Date: Sun, 3 Jan 2010 15:15:37 -0700
From: "Chris Knight" <chris@xxxxxxxxxxxxxxx>
To: "'Mailing list for the International Radio Club of America'"
<irca@xxxxxxxxxxxxxxxx>
Subject: Re: [IRCA] New article on terminated loop remote resistance
control
Message-ID: <E70DBC2D579149848ED0CB30B4E2221F@ChrisPC>
Content-Type: text/plain; charset="us-ascii"
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/