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.

At HF and with low SWR, anything of RG213 size or larger should be OK as
regards cable heating... but in reality you are not aiming to reduce the
losses "to a minimum". You're actually making a three-way balance
between losses, availability and cost.

(Re availability and cost: people in the USA should note that Ross is in
New Zealand. Coax is heavy, and international shipping costs are
horrendous, so Ross has a much narrower range of options than you do.)

"Cost" will also include the cost of repairs and replacement - and this
can be a big consideration with a long run of cable because it's
extremely important to keep the jacket free from any damage where water
can get in. Capillary action can suck water into the braid over very
long distances from the initial location of the damage, and corrosion of
the braid can drastically increase the losses. So even minor physical
damage can have big electrical consequences, and can effectively destroy
a long section of line.

I'm in a similar situation here, with a new tower and LF verticals. The
cables will have to run a long distance over rough land covered with
thorns and sharp stones... and it's usually wet too. For all those
reasons, I am not going to use braided coax, but will try *very very*
hard to locate some surplus hardline.

The advantage of foam-filled hardline is that it's largely immune to
minor damage from the outside. If the plastic jacket is cut or even
removed completely, it doesn't matter at all because you still have
solid copper to keep the water out. And even if you take a slice off the
copper sheath with the mower (BTDT), water will not migrate along the
inside because the closed-cell foam is firmly bonded to the inside
surface of the sheath.

You certainly don't have to buy hardline at new prices - though even
there you might be pleasantly surprised (for example there's an outlet
in VK-land whose prices are very reasonable). Your options will depend
on what's available in ZL, and to find out you may have to tap a few
contacts.

For example, in the UK there's a lot of surplus hardline is coming out
of cellular, broadcast and other VHF/UHF/microwave sites as they are
being upgraded to the next generation. A lot fo this goes straight to
scrap copper, but some gets diverted into the surplus market. Short
lengths appear quite often at radio flea markets ("rallies"), and if you
ask, the guys generally have much longer lengths back home at much lower
prices.

(In the USA they also have aluminium-jacketed cable TV hardline. It
doesn't exist in the UK, but if it's relevant in ZL there are people in
this newsgroup who know about it.)

Crazy as it may sound, the larger sizes of hardline can be cheaper on
the surplus market than the more popular "half-inch" size. The larger
cables are more difficult to transport and less convenient to handle, so
there are fewer buyers and that drives the price down. Even so, 2-3
people can handle the lengths you are considering, and in a fixed
installation you only have to lay it once... and then you really could
say you've reduced the losses "to a minimum".




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