Hi,

Saw a picture somewhere of an in-line lightning protector for a HF radio
receive only antenna.
Coax style.
Apparently has the typical gas tube, and when activated shorts the center
conductor to the braid.

Was wondering a bit about this.

I seem to remember in the old days, there was always a third tap on these
sort of things that you ran a solid ground to, e.g., a water pipe.

Does merely shorting to the braid provide "good" protection ?

Any thoughts would be appreciated.

Also want to ask: what about voltage surges of a few hundred volts or so
induced on an antenna lead from a nearby lightning strike perhaps
..
The levels way below what would trip a gas tube I would imagine, but still
more than enough to ruin a front end of a receiver.

How does one protect against these without breaking the bank doing so ?

Thanks,
Bob

"Robert11" wrote in
:

Hi,

Saw a picture somewhere of an in-line lightning protector for a HF
radio receive only antenna.
Coax style.
Apparently has the typical gas tube, and when activated shorts the
center conductor to the braid.

Was wondering a bit about this.

I seem to remember in the old days, there was always a third tap on
these sort of things that you ran a solid ground to, e.g., a water
pipe.

Does merely shorting to the braid provide "good" protection ?

Any thoughts would be appreciated.

Also want to ask: what about voltage surges of a few hundred volts or
so induced on an antenna lead from a nearby lightning strike perhaps
.
The levels way below what would trip a gas tube I would imagine, but
still more than enough to ruin a front end of a receiver.

There are two issues, the differential impulse, and the common mode
impulse.

The shunt gas discharge tube will fire on the differential impulse
voltage, although relatively slowly, even if it includes a radioactive
isotope to assist ionisation.

More importantly perhaps is that there is likely to be a substantial
common mode current impulse and that will induce a transient voltage
gradient in your grounding system. That transient may cause potential
differences across equipment interfaces generally, possibly sufficient to
damage them. There is also a risk of injury or death to persons.

The type of suppressor you describe does precious little to deal with the
common mode current impulse. The 'third wire' assists shunting common
mode current to ground before entering the equipment room.


How does one protect against these without breaking the bank doing so
?

Disconnect antenna conductors when not in use, and do not use them unless
the probability of lighting is low?

Owen

Hi Bob,

It takes about 100 volts for the neon tube to strike. The back to back
diodes in the receiver antenna input should protect against this. The
duration of a lightning strike is so brief that insufficient heat will be
generated to destroy the diodes.
BUT
The neon or any spark gap protection device cannot protect against a direct
lightning strike, only a near miss.

Shorting the coax centre to the braid may not be good electrical practice
but will provide sufficient protection for all practical purposes against
static build up and lightning strikes within around 100 yards from your
antenna.

When at sea in the merchant navy a similar system did withstand a direct hit
while I was in the radio room. The whole room lit up with a blue glow and
there was a terrific crash from the antenna switching box as the strike
arced to the ground through the ship's superstructure. Probably helped to
have 20,000 tons of steel in contact with the ocean!

The receiver (Marconi Apollo - wadley loop tuning and digital frequency
readout on nixie tubes) blanked for about 5 seconds and then came back.
Marconi know how to build stuff in those days. :-)

Any protection is better than nothing, a spark gap (old automobile spark
plug) or small neon tube, a couple of back to back diodes and a 5 megohm or
higher resistor across the diodes to provide a static discharge path will do
the job for pennies.

Regards

Mike G0ULI

"Robert11" wrote in message
...
Hi,

Saw a picture somewhere of an in-line lightning protector for a HF radio
receive only antenna.
Coax style.
Apparently has the typical gas tube, and when activated shorts the center
conductor to the braid.

Was wondering a bit about this.

I seem to remember in the old days, there was always a third tap on these
sort of things that you ran a solid ground to, e.g., a water pipe.

Does merely shorting to the braid provide "good" protection ?

Any thoughts would be appreciated.

Also want to ask: what about voltage surges of a few hundred volts or so
induced on an antenna lead from a nearby lightning strike perhaps
.
The levels way below what would trip a gas tube I would imagine, but still
more than enough to ruin a front end of a receiver.

How does one protect against these without breaking the bank doing so ?

Thanks,
Bob

"Mike Kaliski" wrote in
:

....
Any protection is better than nothing,

.... unless it lulls you into a false sense of security ...

a spark gap (old automobile
spark plug) or small neon tube, a couple of back to back diodes and a
5 megohm or higher resistor across the diodes to provide a static
discharge path will do the job for pennies.

as most of these may.

