Antenna ground or rig ground?
 

Here's a simple question. I want to connect my transceiver to several
antennas using 450 ohm ladder line and a balanced tuner. I found a
couple of small double pole double throw knife switches for the ladder
line. There are only two ways to hook these up. I can hook the tuner
output to the center with the ground on the bottom and the antenna on
the top connectors. This will allow me to connect the transceiver to
the antenna or to ground. The second way is to connect the
transceiver to the top contacts, the antenna to the center, and ground
to the bottom contacts. This will let me connect the antenna to the
radio or to ground. Is it better to ground the radio and let the
antenna float? Or to ground the antenna and let the radio float?
Of course if I leave the switch handle sticking straight up nothing is
connected to anything.
I am inclined to think grounding the antenna is better but I have been
wrong before.

Thanks and 73 Gary N9ZSV

Antenna ground or rig ground?
 

Gary Pewitt wrote:
Here's a simple question. I want to connect my transceiver to several
antennas using 450 ohm ladder line and a balanced tuner. I found a
couple of small double pole double throw knife switches for the ladder
line. There are only two ways to hook these up. I can hook the tuner
output to the center with the ground on the bottom and the antenna on
the top connectors. This will allow me to connect the transceiver to
the antenna or to ground. The second way is to connect the
transceiver to the top contacts, the antenna to the center, and ground
to the bottom contacts. This will let me connect the antenna to the
radio or to ground. Is it better to ground the radio and let the
antenna float? Or to ground the antenna and let the radio float?
Of course if I leave the switch handle sticking straight up nothing is
connected to anything.
I am inclined to think grounding the antenna is better but I have been
wrong before.

Thanks and 73 Gary N9ZSV

Ground the antenna, ground the rig chassis, float the rig RF In.

Antenna ground or rig ground?
 

Gary,
The biggest problem would be in trying to use the radio without
connecting an antenna to it. If you can be sure of always doing that,
then I would ground the unused antenna (personal preference, radio is
grounded anyway). Same thing if you ground the radio's antenna
connection. If you forget, it causes problems, sometimes big ones. I
tend to make allowances for my bad memory. You may not have that
problem, so...
- 'Doc

Antenna ground or rig ground?
 

On Sat, 11 Oct 2008 22:12:20 -0500, Gary Pewitt
wrote:

I found a
couple of small double pole double throw knife switches for the ladder
line. There are only two ways to hook these up.

Hi Gary,

I see your problem right here.

There are four ways to hook these up.

73's
Richard Clark, KB7QHC

Antenna ground or rig ground?
 

Richard Clark wrote:


Hi Gary,

I see your problem right here.

There are four ways to hook these up.

73's
Richard Clark, KB7QHC

Hmmm, I guess you post implies you are a bit short on beginning with the
first way?

How typical ... yawn

Regards,
JS

Antenna ground or rig ground?
 

On Sun, 12 Oct 2008 18:16:25 -0700, John Smith
wrote:

Richard Clark wrote:
There are four ways to hook these up.

How typical ... yawn

Go back to sleep, Brett. You certainly added nothing.

Switch one center posts: Rig - now called the rig switch
Switch two center posts: Antenna - now called the antenna switch

Rig switch position 1: both sides to ground
Rig switch position 2: both sides to antenna switch position 1
Antenna switch position 1: both sides to rig switch position2
Antenna switch position 2: both sides to ground

Rig can be
1. open
2. grounded
3. to switched antenna

Antenna can be
1. open
2. grounded
3. to switched rig

Both rig and antenna can be independantly open or grounded, or
interconnected. No real advantage in the open positions, but they are
available as a 6 state solution. As such, a 4 state solution that was
sought.

More switches, more states. Classic cross-point switching.

73's
Richard Clark, KB7QHC

Antenna ground or rig ground?
 

Richard Clark wrote:

...
Go back to sleep, Brett. You certainly added nothing.
...
73's
Richard Clark, KB7QHC

I'll wakeup, when something interesting comes about ...

Regards,
JS

Antenna ground or rig ground?
 

Richard Clark wrote:
Rig can be
1. open
2. grounded
3. to switched antenna

Antenna can be
1. open
2. grounded
3. to switched rig

As a refinement I'd put a dummy load on switch #1 so that the choices would be:
Rig can be:
1. Open
2. To dummy load
3. To switched antenna

The antenna switch would remain the same -- open, grounded or to switched rig.

