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Old 20-03-2016, 08:28   #1
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Coax Connectors

I am replacing the VHF cable to the masthead antenna (new as well) after 30 years of service. My mast is deck stepped and there are 2 lengths of cable... one runs from the VHF at the nav station through the deck... and connects to a cable running from the antenna through the mast to its base. The present connection is a double ended female and the two cables have makes at both ends. The connection is then pushed up inside the mast out of direct contact with water. I think this is not an uncommon approach.

I decided to use higher gain less loss LMR 400 cables.

There is a deck gland which allows for various thickness cables...

The problem I may face...yet to be determined when I have a closer look... is can I snake the cable from the VHF to the mast with the rather large PL259 connectors?

The cable supplier made the cables up with one male and one female what they called FME connectors which screw together. But there is no "nut" and it seems that I would have to spin one cable to make the connection. DUMB. I am sending these cables back to be done properly.

So the questions are:

What is the best way to connect the two cables?

What is the smallest connector to connect 2 LMR 400 cables?


The size of the connector is an issue because the one that runs to the VHF is in a plastic conduit (ID unknown at this time) which I suspect MAY not accommodate the diameter of the PL 259. The PL259 end may have been made in the field by the installed of the radio back in the last century. The present "joint" is a double end female for the doubled ended male PL259 cables.

I would like to avoid a field made cable to connector end.

Whatever the connection will be it will be sealed in heat shrink tubing.
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Old 20-03-2016, 08:41   #2
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Re: Coax Connectors

Good article here by Mainsail Easy VHF Connections Photo Gallery by Compass Marine How To at pbase.com
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Old 20-03-2016, 08:43   #3
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Re: Coax Connectors

Thanks... but the guide are for field made connections.
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Old 20-03-2016, 08:58   #4
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Re: Coax Connectors

The FME connector sounds like what you are needing. You do not have to "spin the cable" to connect the male and female connectors. The male threaded sleeve should turn without turning the cable itself. I would take another look at the connectors before returning them.
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Old 20-03-2016, 09:14   #5
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Re: Coax Connectors

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Originally Posted by transmitterdan View Post
The FME connector sounds like what you are needing. You do not have to "spin the cable" to connect the male and female connectors. The male threaded sleeve should turn without turning the cable itself. I would take another look at the connectors before returning them.
The male and the female both have heat shrink over them and although the male has 32 flats on the shaft it is impossible to turn it even with a wrench.

Perhaps I should cut the heat shrink back?

I did... does not turn...
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Old 20-03-2016, 12:39   #6
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Re: Coax Connectors

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Originally Posted by Sandero View Post
The male and the female both have heat shrink over them and although the male has 32 flats on the shaft it is impossible to turn it even with a wrench.

Perhaps I should cut the heat shrink back?

I did... does not turn...
One of the halves of the connector should be free turning. Does it look like this?

https://en.wikipedia.org/wiki/File:FMEconnector.jpg

If not post a picture of what you have.
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Old 21-03-2016, 14:16   #7
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Re: Coax Connectors

You could do an SMA male and SMA female on the LMR400 no problem.. very small connectors.
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Old 21-03-2016, 14:30   #8
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Re: Coax Connectors

FME are generally used for external cell phone antenna cables. Nothing "wrong" with them, but UHF connectors (PL-259 and SO-239) are standard, and if you need to swap something out at some time in the future--it is easier to do when you've got standard connections.


The "double female" is also known as a "barrel connector" or a "bulkhead connector", depending on whether it is just used to join two cable, or installed through a bulkhead (wall or deck) permanently, and the cables both screwed into it.


Again, all standard UHF fittings in normal installations.


A conventional installation would be to put a bulkhead connector through the deck (they are available in 1-2-3-4-5-6-7-8 etc. inch lengths) with a waterproof bedding compound, and then screw the cable from the mast in above deck, and a second cable run below deck. Nothing needs to go through a gland, the bulkhead connector is waterproof, and you use some cable wrap (butyl or silicone tape) over the connection to ensure a watertight seal. A bail or guard over it prevents it getting stepped on.


