-pressurized rigid coax is foam dielectric....all the Cable TV Hardline is foam dielectric cable....
{Most TV and Radio broadcast stations (all full-power stations!) use either dry-air pressurized coaxial transmission line or even uhf waveguide to reduce transmission line losses even further, as 1000' of foam-dielectric line has a lot of loss at vhf/uhf freqs, can you imagine what RG-213 loss would be???}


I'm NOT telling you that you must use a foam-dielectric cable, but if you are concerned about "moisture wicking" / "water intrusion", understand that this will also happen with solid dielectric cables, if you don't install and waterproof the connections properly....



I hope this helps.....

John
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Old 21-03-2013, 17:37   #109
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Re: Please Recommend a Quality VHF Masthead Antenna

Dockhead,
In addition to my earlier experiences / examples, the most often used cable for VHF masthead antennas on sailboats around here is RG-8x and it's a foam-dielectric cable....(of course, RG-8x is not a real mil-spec cable, so there are many variations around, depending on manufacturer...but all are foam-dielectric)....

And, as I wrote above, I've been using many foam dielectric cables for years....and on-board, have had LMR-240 (in the mast) and LMR-400uf (in the bilge/behind cabinetry) working for over 8 years now....no worries...





As for "silver-plating".....
Quote:
Originally Posted by Dockhead View Post
Can anyone explain whether silver either in antennae or in coax (I asked that question in another thread) is really valuable, and worth a price premium?
RG214 coax with silver covered copper conductors and double braids is about triple the cost of regular mil spec all copper RG214. Is it worth it?
a) the silver-plating of critical RF components, really has little measureable effect at VHF freqs....but is used in cavity filters, etc. and other critical RF components where every 1/100 of a db is important.....
But silver-plating of cabling usually has NO measureable effect until low-microwave freqs.....(however, even at microwave freqs, it is still the size/surface area of the cable, the cable's dielectric, and the accuracy of cable construction, that are the main determiners of the cable's loss)

Bottom line: "silver-plated" cabling for VHF is a waste of $$$!!!
(although the increased isolation of the double-shielding IS useful in some vhf applications, such as external filter assemblies, cavity connectivity, etc. but flexible Heliax is also used quite a bit....and even 97-98% braid over a solid bonded-foil coax is becoming more common thesedays....)







b) Coaxial cable loss at freqs below a couple 1000 MHz, is NOT effected by the silver plating of the conductors....actually almost all coaxial cable loss is based on the size (surface area) of the conductors and the dielectric used (a vacuum would be ideal, but dry air is almost as good....and high-vel-factor foams are pretty good as well...)
Quote:
Originally Posted by Dockhead View Post
..any advantage from silver is not reflected in the specs of the cable. I would think that attenuation would be the whole story, not so? It's no different. Maybe it's more durable, for some reason?
The silver-plating will have NO effect at all....






c) As I posted earlier, you should have no issues with high-quality foam dielectric cable, such as Times LMR-400uf or Davis Bury-Flex...
Quote:
Originally Posted by Dockhead View Post
LMR400 has the foam dielectric with many reports of water problems. It is available in the UK, and it is less expensive than the silver-coated RG214, but I think I won't risk that at my masthead. Perhaps some direct-burial type, but still -- the foam is inherently risky for marine use, it seems to me?
I'm not sure where you're hearing of all the problems, but if you feel you can't get past this issue, then either use a "flooded" cable, also called "DB", for "direct-burial" (or just accept the normal loss like most, and use Belden RG-213/u)
Quote:
LMR-UltraFlex: A stranded center conductor and a more flexible jacket make LMR-UltraFlex ideal for applications requiring repeat bending. Available sizes include 240, 400, and newly introduced 500 and 600. Attenuation is about 15% higher than for standard LMR cables. LMR-UltraFlex cable accepts standard LMR connectors.

LMR-DB: Watertight flexible coax meets Industry Standard watertightness tests ASTM D4565, REA PE39, ANSI S-84-608 while maintaining the same excellent performance properties as standard LMR. The inert flooding compound completely eliminates all paths of water migration and ingress for long term reliability (10 year warranty)
FYI, flooded cabling is usually a pain in the ass to install connectors on (lots of gooey/sticky stuff) and proper connections/connectors are required....(If you're going with LMR cables, I usually recommend the Times matching connectors, etc..)

Times LMR-400DB is $1.15/ft here in the states....not sure what it costs in the UK....(perhaps an e-mail to Times Microwave sale dept. would put you in touch with a UK distributor???)
Times Microwave LMR-400DB 3/8" LMR400 Flooded | TESSCO





Now, with this settled, maybe we can talk about anchors???

Fair winds....

John
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Old 21-03-2013, 22:53   #110
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Re: Please Recommend a Quality VHF Masthead Antenna

Wow, thanks for all the tremendously enlightening information. I finally feel like I understand a little bit about coax. Who would have thought that it is such a complicated subject!?

