Re: [IRCA] New article on terminated loop remote resistance control

["Chris Knight" <chris@xxxxxxxxxxxxxxx>]

Hi Kevin,

Very nice article! The only question I have right now is how are you
interfacing the control unit to the vactrol? What I would do is interface a
coax cable to the control box via a SO-239 connector and outside to the
antenna. The coax impedance wouldn't matter as the control voltage is DC.
The Vactrol will operate down to -40 degrees C according to the datasheet.
So cold Colorado weather won't be a problem. ;-)

I made notes on your article. The LM7805 can have input voltages ranging
from 7V to 35V DC. This will work great if powering the control unit from a
car battery or a ham radio power supply. Power at V1 shouldn't drop below
around 1.7V for full range on the vactrol LED. I calculated voltage in your
circuit to be 2.75V at V1 which is perfect. The LED can drop up to 1.7V and
the resistor, Rs, would safely drop the remainder (V1-Vled).

So, the only thing I can think of as an added option would be the ability to
bring Rout down to zero ohms, maybe through a switch that would also trade
out the impedance matching transformer with one better suited for a loop.
This should give you a bidirectional pattern, if you need it, and more gain
over a terminated loop.

I don't know if you are aware of the existance of digitally-controlled
variable resistors. These could spawn a new generation of remote phasing
control among hobbyists using computers as the control unit. Think of the
possibilities!

Now on to reading your next article. Keep up the great work!

73,

Chris

Chris Knight (N0IJK)
Fort Lupton, Colorado
http://sites.google.com/site/ftluptonulrlogs/

-----Original Message-----
From: irca-bounces@xxxxxxxxxxxxxxxx [mailto:irca-bounces@xxxxxxxxxxxxxxxx]
On Behalf Of Kevin S
Sent: Sunday, January 03, 2010 11:56 AM
To: ultralightdx@xxxxxxxxxxxxxxx; irca@xxxxxxxxxxxxxxxx
Subject: [IRCA] New article on terminated loop remote resistance control

Hi all:

For those of you using or looking at a EWE, Super Loop, Pennant or other
terminated loop antenna, just posted to DXer.ca and the Yahoo UltralightDX
group is an article about a controller which precisely varies the resistance
over a selected range.  In experimenting with a Conti Super Loop, I have
found that a single resistance value will not provide acceptable nulls for
the entire band (the optimum value can vary by several hundred ohms
depending on the target), and that the ability to fine-tune the resistance
can make a big difference, since being off by
50-75 ohms might miss the null altogether.  This remote termination design
allows you to stay in front of the radio while you tweak the resistance for
the best null.  Thanks to Steve Ratzlaff for the bulk of the design and
construction!

Here's the DXer.ca link:
http://www.dxer.ca/file-area/cat_view/87-ultra-light-radio-files-area/97-ulr
-antennas
It is also in Section 5 of the Yahoo UltralightDX group files section.

Kevin S
Bainbridge Island, WA

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