Then in the cabin, a separate run of coax goes from the bulkhead to the radio, with a drip loop below the bulkhead connector (just in case) and optionally, a second interior cable that you use to directly ground the bulkhead fitting, so a lightning strike (especially while you are off the boat) goes to ground, rather than into the electrical system.


UHF fittings "ain't the best" for many installations, but the fact that they are standard often overweighs any other considerations. At marine VHF frequencies, their performance is also plenty good enough, and they are physically robust.
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Old 21-03-2016, 14:47   #9
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Re: Coax Connectors

I would not be afraid to put to sea with standard connectors used in the wireless industry. The reality is that in most of the world SMA, BNC, type-N and FME are much more common than PL-259. I think the only people still using PL-259s are hams, CBers and marine VHF. Any island with a cell tower will have plenty of SMA and type-N connectors and an assortment of adapters on the local cellular/satellite TV utility truck. Plus they will have the proper tool for crimping these connectors and weather seal kits too.
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Old 23-03-2016, 14:55   #10
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Re: Coax Connectors

Sandero, et al,

Part I:

~~ First off, PLEASE do yourself a favor and make darn sure you need LMR cabling before you order it (again) / use it...
(on a 36' boat, I cannot think of any reason to try and gain 1/2db, versus RG-213!!)

~~ Secondly, if you do decide that you need it, PLEASE make darn sure that you're using the "UF" version, such as LMR-400UF....NOT LMR-400
https://www.timesmicrowave.com/docum...LMR-400-UF.pdf

If you need explanations of the "why's" of the above recommendations, see below...


~~ Thirdly, if you've made the choice to use LMR cables, and have chosen LMR-400UF, PLEASE ask your supplier what connectors they use, be specific...you want to know the brand!! (because as odd as it sounds, Times Microwave does not make "UHF" connectors for LMR-400UF cable, N, SMA, mini-UHF.....yes, but not UHF/PL-259!)
https://www.timesmicrowave.com/docum...LMR-400-UF.pdf

Or simply call Texas Towers or DX Engineering...
Texas Towers, Coax Jumpers Page

http://www.dxengineering.com/search/...2%2B4294952392



~~ Fourth....If you need pre-made cable assemblies (a good idea for most), please look to Texas Towers or DX Engineering...
They're both great companies, and I've done business with both for many years!

Texas Towers, Coax Jumpers Page

http://www.dxengineering.com/search/...2%2B4294952392




~~ And finally, fifth....
Some may think I'm speaking heresy when I write this, but if you look beyond the internet marketing and talk to others who've not only been doing this for decades, but also understand the intricacies of RF, you'll find this is a FACT...

For transmitting, antenna feedlines, and equipment interconnections, at all MF, HF and VHF freqs (actually up to about 400 - 500mhz), there is NO REASON to use anything other than "UHF connectors" (aka PL-259's / PL-258's / SO-239's)....
Talking about the venerable and ubiquitous Amphenol 083-1SP / PL-259-type connector....(and the 083-1J PL-258/"barrel") assembled/soldered correctly, onto a piece of name-brand RG-213, etc., will last decades!!
PL-259, UHF Straight Solder Plug for RG-8 | 083-1SP | Amphenol RF
http://www.dxengineering.com/parts/aml-83-1sp

Adapter, UHF Jack to UHF Jack, Non-Constant | 083-1J | Amphenol RF

As long as you weather-proof external connections, these connectors work well...
They have both, large and solid center pins and excellent shield contacts, and are very serviceable even at high transmit powers....and work very well even at VHF frequencies, without VSWR issues!

Here's a photo from an old friend, showing 23 different connectors/adapters, with 0.5db loss, transmitting exactly 100 watts thru them at 28.5mhz....and some of those are F, RCA/Phono connectors (never designed for RF transmit!)...
Enjoy!



