[TenTec] openwire feed OT

[Robert & Linda McGraw K4TAX]

I would comment that using coax or shielded cable with a high SWR produces a 
very lossey condition.

RG-8X at 3.9 MHz will have 2.1 dB loss per 100 ft. with a SWR of 10:1
RG-8 at 3.9 MHz will have 1.5 dB loss per 100 ft. with a SWR of 10:1

RG-6 at 3.9 MHz will have 3.4 dB loss per 100 ft with a SWR of 20:1
RG-8X at 3.9 MHz will have 3.5 dB loss per 100 ft with a SWR of 20:1
RG-8 at 3.9 MHz will have 2.5 dB loss per 100 ft with a SWR of 20:1

In the above example the vinyl covered balanced line will have 1.1 dB loss 
per 100 ft with a SWR of 20:1

As to broad antennas, the more loss in the line, the broader the antenna 
will seem to be at the transmitter end.  The attenuation in the cable works 
both ways.  Thus lower reflected power at the transmitter due to loss in 
both directions, to the antenna and reflected back to the source.  A piece 
of RG-58 open at one end will have ~10 dB of loss and will look like a dummy 
load at 29 MHz.

Your mileage may vary.

73
Bob, K4TAX


----- Original Message ----- 
From: "John T Fleming" <W3GQJ at earthlink.net>
To: "'Discussion of Ten-Tec Equipment'" <tentec at contesting.com>
Sent: Tuesday, January 31, 2006 4:14 PM
Subject: Re: [TenTec] openwire feed OT


> At a field day operation a couple of years ago, our club installed an 80
> meter loop.  It was fed with "ladder wire."  I say that in quotes because
> the fellow that built it had 100 feet of the twin coax that they used for
> the DirecTV dishes.  Each leg of the loop was connected to a center lead.
> The shield was grounded at the tuner and the center leads were attached to
> the ladder line connections.  It worked well and was quite broad.  The
> shielded cable would solve the problem of going through a wall.
>
> 73,
> John