On Sun, 29 Aug 2021 13:56:42 -0400, time-nuts-request@lists.febo.com wrote: Re: time-nuts Digest, Vol 208, Issue 24 (messages 2, 4, and 15) > ------------------------------2 Date: Sun, 29 Aug 2021 09:51:39 -0400 From: Bob kb8tq <kb8tq@n1k.org> Subject: [time-nuts] Re: Query about List and about 10 MHz Distro To: Discussion of precise time and frequency measurement <time-nuts@lists.febo.com> Hi Skin depth is what gets you with most coax at 10 MHz, even with the “double shield” stuff. Hardline with a nice heavy outer would do better. It’s not terribly practical around the typical lab. Might not be a bad choice for a “burry in the yard” setup though. With normal cable, the losses from the soil at normal burial depths make a good shield, that makes dealing with it questionable even there …. Bob >> On Aug 29, 2021, at 9:36 AM, Robert DiRosario <ka3zyx@comcast.net> wrote: What about double shielded RG-223, or Thinnet ethernet cable? Most Thinnet has both a braided shield and a foil wrap. Robert > ------------------------------3 Date: Sun, 29 Aug 2021 09:21:32 -0500 From: Dana Whitlow <k8yumdoober@gmail.com> Subject: [time-nuts] Re: Query about List and about 10 MHz Distro To: Discussion of precise time and frequency measurement <time-nuts@lists.febo.com> I believe that a significant problem in my case was not leakage through the shield, but rather common-mode currents on the cable. My experiences were with RG-6 style cable, namely a cable that mostly went around the outside of the house for TV distribution. I get all the TV I want with an indoor dipole, and I had had plans of using that TV cable for ham purposes. One thing I have noted is that adding ferrite common mode chokes near the ends of the cable did help quite a bit, just not enough. > ------------------------------15 Date: Sun, 29 Aug 2021 13:29:26 -0400 From: Robert DiRosario <ka3zyx@comcast.net> Subject: [time-nuts] Re: Query about List and about 10 MHz Distro To: time-nuts@lists.febo.com Andrew Sureflex (FSJ) is a lot more flexible then the LDF4 Healix, which is what you find a lot of on ebay and at hamfests. Here is some 1/4" Sureflex, new: Andrew Type N Male to Type N Male Sureflex Cable 30 feet F1RNA-PNMNM-30-L1 NEW! https://www.ebay.com/itm/173863049072 US $30.00 + $13.02 Shipping. For two pieces shipping goes to $16.33, for three $22.90 You can cut it with a hacksaw, do NOT use wire cutters. Connectors can be installed with just hand tools. If you move the test equipment around it's not very practical, but if it's setup on a bench or in a rack it will work. Robert Those large 10 MHz distribution systems typically used Heliax cable, which as a solid copper foil shield, with better than 100 dB/meter shielding effectiveness (SE). Actually, I think that's the limit of their ability to measure SE. Back when we did underground nuclear tests, the cable connecting down-hole instruments to instruments a safe distance away were Heliax. At power-line frequencies, the skin depth well exceeds the thickness of any reasonable shield, so the transfer impedance (between inside skin and outside skins) is the DC resistance of the shield. Power-frequency ground loops can be a problem, and common-mode chokes are not effective against this, but 10 MHz RF transformers intended for galvanic isolation are. May also need a blocking capacitor to prevent transformer core saturation. As for common-mode chokes, one can implement such things by winding insulated coaxial cable multiple times through a big ferrite toroid core. The insulation jacket prevents the cable shields from shorting to one another. This dodge also works for shielded twisted pair cable. This dodge is discussed in the books on Balun Transformers, and is raised to a high art in the book on Coaxial AC Bridges. Joe Gwinn