{please understand in my professional career, I use mostly "N" connectors, along with some "SMA" and even some "F"....but, in HF and VHF comms I use "UHF-connectors" (aka PL-259's)....and so does EVERYONE else....
At freqs below 400mhz, and especially with transmit powers, there is no reason not to...}




Part II
And, on a 36' boat....
The difference that you'd see between a NEW and PROPERLY terminated / installed RG-213 cable run versus one with LMR-400 is negligible!!!
(please note that even if you used some new RG-8x, you'd not notice a difference in such a short run of ~ 60' - 70'...)
BUT....
But, chances are quite high that you will notice a difference between your old cable/connections and anything new that you install! (and this is what leads so many non-tech sailors to rave about "how good this cable is", etc...when in reality it's because it is NEW, with NEW connectors, and most likely properly connected/installed!)

I've posted about this at length, many times in the past...
Do a search, and read the particulars....but, in a nutshell, you're seeking an approx. 1/2db advantage from LMR-400 versus a good quality RG-213 (for a 50' - 60' run of cable)...
There is no way that you or I, could ever tell this difference...
(heck you ma get a 1/2 advantage if you clean the bird poop off the VHF antenna!


Here is a great thread which explains all the "why's"!
Have a look...

VHF and AIS Radiowave Propagation and VHF and AIS Radio Range



I do hope this helps..

Fair winds...

John
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Old 23-03-2016, 15:52   #11
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Re: Coax Connectors

John- You missed one.(G)
If the guys who made the radio, made it with a UHF connector on the back, they probably thought that was good enough. AND, if you ever have to plug another length of cable in, guess what connector will be needed to fit the UHF connector on the radio?


Right.(G)


There's often a reason why 50+ year old standards are still standard. Even if it is only because "that's standard."


Now, as to proper stress relief and hangers on the long vertical cable run...
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Old 23-03-2016, 17:25   #12
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Re: Coax Connectors

Thank you John!

I think I will use the RG213... and PL259's and see if I can get the supplier you recommended to send me the cables and toss the LMR400 cables in the bin or give them away!

A lesson learned and it wasn't too spendy and I didn't install it... so no time wasted.

Jeffrey
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Old 24-03-2016, 04:12   #13
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Re: Coax Connectors

I am not thinking of yet another installation problem. I just read the minimum bend radius of RG 213 is 5".

Now I am thinking I can possibly pass RG213 through the deck and bend it in the small space of between the headliner and the deck... or even behind the VHF radio... which is probably 3"... So I am thinking I must find and use some right angle connectors. Web search begins...
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Old 24-03-2016, 05:18   #14
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Re: Coax Connectors

John is right, and echoes all my thoughts on LMR-400, LMR-240, etc. There's simply no reason on a mid-size sailboat to use LMR cables, IMHO.

And, while RG-213 is "standard" and I use it a lot, I personally prefer RG-214 because it has a double shield as well as tinned conductor and shields. If you want to go whole hog, the military version RG-214/Mil is great, though pricey. It has silver conductors/shield.

A very good source for all coax is the RF Connection The RF Connection Home Page

The choice of PL-259 UHF connectors is important. These come from a variety of sources and manufacturers and are NOT created equal. Some are very shoddy. Even the "gold-plated" Shakespeare brand is to be avoided....I've seen them pull apart easily. Spend the extra $1 or so and get genuine Amphenol connectors. And, after they are properly installed onto the coax, be sure to waterproof the connection as well as possible, using adhesive heat shrink, weatherproof seal, or even good electrical tape properly applied. If you do it right, these will last decades with no noticeable deterioration.

Bill
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Old 24-03-2016, 05:19   #15
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Re: Coax Connectors

Quote:
Originally Posted by Sandero View Post
I am not thinking of yet another installation problem. I just read the minimum bend radius of RG 213 is 5".

Now I am thinking I can possibly pass RG213 through the deck and bend it in the small space of between the headliner and the deck... or even behind the VHF radio... which is probably 3"... So I am thinking I must find and use some right angle connectors. Web search begins...
What I have...

RG213 in the mast and though an Index fitting at deck level ( deck stepped mast ) with about 3 inches inside the boat... 8X from there to the radio.. connected with 259 bits and bobs. .. all happens in a little box at base of mast in cabin.

Makes it easy to pull the mast and also lighter stuff running under the headliner.

As John says signal degradation is negligable..
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