One method of terminating Rhombics documented in a number of older
references, that may eliminate the termination resistor, is to fabricate a
long, tapered, unterminated, stainless steel or nichrome transmission line
at the far end of the rhombic. The old army manual on rhombics shows this
transmission line dissaaptor in their drawings as being dropped from the far
vertex, and running back along the center line of the rhombic towards the
center supported near the ground on small poles.
The rate of taper (convergence of the transmission line conductors) is what
has to be determined, and also the lossiness of the nichrome or SS wire
used. Done right, the lossiness of the tapered, terminating transmission
line does two things, dissapates power, and provides a lossy return line
for the reflected wave which returns from the distant, open end of the lossy
line. Same as using a long piece of RG 58, unterminated, as a dummy load
for testing of VHF transmitters.
All the Best, 73,
Pat Barthelow aa6eg@hotmail.com
http://www.jamesburgdish.org
Subscribe: http://bambi.net/jamesburg.html
Jamesburg Earth Station Moon Bounce Team
From: "Chet Moore" <ChetMoore@cox.net>
To: "Rick Stealey" <rstealey@hotmail.com>,
<k4tmc@aol.com>,<towertalk@contesting.com>
Subject: Re: [TowerTalk] HF Vee Beam Experience?
Date: Thu, 13 Sep 2007 13:13:51 -0400
Rick,
OK, I'll bite. How well does it work I used a rhombic up at KL7AIZ
that
was 500 feet per leg, terminated at the far end.. That one loaded on all
bands and was dynamite. A rhombic at this QTH is not feasable.
Press on regardless
73
Chet N4FX
----- Original Message -----
From: "Rick Stealey" <rstealey@hotmail.com>
To: <k4tmc@aol.com>; <towertalk@contesting.com>
Sent: Thursday, September 13, 2007 10:11 AM
Subject: Re: [TowerTalk] HF Vee Beam Experience?
>
>>terminating resistors?
>
> Hi Henry,
> I homebrewed one a year ago, on the way to building a Rhombic (first
half
> of
> my rhombic). It didn't do much for me in the way of excitement so I
> completed the Rhombic project and then only needed one terminating
> resistor.
> I was looking for a 500 watt 600 ohm resistor, and you are right, they
> aren't common items. I checked with a company called Carborundum I
think
> it
> was, who make Globar resistors but they wanted something well over $100
> for
> it. Had to get them to "quote" my request, couldn't get a price from
> their
> web site. So I looked for alternatives and an interesting alternative
was
> to get a 50 ohm dummy load and use a balun (an un-un in the case of a
vee
> beam since you are connecting to ground) like a 9:1 type to match the 50
> ohms up to 450 ohms.
>
> As to performance... that's another subject, that's not what you asked,
> is
> it?
>
> Rick K2XT
>
> _________________________________________________________________
> Get a FREE small business Web site and more from Microsoft® Office Live!
> http://clk.atdmt.com/MRT/go/aub0930003811mrt/direct/01/
>
>
--------------------------------------------------------------------------------
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|