Dave Shrader wrote:
SNIP
SNIP
SNIP: for a high power solid state station,
1500 watts, the matched RMS voltage is 274
volts, the maximum peak to peak is 274*2.828
= 774 volts p-p. Any surge device must
accommodate the high RMS voltage and yet the
receiver/transceiver front end must tolerate
774 volts p-p without damage.
Deacon Dave, W1MCE

I gently disagree with your inclusion of the word receiver (with
respect to tolerating 774 volts). That's why the T/R switch has an
isolation spec that is much greater than 0dB. In receive mode the
transceiver might be damaged by voltages much less than 774 volts.

To confirm, simply transmit 1500 watts into your receiver.

Your analysis is probably more-or-less valid for 1500 watt
transmitters (or similar transceivers when transmitting).

Unfortunately, most transceivers have a very high duty cycle for being
in receive mode.

You sniped his last staement. He concluded by this that no protection scheme
was going to help, other than disconecting, as that voltage would damage
the reciever.

"J. Harvey" wrote in message
om...
Dave Shrader wrote:
SNIP
SNIP
SNIP: for a high power solid state station,
1500 watts, the matched RMS voltage is 274
volts, the maximum peak to peak is 274*2.828
= 774 volts p-p. Any surge device must
accommodate the high RMS voltage and yet the
receiver/transceiver front end must tolerate
774 volts p-p without damage.
Deacon Dave, W1MCE

I gently disagree with your inclusion of the word receiver (with
respect to tolerating 774 volts). That's why the T/R switch has an
isolation spec that is much greater than 0dB. In receive mode the
transceiver might be damaged by voltages much less than 774 volts.

To confirm, simply transmit 1500 watts into your receiver.

Your analysis is probably more-or-less valid for 1500 watt
transmitters (or similar transceivers when transmitting).

Unfortunately, most transceivers have a very high duty cycle for being
in receive mode.

"CW" wrote:
You snipped his last statement. He concluded
by this that no protection scheme was going
to help, other than disconecting, as that
voltage would damage the receiver.

You're right - I misinterpreted his statement. I failed to notice
that he intended the word 'must' to represent an impossible (or at
least difficult) requirement.

Regards.

"Andy Cowley" wrote in message
...
strike. A spark gap that can conduct a lightening strike would
be the size of a small truck.

The only way to make sure you have a working station after a
lightening strike on your aerials is to take out good insurance.

vy 73

Andy, M1EBV

Nonsense. Every insulated AM broadcast station antenna has an arc
gap at the base. How many stations get struck by lightning each year
and keep on operating?

Pete

Uncle Peter wrote:
Every insulated AM broadcast station antenna has an arc
gap at the base. How many stations get struck by lightning each year
and keep on operating?

1732?
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
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I would like to advise that an AM Broadcast station and an Amateur
station have at least one significant difference.

The AM Station is most likely running a vacuum tube amplifier at high
voltages with high voltage capacitors in the output stage. Also, they do
not have a solid state receiver connected to the same transmission line.
Therefore, they have a high tolerance to peak voltages.

Most Amateur stations, excluding members of the Kilowatt Alley Society,
have solid state finals and very sensitive solid state receiver circuits
that do not have KV level tolerance to transient voltages.

Conclusion, your argument is not totally valid!

Deacon Dave, W1MCE


Uncle Peter wrote:

"Andy Cowley" wrote in message
...
strike. A spark gap that can conduct a lightening strike would

be the size of a small truck.

The only way to make sure you have a working station after a
lightening strike on your aerials is to take out good insurance.

vy 73

Andy, M1EBV


Nonsense. Every insulated AM broadcast station antenna has an arc
gap at the base. How many stations get struck by lightning each year
and keep on operating?

Pete

(Richard Harrison) wrote in message ...
Art, Kb9MZ wrote:
"---the local radio station has a line to ground with a large gap which
regularly arcs because of static build up. Most stations go off the air
momentarily when lightning strikes.'

AM broadcasters use unbalanced vertical radiators driven against a
ground radial system.

snip
Towers often get direct lightning hits. The paint remains pristene in
all the gaps I`ve seen. The arc to ground is always to the Faraday
shield between the tower coupling coils.




Can I assume then that broadcast coupling coils are always apart
to accomodate a faraday shield between them ? Is this an F,C,C, requirement?
Can't see how a Faraday shield can be used if they are link coupled
i.e. interleaved. I was contemplating an interleaf coupling until
I realised that I would have to do away with the Faraday shield !
Regards
Art





That picket fence between the
coils is pock marked like the face of the moon from tower strikes.
Splattered copper abounds.

