On Fri, 2008-05-02 at 08:34 -0700, Denton wrote:
> When we did some remodeling, my station got moved to a room without direct
> access to the outside, but I was able to run 400 ohm feeders thru an inside
> wall well away from other wiring...went from the inside wall, down
> underneath the house and then thru the old wooden siding for outside access.
> The hf ant is a loop fed with homebrew 600ohm feeders.
> One thing I have yet to try is running a pair of 75 ohm, with both coaxial
> shields tied together, with the shields grounded in the shack...in lieu of
> the 400 ohm feeders...to the outside 600 ohm feeders.
> I use a Palstar BT1500A double L balanced transmatch in the shack...that
> give me 80 thru 10 meters on the 230 ft horizontal loop with a decent match.
> I don't run an afterburner...just barefoot at most 100 watt output.
> Wonder if using 75 ohm satellite receiver cable will suffice for shielded
> twin lead? The run would be less that 25 ft for the shielded twin lead.
I'm not much of a fan of TV cable because it often uses aluminum foil
and a bit of aluminum braid for the shield and getting and maintaining
good connections are difficult.
The shielded twin lead scheme works, though being 150 ohms instead of
400 the tuner will see a different impedance. VOA used that scheme at
the 250 KW power level, but with 150 ohm coaxes made of 1/2" copper
water pipe for the center conductor and 8" irrigation tubing for the
outer conductor. At last that's what the Collins 250 KW AM short wave
transmitter I helped build used.
73, Jerry, K0CQ
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|