I'd rather run my rig into a somewhat reasonable load rather than a short to
ground during the inevitable instance of forgetting to set the switch properly.

If running less than say 200 watts output then one could even use an
incandescent light bulb for the dummy load. It would presumably light up if
one were to inadvertently transmit in that configuration. So, the rig would
be at least partially protected and the operator would have some indication of
why no one is answering his CQ. Maybe a *red* light bulb?

One could also physically (not electrically) parallel the switches so there
were only two configurations. The rig connected to the antenna =OR= the rig
connected to the dummy and the antenna connected to ground. That would be cool.

73,
--
HZ

Antenna ground or rig ground?
 

On Mon, 13 Oct 2008 15:15:44 -0600, Hank Zoeller
wrote:

Richard Clark wrote:
Rig can be
1. open
2. grounded
3. to switched antenna

Antenna can be
1. open
2. grounded
3. to switched rig

As a refinement I'd put a dummy load on switch #1 so that the choices would be:
Rig can be:
1. Open
2. To dummy load
3. To switched antenna

The antenna switch would remain the same -- open, grounded or to switched rig.

I'd rather run my rig into a somewhat reasonable load rather than a short to
ground during the inevitable instance of forgetting to set the switch properly.

If running less than say 200 watts output then one could even use an
incandescent light bulb for the dummy load. It would presumably light up if
one were to inadvertently transmit in that configuration. So, the rig would
be at least partially protected and the operator would have some indication of
why no one is answering his CQ. Maybe a *red* light bulb?

One could also physically (not electrically) parallel the switches so there
were only two configurations. The rig connected to the antenna =OR= the rig
connected to the dummy and the antenna connected to ground. That would be cool.

Hi Hank,

Sounds like good advances toward full use of the two switches.

73's
Richard Clark, KB7QHC

Antenna ground or rig ground?
 

"Gary Pewitt" wrote in message
...
Here's a simple question. I want to connect my transceiver to several
antennas using 450 ohm ladder line and a balanced tuner. I found a
couple of small double pole double throw knife switches for the ladder
line. There are only two ways to hook these up. I can hook the tuner
output to the center with the ground on the bottom and the antenna on
the top connectors. This will allow me to connect the transceiver to
the antenna or to ground. The second way is to connect the
transceiver to the top contacts, the antenna to the center, and ground
to the bottom contacts. This will let me connect the antenna to the
radio or to ground. Is it better to ground the radio and let the
antenna float? Or to ground the antenna and let the radio float?
Of course if I leave the switch handle sticking straight up nothing is
connected to anything.
I am inclined to think grounding the antenna is better but I have been
wrong before.

Thanks and 73 Gary N9ZSV

If you have a real problem with lightning in your area, do some reading on
the situation. You might drastically redesign your grounding situation. The
grounding should be tied together at the service entrance, so the antenna
entrance should be near there and all tied together with low resistance to
ground. This means the tuner should be there too or at the antenna The
radio should be grounded to the entrance also. It is important that all
grounding should be done outside the building rather than through the floor.
That would bring the major current of a strike through your house. There
are ARRL tis documents on the subject and a bunch of others.

Antenna ground or rig ground?
 

"JB" wrote in message
...

"Gary Pewitt" wrote in message
...
Here's a simple question. I want to connect my transceiver to several
antennas using 450 ohm ladder line and a balanced tuner. I found a
couple of small double pole double throw knife switches for the ladder
line. There are only two ways to hook these up. I can hook the tuner
output to the center with the ground on the bottom and the antenna on
the top connectors. This will allow me to connect the transceiver to
the antenna or to ground. The second way is to connect the
transceiver to the top contacts, the antenna to the center, and ground
to the bottom contacts. This will let me connect the antenna to the
radio or to ground. Is it better to ground the radio and let the
antenna float? Or to ground the antenna and let the radio float?
Of course if I leave the switch handle sticking straight up nothing is
connected to anything.
I am inclined to think grounding the antenna is better but I have been
wrong before.

Thanks and 73 Gary N9ZSV

If you have a real problem with lightning in your area, do some reading on
the situation. You might drastically redesign your grounding situation.
The
grounding should be tied together at the service entrance, so the antenna
entrance should be near there and all tied together with low resistance to
ground. This means the tuner should be there too or at the antenna The
radio should be grounded to the entrance also. It is important that all
grounding should be done outside the building rather than through the
floor.
That would bring the major current of a strike through your house. There
are ARRL tis documents on the subject and a bunch of others.


