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Re: Topband: Problem with compression F connectors on Quad RG-6

To: <w2lk@bk-lk.com>, <topband@contesting.com>
Subject: Re: Topband: Problem with compression F connectors on Quad RG-6
From: "ZR" <zr@jeremy.mv.com>
Date: Thu, 9 May 2013 09:54:51 -0400
List-post: <topband@contesting.com">mailto:topband@contesting.com>
Im another who has been using the RF Industries tool for well over 20 years for both 50 Ohm and mostly CATV or Belden RG-11 foam. No failures or funny things happening.

Carl
KM1H


Mike,

Here's a link to an article on crimp UHF connectors with suppliers. It's from 2008 so the prices may have changed:

http://www.eham.net/articles/19257

Today, you can get a crimp tool from a number of suppliers ranging from the low $30s and up. I have been using RF Industries UHF Crimp connectors with RG213 and LMR400 for years with excellent results.
Make sure you have the correct connector for the coax you are using.
I always solder the center conductor in the connector rather than crimping it. No more connector problems, no shorts or melted dielectric, etc. and much faster and easier to get it right.

W3LPL and others have mentioned many times that the extra cost of the connectors is small compared to the cost of the entire installation and is worth it to reduce or eliminate a common point of failure.

Les W2LK



On 5/8/2013 6:16 PM, Michael Tope wrote:
On 5/7/2013 7:55 PM, Tom W8JI wrote:

LMR400 or any cable, in sensitive applications, requires a solid bond to the shield that carries the vast majority of return current. In the case of almost all cables on HF and higher, that is the innermost foil. Of course it is different at audio or lower frequencies.

One common connector problem comes from not forcing the woven shield tight against the foil at the connector, or having the foil or woven shield tarnish or corrode. The path to the inside of the foil is out on the braid to an eventual contact point, then back on the outside of the foil to the foil edge. At the edge current can go inside. This is like adding 2X the length of the path to the connection point in overall shield connection path length.

(Current can also "get in" across the edge of a longitudinal seam, if the seam's overlap is insulated. The problem with that is the seam can kill UHF performance.)


If you solder to the shield of LMR400, and put it on a network analyzer and measure the "stub" characteristics, many times (not always) it will move around as the cable is flexed. This is because the soldering heat contracts the dielectric, releasing pressure between the braid overlay and the foil. Now you have a crummy connection that changes electrical length of the connection to the "real" shield.

Even if you do things right, once the foil and braid develop an oxide layer the connection goes away. This can work its way out for several feet of cable length, really messing up a cable. This will not show with a single shield.

Cables with foil have to be installed and treated correctly. The more layers you add, the more careful we must be. Since the extra layers are pretty much meaningless, the best practice is to avoid them. Use a good shield against the center and connect to it at the connector.


Tom,

I'll have to admit that I haven't given this much thought, but what you are saying about the foil to braid contact makes perfect sense. I do recall one friend who is a rabid VHF/UHF repeater builder complaining that LMR-400 has issues with IMD. Perhaps this is why. Can you recommend a source for a good LMR-400 crimp connectors and the corresponding installation tools? To date I've been soldering PL-259s on all the LMR-400 I've used as if it were regular single shield RG8. I haven't had any hard failures, but clearly there is some risk to doing this depending on the application. In fact I do recall some phantom inter-station QRM that would come and go when we had an SO2R setup running at W6UE some years back. Some of the coax used in that setup was LMR-400 with soldered PL-259s.

73, Mike W4EF.................

All good topband ops know how to put up a beverage at night.
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Topband Reflector



All good topband ops know how to put up a beverage at night.
_________________
Topband Reflector


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All good topband ops know how to put up a beverage at night.
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Topband Reflector

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