[amsat-bb] Re: [Mw] Pre Fab Coax sections

Lloyd Crawford n5gdb at austin.rr.com
Thu May 21 17:59:29 PDT 2009

Glenn Little and others,

There is a neat way to use type N connectors on LMR400 and LMR400UF. I wrote 
an article for QST/QEX on the method and passed it to Ray Mack, W5IFS, who 
is an editor for QEX. He has not passed the article on as yet, though. 
Basically, the diameter of the inner conductor is too large for the typical 
N connector, therefore that diameter must be reduced to fit. The way to do 
that reduction effectively when you are making up a number of cables is to 
make a set of "Center Conductor Reduction Dies." Start with inch-long 
sections of 3/8-inch cold rolled steel and drill all the way through each 
piece with a series of numbered drills starting with the largest drill that 
is the diameter of the center conductor and ending with the drill that just 
enters the center pin of the N connector. This work is best done on a metal 
working lathe to get a concentric hole. Center drill the entry end to 
provide a starting chamfer. Using a thin cutoff wheel in your Dremel 
Moto-Tool, make two cross cuts on the centerline to about 1/8-inch below the 
chamfer on that end and once on the other end without a chamfer. Now, using 
the dies in descending sequence, chuck the die in an electric drill. Strip 
the end of the cable and expose a little more of the center conductor than 
is needed. Insert the cable into the reduction die and spin the drill motor 
until the end reaches the insulation (there will be a short section of 
unreduced center conductor). Reverse the die in the drill and finish the cut 
to the insulation. Move to the next die. Occasionally, trim the copper flash 
that develops. Stop when the center conductor enters the center pin of the N 
connector. For LMR400UF, you must make the center conductor a solid 
conductor by tinning the exposed center conductor. Again, inspect the face 
of the insulation and remove any copper flash to prevent a possible short. 
Now, you can assemble the cable to the N connector just as you would 
assemble it using RG8 cable. The cutting edges of the reduction die are 
those slots that you cut using the Dremel (you could do it with a hack saw 
as I did at first, but the Dremel is much faster). I have assembled about 40 
N-M and N-F connectors to LMR400 cables using this method which really beats 
trying to reduce the center conductor with a file when you have many 
connectors to install.


Lloyd Crawford, N5GDB, EM10bf
n5gdb at austin.rr.com
Roadrunners Microwave Group
----- Original Message ----- 
From: "D. McGarrett" <dmcgarrett at optonline.net>
To: "Glenn Little WB4UIV" <glennmaillist at bellsouth.net>
Cc: "Microwave list" <microwave at echo.valinet.com>; "'Amsat - BBs'" 
<amsat-bb at amsat.org>; "Jim Sanford" <wb4gcs at amsat.org>
Sent: Thursday, May 21, 2009 6:41 PM
Subject: Re: [Mw] [amsat-bb] Pre Fab Coax sections

> Glenn Little WB4UIV wrote:
>> If you like throwing money at the problem, try Pasternack.
>> 5 feet at $83.00 at S. M. Electronics.
>> 5 feet at $78.25 at Pasternack.
>> I always build my own. That way I can only blame myself for bad cables.
>> 73
>> Glenn
> I don't have a solution for you, but when I was a working engineer, I
> found that Pasternack was one of
> the most expensive solutions (to anything!) there was.  I never heard of
> S.M. Electronics.  Google will
> give you a list of  connector manufacturers and sales people.  I'm with
> Glenn--build your own!      LMR-xx cable is a product of Times
> Microwave.  Excellent cable!
> (If you can use LMR-400, it will be a lot cheaper, but you _can't_  use
> regular type N connectors on it.)
> On the other hand, type N connectors are a lot easier to use than the GD
> UHF connectors, and
> work a heck of a lot better--but you probably know that already.
> _______________________________________________
> Microwave mailing list
> microwave at lists.valinet.com
> http://www.valinet.com/mailman/listinfo/microwave

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