FME Coaxial Cable Connectors

VHF Marine Band radios, protocol, radio communication theory, practical advice; AIS; DSC; MMSI; EPIRB.
jimh
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FME Coaxial Cable Connectors

Postby jimh » Sun Dec 20, 2015 7:55 am

Recreational boaters may not be familiar with the FME connector. The FME acronym comes from "For Mobile Equipment." The FME family is a newer family of coaxial cable connectors often used with RG-58-type 50-Ohm transmission lines or other smaller diameter lines, as well as RG-8X cable. The FME connector has been designed to have a very small diameter in order to allow a coaxial cable with a pre-installed FME connector to be snaked through tight passages during installation. FME connectors are used by MORAD in their accessory transmission lines for their antennas.
The FME connector is similar in size to the Mini-UHF connector.

In recreational boating, the Mini-UHF connector has come to be used by at least one antenna manufacturer (Digital Antennas). They pre-install a Mini-UHF female (or jack) connector on the transmission line of some of their antennas and supply an appropriate adapter to convert to a standard size UHF plug for connection to equipment. Having the coax include a pre-installed connector has been seen as a significant benefit by many boaters, for whom otherwise having to install a connector would be a burden.

The FME connector can be employed in the same manner. A possible advantage of the FME connector over the Mini-UHF connector is the availability of the FME connector from many sources, along with the necessary adapter, and perhaps a slight advantage in a smaller overall diameter.

Using AMPHENOL parts, and MOUSER as the distributor, FME connectors and adapters are easily sourced. The cable-end connector is Amphenol part number 192102, FME STRAIGHT CABLE JACK. Mouser has these in stock at $2.06 as their part number 523-192102. The hex-shaped retaining nut is only 0.315-inch (8-mm) across the flats. The overall length of the connector is about 1.1-inch. This connector is for RG-58C/U or similar cable.

182102FME_CableJack.png
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FME STRAIGHT CABLE JACK

The adapter is Amphenol part number 192110, RF Adapter, Between Series, FME PLUG to UHF PLUG. Mouser has these in stock at $5.12 as their part number 523-192110.

FMEtoUHF.png
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FME plug to UHF plug adapter

I like the design of this adapter. It has flats on the body of the connector so it can be held with a small wrench. The FME cable end connector can then be tightened snugly into the adapter using another wrench (on the hex nut of the FME connector).

The FME cable-end connectors are all designed for installation with crimp tools. The recommended hexagonal crimp diameters are 0.068-inch and 0.213-inch. The recommended crimp tool is Amphenol part number 47-10070. Mouser stocks this tool as their part number 523-47-10070 at about $92.

All three element of this connector system, the cable end connector, the FME to UHF adapter, and the crimp tool, are also available from alternate suppliers such as SHOWMECABLES.COM in Missouri (to which hyperlinks are given in the preceding text). Again, the most expensive element is the crimp tool, but at about half the price of the Amphenol-brand, the $29 no-brand crimp tool may be a tolerable expense for some boaters.

crimpTool.png
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According to the Amphenol specifications, their FME connector can be used with the following cable types:

--RG-58, RG-58A, RG-58C
--RG-141
--RG-303
--LMR195, and
--Belden 7806A.

The connector is a 50-Ohm impedance connector and is rated to 1-GHz.

The Amphenol FME series is also available for RG-8X or Time LMR240 cable, which has a larger diameter. The Amphenol part number is 192116. Mouser sells these for $11.78. The alternate supplier, SHOWMECABLES.COM has similar connectors for much less, only $3.55.

jimh
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Re: FME Coaxial Cable Connectors

Postby jimh » Sun Dec 20, 2015 10:28 am

An instance of FME connectors in an antenna product intended for recreational marine users can be found in the DIGITAL YACHT GV30 AIS-VHF and GPS combination antenna. The GV30 has two coaxial transmission lines, one for VHF and one for GPS, terminated with FME connectors. They supply two adapters, one for conversion to a TNC connector for the GPS antenna, and another for conversion to BNC for the AIS-VHF antenna.

The TRAM combo VHF/GPS 39-inch antenna is another instance of use of FME connectors. This antenna comes with two transmission lines terminated in FME connectors and four adapters, permitting the FME connectors to be changed to mate with UHF, BNC, TMC, or SMA connectors, and demonstrating the wide range of connector families the FME cable mount connector can be adapted to.

And, as already mentioned, the respected antenna manufacturer MORAD use FME connectors in their transmission line accessory products.

jimh
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Re: FME Coaxial Cable Connectors

Postby jimh » Sun Dec 20, 2015 4:28 pm

The motivation or argument for using a pre-installed FME jack connector on an antenna transmission line seems clear: the connector can be installed prior to the actual installation of the antenna on the boat, and under more favorable conditions. The small diameter of the FME connector permits the antenna transmission line to be fed or routed through conduits or bulkheads with passage diameters not much larger than the transmission line itself.

Traditionally the practice of antenna installation on boats was to not have a connector on the transmitter-end of the transmission line, and to route the transmission line to the radio from the antenna without a connector attached. Once the unterminated coaxial cable was brought to the radio, then the connector would be installed. This often meant installing the connector under less than idea conditions, with poor lighting, in tight spaces, and with limited access to get tools to the work. It also meant that the installer must be skilled in the attachment of the connector--an assumption that cannot always be made when the installer is just the boat's owner who may lack skill, training, or experience with installing a particular connector. Even experienced installers can benefit from avoiding having to attach a connector to a transmission line in-situ on the boat.

The best situation for installing a connector is to perform the installation on a bench and with fixtures, with good lighting, and specialized tools. An antenna manufacturer could easily add this step to the process of fabricating the antenna and its transmission line. This would guarantee consistent and reliable installation of the connector. With a pre-installed small-diameter connector on the antenna's transmission line, all that is left for the installer to perform is the mating of the transmission line connector to the adapter and then to the UHF-series jack on the radio. Although even that task can go wrong, the chances for failure are much slimmer.

Routing just the bare transmission line cable to the radio without a connector, and then installing a PL-259 connector on the cable (with a diameter much larger than the cable itself) creates a situation in which the transmission line is now captive, that is, it cannot be removed because it likely has passed through access holes or conduits whose inner diameter is much smaller than the now-attached PL-259 connector. Using an FME connector on the transmission line prevents this from occurring, and will allow the transmission line to be removed some time later with the FME connector still intact.

peteinsf
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Re: FME Coaxial Cable Connectors

Postby peteinsf » Fri May 26, 2017 7:59 pm

Love FME. I have a tackle box fill of all the variations. It started as a mistake, I ordered the wrong Larsen NMO mount 10-15yrs ago that had one on it, snaked it through my pickup and have never looked back.

Smart design, only a tiny bit bigger than the cable--must be German.

jimh
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Re: FME Coaxial Cable Connectors

Postby jimh » Sat May 27, 2017 12:08 am

I don't know the inventor of the FME connector, but I don't think it was from Germany. There are DIN (German Institute for Standardization) radio-frequency coaxial cable connectors, but they are quite large and cost a fortune. Compare at:

https://en.wikipedia.org/wiki/7/16_DIN_connector

If you long for a DIN connector, here is one for RG-8/U and it is only $45:

http://www.mouser.com/ProductDetail/Amp ... rRxg%3D%3D