[Moon-Net] coaxial cable + antenna rotator

John Regnault john.regnault at btinternet.com
Wed Apr 21 13:09:32 CEST 2021

Hi Dick,


Ecoflex is bad news around rotators as is H100, LMR400 and many other types
of semi-air spaced cable.


I have used Comscope/Andrews FSJ4-50B for many years in a simple loop
arrangement on TX. I have a failure, either inner or outer conductor
fracturing due to work hardening in this loop every couple of years! I
expect that to happen and hold replacement cables. See the old picture of an
EME array on my QRZ.com page.

I use M&P Ultraflex 10 on RX with no issues.


However, last year it was explained to me that a simple loop put excessive
twisting stress on the cable and that a spiral was what was used in
professional applications.

They used a Comscope(Andrews)  3m long FSJ4-50B patch lead. This is almost
identical to SCF12-50

Another amateur's system is shown in the attached picture. Set at fully
wound to be 2.5 turns of 300mm diameter

When fully unwound this opens out to 1.5 turns around 450mm diameter.


I have not yet seem a failure with this system but after only 6 months it is
early days.



John G4SWX



Date: Tue, 20 Apr 2021 13:52:25 +0200

From: "pa4vhf" <pa4vhf at gmail.com <mailto:pa4vhf at gmail.com> >

To: <moon-net at mailman.pe1itr.com <mailto:moon-net at mailman.pe1itr.com> >

Subject: [Moon-Net] coaxial cable + antenna rotator

Message-ID: <C42D5494C5104D6BAD0355B1900B01C0 at GebruikerPC>

Content-Type: text/plain; charset="iso-8859-1"


Hello all,


I have some questions regarding the use of low loss coaxial cables in
combination with antenna rotator.


The cable should be flexible and able to withstand a lot off repeated


>From stories found in the internet I learned that Ecoflex 15 should be
avoided because of known issues with the foil of the outher conductor
getting cracked, or thored apart due to the movements of the cable when
turning the antennas.

This leads to increased loss, and return loss (swr) issues especially on
70cm and up.


So, I thought Messi Paoline Hyperflex 13 or Ultraflex 13 could be a suitable

However from the 70cm EME chat I learned that someone experienced the same
problems with the foil as observed on Ecoflex 15.

Fact is that I did not found anyone else reporting about these problems with
the M&P 13mm cable, so is this an incident or a structural problem?


Also did not find any complains about the regular 10mm cables, like Ecoflex
10, hyperflex 10 etc. so these might be ok, but have more losses on 70cm and


For now SCF12-50 (1/2" ultraflexible hardline) looks to me as the best
alternative, from loss and price perspective.

The standard 1/2" hardline like, LDF4-50 or LCF12-50 might be not flexible
enough, so bigger loops needed...

LMR600-UF might be another one, but much expensiver and maybe difficult to
get, including connectors.


So, anyone has experience with the use of SCF12-50 as a cable in a rotatable
system and what should be a 'safe' loop radius?

Also interested in other comments, tips, ideas and experiences regarding
this subject.


73 and CU on 432MHz EME


Dick, PA4VHF


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