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Re: [IRCA] Vactrol luvin' !!
I'm going with everything that's been said, with one comment. I too was a
multi-turn-pot user. But I've found that I can get all the granularity I
need with a single-turn pot, with a current-limit resistor feeding the
Vactrol that was selected to make nulling occur near the middle of pot
rotation.
Nick's the e-mail historian and I bet he could find my early D-Kaz e-mails
questioning whether extension of the null-pot resistance of a D-Kaz by
copper wire to the shack was a good thing. But I also seemed to find that
if lengths were kept below 100 feet or so, such an extended null-pot worked
okay.
Fast-forward to May 2016 and a D-Kaz that was installed with critical
attention to its symmetry and a uniform level above ground. And it had a
Vactrol. With this install I found 30 to 40+ db nulls on a lot more
stations and a lot more signals were minimized without constant re-tweaking
of the Vactrol.
So my question is: Was the null-depth improvement and consistency caused by
the better physical installation? Or is because with the Vactrol there's no
longer any direct extension of the null-end circuit via copper to a remote
pot?
Cheers!
Mark Durenberger
There's SO much I still don't know!
-----Original Message-----
From: Nick Hall-Patch
Sent: Saturday, May 21, 2016 7:36 PM
To: Mailing list for the International Radio Club of America
Subject: Re: [IRCA] Vactrol luvin' !!
Glad you're enjoying the Vactrols Neil. They've been in use here for
well over a decade with the Flags, and using Mark Connelly's clever
design to feed the control voltage through the matching
transformer....documented in a DXer's Technical Guide (IRCA Bookstore
has them), and posted by Mark on the web.
Once I moved over to FLG-100's four years ago, the Vactrols had to
stay, so separate control lines were put out. Not quite as elegant
as Mark's design, but absolutely necessary to retain the Vactrols as
you have been finding out. Elegance can take a break.
When I've used DKaz antennas, the range of control resistance seems
quite a bit tighter than with the Flags,so yes, I do like the 10 turn
pots also, though I believe Dallas Lankford used a couple of
resistors and a single turn pot to zero in on the desired range of
resistance.
best wishes,
Nick
At 00:13 22-05-16, you wrote:
Where have these things been all my life and why didn't I use them in lieu
of termination resistors (Rt) previously is what I must ask! With some
good weather today and a drying antenna field I did some work on two DKAZ's
today and reinstalled the Vactrol setup.
I have only one setup from a friend who makes his own for his DKAZ DXpeds.
I will stress that having a multi turn pot or a smaller pot in series for
fine tuning is very useful. No one setting is going to be optimal for every
frequency or deviation from 180 degrees from beampeak but I have found a
setting that seems better than anything I ever could obtain using and
manually fine tuning fixed resistor combos.
Here's some examples from daytime DX today. Locals on 1330 and 1430 are
both at about 102 deg and 13 miles away. My DKAZ aims due west 270 deg so
90 deg should the spot of best back null per theory. 1330 WKTA's ethnic is
so clobbered that I cannot hear a trace of it under WNTA. Without touching
the Vactrol pot 1430 WEEF's ethnic is also inaudible under WCMY which isn't
strong and has two more stations under it. I've never had nulls this good
or stable on those two before even with phasing!
With the same pot setting, WHFB 1060 at 94 deg is also crushed and WRHL is
basically alone. WLW and WJR aren't strong here days, but they are gone
with the same pot setting and WKZO 590 is basically lost under Omaha's
KXSP. Yes you can get Nebraska in the daytime in NE IL thanx to good ground
conductivity. Note also that Chcago's WRTO 1200 at 140 deg while not gone
is deeply nulled with that setting. Fun also to have Clinton IA's GYer KROS
1340 dominant.
I'll break out the ohm meter and measure what Rt the Vactrol is providing
tomorrow and likely move the setup to my other west DKAZ as I've been
having trouble getting deep back nulls since repairing it after severe
storm damage.
I'd recommend that anyone considering a terminated loop type of antenna
strongly consider using a Vactrol as it is much faster and easier than
walking back and forth manually adjusting resistances. My Vactrol is
connected to the control unit with two separate wires about 250 ft long and
clearly nulls aren't spoiled. A nice pure resistance is created by the
Vactrol and applied to the termination end.
73 KAZ Barrington IL (35 miles NW of Chicago)
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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
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_______________________________________________
IRCA mailing list
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Be sure to register now for the Joint DX Convention
Kansas City, September 9 to 11. Hotel space is filling up.
Registration info:
http://www.nrcdxas.org
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: irca@xxxxxxxxxxxxxxxx