You will also want to dispense with the switches and use lightning arresters
so you won't be hanging onto several thousand volts built up on the switch.

Antenna ground or rig ground?
 

I guess I wasn't too clear. I wanted to use one switch each for two
ladder line lead ins. Since no one I can find makes arrestors for
ladder line I am building my own from spark plugs threaded into a big
copper plate which is grounded with copper strap to 5 ground rods in a
fairly small circle outside the shack window. It's about 70 ft to the
200 amp service box from the bedroom I am using for my shack.
I just won a bid on ech bay for a double throw make before break knife
switch which I'll be using also. I'm going to buy one of those MFJ
window lead through plates with multiple ladder line connectors or
maybe make my own version.
I am wondering, instead of using just two spark plugs, if it might be
more effective to use 3 pairs in line with the first pair having
really wide gaps, the second having a medium gap, and the third having
a small gap around .035"? I am going to enclose them to keep them dry
and they will be grounded to the same rods as everything else.
I'll also have a Drake R-8 receiver in my bedroom hooked to an
Evesdropper trap dipole with a Zap Trap arrestor on the co-ax. It's
too far to run a ground to the other end of the house so I plan to
ground it outside of my window. I know that's not the best way but I
don't want to run an 80 foot ground cable to the shack ground.
Thanks for all the good advice. 73 Gary N9ZSV




On Sat, 11 Oct 2008 22:12:20 -0500, Gary Pewitt
wrote:

Here's a simple question. I want to connect my transceiver to several
antennas using 450 ohm ladder line and a balanced tuner. I found a
couple of small double pole double throw knife switches for the ladder
line. There are only two ways to hook these up. I can hook the tuner
output to the center with the ground on the bottom and the antenna on
the top connectors. This will allow me to connect the transceiver to
the antenna or to ground. The second way is to connect the
transceiver to the top contacts, the antenna to the center, and ground
to the bottom contacts. This will let me connect the antenna to the
radio or to ground. Is it better to ground the radio and let the
antenna float? Or to ground the antenna and let the radio float?
Of course if I leave the switch handle sticking straight up nothing is
connected to anything.
I am inclined to think grounding the antenna is better but I have been
wrong before.

Thanks and 73 Gary N9ZSV

Antenna ground or rig ground?
 

Gary,
The 'spark gap' type arrestor is about the most worthless you could
possibly use. More than one reason for that, the simplest being that
by the time it ever bridges that 'gap', it's already gotten to the
radio (path of least resistance). Diverting 'some' of that lightning
strike is probably better than none though, maybe. Good luck.
- 'Doc

Antenna ground or rig ground?
 

Doc, what else can you use for ladder line? Everything I've found is
for co-ax only. Parallel two co-ax arrestors?
I definetly want to run open line as I am going to have a long run to
the antennas. I live on a 29 acre heavily wooded 100 foot hill top in
western Arkansas so I have lots of room for -big- antennas but can
only afford homemade wire designs.
Thanks and 73 Gary N9ZSV




On Tue, 21 Oct 2008 17:03:33 -0700 (PDT), wrote:

Gary,
The 'spark gap' type arrestor is about the most worthless you could
possibly use. More than one reason for that, the simplest being that
by the time it ever bridges that 'gap', it's already gotten to the
radio (path of least resistance). Diverting 'some' of that lightning
strike is probably better than none though, maybe. Good luck.
- 'Doc

Antenna ground or rig ground?
 

I know that's not the best way but I
don't want to run an 80 foot ground cable to the shack ground.
Thanks for all the good advice. 73 Gary N9ZSV


I see why you want to ground close to the shack for your single point
ground. This is good. But you will then have two grounds. One being the
ground outside your window and the other being the service entrance ground
with all the "green wire" grounds connected to it (the 3rd conductor in all
your ac line cords). When there is a strike there WILL be a potential
difference between these two grounds. That means for those few microseconds
they will NOT act as one ground and therefore there will be currents flowing
between these two points. You don't want this happening. The NEC code
requires you to bond your external grounds together, meaning you should run
a conductor outside your house from the shack ground to the service entrance
ground. It is a good idea to install ground rods every 16 feet along this
run. And the same conductor should be connected to any tower ground you
have as well.
There's tons of information on this subect. The antenna email reflector
archives is a good one, as well as the QST series about 4-5 years ago.
I know you don't want to do it, but the purpose of that 80 feet of wire is
important. Without it, all of your other work could be for naught.

