Hello:

I am contemplating constructing an antenna where a center-fed HALF WAVE
will be bent in a loop, only to be isolated at the almost-touching ends
by a relay or some other means of a remotely controlled switch. When
the relay contacts are open I will have very high RF voltages between
the contacts, probably "a few KV" or even more. Are there any
suggestions on where I could find a relay, if any, for this? Or any
other means for doing this? An additional constraint is that the
switching device needs to be light and small (say, 1-2 oz or 20-50
grams). Some ideas I have come up with a

- A small vacuum relay (supplier, type?).
- A home-made relay, providing more contact spacing than usually
available.
- A DC-motor (toy-type) driven mechanism to open and close contacts.
- A mercury switch that could be tilted to make or break the contacts.
- A string-operated switch to open and close the contacts (would run up
the antenna mast).

Any comments or suggestions?

73 - Kristinn, TF3KX

TF3KX wrote:

Any comments or suggestions?

I assume you are going to switch the loop for lowest band into a bent
dipole, and close the relay on higher bands.

You might consider a trap, because a relay would have to be very
special at any power level. You are deealing with much more than twice
the voltage at the ends of a normal dipole from contact to contact.

I think your only hope for a relay is a high voltage vacuum relay with
wide terminal spacing and good coil insulation. One of the large high
voltage glass vacuum relays would be best.

It might be possible to build a trap and adjust antenna length so it
would work, but the trap would have to be very special in construction.
It may not be practical.

73 Tom

TF3KX schreef:
Hello:

I am contemplating constructing an antenna where a center-fed HALF WAVE
will be bent in a loop, only to be isolated at the almost-touching ends
by a relay or some other means of a remotely controlled switch. When
the relay contacts are open I will have very high RF voltages between
the contacts, probably "a few KV" or even more. Are there any
suggestions on where I could find a relay, if any, for this? Or any
other means for doing this? An additional constraint is that the
switching device needs to be light and small (say, 1-2 oz or 20-50
grams). Some ideas I have come up with a

- A small vacuum relay (supplier, type?).
- A home-made relay, providing more contact spacing than usually
available.
- A DC-motor (toy-type) driven mechanism to open and close contacts.
- A mercury switch that could be tilted to make or break the contacts.
- A string-operated switch to open and close the contacts (would run up
the antenna mast).

Any comments or suggestions?

73 - Kristinn, TF3KX


IMHO two high power relays would be an option, about 10 inches seperated
from each other.

For example Titanex (www.titanex.de) sells good High Power Ceramics
Relais for this purpose:
http://www.titanex.de/frames/acc.html#UB6-9 (HPRL) with power handling
of 5 kW each.

Palstar in the US use high power relais in some of theire antenna
tuners, but those relays are not ceramic.

Good luck!


--

73,
Hans Remeeus (PA1HR)
http://www.remeeus.eu
Communication is about people, the rest is technology.

TF3KX wrote:
Hello:

I am contemplating constructing an antenna where a center-fed HALF WAVE
will be bent in a loop, only to be isolated at the almost-touching ends
by a relay or some other means of a remotely controlled switch. When
the relay contacts are open I will have very high RF voltages between
the contacts, probably "a few KV" or even more. Are there any
suggestions on where I could find a relay, if any, for this? Or any
other means for doing this? An additional constraint is that the
switching device needs to be light and small (say, 1-2 oz or 20-50
grams). Some ideas I have come up with a

- A small vacuum relay (supplier, type?).
- A home-made relay, providing more contact spacing than usually
available.
- A DC-motor (toy-type) driven mechanism to open and close contacts.
- A mercury switch that could be tilted to make or break the contacts.
- A string-operated switch to open and close the contacts (would run up
the antenna mast).

Any comments or suggestions?

73 - Kristinn, TF3KX

Dunno.. I used to use 24 volt relays that normally are used for
fan motors, etc, but I never fed at a high voltage point. I did run
a lot of power though. They always worked fine, but who knows
with a real high potential.. Might arc over.. I've heard tell of one
kinda weird method that supposably will work. I've never tried it
though. You run a line of coax from that open point on the antenna,
to the shack, and use a switch on the end of the coax to open
and close. Like I say, I've never tried it myself, so it' may or
may not work...
MK

Hans Remeeus wrote:
For example Titanex (www.titanex.de) sells good High Power Ceramics
Relais for this purpose:
http://www.titanex.de/frames/acc.html#UB6-9 (HPRL) with power handling
of 5 kW each.

Palstar in the US use high power relais in some of theire antenna
tuners, but those relays are not ceramic.

Good luck!


I would say good luck also if I assumed a relay could actually be rated
for a certain number of "kW".

A relay that easily takes 50kW in a 50 ohm system could fail at 100
watts in an application like this, so it is foolish to even look at
power ratings in other applications.

In this case when the relay is open he will have very high voltages
across the contacts even with very modest power. When the relay is
closed he will have a few amps of current at low power up to 5 or 10
amps at kilowatt levels.

Not only will he have high voltage between contacts, he will have high
voltages from the contact to ground.

