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: [email protected] [mailto:[email protected]] On Behalf Of Kevin S Sent: Sunday, January 03, 2010 11:56 AM To: [email protected]; [email protected] 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 _______________________________________________ IRCA mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: [email protected]