You hear momentary disconnects during lightning strikes when listening
to an AM station during this kind of storm. This is a defense mechanism.
When lightning creates an arc, the conductive plasma path allows RF to
continue feeding the ionization. This allows an arc to keep alive that
the r-f is too feeble to strike for itself.

Transmitter output into the plasma short circuit is an overload capable
of transmitter damage.

To counter the arc problem, the coax is d-c isolated with capacitors at
the ends of the center conductor. The close-spaced coax usually gets an
arc when the antenna system is overloaded. The coax has a high
common-mode impedance.

A relay d-c power supply and a d-c relay coil are connected in series
and this series combination is connected between the center conductor
and coax shield.

An arc completes the d-c path for the relay coil. Relay activation is
used to momentarily kill the transmitter, extinguishing the arc.

Best regards, Richard Harrison, KB5WZI

On Fri, 19 Dec 2003 23:09:28 GMT, Dave Shrader
wrote:

I would like to advise that an AM Broadcast station and an Amateur
station have at least one significant difference.

The AM Station is most likely running a vacuum tube amplifier at high
voltages with high voltage capacitors in the output stage. Also, they do
not have a solid state receiver connected to the same transmission line.
Therefore, they have a high tolerance to peak voltages.

My tower gets hit on average about 3 times a year. In the last 19
years I've only lost the front end out of one receiver and had a piece
of heliax blown out about 30 feet from the top of the tower.

I rarely if ever, disconnect any equipment except the computers and
with those I worry about the phone lines more than the radio station.
In the same period I've lost three computers.


Most Amateur stations, excluding members of the Kilowatt Alley Society,
have solid state finals and very sensitive solid state receiver circuits
that do not have KV level tolerance to transient voltages.

I have two KW amps hooked up to two different systems with 4 solid
state transceivers connected to the antennas. The HF rigs are
connected to the antennas through the relays in the KW amps. So the
receivers are always on the antennas except when transmitting.

Other than the amps everything here is solid state.

One of the antenna systems is near the bottom of
http://www.rogerhalstead.com/ham_files/tower.htm

here's a bit about the ground system:
http://www.rogerhalstead.com/ham_files/ground.htm

Conclusion, your argument is not totally valid!

Works for me, or has so far.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair?)
www.rogerhalstead.com
Return address modified due to dumb virus checkers


Deacon Dave, W1MCE


Uncle Peter wrote:

"Andy Cowley" wrote in message
...
strike. A spark gap that can conduct a lightening strike would

be the size of a small truck.

The only way to make sure you have a working station after a
lightening strike on your aerials is to take out good insurance.

vy 73

Andy, M1EBV


Nonsense. Every insulated AM broadcast station antenna has an arc
gap at the base. How many stations get struck by lightning each year
and keep on operating?

Pete

On Fri, 19 Dec 2003 15:07:07 -0500, " Uncle Peter"
wrote:


"Andy Cowley" wrote in message
...
strike. A spark gap that can conduct a lightening strike would
be the size of a small truck.
Most damage comes from the voltage induced by nearby strikes
rather than direct hits, so the spark gap doesn't have to be a
monster.

Devices like PolyPhasers keep the voltage across the coax to a low
level. If they get poked too hard they short. If they get poked
really hard they blow apart. I had one short about a year ago, but
there was no damage to the equipment. OTOH the PolyPhaser is over $50.
Still, it was a good trade. The rig on that line is a TM-V7A and it
was on at the time of the strike.


The only way to make sure you have a working station after a
lightening strike on your aerials is to take out good insurance.

In a way. It means you will eventually have a working station. OTOH
there are no guarantee, but it never hurts to move the odds in your
favor by using good grounding techniques and protective devices, or
throwing the coax out the window.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair?)
www.rogerhalstead.com
Return address modified due to dumb virus checkers

vy 73

Andy, M1EBV

Nonsense. Every insulated AM broadcast station antenna has an arc
gap at the base. How many stations get struck by lightning each year
and keep on operating?

Pete

Link coupling is possible with a Faraday shield on the link only.

The main tuning coils have a 'gap' of sufficient size to accommodate the
link. The link is shielded.

Back in the 'olden days', 1955, I used a shielded link from B&W in a 40
meter home brew project [a pair of 807s in PP].

Deacon Dave, W1MCE
+ + +