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Old 03-02-2014, 01:39   #136
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Re: Amazing Power of Good Antennas

I had the usual cheapo "print-circuit J-pole" in fiberglass casing marine vhh, which was damaged when the stepped down the mast.
Since then I replaced by a 1/2wave base fed whip antenna (Glomex) reportedly having 3dB gain. Hell 0 dB gain would be OK for me. For me this is the most convenient vhf antenna type for mastmounting: low windsurface, flexible because it is a SS whip, and it has a SO239 type of female socket for connection, which can be sealed perfectly with amalgamating tape. No to worry anymore.
As important is the quality and loss figures for the coax, it makes the difference between getting 75% or 25% of your transmitter power in the antenna base.

Jan
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Old 03-02-2014, 22:11   #137
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Re: Amazing Power of Good Antennas

I was talking to a guy at Davis RF last week regard RG213 Coax vs LMR400, and after some discussion, he recommended Belden 9913F7 ($1.04/ft) over the RG213 & LMR400 - having comparable dB of the LMR400 - and better flexibility...

is anyone familiar with this Coax?
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Old 03-02-2014, 22:41   #138
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Re: Amazing Power of Good Antennas

It's a 52ohm cable. I'm not sure if that matters or not in your case. Regular 9913 cable is 50ohms. If same price the 9913 looks pretty good. Online lmr400 seems less expensive than either Belden cable.

http://www.universal-radio.com/catalog/cable/coax.html


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Old 03-02-2014, 22:49   #139
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Re: Amazing Power of Good Antennas

I see that... 51.5 Ohms +/- 2 Ohms...

Not sure what to do with that...

I think the point of the 9913F7 over the LMR400 was the flexibility...
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Old 03-02-2014, 23:54   #140
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Quote:
Originally Posted by Capt'n Ricko
I was talking to a guy at Davis RF last week regard RG213 Coax vs LMR400, and after some discussion, he recommended Belden 9913F7 ($1.04/ft) over the RG213 & LMR400 - having comparable dB of the LMR400 - and better flexibility...

is anyone familiar with this Coax?
RG213 comes with either a solid or stranded core. The stranded core type is much more flexible. I believe it's called RG213/U.

LMR400 has a foam core, not solid like RG213, and some people think that's risky for marine use.
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Old 04-02-2014, 07:03   #141
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Re: Amazing Power of Good Antennas

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Originally Posted by Dockhead View Post
RG213 comes with either a solid or stranded core. The stranded core type is much more flexible. I believe it's called RG213/U.

LMR400 has a foam core, not solid like RG213, and some people think that's risky for marine use.
A bit confusing...

Wire used for the center conductor is either stranded or solid. Belden 9913 is solid but the 52 ohm variety is stranded.

Some believe that foam insulation (stuff between inner and outer conductor) is prone to trapping water and also believe solid insulation is not as susceptible to water intrusion. Probably this is so but good sealing of both ends will prevent intrusion of water.

Foam insulation and stranded inner usually makes for a more flexible cable.

Given the price of LMR-400 is $1/ft online that seems like a good deal if you can get it. Use it for the vertical mast run and use a LMR-400 Ultraflex pigtail from the step to the radio. Done right the barrel connector will at most add 0.15dB loss and will make unstepping much easier.
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Old 04-02-2014, 10:52   #142
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Quote:
Originally Posted by transmitterdan

A bit confusing...

Wire used for the center conductor is either stranded or solid. Belden 9913 is solid but the 52 ohm variety is stranded.

Some believe that foam insulation (stuff between inner and outer conductor) is prone to trapping water and also believe solid insulation is not as susceptible to water intrusion. Probably this is so but good sealing of both ends will prevent intrusion of water.

Foam insulation and stranded inner usually makes for a more flexible cable.

Given the price of LMR-400 is $1/ft online that seems like a good deal if you can get it. Use it for the vertical mast run and use a LMR-400 Ultraflex pigtail from the step to the radio. Done right the barrel connector will at most add 0.15dB loss and will make unstepping much easier.
Although I have a 100' run of cable from ghe top of my mast to my nav table, I opted for RG213/U and passed on the lower loss, foam core LMR400. My reasoning was the main VHF antenna is a mission critical safety issue, and pulling new cable in case of failure with the mast in is unrealistic. So I took a more conservative approach at the cost of a couple of dB. Others may choose different priorities, of course.
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Old 04-02-2014, 12:22   #143
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Re: Amazing Power of Good Antennas

Universal's web page shows the 9913 family has an "air dielectric" which I assume means foam. I'm on the side that says this is probably wrong in a boat's mast, because the cable usually will not be properly supported, and the foam will be pinched by the supports, and the cable stretched out more from gravity on the vertical run, so the dielectric will be compressed and distorted.

