De-tuning an electric fence is something I have thought about (I have some here).
Two possible ideas (these are not proven - so I won't say "solutions"). If the fence doesn't need to be active while "detuned" - you can break it up into odd multiples of quarter wavelengths (mind your velocity factors). If the fence does need to be active - you can do step #1 - but then put some kind of choke in series of the places you break it up. The one beverage I have near electric fences doesn't run too close to the wires except at one point where they are nearly perpendicular. Tree N6TR On Thu, Aug 15, 2013 at 7:57 AM, Shoppa, Tim <[email protected]> wrote: > Short of expensive fast vacuum relays, what sort of readily available T/R > (not QSK) relays handle QRO power at non-50-ohm points? > > If it was purely 50 ohms, I wouldn't feel bad using a big ice cube relay. > But I suspect that on many bands the voltages at the base of the antenna > would easily jump the air gap in that kind of relay. > > I'm thinking not just of detuning the transmit antenna but also general > band change activities that right now I go over to the L network at the > base of the antenna to do. That's the wall of my shack so not a huge > distance but it would be cool to do band change activities all from the > operating seat rather than go over to the wall and move banana plugs like I > do right now. > > Tim N3QE > > -----Original Message----- > From: Topband [mailto:[email protected]] On Behalf Of > Charlie Cunningham > Sent: Thursday, August 15, 2013 10:49 AM > To: 'Tom W8JI'; 'Tomas Magyla'; [email protected] > Subject: Re: Topband: How to detune a wire Inverted L? How to > 'detune'electrical fence > > Sounds like a robust relay, just above the feed-point would de-tune the L > rather nicely. At least that was my thought. Probably simpler and more > straightforward than trying to detune it in the shack. > > Charlie, K4OTV > > -----Original Message----- > From: Topband [mailto:[email protected]] On Behalf Of Tom > W8JI > Sent: Thursday, August 15, 2013 10:39 AM > To: Tomas Magyla; [email protected] > Subject: Re: Topband: How to detune a wire Inverted L? How to > 'detune'electrical fence > > > Q1) Would a simple relay disconnecting the vertical wire at the TX > > antenna feedpoint be good for detuning TX antenna? (I am using a piece > > of wire attached to 18m Spidermast for the vertical section) and > > another piece of horizontal on the top. > > > > Q2) Are there any practical solutions for detuning TX antenna by using > > some circuitry at the shack end instead? > > > > Q3) What in practice could be done about the impact of the electrical > > fence? (other then moving RX antenna as far away as possible/ and > > considering using a shielded coax loop / or Waller Flag to 'null' the > > fence > > out?) > > > > > > Assuming it is a 1/4 wave L, anything that electrically opens the base of > the antenna at the feedpoint with maximum possible impedance detunes the L. > > Depending on any networks or transmission lines between the detuning > switch and the element, the optimum termination at the switch might be > almost anything. It is quite possible to detune the antenna from the shack, > although it will generally require a certain value of inductance or > capacitance to be switched in. I detune my 200 ft tower, fed through an L > network, about 50 feet from the element and L network with a short. > > Tom > > _________________ > Topband Reflector > > _________________ > Topband Reflector > _________________ > Topband Reflector > _________________ Topband Reflector