Rick K2XT

Antenna ground or rig ground?
 

On Tue, 21 Oct 2008 18:45:59 -0500, Gary Pewitt
wrote:


I guess I wasn't too clear. I wanted to use one switch each for two
ladder line lead ins. Since no one I can find makes arrestors for
ladder line I am building my own from spark plugs threaded into a big
copper plate which is grounded with copper strap to 5 ground rods in a
fairly small circle outside the shack window. It's about 70 ft to the
200 amp service box from the bedroom I am using for my shack.
I just won a bid on ech bay for a double throw make before break knife
switch which I'll be using also. I'm going to buy one of those MFJ
window lead through plates with multiple ladder line connectors or
maybe make my own version.
I am wondering, instead of using just two spark plugs, if it might be
more effective to use 3 pairs in line with the first pair having
really wide gaps, the second having a medium gap, and the third having
a small gap around .035"? I am going to enclose them to keep them dry
and they will be grounded to the same rods as everything else.
I'll also have a Drake R-8 receiver in my bedroom hooked to an
Evesdropper trap dipole with a Zap Trap arrestor on the co-ax. It's
too far to run a ground to the other end of the house so I plan to
ground it outside of my window. I know that's not the best way but I
don't want to run an 80 foot ground cable to the shack ground.
Thanks for all the good advice. 73 Gary N9ZSV




On Sat, 11 Oct 2008 22:12:20 -0500, Gary Pewitt
wrote:

Here's a simple question. I want to connect my transceiver to several
antennas using 450 ohm ladder line and a balanced tuner. I found a
couple of small double pole double throw knife switches for the ladder
line. There are only two ways to hook these up. I can hook the tuner
output to the center with the ground on the bottom and the antenna on
the top connectors. This will allow me to connect the transceiver to
the antenna or to ground. The second way is to connect the
transceiver to the top contacts, the antenna to the center, and ground
to the bottom contacts. This will let me connect the antenna to the
radio or to ground. Is it better to ground the radio and let the
antenna float? Or to ground the antenna and let the radio float?
Of course if I leave the switch handle sticking straight up nothing is
connected to anything.
I am inclined to think grounding the antenna is better but I have been
wrong before.

Thanks and 73 Gary N9ZSV

There is an alternative. Run a #2/0 (67.4 mm^2) bare copper buried 1
foot (300 mm) below grade between them. Bit of a pain, but bonds the
two grounds right proper.

Antenna ground or rig ground?
 

On Tue, 21 Oct 2008 17:03:33 -0700 (PDT), wrote:

Gary,
The 'spark gap' type arrestor is about the most worthless you could
possibly use. More than one reason for that, the simplest being that
by the time it ever bridges that 'gap', it's already gotten to the
radio (path of least resistance). Diverting 'some' of that lightning
strike is probably better than none though, maybe. Good luck.
- 'Doc


It is also dependant on what kind of equipment is connected as well.
If it is just a Rx, a Telco type would be appropriate. If a high
power Tx perhaps an electric service entrance type would be more
appropriate.

Antenna ground or rig ground?
 

Gary Pewitt wrote:
I guess I wasn't too clear. I wanted to use one switch each for two
ladder line lead ins. Since no one I can find makes arrestors for
ladder line I am building my own from spark plugs threaded into a big
copper plate which is grounded with copper strap to 5 ground rods in a
fairly small circle outside the shack window. It's about 70 ft to the
200 amp service box from the bedroom I am using for my shack.
I just won a bid on ech bay for a double throw make before break knife
switch which I'll be using also. I'm going to buy one of those MFJ
window lead through plates with multiple ladder line connectors or
maybe make my own version.
I am wondering, instead of using just two spark plugs, if it might be
more effective to use 3 pairs in line with the first pair having
really wide gaps, the second having a medium gap, and the third having
a small gap around .035"? I am going to enclose them to keep them dry
and they will be grounded to the same rods as everything else.
I'll also have a Drake R-8 receiver in my bedroom hooked to an
Evesdropper trap dipole with a Zap Trap arrestor on the co-ax. It's
too far to run a ground to the other end of the house so I plan to
ground it outside of my window. I know that's not the best way but I
don't want to run an 80 foot ground cable to the shack ground.
Thanks for all the good advice. 73 Gary N9ZSV




