[TowerTalk] Voltage at ends of yogi parasitic elements?

[Rob Katz]

Thank you Hardy and everybody for your responses.  I’ve built many wire yagis that are loaded in the middle.  I’m looking to put up a new 3-el on 40m with a rope catenary as the “boom,” so I want to eliminate the weight in the middle to reduce the sag.  It’s also over my driveway, so I don’t know if dropping open-wire line would pass the XYL test :-)  It looks like the end voltage would be too high for relays, but I’m still curious to have a number on that voltage if someone can figure it out.

I appreciate all the generous folks in this group!

73,
   Rob  K4OV



> On Oct 17, 2016, at 06:46, Hardy Landskov <n7rt at cox.net> wrote:
> 
> Rob,
> I would switch in an inductor for a reflector and a capacitor for a director at the CENTER of the element. Use a shorted stub for the reflector and an open wire stub for the director.
> The voltage at the ends is very high even in parasitic elements and you would have the problem of RF getting into the switching wires. Not many relays will survive that environment and I don't know anyone who has tried that.
> I would try running 1/2 wave open wire line down to the ground and switch in the lumped elements there. Then put lumped elements in at the antenna. Of course you need split parasitic elements.
> I have built 2 el 80 meter Yagis with a DE and Reflector using open wire line(1/2 inch Al tubing) back to the center of the antenna so I could reach the stub and adjust the shorting coil for F/B ratio. Then used a latching relay to short out a portion of the line to go to the fone band. Of course a matching network would have to be switched in going from CW to FONE.
> But if you are working with wires, a spring loaded knife switch will work. But you would have to go out to the tower to change directions.
> I think I remember one guy who used retractable radio antennas from cars in a junk yard.
> And there is SteppIR if your VISA card can stand the hit.
> 
> I would be interested in other solutions myself.
> Hardy N7RT/4
> 
> 
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Rob Katz
> Sent: Sunday, October 16, 2016 11:09 PM
> To: towertalk at contesting.com
> Subject: [TowerTalk] Voltage at ends of yogi parasitic elements?
> 
> I’m playing with some wire yagis, and I’d like to put relays at the ends of the parasitic wires to switch the director to a reflector (and vice versa).  If I’m driving the antennas with a full 1.5 KW, what would be the maximum voltage that I can expect at the ends of the PARASITIC elements?  Even a rough estimate would be useful, I just need to get a sense of what kind of a relay I would need to use.
> 
> 73,
>   Rob  K4OV
> 
> --
> 
> Rob Katz, Senior Partner
> 919-219-5324
> 
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