I think for my VHF antenna I will go with RG213U. I just don't need the last 1.3dB of ERP so much that's worth either the cost of LMR400, or even a small risk of water problems.

But for the mobile and ham antennae, I will now be able to choose and use foam dielectric coax with some confidence - thanks!!
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Old 22-03-2013, 04:47   #111
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I think you should just sail over here so you can get all the good stuff for good prices
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Old 22-03-2013, 07:39   #112
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Re: Please Recommend a Quality VHF Masthead Antenna

Dockhead,
You're welcome!!


BTW, I forgot to mention that even though Times markets the flooded LMR400DB as "highly flexible" it really is not that flexible, as it has a solid center conductor, not stranded (as the LMR400uf has), and they're comparing their cable's flexibility to solid corrugated copper transmission line (aka Heliax)....so, I would NOT want to try to install this stuff in my mast!!!
(unlike RG-213/u, it cannot be bent / curved too tightly...)
Quote:
Originally Posted by Dockhead View Post
I think for my VHF antenna I will go with RG213U. I just don't need the last 1.3dB of ERP so much that's worth either the cost of LMR400, or even a small risk of water problems.
This is a good choice....



FYI, while I do recommend "name brand" cables (Davis, Belden, CommScope, Times, etc.), a good simple indicator of decent cable (vs.cheap/crap cable) is how tightly it is constructed.....you should NOT be able to budge the outer jacket / nor twist the jacket / etc.....nor after cutting the jacket and braid, should you be able to easily strip the PE dielectric off the center conductor.....
If you can do these things easily, the cable has little/no construction tolerance, and is suspect.....(personally, I'd call it crap, and toss it in a dumpster....which I have actually done!)
If you cannot find "name brand" coax, give the coax a good once over, twist it, pull it, yank it, and then take your knife and cut the jacket off...inspect the braid, it better be really tightly woven....and then cut it off and look at the dielectric and try to strip it off with your knife, if it falls off easily, the cable is suspect....


Just some tips that might help...

Fair winds..
John
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Old 28-04-2013, 14:44   #113
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Re: Please Recommend a Quality VHF Masthead Antenna

Update:

So I bought the Galaxy dipole antenna like Nick's, only the newer version with silver plated elements. I mounted it much like the way Nick mounted his, on a pedestal bolted to the masthead truck.

I pulled RG213 cable up to the masthead. Shortened the Galaxy's pigtail and put on Amphenol "N" type connectors.

One problem I have is that none of my heat shrink tubes are wide enough for the "N" type connectors, which are fatter than PL259.

I have some self-amalgamating tape, but this doesn't seem like as good a solution as heat shrink. I wonder about putting some kind of junction box on the masthead to protect the connectors.


I also bought a Diamond VHF/UHF ham antenna, and mounted that on my lowest spreader. I pulled RG213 cable up there, too. It's a 1.2 meter fiberglass job with its own radials, so it doesn't require a ground plane. I soldered on an Amphenol PL259 connector since the Diamond antenna has an SO239. It will be connected at first to my Sitex AIS transponder. In June, my brother will come from the States to visit and will bring me a VHF/UHF ham radio which I will also use on this antenna. I'll have to figure out some kind of coax switch for sharing the antenna.
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Old 28-04-2013, 14:55   #114
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It must be beginning to look like a Russian spy trawler by now!!

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Old 28-04-2013, 15:11   #115
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Re: Please Recommend a Quality VHF Masthead Antenna

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.

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Old 28-04-2013, 15:11   #116
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Re: Please Recommend a Quality VHF Masthead Antenna

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It must be beginning to look like a Russian spy trawler by now!!

Dave
LOL!

Yes, well, the mast is still horizontal, but day after tomorrow, when the mast is stepped, she will be bristling with antennae! Russian spy trawler -- I like that. Only they never used sails on those, as far as I know . . .
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Old 28-04-2013, 15:15   #117
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Re: Please Recommend a Quality VHF Masthead Antenna

Quote:
Originally Posted by s/v Jedi View Post
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.

OK, thanks for that.

You wouldn't consider a junction box? Wouldn't that solve the problem for all time?
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Old 28-04-2013, 15:23   #118
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Re: Please Recommend a Quality VHF Masthead Antenna

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OK, thanks for that.

You wouldn't consider a junction box? Wouldn't that solve the problem for all time?
I would rather paint it with tar... I hate junction boxes.
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Old 28-04-2013, 15:42   #119
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Re: Please Recommend a Quality VHF Masthead Antenna

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I would rather paint it with tar... I hate junction boxes.
Why??
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Old 28-04-2013, 15:53   #120
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Re: Please Recommend a Quality VHF Masthead Antenna

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Why??
Because I think tar would work better than a box. The box would be long, narrow and flat... with two cable glands, one at each end, that you somehow need to get N-type connectors through. I envision drama

Rescue tape stays good forever when protected from UV.
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