On Sat, 11 Oct 2008 22:12:20 -0500, Gary Pewitt
wrote:

Here's a simple question. I want to connect my transceiver to several
antennas using 450 ohm ladder line and a balanced tuner. I found a
couple of small double pole double throw knife switches for the ladder
line. There are only two ways to hook these up. I can hook the tuner
output to the center with the ground on the bottom and the antenna on
the top connectors. This will allow me to connect the transceiver to
the antenna or to ground. The second way is to connect the
transceiver to the top contacts, the antenna to the center, and ground
to the bottom contacts. This will let me connect the antenna to the
radio or to ground. Is it better to ground the radio and let the
antenna float? Or to ground the antenna and let the radio float?
Of course if I leave the switch handle sticking straight up nothing is
connected to anything.
I am inclined to think grounding the antenna is better but I have been
wrong before.

Thanks and 73 Gary N9ZSV

I'd just use 2 coaxial gas tube suppressors, keeping the parallel
spacing the same as your ladder line. The coaxial suppressors just have
the center conductors going straight through, the little gas pellet
barely making contact inside.

Antenna ground or rig ground?
 

Rick wrote:
I know that's not the best way but I
don't want to run an 80 foot ground cable to the shack ground.
Thanks for all the good advice. 73 Gary N9ZSV


I see why you want to ground close to the shack for your single point
ground. This is good. But you will then have two grounds. One being the
ground outside your window and the other being the service entrance ground
with all the "green wire" grounds connected to it (the 3rd conductor in all
your ac line cords). When there is a strike there WILL be a potential
difference between these two grounds. That means for those few microseconds
they will NOT act as one ground and therefore there will be currents flowing
between these two points. You don't want this happening. The NEC code
requires you to bond your external grounds together, meaning you should run
a conductor outside your house from the shack ground to the service entrance
ground. It is a good idea to install ground rods every 16 feet along this
run.

It's not clear why you'd need ground rods along your NEC bonding jumper.
If you're trying to make it do double duty as part of a grounding
ring, maybe? But then, it's the "grounding electrode", and can't serve
as the jumper.

Depending on the distance, too, the bonding wire's not going to help
with the microseconds of transient (as the transient propagates down
that bonding wire)...

Electrical safety ground (green wire) is one thing, Lightning
dissipation is another, and common reference potential is yet another.
The first two have to be connected because of NEC. The first and third
are usually connected because of coax connectors with the shield
connected to the chassis.

But in terms of minimizing transient damage to your equipment, whether
or not it happens to be grounded isn't as important as whether all the
equipment goes up and down together. You could put it all in a metal
cage and suspend it from an insulator and let lightning hit it, without
problems. (people do this for HV measurements on tesla coils and EMP
testing)




And the same conductor should be connected to any tower ground you
have as well.



There's tons of information on this subect. The antenna email reflector
archives is a good one, as well as the QST series about 4-5 years ago.
I know you don't want to do it, but the purpose of that 80 feet of wire is
important. Without it, all of your other work could be for naught.

Rick K2XT

Antenna ground or rig ground?
 

Better to run fat Copperweld AROUND the house and clamp to several ground
rods then rather than having lightning going THROUGH the house from one
ground point to the other. Everything you do should make Primary, secondary
strikes and surges want to drain outside and away from the house/shack/site.

A large coil or high value resistor is a good thing for bleeding off static
charges on a line so that when you throw the switch, nothing goes through
you to ground. It is common for antennas that don't have some DC grounding
feature to build static charges if open. Your antenna tuner or the input
transformer of your receiver has to drain that. Polyphaser makes good
coaxial type surge protectors, but I'm not sure about Ladder line. The gap
type arrestor does have limitations because you have to keep the gap wide
enough to avoid problems with the transmitter. Multiple series gaps only
raises the firing voltage, but the breakdown voltage will be set by the
largest gap in the series. A gap at .035 will fire at about 2-10kv
depending on humidity. You only want it wide enough so that it won't arc
when keying the transmitter. If there is a direct hit they will probably
explode or at least blow the electrodes away.

