Dave is 100% correct.
After seeing K1LT present a paper at Dayton 2008 where he used the W8JI
short verticals in his 160 meter beam forming vertical array - I switched to
them.
Look at page 14 of his paper
http://www.kkn.net/dayton2008/beam_steering_on_160_meters.pdf
My 92 ft spaced DXE 4 square 160 meter RX array with W8JI short verticals
works great. Very stable and great F/B.
Getting the base of each vertical to 75 ohms +j0 was easy. I used a 68 ohm
resistor with a 31 uH coil - just like K1LT did.
73!
Tim K3LR
-----Original Message-----
From: topband-bounces@contesting.com [mailto:topband-bounces@contesting.com]
On Behalf Of Dave Robinson
Sent: Saturday, September 26, 2009 10:03 AM
To: topband@contesting.com
Subject: Topband: DX Engineering Receiver 4 Square uing W8JI Passive
Elements
One variation of the this system that hasn't been mentioned is to use W8JI
passive elements instead of the active elements. DXE doesn't sell these
passive elements, but you can find all the info you need at W8JI's web site.
The advantages of the passive elements are that they are less expensive, you
can locate them closer to the tx antenna without overload problems (noise
may force may you to detune the tx antenna) and lightning isn't a problem.
Because I've only got a a couple of acres to work with, I'm using only 70'
spacing and so the dimensions need to be exact and the impedance of each
element need to be pretty close to one another. I use 4 20' long ground
radials. I use the MFJ-259B to closely set each elements resistance with a
multi-turn pot. Because the elements are so short (20' high plus 20'
sloper wires) BC interference isn't a problem with the MFJ-259B
I usually have to run an external preamp like the ICE unit and on
exceptionally quiet nights I can run a second unit in series. Results from
Michigan: I've heard and worked VQ9LA, 3Y0X, ST2A, SU9HP, 9X0R, ZL7T, 4X4ZR,
EY8MM etc, so I think it works pretty good. Is it as good as staggered
phased beverages? No, but I do think it is close to a single beverage.
The RDF numbers in the ON4UNs Lowband DXing book confirm this.
Dave, AG8B
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|