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- Subject: Re: [NRC-AM] Vactrol luvin' !!
- From: Mark Connelly <markwa1ion@xxxxxxx>
- Date: Sun, 22 May 2016 00:44:38 -0400
- Delivered-to: irca@xxxxxxxxxxxxxxxx
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Great to hear about the Vactrol success there, Neil. You probably remember the first go-'round with Vactrols was about 20 years ago with Steve Byan's Beverage termination box:
http://www.w0btu.com/Remote_Beverage_termination_control.html
This was used successfully at a couple of Newfoundland DXpeditions.
Among the earliest uses on terminated loops was this one from 2000:
http://www.qsl.net/wa1ion/doc1/pennant.pdf
(Ignore the web links in that 16 year old article - no longer good since AOL and Geocities killed off their web hosting services.)
Anyway I'm going to be laying out a new east-west terminated loop - initially just Kaz, Flag, or SuperLoop farther behind the house from where the previous one was. This should result in less noise pick-up. Due to the density of the grove of black locust trees back there, it might be difficult to go with a double loop (DKAZ, Bowtie, etc.) layout without a lot of branch trimming. The first go at termination will probably be the Vactrol at the west end and control voltage passed through the east feedline and then the two antenna wires similar to what was done in the Pennant article of 2000. First I run that with the regular Kaz or Flag and then - if I can somehow jury-rig a DKAZ, DHDL, or Bowtie - with that. I'd certainly like to have a wide back null that substantially reduces the NYC / Philly / Baltimore / DC "I-95" corridor at the same time that it takes down the more northerly "I-90" corridor through upstate NY, ON, western PA, OH, IN, MI, IL, WI, etc. in the Great Lakes region. With a regular single-loop, knocking down WBAL-MD 1090 / WFED-DC 1500 required a different antenna from one that would take out Albany, Buffalo, and Toronto.
What might happen is that, because of low gain, the DKAZ or Bowtie may need an amp at the forward side, thus making more of a need for a second twisted-pair line to run out to the Vactrol box on the null side.
All the testing done by Durenberger et al. in recent chats tends to back up the improvements that can be made by using Vactrol over in-shack termination (9:1 transformer at antenna, twisted pair to 500 ohm operating position pot). When I ran a Bowtie about 5-6 years ago I noted that NYC low-band stations were nulling at different settings from high-band ones. Perhaps I would have had more broadband nulling - similar to what I get on a single-loop design - if I went with the Vactrol instead. Downside is that you give up the flip-of-a-switch pattern reversal capability.
In any event, once I get things running on that antenna, I'll report the results.
Meanwhile the north-south SuperLoop (terminated in 910 ohms fixed on the north side) is still the "main gun" especially at this time of year when more of the interesting DX is from Latin America rather than Europe.
Mark Connelly, WA1ION
South Yarmouth, MA
-----Original Message-----
From: Neil Kazaross <neilkaz58@xxxxxxxxx>
To: irca <irca@xxxxxxxxxxxxxxxx>
Cc: ABDX <ABDX@xxxxxxxxxxxxxxx>; am <am@xxxxxxxxxxx>
Sent: Sat, May 21, 2016 8:13 pm
Subject: [NRC-AM] Vactrol luvin' !!
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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