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Old 07-07-2020, 02:59   #1
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Keeping the VHF coax in one piece: FME to PL259?

I intend to keep my RG213 in one piece skipping the deck level connector in order to avoid a possible corrosion spot and possibly reduce losses.

The female FME-plug seems small enough to get trough holes and I could adapt it to PL259 at the VHF kit. Anybody doing that? Or always recrimp a PL259? How much loss should I expect if I use an adapter?
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Old 07-07-2020, 03:34   #2
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Re: Keeping the VHF coax in one piece: FME to PL259?

I made my VHF feedline a single run of RG-214 with no connector at the mast base. With very good results.



Just pull the cable before installing the connector. Simples. Why would you mess with an adapter? uzzled:
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Old 07-07-2020, 04:53   #3
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Re: Keeping the VHF coax in one piece: FME to PL259?

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I made my VHF feedline a single run of RG-214 with no connector at the mast base. With very good results.



Just pull the cable before installing the connector. Simples. Why would you mess with an adapter? uzzled:
What do you do when the mast comes down for winter? You have a large hole at the mast base allowing the PL259 trough?
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Old 07-07-2020, 05:46   #4
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Re: Keeping the VHF coax in one piece: FME to PL259?

The loss of a properly soldered coax connector is negligible as is any good quality connector between sections. Lots of testing has been done stringing connectors together with no measurable loss. Sealing them to preclude moisture isn’t very difficult. What is problematic is crimping coax - most people crush the dielectric in the process or don’t adequately crimp, the result of both is a poor connection easily avoided by soldering.
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Old 07-07-2020, 05:58   #5
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Re: Keeping the VHF coax in one piece: FME to PL259?

My mast is 23 meters high, so it doesn't come down for the winter.

If I did want to take it down, I'd just pull the cable out from the nav table to the mast base.

If in your case that wouldn't work, you could just cut it off.
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Old 07-07-2020, 06:31   #6
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Re: Keeping the VHF coax in one piece: FME to PL259?

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Originally Posted by GTom View Post
I intend to keep my RG213 in one piece skipping the deck level connector in order to avoid a possible corrosion spot and possibly reduce losses.
I work in the radio communications industry.

The losses from a properly installed, high-quality connector on RG213 are too small to measure without laboratory-grade equipment. There are well-sealed, mechanically strong connectors available. I would use an N connector at the base of the mast.

Quote:
The female FME-plug seems small enough to get trough holes and I could adapt it to PL259 at the VHF kit. Anybody doing that? Or always recrimp a PL259? How much loss should I expect if I use an adapter?

I haven't run into FME connectors and don't know much about them. How did you decide on FME? A quick check of my usual suppliers doesn't show any available for RG213. You might consider a TNC connector. You should use a crimp-on connector. They are smaller in diameter and more reliable than the other styles.

There won't be any measurable loss from an adapter.

You might also consider using a short whip (12-48") of, say, RG400, instead of an adapter, because it is light and flexible and will not put as much stress on the connector on the radio during installation and maintenance, and will not have to be anchored in place as carefully.


A fact to consider is that marine VHF performance isn't materially affected by antenna gain or feedline losses (within reason). Line of sight is limiting.
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Old 07-07-2020, 08:26   #7
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Re: Keeping the VHF coax in one piece: FME to PL259?

Sounds like you are dealing with deck stepped, and this probably works best with keel stepped, but it does help with typical VHF antenna problems:
A convenient place to disconnect the mast/antenna from the ship, a transition, point for larger coax to smaller RG8X for running to the radio(s), a way to ground the antenna when not using the VHF, and surge protection for nearby lightning (gas discharge tube).


I have two VHF radios and this coax switch allows me to use either radio. For a single radio just leave one coax blank. Alpha Delta coax switch, less then $100 US and pretty high quality.


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Old 07-07-2020, 09:42   #8
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Re: Keeping the VHF coax in one piece: FME to PL259?

Install a ThruDex watertight fitting in deck at mast base.
Make your mast section RG213 long enough to go down thru the ThruDex to boat interior.

Use another length of RG213 to reach from the ThruDex area to the radio.
Solder PL258's & use a SO239 coupler near ThruDex.
Do not tape/seal this splice coupling.
Your coax is now spliced indoors & is easy to uncouple for mast removal.
One part of the ThruDex watertight fitting stays on the mast coax , is separated by removing 4 SS screws, & stays with the removed mast.

Other size ThruDex are available for NavLight,etc. wires.


Mine have been in service for 12yrs now.


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Old 07-07-2020, 10:23   #9
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Re: Keeping the VHF coax in one piece: FME to PL259?

We have a Blue Sea Systems cable clam mounted to the deck near the mast step. Which is big enough to fit the connector through when removed.

https://www.bluesea.com/products/1003/CableClam_1.40in



We also use a ICOM black box radio mounted near the cable entrance so its one continuous cable from the radio to the antenna.

When the mast comes down, I just disconnect the cable from the radio and feed it through the hole with the cable clam removed.
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Old 07-07-2020, 11:21   #10
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Re: Keeping the VHF coax in one piece: FME to PL259?

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Originally Posted by Jammer View Post
I haven't run into FME connectors and don't know much about them. How did you decide on FME? A quick check of my usual suppliers doesn't show any available for RG213. You might consider a TNC connector. You should use a crimp-on connector. They are smaller in diameter and more reliable than the other styles.

There won't be any measurable loss from an adapter.

You might also consider using a short whip (12-48") of, say, RG400, instead of an adapter, because it is light and flexible and will not put as much stress on the connector on the radio during installation and maintenance, and will not have to be anchored in place as carefully.


A fact to consider is that marine VHF performance isn't materially affected by antenna gain or feedline losses (within reason). Line of sight is limiting.
The FME idea came when I was looking for the antenna, found the Glomex RA106SLSFME first (abandoned that later for the RA109 which is SO239). Indeed, it is hard to find in RG213 size I think I saw one. Basically the point is to keep the fitting size close to the 10mm cable size. I'll look at the TNC.

Quote:
Originally Posted by ABJ87 View Post
We have a Blue Sea Systems cable clam mounted to the deck near the mast step. Which is big enough to fit the connector through when removed.
https://www.bluesea.com/products/1003/CableClam_1.40in

We also use a ICOM black box radio mounted near the cable entrance so its one continuous cable from the radio to the antenna.
When the mast comes down, I just disconnect the cable from the radio and feed it through the hole with the cable clam removed.
That's an option too, bit reluctant to broaden the hole to 20mm though.
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Old 07-07-2020, 12:15   #11
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Re: Keeping the VHF coax in one piece: FME to PL259?

Not the question that you asked, but...


You could run RG58C. It's lighter which means less weight aloft. It's easier to install. It's cheaper. The extra loss works out to about 2 dB on a sailboat. It would rarely if ever make a difference in ability to carry out communications.

RG213 is great stuff. For UHF, notably 900 MHz systems, it's important because the losses are higher. Not usually worth it for VHF though.
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Old 10-07-2020, 18:51   #12
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Re: Keeping the VHF coax in one piece: FME to PL259?

a pl259 isn't much bigger then a rg213 cable... might as well pull both through the hole.


I can't imagine an FME connector for a 213 cable. the connector is way smaller then the cable.
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