[Towertalk] Commercial 300W Amp

[Jon Ogden]

on 10/15/02 9:06 PM, Jason Hissong at jhisson1@columbus.rr.com wrote:

> Thanks for the recommendation.  I am stepping up from an inverted V at
> 30-35' to a Hexbeam (I got if for the size, weight, and multiband antenna)
> at 40'-45'.  Was wondering if an amplifier would do much better for me.  One
> of the reasons for staying below 600watts is to reduce any interference I
> may cause and also to prevent having to put 220V in the shack.  What would
> be the best coax at a run of 100'?  I keep hearing something called
> hardline, would this be the best?

Jason,

First of all, why do you think you would create interference at 600 W?  All
too often hams are shamed into thinking they are the problem.  If you have a
well put together station, the interference is generally NOT your problem.
So if that's the reason for staying below 600 Watts, then don't worry about
it.  But that's what the RFI reflector is for!  :-)

In terms of coax, at 100 feet, you have a lot of options.  Hardline is
called hardline because it has generally a solid shield.  Simply put - it's
hard.  The biggest source of hardline is surplus from CATV installs.
However, that is 75 Ohms and so a lot of people use some 50 to 75 Ohm
transformers at each end to correct for that.

Another form of hardline is "Heliax."  This stuff is excellent and consists
of a solid inner conductor and a corrugated, solid copper outer conductor.
It comes in a variety of thicknesses all the way up to something like 7 or 8
inches!  This is what broadcasters use.  Heliax of any size tends to be
pretty expensive (I think the cheapest is something like 1.50 or 2.00 per
foot) and requires special connectors.  A lot of hams do run heliax for
their long cable runs.

For the money at 100 feet your best bet is LMR style cable.  It is excellent
and the price is reasonable.  LMR 400 is the most popular style as it is
about the same size as RG-8 and has about 0.3 dB loss at 100' at 30 MHz.
Cost is about $0.90 per foot for LMR400 ultra flex and around $0.65 per foot
for the standard LMR400.  Cable Experts also sells their CXP1318FX for
around $0.60 per foot.  While this is their own brand of cable, it compares
very well to LMR400 ultra flex.  I have that cable and some LMR 400
equivalent (by Belden) on my tower.


The bottom line is not to shy away from full legal limit because of
interference fears.  Yes, it may cause some problems you'll have to debug at
your QTH.  Trust me - I have a kitchen full of touch sensors and I had to
debug everyone of them!  But it's not that bad and the results are well
worth it.  As for the neighbors - if they complain - you work with them but
never admit it being your "fault."  Read up on the ARRL literature on RFI
and whose responsibility it is, etc.  Then go and ask around on the RFI
reflector.

73,

Jon
NA9D

-------------------------------------
Jon Ogden
NA9D (ex: KE9NA)

Life Member: ARRL, NRA
Member:  AMSAT, DXCC

http://www.qsl.net/ke9na

"A life lived in fear is a life half lived."