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Re: [IRCA] DKAZ Construction Help Request
Hi Michael,
So... were you proposing the terminated end of the DKaz will actually
not be terminated until it reaches the Vactrol after a 70' length of
twisted pair? And the extension from the feedpoint end will also
simply be another 70' of twisted pair eventually terminated in a
balun (and the balun would be unnecessary if you used a FLG100 at
that point)? I never say never, especially as I have done
something similar with an ALA100 in a difficult situation, but it was
only a few meters of twisted pair in that case. I'm not sure that
it's a very RF sanitary arrangement if you're trying to get deep nulls.
If that's so, then I maybe it would be better to look at Mark's
scheme, page 5 of his document.
But....there's a 9:1 impedance transformation at both ends in Mark's
scheme, so at his switching point, you are looking at about 100 ohms
impedance. FLG100 is a wonderful device, but its input impedance is
closer to 1000 ohms, so there will be a fair impedance mismatch, and
you may be disappointed if you plan to make a special purchase for
this project. If you have an ALA100 already, that may work as well
as the other two amplifiers. Both it and the FLG100 are designed to
be used with coax however, and if I'm not mistaken, you want CAT5
back to the shack with one pair for signal, one for power, one for
Vactrol control and the remaining pair for controlling the relay (do
you have enough pairs?). This is complicated enough that you may as
well design in the receiver interface box for the FLG/ALA100 out
there as well, popping in a matching transformer / balun from 50:100
ohms, and at that point, I admire your ingenuity, but hope that you
are not paying yourself by the hour!
The Vactrol is also meant to work at around the 900 to 1000 ohm
termination of the DKaz, not the 100 ohm approximately that would be
found with Mark's system (he uses a low value pot rather than a 1kohm
pot at that point, see page 11 of his document). So some parallel
resistance needs to be shunted to the Vactrol's resistance
also. Things are not impossible, but they are getting complicated.
Like Mark says, shout if anything here sounds useful. I don't want
to be discouraging, but you have set yourself quite a fine
engineering problem here!
best wishes,
Nick
At 23:02 07-05-16, you wrote:
I would like to install a couple of reversible DKAZ's (DKAZi?) and
am wondering what you all think about extending the two ends towards
the middle using CAT5 and attaching them to a 4PDT relay. I would
have a Patented Colin Newell Vactrol and a balun at that point and
run these back to the house, also using CAT5.
I thought that bringing the end points back the 70 feet to the
middle would keep the Vactrol within the 100 foot length limit
recommended to maximize null depth, but am a little concerned about
any interaction with the antenna because they would be running more
or less in parallel.
I am also wondering what you would recommend for a broadband
amplifier - it seems that the options are Wellbrook, Kiwa, and DX
Engineering. I wanted to use CAT5 instead of coax to keep feedline
costs down if at all possible, and it's likely that the feedline
length will be on the order of 250 feet. With a length like that
would it be better to have the amp at the antenna or is it OK to
have it in the house? What configuration are others using to do this?
I really appreciate any help you could offer. This is my first
antenna project in many years!
Kind regards,
Michael Yule
Upper LaHave, NS
Sent from my iPad
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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
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