(Dave Platt) wrote in news:12aroqj2chrpu45
@corp.supernews.com:


Triangle will work fine.

160m probably not; it's a bit short. It would help if you included a
relay opposite the feedpoint to open it on 160m.

I've read of people using an L/C resonant trap instead of a relay, for
just this purpose. The trap opens the loop on the lowest band, and
appears as a capacitive reactance in series with the loop on the
higher-frequency bands.




That's interesting, Dave. Thanks. Will look into that as a relay would
be tricky given the location and height of my proposed loop.

Ed

Trap seems like a fine idea...

If it were not a multiband loop, I think you could use a relay with the
coil in parallel with the contacts, so you could run DC on the feedline
(if it were a dual bander of some sort) but the high voltages present
on the open wire feeder would make it awfully hard to choke off the RF
for whatever DC injection scheme you were using. I think you'd
basically need a tuner with DC continuity, and the CLC tee that is so
common in tuners isn't one.

I guess you need a big enough C on the higher bands to look like a
short circuit in that trap if you want to have the loop appear to be a
closed loop, but maybe that's not very important.

73,
Dan

A relay inserted in an antenna wire can be operated via a pair of
wires (20 gauge twin speaker cable) which, in parallel, form the
single antenna wire.

At the shack end, DC power is fed into the pair of wires via an RF
choke. The choke consists of a pair of wires (more 20 gauge twin
speaker cable) wound on a ferrite rod.

Been there. Done that! I used a single-contact reed relay.
----
Reg.

Reg Edwards wrote:
A relay inserted in an antenna wire ...
Been there. Done that! I used a single-contact reed relay.

No arcing problems?
--
73, Cecil http://www.qsl.net/w5dxp

Reg Edwards wrote:
A relay inserted in an antenna wire ...
Been there. Done that! I used a single-contact reed relay.

No arcing problems?
--
73, Cecil
==================================
No arcing problem that I ever detected. Transmitter was 100 watts. I
think the relay was rated at 750 volts and it may have been a vacuum
type. Only used on the 160 and 80m bands.

It eventually failed because of intermittent contact on receive when
no wetting current flowed. Perhaps it should have been mercury
wetted.
----
Reg.

Reg Edwards wrote:
No arcing problem that I ever detected. Transmitter was 100 watts. I
think the relay was rated at 750 volts and it may have been a vacuum
type.

That's a pretty husky reed relay but you are lucky
it didn't arc. Peak-to-peak across that relay was
higher than 750 volts if it was installed in a 1/2WL
dipole.
--
73, Cecil http://www.qsl.net/w5dxp

Reg Edwards wrote:
No arcing problem that I ever detected. Transmitter was 100
watts. I
think the relay was rated at 750 volts and it may have been a
vacuum
type.

That's a pretty husky reed relay but you are lucky
it didn't arc. Peak-to-peak across that relay was
higher than 750 volts if it was installed in a 1/2WL
dipole.
--
73, Cecil
========================================

The voltage between the relay contacts, when open, can be considerably
less that the voltage at the end of the live wire relative to ground.

The capacitance between the open-circuit contacts of a reed relay is
very small. And there is a larger capacitance between the two antenna
wires on either side of the relay contacts. There is also capacitance
between each of the two wires and ground.

If the input impedance of the wire on the remote side of the relay is
not low then we have a voltage divider.

So the voltage which appears across the relay contacts can be
considerably less than the volts between the live wire and ground.

If I remember correctly, the relay was located more than
1/4-wavelength along an end-fed wire on the 160m band. There was a
random but not very long length of wire on the far side of the relay.
The antenna was only about 20 feet above ground, ie., quite lossy.
The details of what experiments took place I can't remember. Perhaps
something to do with input impedance measurements and treating antenna
wires as transmission lines.

If the open-circuit relay contacts did not arc over with 100 watts
then it was more by design than good luck. ;o)

I've just had a search round my junk boxes to see if I stll have the
reed relay. It was built into a small plastic box with a few
decoupling capacitors and 3 binding posts. But, unhappily, no signs
of it.

And my suggestion to operate a relay in an antenna wire via Radio
Shack speaker wire stll holds good.
----
Regards, Reg, G4FGQ.