I do recall taking an early (probably the first) Collins digitally tuned
receiver to a coast radio station for evaluation. It had inverse parallel
diodes across the RF amp input for protection of the FETs and was totally
unusable as when the on-site 500kHz transmitter was keyed up, it wiped
out all of the receivers (not just this one) with broadband noise. It
took a few minutes to realise what was causing ALL of the ROs to hear the
station callsign, not as a beat note, but as noise as if it was near to
where they were listening and just needed to be tuned in. Whilst the
Collins was connected to an antenna, it caused havoc, even if powered
off!

Beware of the effects of inverse parallel diodes across the antenna.

Owen

Hi Owen,

Point taken. The standard Marconi ship station fed the receive antenna
through the back contacts of the key, so the receiver was always
disconnected whenever the transmitter was operating. I remember having to
pay about £15 extra for my CMOS TTL electronic keyer to be fitted with a
changeover relay rather than direct keying so I could use it with the
standard Marconi ship installation. Still working fine today after 34 years
of use!

I don't recall ever operating close enough to any other stations for the
diodes to cause me a problem, although I did once upset a Russian warship
when operating from Angola. My signals were apparently overloading their
equipment...

Regards

Mike G0ULI

"Owen Duffy" wrote in message
...
"Mike Kaliski" wrote in
:

...
Any protection is better than nothing,

... unless it lulls you into a false sense of security ...

a spark gap (old automobile
spark plug) or small neon tube, a couple of back to back diodes and a
5 megohm or higher resistor across the diodes to provide a static
discharge path will do the job for pennies.

as most of these may.

I do recall taking an early (probably the first) Collins digitally tuned
receiver to a coast radio station for evaluation. It had inverse parallel
diodes across the RF amp input for protection of the FETs and was totally
unusable as when the on-site 500kHz transmitter was keyed up, it wiped
out all of the receivers (not just this one) with broadband noise. It
took a few minutes to realise what was causing ALL of the ROs to hear the
station callsign, not as a beat note, but as noise as if it was near to
where they were listening and just needed to be tuned in. Whilst the
Collins was connected to an antenna, it caused havoc, even if powered
off!

Beware of the effects of inverse parallel diodes across the antenna.

Owen

On Sep 25, 3:20*pm, "Mike Kaliski" wrote:
Hi Owen,

Point taken. The standard Marconi ship station fed the receive antenna
through the back contacts of the key, so the receiver was always
disconnected whenever the transmitter was operating. I remember having to
pay about £15 extra for my CMOS TTL electronic keyer to be fitted with a
changeover relay rather than direct keying so I could use it with the
standard Marconi ship installation. Still working fine today after 34 years
of use!

I don't recall ever operating close enough to any other stations for the
diodes to cause me a problem, although I did once upset a Russian warship
when operating from Angola. My signals were apparently overloading their
equipment...

Regards

Mike G0ULI

"Owen Duffy" wrote in message

...

"Mike Kaliski" wrote in
:

...
Any protection is better than nothing,

... unless it lulls you into a false sense of security ...

a spark gap (old automobile
spark plug) or small neon tube, a couple of back to back diodes and a
5 megohm or higher resistor across the diodes to provide a static
discharge path will do the job for pennies.

as most of these may.

I do recall taking an early (probably the first) Collins digitally tuned
receiver to a coast radio station for evaluation. It had inverse parallel
diodes across the RF amp input for protection of the FETs and was totally
unusable as when the on-site 500kHz transmitter was keyed up, it wiped
out all of the receivers (not just this one) with broadband noise. It
took a few minutes to realise what was causing ALL of the ROs to hear the
station callsign, not as a beat note, but as noise as if it was near to
where they were listening and just needed to be tuned in. Whilst the
Collins was connected to an antenna, it caused havoc, even if powered
off!

Beware of the effects of inverse parallel diodes across the antenna.

Owen

I found that all very interesting. Mike stick around

On Thu, 24 Sep 2009 15:15:01 -0400, "Robert11"
wrote:

Saw a picture somewhere of an in-line lightning protector for a HF radio
receive only antenna.
Coax style.
Apparently has the typical gas tube, and when activated shorts the center
conductor to the braid.

See:
http://www.polyphaser.com/productdata.aspx?class=coax

This is what I use on the local mountain top sites.
http://www.polyphaser.com/cms_spol_app/Translations/English/B50.pdf
Note that we don't have much lightening on the left coast, so I don't
have much history on how well it works. The one site where we did
take a nearby hit, managed to blow up some unprotected ethernet to
coax translators, and some cheap sacrificial ethernet switches.

Also, not all lightning protectors use a gas tube. I have an older
Polyphaser with ZnO ceramic elements. When hit with sufficient
energy, the ZnO expands and closes a gap. Polyphaser places 4 of
these in series from the center conductor to ground. My guess(tm), is
that when hit by lightning, one of them might stay shorted. 4 hits,
and it's totally shorted and must be replaced. However, I'm not sure.
I'll post a photo when I find it.

Was wondering a bit about this.

