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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


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