[TowerTalk] Terminate braid at top of tower...or

[Jim Thomson]

Date: Tue, 4 Nov 2014 07:38:21 -0600
From: "john at kk9a.com" <john at kk9a.com>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Terminate braid at top of tower...or

Array Solutions mounts their choke in a small plastic Nema junction box.
They use small Teflon coax and I believe it is around a single core in
some of their models. DX Engineering mounts their chokes in a small
aluminum enclosure.  Cal-Av mounts theirs in PVC tubing. Is heat a big
concern?

John KK9A


##  array solutions uses 4 turns of the big RG-393 teflon coax around 4 x type 31 cores,
2.4 inch variety. It all sits in a big nema box. 393 is double braid stuff, silver plated braids.
The braids are separated, and one goes to each diagonal  corner of the 7-16 Din connector. 
The internal and external coax loops are solenoid wound...with small ty-raps used to ty off
to the side walls, and used to align the external loops.   The cores sit dead center in the box.
External loops don’t stick out much from the cores.   They rate them for 160-10m use...and also
10-20 kw......which I find hard to believe. I had em put 7-16 dins on both ends..and use em for
line isolators to kill residual rf.   They appear to be 3+ k ohms on 20-10m...and slightly less
on the lower bands.  No stray C to the boom.... or mast.

##  the Cal-AV baluns use  RG-393, with 17 inches worth of the large type 43 bead slid over them.
Silicone varnish goop is put inside..and its done with a vac chamber.   The 10 ga silver plated, stranded
teflon leads are silver soldered..and ditto the 7-16 Din at the other end.   The 10 ga wire is unique, Each
layer is wound in opposite directions. End result is... when u bend the leads at say a 90 deg angle, they
stay put. They wont flex back on you. The teflon on the 10 ga wire is also etched in a lab in Colo.
Apparently the silicone goop sticks better when etched.  Big circular lugs used on the ends of the
10 ga wire for connection to yagi.  Crimped and soldered. No way to get water inside, since all the air
has been evacuated, and replaced with the silicone glop.  Laff all you want, but you can stuff 12 kw
through em on ssb +cw all day long.   Dead cxr wont blow em up either.   The 17 inch long version is used
on 40-6m.  The 24 inch long version is used on 80m.  You can also use em as a billy club.  160M is
36 inchs long.

## what else works is the .75 inch OD type 43 beads.  These are .4 inch ID  and 2 inches long.   They
slide nicely over RG-393..which is .392 inch od.  They wont slide over RG-213.... which is .405 OD. 
2 x friends had terrible RFI with qro+....the quick fix was to slide 30 inches worth of beads on 393
coax...  right on the output of the amp..problem solved.  The type 31 ferrite that had been placed on the
dsl modems etc,  didn’t work.   The type 31 torroid line isolators also work on the output of an amp.
The real fix is to do it correctly..at the feedpoint of the yagi.   That’s not always easy..esp when a fubar
balun is used a mile out on the boom..and you have to wait till spring....and a crane..or tram. 

##  has anybody actually compared a 1k Z balun vs a 4-8k Z balun...and seen their noise level drop ??
In most cases, 1-2 K CM is plenty... and no pattern degradation on a yagi.  If you could get local noise
to drop a bunch with 4-8k CM baluns, Im all for it. 

Jim   VE7RF