On Sat, 10 Dec 2005 18:40:43 +1300, "Ross Biggar"
wrote:

I am putting up a second tower , but it will be about 200feet from the shack
and about 70feet high.
What coax is recommended to reduce loss to a minimum,and to feed a multiband
beam with a 2kw amplifier.
Hard line excepted due to cost.

Ross,

Interesting to see use of such a long line. We have been reliably
informed that nobody uses more than 75' or so!

Starting with the question "what is wrong with commonly available
RG213", you would expect a loss around 2.4dB in a 100m run (200' + 70'
+ 30' tails) with an average VSWR of 1.5.

Given that the lowest ambient noise level on 20m is around 20dB above
typical receiver noise floor, the impact of 2.4dB of loss on receive
is insignificant.

On transmit, you will lose about 45% of your power in the line, so
with your 2KW (output?) amplifier, you will still have 1100W arriving
at the antenna. Will that do the job OK?

Is ladder line the panacea? Wireman 554 directly connected to a 50 ohm
load would have a loss of ~1.7dB and a little extra for baluns brings
you close to 2dB, so it is not a whole lot better than RG213. However,
if you used a 9:1 balun at each end, you would expect line loss of
~0.6dB and a little extra for baluns brings you close to 0.8dB. Now
that seems respectable. Problem is that you live in the land of the
long white cloud, and ladder line performance is degraded
significantly when wet, so it might not be acceptable in your
situation when wet.

Lets look at home made open wire line using 2mm copper spaced 150mm
for a 600 ohms line. If you used the same 9:1 balun at each end, you
would expect line loss of ~0.2dB and a little extra for baluns brings
you close to 0.4dB. Now that seems quite good. Anecdotally, such an
air spaced line is not affected significantly by weather / water, but
that will depend on the quality of the insulators and your rigging
methods.

Remember that the open wire solutions above need to be tuned feeders
or you will need an ATU. I suggest that you will need the ATU for
multi band operation, so you should allow another tenth of a dB or so
for ATU loss.

Someone will probably suggest that LDF6-50 (32mm (1.25") hardline)
could achieve 0.3dB loss, but could you afford it, would it be good
value?

Owen
--

Owen Duffy wrote:
Interesting to see use of such a long line. We have been reliably
informed that nobody uses more than 75' or so!

Actually, the assertion was that 75' is about average. And
even this special case problem doesn't rise to the level of
your 100 meter example.
--
73, Cecil http://www.qsl.net/w5dxp

On Sat, 10 Dec 2005 21:50:15 GMT, Owen Duffy wrote:

[good stuff snipped]
|
|Someone will probably suggest that LDF6-50 (32mm (1.25") hardline)
|could achieve 0.3dB loss, but could you afford it, would it be good
|value?

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.

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

Wes Stewart said:
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.


It might be that the BuryFlex is still in use and has not been removed from
service as the Heliax you cite has been. After all Davis BuryFlex 9914 does
have a warranted - 20 year service life -

Is there any other coax with such a warranty?
---

Charlie

Charlie wrote:

Wes Stewart said:
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.

It might be that the BuryFlex is still in use and has not been removed from
service as the Heliax you cite has been. After all Davis BuryFlex 9914 does
have a warranted - 20 year service life -

Is there any other coax with such a warranty?
---

Charlie

I don't seem to be able to find any mention of a warranty on their site - can
you point it out for me?

Dave

At the bottom of this page the ** footnote
1. http://www.davisrf.com/ham1/coax.htm

"note that Bury-Flex has a 20+ year abrasive resistant jacket of PE"


--

Charlie


"Dave Holford" wrote in message
...


Charlie wrote:

Wes Stewart said:
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.

It might be that the BuryFlex is still in use and has not been removed
from
service as the Heliax you cite has been. After all Davis BuryFlex 9914
does
have a warranted - 20 year service life -

Is there any other coax with such a warranty?
---

Charlie

I don't seem to be able to find any mention of a warranty on their site -
can
you point it out for me?

Dave

That's a guarantee??

Dave

Charlie wrote:

At the bottom of this page the ** footnote
1. http://www.davisrf.com/ham1/coax.htm

"note that Bury-Flex has a 20+ year abrasive resistant jacket of PE"

--

Charlie

"Dave Holford" wrote in message
...


Charlie wrote:

Wes Stewart said:
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.

It might be that the BuryFlex is still in use and has not been removed
from
service as the Heliax you cite has been. After all Davis BuryFlex 9914
does
have a warranted - 20 year service life -

Is there any other coax with such a warranty?
---

Charlie

I don't seem to be able to find any mention of a warranty on their site -
can
you point it out for me?

Dave