On Sun, 11 Dec 2005 05:39:27 +0000, Wes Stewart *n7ws*@ yahoo.com
wrote:


I wasn't going to go that far, and I realize it's probably not common
in ZL but I've bought lengths of LDF5-50 at ham flea markets. The
last purchase, claimed to be about 10 meters worth, but by my
estimation at least twice that long, and new and unused, cost me $10
U.S.

Most of this stuff is leftover or removed from commercial two-way or
cell phone use and shows up all of the time. LDF4-50 is even more
common. I often buy short pieces that have been cut down, just for
the connectors that are still on one end.

I find it curious that Andrew cable is seen so often at these events
and yet I've -never- even seen a piece of Davis cable, dispite the
claims that miles of it are in commercial use.

I agree with Ian's comments, the larger sizes are often available here
as they are less attractive to hams. But if you buy 3 or 4 lengths of
LDF5 or LDF6 and use connectors to join them, you will run into big $
unless the connectors come very cheap.

Andrews has some braid+foil / foam coax, and they perform roughly
similarly to LMR400, BuryFlex and 9913.

To my mind LDF4-50 would be acceptable in this configuration, and the
great advantage is that if water gets in somewhere, it doesn't wick
right down the cable. I haven't handled BuryFlex, and I saw the claim
it is waterproof, but I suspect it is not as waterproof as Heliax type
cable where the closed cell foam dielectric is bonded to the inner and
outer conductor with an adhesive, and there is no braid to form a
natural wick.

I am in the throes of replacing feedline on a HF dipole to repair
damage by birds. The birds don't seem to eat PE irrigation tube, so I
have fitted RG6 with a W2DU style balun inside 13mm PE tube to defeat
the birds. The birds have attacked the LDF4-50 on the VHF/UHF
antennas, but even if they make a hole in the copper, it doesn't seem
to affect cable performance measurably, probably because the water
can't travel up and down the cable from the hole.

Still, parts of ZL have Keas, and they will eat anything, especially
rubber or plastic! So I feel for our ZL friends running coax over 60m
of ground.

BTW, I added BuryFlex to my online line loss calculator, 9913 and C2FP
were already there.

I still like the open line option, but it will be real important to
use effective baluns to adequately ensure balance. It used to be
common commercial practice when HF Radio was used more widely for
international telephony / telegraphy.

Owen
--

On Sun, 11 Dec 2005 06:06:08 GMT, Owen Duffy wrote:

On Sun, 11 Dec 2005 05:39:27 +0000, Wes Stewart *n7ws*@ yahoo.com
wrote:


I wasn't going to go that far, and I realize it's probably not common
in ZL but I've bought lengths of LDF5-50 at ham flea markets. The
last purchase, claimed to be about 10 meters worth, but by my
estimation at least twice that long, and new and unused, cost me $10
U.S.

Most of this stuff is leftover or removed from commercial two-way or
cell phone use and shows up all of the time. LDF4-50 is even more
common. I often buy short pieces that have been cut down, just for
the connectors that are still on one end.

I find it curious that Andrew cable is seen so often at these events
and yet I've -never- even seen a piece of Davis cable, dispite the
claims that miles of it are in commercial use.

I agree with Ian's comments, the larger sizes are often available here
as they are less attractive to hams. But if you buy 3 or 4 lengths of
LDF5 or LDF6 and use connectors to join them, you will run into big $
unless the connectors come very cheap.

I have a ham friend who uses long runs of coax to his several towers.
He is a big gun on 80 and 160 meters, so this mainly applies at m-f to
h-f. He uses a lot of LDF5-50 that he obtains in shorter pieces.

His technique, as he briefly described it to me, is to -not- use
connectors but splice the lengths directly. The center conductor on
these cables is hollow, so he inserts a short length of brass or
copper into the ID and solders it in place.

I don't know whether he adds any insulation next or not, but I would
envision injecting some low-expansion spray foam later. He then wraps
the outer conductor with brass or copper foil and solders this in
place. (Here is where I would inject the foam.)

This is then wrapped with tape for protection. I would use a double
layer of #27 3M tape with an overwrap of plastic electrical tape.

To strengthen the joint mechanically, he straps on a length of steel
angle using stainless hose clamps. For lines on or in the ground this
stays in place. For runs up the tower, after the line is in place,
strapping to the tower is sufficient support.

Wes Stewart wrote:
I agree with Ian's comments, the larger sizes
[of hardline]
are often available here
as they are less attractive to hams. But if you buy 3 or 4 lengths of
LDF5 or LDF6 and use connectors to join them, you will run into big $
unless the connectors come very cheap.

Generally the same applies to the connectors as to the cable itself -
the surplus prices are much lower than the new prices, and larger sizes
may even be cheaper.

However, I do agree that you don't need connectors in order to make a
splice in a static installation. This technique makes a solid splice,
with a low SWR even at 432MHz:

I have a ham friend who uses long runs of coax to his several towers.
He is a big gun on 80 and 160 meters, so this mainly applies at m-f to
h-f. He uses a lot of LDF5-50 that he obtains in shorter pieces.

His technique, as he briefly described it to me, is to -not- use
connectors but splice the lengths directly. The center conductor on
these cables is hollow, so he inserts a short length of brass or copper
into the ID and solders it in place.

And for the smaller sizes with a solid center conductor, splice with a
short length of hobby brass tuning over the outside.

I don't know whether he adds any insulation next or not, but I would
envision injecting some low-expansion spray foam later.

The foam is mostly empty space anyway, so even at UHF an inch or so will
hardly be missed.

He then wraps the outer conductor with brass or copper foil and solders
this in place.

In some sizes, a slit length of copper water pipe can work too.

This is then wrapped with tape for protection. I would use a double
layer of #27 3M tape with an overwrap of plastic electrical tape.

To strengthen the joint mechanically, he straps on a length of steel
angle using stainless hose clamps.

Yup, all of the above. It works fine.

The overall conclusion is that - both physically and financially - large
hardline is nowhere near as 'hard' as most people think.


BTW, I do have one genuine Andrew splice for LDF5-50, which I'm hoarding
for some undefined future need. It's truly a thing of wonder...
especially the insert that connects the two hollow center conductors.
One end screws in with a tapered variable-pitch thread, so the other end
has to have a tapered variable-pitch *left-hand* thread. Only a CNC
programmer with far too much time on his hands could have thought of
that.



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek