[time-nuts] Don't use cheap cables -- a cautionary tale

David davidwhess at gmail.com
Sun Mar 3 17:37:59 EST 2013


After a couple of bad experiences with foamed polyethylene that got
contaminated and solid polyethylene where heat had allowed the center
conductor to shift, I have stuck with RG-142 and RG-400 style coax for
short patch cables.

For little stuff that gets soldered into place, I use add RG-316 and
RG-178.  Teflon makes all of these cables easy to solder without
damage.

On Sun, 3 Mar 2013 14:08:15 -0500 (EST), johncroos at aol.com wrote:

>I could not agree more, having been burned once or twice.
>
>One batch of "50 Ohm" cables was clearly marked 75 Ohms when received. These used some form of
>relatively high resistance foil shield and a drain wire for the outer conductor. The high resistance permitted
>a ground loop with hum on my 10 MHz reference thus FMing my signal generator.
>
>A couple of things to note:
>
>Measure the DC resistance between the connector bodies it should be way less than 1 Ohm, perhaps
>0.1 ohm above what you see with the probes shorted.
>
>The previous regarding RG-58 apply unless the cable is labeled with a manufacturers part number and that is stated in the vendors spec -
>
>Such as 
>
>BELDEN 8262 RG-58U Coaxial BNC M/M Patch Cable 10FT.
>
>RG58 C/U MIL C17 50 OHMS stamped on the cable.
>
>These were from - Digital Connections - cablesellforless at yahoo.com and purchased via eBay. The price was very reasonable.
>
>Testing with a HP ANA showed very low VSWR and the expected insertion loss up to 1 GHz. Shield resistance was very low, as expected. I have used these in lengths from 3 ft to 20 ft with no difficulty.
>
>The key here is the Belden part number in the vendors ad  that can be checked to see what you are getting. The MIL SPEC and RG58 etc was stamped on the cables when received.
>
>For outstanding performance use RG-223 which is slightly larger than RG-58 and is a 50 Ohm cable
>having a very dense double sliver plated braid shield.
>
>You can buy these made up for a small fortune or buy an odd lot of RG-223 on eBay and make your own. Pasternak has the connectors with the appropriate diameter nuts and collars. The connectors for Rg-58
>are had to make work on RG-223. Connectors for Type N and SMA are also available.
>
>Installing  clamp style connectors on RG-223 requires a certain amount of passion (and a stainless steel welders tooth brush to comb the braid) but hey, no pain no gain.
>
>-73 john k6iql


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