Articles on the subject.
http://www.polyphaser.com/technical_notes.aspx

Ham Radio protection:
http://www.polyphaser.com/cms_spol_app/techdocs/Ham%20Radio.pdf
See Pg 6 for some interesting comments on receiver protection. Quoting
in part:

Coax protectors should be units that have dc blocking on the center
pin. This serves as a high pass filtering that prevents the
lightning's low frequency energy from continuing to your equipment.
The strike energy is picked off and diverted into the ground system
in a controlled way. The dc blocking ensures the operation of the
protector regardless of the input circuitry of the equipment.

Did you know that spark gap protectors with dc continuity will not
work on receivers and shunt fed duplexers? The shunt to ground
inside a receiver (coil to ground for static draining) prevents the
low frequency lightning energy from turning on the dc continuity
protector. The coil shunts the energy to ground all right, but it
is at the wrong place. If the coil can't handle the energy (half
the coax surge energy is on the center pin), the coil will open up
and the current will translate to a large open voltage source
capable of arcing anywhere within the radio.

I seem to remember in the old days, there was always a third tap on these
sort of things that you ran a solid ground to, e.g., a water pipe.

Yep. The current needs to go somewhere to get to ground. Best
through a big fat wire ending in a good ground than through your
equipment. Incidentally, a water pipe is not a decent ground for
lightning protection.

Does merely shorting to the braid provide "good" protection ?

No. If lightning came down your coax cable and to shorted braid it
must have a path to continue to ground. Just a shorted coax will send
it through your equipment, probably through the AC power cords, and
then through the house wiring. I've seen photos of the wall blown out
when that happens. Bad idea.

Polyphaser also suggests that a DC short in the radio is inadequate:
http://www.polyphaser.com/cms_spol_app/techdocs/Built-in%20Coax.pdf

Any thoughts would be appreciated.

Also want to ask: what about voltage surges of a few hundred volts or so
induced on an antenna lead from a nearby lightning strike perhaps
.
The levels way below what would trip a gas tube I would imagine, but still
more than enough to ruin a front end of a receiver.

A high value resistor should bleed off any charges. As others have
suggested, a neon lamp and/or back to back diodes, should also work.

How does one protect against these without breaking the bank doing so ?

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

How does one protect against these without breaking the bank doing so ?

Go on Mousers web site and look at gas tubes made by Littelfuse. Go to
Littelfuses web site from the link on Mousers site and check out the specs
on gas tubes. Compare them to the specs on your $50-70 commercial lightning
arrestor.
Then note that what's in that little casting box is two coax connectors, one
capacitor and one $2-3 gas tube and you have the answer to your question.
Myth revealed.

Rick K2XT

On Mon, 28 Sep 2009 14:20:29 GMT, "Rick" wrote:

How does one protect against these without breaking the bank doing so ?

Go on Mousers web site and look at gas tubes made by Littelfuse. Go to
Littelfuses web site from the link on Mousers site and check out the specs
on gas tubes. Compare them to the specs on your $50-70 commercial lightning
arrestor.
Then note that what's in that little casting box is two coax connectors, one
capacitor and one $2-3 gas tube and you have the answer to your question.
Myth revealed.

Yep.

Data sheets on the ceramic gas tubes by Littelfuse:
http://www.littelfuse.com/searchresults.html?NN=0%3aTechnology%3a157

Inside a 900Mhz cellular lightning protector. The two wires are an
interdigital bandpass filter:
http://802.11junk.com/jeffl/pics/lightning/polyphaser-02.jpg
I don't think these look like they were made by Littelfuse.

Unfinished panel:
http://802.11junk.com/jeffl/pics/lightning/panel.jpg
Mostly CATV protectors.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS

On Sep 28, 10:20*am, "Rick" wrote:
How does one protect against these without breaking the bank doing so ?

Go on Mousers web site and look at gas tubes made by Littelfuse. *Go to
Littelfuses web site from the link on Mousers site and check out the specs
on gas tubes. *Compare them to the specs on your $50-70 commercial lightning
arrestor.
Then note that what's in that little casting box is two coax connectors, one
capacitor and one $2-3 gas tube and you have the answer to your question.
Myth revealed.

Rick * K2XT

Rick or anyone else for that matter.

Can anyone suggest a strategy for reasonably safe operation of a
station when lightning is actually present in the area. The stations
located at the weather service offices are used to receive real time
weather reports from AROs. If they go off the air during lightning
events the whole network becomes useless to the weather service.
Television and radio stations continue to operate even after direct
strikes to their antennas so it must be possible to provide protection
that does not involve shutting down when lightning is present. Can
anyone draw me a written sketch of how that gets done so that I can
make a more knowledgeable decision on whether or not to try to
replicate the technique.

--
Tom Horne