That virtually excludes conventional relays, and it even excludes many
types of vacuum relays. The popular ceramic vacuum relays normally have
too low of coil to contact breakdown plus the terninal spacing is much
less than 1/2 inch.

He probably can get by with a conventional ceramic vacuum relay like an
RJ1A (about $50 US surplus) at low power levels (normally considered a
"5kW relay, whatever that means) , but if he runs more than a few
hundred watts and especially if there is moisture in the air he will
need a HV glass vacuum with opposing terminals for contacts and a long
insulation bar on the transfer solenoid bar.

Power levels depend on the application, and he has picked about the
toughest application I can think of.

73 Tom

wrote:
In this case when the relay is open he will have very high voltages
across the contacts even with very modest power. When the relay is
closed he will have a few amps of current at low power up to 5 or 10
amps at kilowatt levels.

I performed this same function in Arizona with a $5 relay.
There is a surplus store beside the freeway in South Phoenix.
They carry surplus relays from the local power company. Some
of those relays are high voltage rated. I choose a SPST relay
that had four contacts. Two contacts were about an inch apart
and, when energized, were shorted by an insulated shorting bar.
When not energized, there was a total of at least one inch of
air gap in the contact path, maybe more. The contacts were
about 1/4" in diameter.

I was running 100 watts. I borrowed a differential high voltage
scope and measured the peak to peak voltage between the ends of
my loop to be somewhat less than ~2500 volts. This was a full
wave 40m loop broken in the middle and tuned to resonance on 80m.
I tested it in increasing increments of 10 watts all the way to
100 watts with no problem. It was before the monsoon season so
the humidity was low. A couple of months later, a severe
thunderstorm broke my upper 2x2 support and brought the whole
thing tumbling down.
--
73, Cecil, http://www.qsl.net/w5dxp

Kristinn, I think I would consider the Jennings RJ1A or the Kilovac
HC-1 high speed vacuum relays. I use them in my amp for QSK
operation.

http://www.mgs4u.com/relay.htm

Good luck.

Win, W0LZ

schreef:
Hans Remeeus wrote:
For example Titanex (www.titanex.de) sells good High Power Ceramics
Relais for this purpose:
http://www.titanex.de/frames/acc.html#UB6-9 (HPRL) with power handling
of 5 kW each.

Palstar in the US use high power relais in some of theire antenna
tuners, but those relays are not ceramic.

Good luck!


I would say good luck also if I assumed a relay could actually be rated
for a certain number of "kW".

A relay that easily takes 50kW in a 50 ohm system could fail at 100
watts in an application like this, so it is foolish to even look at
power ratings in other applications.

In this case when the relay is open he will have very high voltages
across the contacts even with very modest power. When the relay is
closed he will have a few amps of current at low power up to 5 or 10
amps at kilowatt levels.

Not only will he have high voltage between contacts, he will have high
voltages from the contact to ground.

That virtually excludes conventional relays, and it even excludes many
types of vacuum relays. The popular ceramic vacuum relays normally have
too low of coil to contact breakdown plus the terninal spacing is much
less than 1/2 inch.

He probably can get by with a conventional ceramic vacuum relay like an
RJ1A (about $50 US surplus) at low power levels (normally considered a
"5kW relay, whatever that means) , but if he runs more than a few
hundred watts and especially if there is moisture in the air he will
need a HV glass vacuum with opposing terminals for contacts and a long
insulation bar on the transfer solenoid bar.

Power levels depend on the application, and he has picked about the
toughest application I can think of.

73 Tom


Hello Tom,

I know that, but you forgot to quote an important part of my text:

"IMHO two high power relays would be an option, about 10 inches
seperated from each other."



--

73,
Hans Remeeus (PA1HR)
http://www.remeeus.eu
Communication is about people, the rest is technology.

Hans Remeeus wrote:
Hello Tom,

I know that, but you forgot to quote an important part of my text:

"IMHO two high power relays would be an option, about 10 inches
seperated from each other."

That does nothing for breakdown voltages to control cables unless the
relays are a certain construction and wired a certain way. It can help
with antenna end-to-end breakdown voltage.

73 Tom

In article .com,
"TF3KX" wrote:

I am contemplating constructing an antenna where a center-fed HALF WAVE
will be bent in a loop, only to be isolated at the almost-touching ends
by a relay or some other means of a remotely controlled switch. When
the relay contacts are open I will have very high RF voltages between
the contacts, probably "a few KV" or even more. Are there any
suggestions on where I could find a relay, if any, for this? Or any
other means for doing this?

I assume that when used on higher frequencies where the antenna is more
than 1/2 wave long, the relay contacts are to be closed.

If that is what you want to do, and if the higher frequency bands are
even multiples of the lower frequency, then you could connect the ends
of the 1/2 wave antenna to a shorted 1/4 wave stub made out of open
wire. At the lower frequency this would place a very high impedance
between the two ends of the antenna, and at even harmonics where the
stub would be an integer number of 1/2 waves long, it would place a low
impedance between the antenna ends. Cheaper than a relay, too.

David, ex-W8EZE

--
David Ryeburn

To send e-mail, use "ca" instead of "caz".