[Antennas] LMR 400

[Milt, N5IA]

First of all, I respect Chris' explanation, expertise and experience.

I have either made, or been in charge of the making, THOUSANDS of crimp on 
connectors on LMR-400 cable for use up to and including 7 gHz microwave.

However, MPE&E allow me to use  SILVER PLATED, TEFLON INSULATED solder on 
PL-259 connectors on LMR-400 and similar cables at MF, HF, and even in 
duplex use through 500 mHz.

WHY?  Practically all MF and HF gear and many, many of the older commercial 
VHF and UHF pieces of equipment that amateurs can afford were made with, and 
are still made with, female UHF (chassis mount SO-239) connectors.

Rather than use adaptors or crimp on PL-259s (which of all the crimp on 
connectors I DO NOT LIKE) I have always soldered the silver plated, teflon 
insulated PL-259s to the LMR series cables.  That is my preference and MPE&E 
allows me to do that without any problems, even in commercial and amateur 
duplex VHF and UHF systems.

The problem most folks have is getting the tin plated braid soldered to the 
body of the connector.  The problem is NOT that you don't solder to the foil 
sheath.  The braid and the sheath are in constant, permanent contact for the 
entire length of the cable.  Therefore, even if there is not a direct, 
soldered connection to the sheath inside the connector body ( which you 
can't get because it is aluminum foil), that contact is still made 
everywhere, over the entire length of the cable.  Otherwise, the cable would 
not perform as specified and it would be "noisy" in its entirety.

Therefore, IF you are like me and IF you want to solder the CORRECT TYPE 
PL-259 connector to LMR-400, the following technique WILL WORK, and WILL 
WORK WELL, without problems.

You must QUICKLY heat the body of the connector to a temperature that will 
allow the solder to flow through the four holes and migrate throughout the 
inner side of the body of the connector and the tinned braid.  Once the 4th 
hole is done, immediately remove the heat source and apply a wet rag to the 
connector, quickly cooling it.

LONG heating times caused by irons that are TOO small allow the whole body 
of the connector to quickly reach solder melting AND FLOWING temperature 
simply allow all that heat to be conducted by the braid and foil for some 
inches, MELTING the dielectric AND causing oxidation on the surface of the 
braid and the foil.

MPE says that is where most folks have their problems; in NOT getting a good 
solder job done AND with the excessive long term heat creating additional 
problems.

The real keys are: 1: Use a large bodied soldering iron and 2:  have a 2nd 
person to hold and turn the cable/connector so the job can be done QUICKLY 
and 3: then remove the heat by cooling the connector immediately.

YMMV and YE&E will dictate the final results.

Mis dos centavos, de Milt, N5IA




----- Original Message ----- 
From: "Chris Boone" <Cboone at earthlink.net>
To: "'a'" <antennas at mailman.qth.net>
Sent: Saturday, May 30, 2009 3:31 PM
Subject: Re: [Antennas] LMR 400


>I am looking at my LMR400 right now...the center conductor is copper PLATED
> aluminum....the BRAID is tin plated copper (I think) but it has the 
> aluminum
> sheath underneath...soldering to it does not make a good braid to sheath
> connection....MOST of the time in SIMPLEX use, you MAY not ever notice
> it...but in DUPLEX use?? FORGET IT!! Noise maker bigtime and I deal with
> repeaters and duplex systems on a daily basis. I NEVER USE solder on 
> LMR400
> connectors...crimp is better with this type of shielding (yes I try to 
> crimp
> the sheath too...not usually done but it sure makes things better in the
> long run in a rptr or multi freq use mode; such as using di- or 
> tri-plexers)