As opposed to a solid dielectric, which may not be as good initially, but will hold up much better in the years after installation.

At least, that's what I've seen said year after year from all sorts of sources. Everyone who makes or uses it says the solid dielectric is the better choice for this application, unless you use proper professional installation techniques to avoid pinching and stretching. (i.e. Chinese finger traps.)

Ricko, sometimes "the best choice" means "We bought a pallet of this as surplus for half price" and sometimes, that does justify "best". You might want to ask your vendor why he thinks this is best, price or performance, and if he's aware of installation issues for the mainly vertical run, unsupported, that you'll have in the mast.
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Old 04-02-2014, 14:44   #144
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Re: Amazing Power of Good Antennas

From my understanding, the difference in propagation pattern between a 1/2 wave and a 5/8 wave antenna is that a 1/2 wave antenna transmits in a dome shaped pattern, while a 5/8 wave pattern transmits in a horizontal toroid pattern, basically a donut. Because of this, a 1/2 wave antenna transmits quite a bit of energy upward, where no one is going to receive it. a 5/8 wave antenna transmits all power horizontally, thus a 5/8 wave with an identical power output radio will transmit quite a bit more energy in a more useful direction, thus giving quite a bit more useful range. The drawback is that a 5/8 wave requires a ground plane to work properly, which can be done with metal stays radiating out/downward from the mount area.

Based on the whip antennas I've bought, the difference in length between a 1/2 wave and a 5/8 wave is almost imperceptible. The main difference is the length of the coil in the base. I use a double stacked 5/8 wave CP22E for a base antenna (6.5dB gain) and Larsen NMO150 antennas for mobile use. I tune both of them for midband at 154 MHz. If someone absolutely refuses to use a metal ground plane, then I provide them with a wideband antenna, which provides performance somewhere in between 1/2 and 5/8 wave.
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Old 04-02-2014, 16:38   #145
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Re: Amazing Power of Good Antennas

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Originally Posted by socaldmax View Post
From my understanding, the difference in propagation pattern between a 1/2 wave and a 5/8 wave antenna is that a 1/2 wave antenna transmits in a dome shaped pattern, while a 5/8 wave pattern transmits in a horizontal toroid pattern, basically a donut. Because of this, a 1/2 wave antenna transmits quite a bit of energy upward, where no one is going to receive it. a 5/8 wave antenna transmits all power horizontally, thus a 5/8 wave with an identical power output radio will transmit quite a bit more energy in a more useful direction, thus giving quite a bit more useful range. The drawback is that a 5/8 wave requires a ground plane to work properly, which can be done with metal stays radiating out/downward from the mount area.

.........
Depending of course on your angle of heel which for some of us can be regularly as high as 20 degrees. YMMV of course...
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Old 04-02-2014, 17:48   #146
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Re: Amazing Power of Good Antennas

What??

Next you'll be telling me there are waves and swells and all kinds of weird weather!!
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Old 05-02-2014, 07:22   #147
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Re: Amazing Power of Good Antennas

Foam polyethylene dielectric is not much different than solid PE in relation to long term stability. Any decent installation should not have sharp bends or pinching. Whatever cable is used it needs to be restrained and properly supported. If the installer pokes the cable through a hole at the top of an aluminum mast, lets all the weight hang on the edge of the hole with the cable slapping the inside of the mast then bad things will happen no matter what cable is used.

So-called "air dielectric" is a marketing phrase that seems not be challenged very much. Lowest loss coax will have just air (or some inert gas) between the center conductor and the outer. But it's not very practical for a flexible cable. To reduce cost and give flexibility cables with different types of plastic dielectric came along but they have higher loss than air. So someone decided to use foam (plastic with lots of air bubbles) to compromise between the two and cleverly called it "air dielectric" even though it's not really just air.

The real threat from water is when it wicks inside the plastic between the inner or outer conductor and causes corrosion. Neither solid nor foam dielectric is better or worse in that regard. It is necessary to water proof all connectors and try not to cut or puncture the jacket. With a little effort any cable type will stay dry inside.

There are a number of variations of LMR-400 and many other common cable types. It is a good idea to be sure you know what you are getting and why. The 9913 cable is a foam PE cable similar in many ways to LMR-400. They are made by different companies but compete within the same market. I don't think I would pay more for 9913 than for LMR-400. Whichever is less expensive should be fine for marine VHF use.

Use of RG-213/U cable is not a bad thing either. It has higher losses because it is a solid dielectric and usually a stranded inner conductor. It has been used for decades successfully. It may cost 25% less and is more readily available than LMR-400. There is no free lunch.
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