I would seriously read up on the situation in addition to asking questions
on a newsgroup. Polyphaser may still have a free publication you can order
that explains things in depth.


"Gary Pewitt" wrote in message
...

I guess I wasn't too clear. I wanted to use one switch each for two
ladder line lead ins. Since no one I can find makes arrestors for
ladder line I am building my own from spark plugs threaded into a big
copper plate which is grounded with copper strap to 5 ground rods in a
fairly small circle outside the shack window. It's about 70 ft to the
200 amp service box from the bedroom I am using for my shack.
I just won a bid on ech bay for a double throw make before break knife
switch which I'll be using also. I'm going to buy one of those MFJ
window lead through plates with multiple ladder line connectors or
maybe make my own version.
I am wondering, instead of using just two spark plugs, if it might be
more effective to use 3 pairs in line with the first pair having
really wide gaps, the second having a medium gap, and the third having
a small gap around .035"? I am going to enclose them to keep them dry
and they will be grounded to the same rods as everything else.
I'll also have a Drake R-8 receiver in my bedroom hooked to an
Evesdropper trap dipole with a Zap Trap arrestor on the co-ax. It's
too far to run a ground to the other end of the house so I plan to
ground it outside of my window. I know that's not the best way but I
don't want to run an 80 foot ground cable to the shack ground.
Thanks for all the good advice. 73 Gary N9ZSV




On Sat, 11 Oct 2008 22:12:20 -0500, Gary Pewitt
wrote:

Here's a simple question. I want to connect my transceiver to several
antennas using 450 ohm ladder line and a balanced tuner. I found a
couple of small double pole double throw knife switches for the ladder
line. There are only two ways to hook these up. I can hook the tuner
output to the center with the ground on the bottom and the antenna on
the top connectors. This will allow me to connect the transceiver to
the antenna or to ground. The second way is to connect the
transceiver to the top contacts, the antenna to the center, and ground
to the bottom contacts. This will let me connect the antenna to the
radio or to ground. Is it better to ground the radio and let the
antenna float? Or to ground the antenna and let the radio float?
Of course if I leave the switch handle sticking straight up nothing is
connected to anything.
I am inclined to think grounding the antenna is better but I have been
wrong before.

Thanks and 73 Gary N9ZSV

Antenna ground or rig ground?
 

JB wrote:



enough to avoid problems with the transmitter. Multiple series gaps only
raises the firing voltage, but the breakdown voltage will be set by the
largest gap in the series. A gap at .035 will fire at about 2-10kv
depending on humidity. You only want it wide enough so that it won't arc

Humidity doesn't change the breakdown voltage very much. In fact,
increasing humidity increases the breakdown voltage. One correction
table for a "rod gap" with 1/2" square electrodes has a 10% correction
going from 15 torr to 30 torr water vapor pressure and a -16%
correction going from 15 to 2.5 torr, which is nowhere near the 5:1
variation cited above. Interestingly, on this basis water vapor is a
better insulator than nitrogen, since density of the humid air is
actually less. Typical breakdown voltage tolerance on a rod gap is +/- 8%.

Antenna ground or rig ground?
 

enough to avoid problems with the transmitter. Multiple series gaps
only
raises the firing voltage, but the breakdown voltage will be set by the
largest gap in the series. A gap at .035 will fire at about 2-10kv
depending on humidity. You only want it wide enough so that it won't
arc

Humidity doesn't change the breakdown voltage very much. In fact,
increasing humidity increases the breakdown voltage. One correction
table for a "rod gap" with 1/2" square electrodes has a 10% correction
going from 15 torr to 30 torr water vapor pressure and a -16%
correction going from 15 to 2.5 torr, which is nowhere near the 5:1
variation cited above. Interestingly, on this basis water vapor is a
better insulator than nitrogen, since density of the humid air is
actually less. Typical breakdown voltage tolerance on a rod gap is +/-
8%.

That was off the top of my head so I stand corrected but there ARE
variations based on other real world stuff like air pressure and dirt on the
insulators. 5-20kv for inside an engine is real world but that depends on
other stuff too, like what kind of spark-plug, compression, resistors,
mixture, timing, but I digress. The point is the gap may have to be
adjusted for best results and might be too wide for protection. I invited
him to read up on the subject because I have other projects I have my head
into

So what are your experiences with spark gap transmission line arresters?
Perhaps you have the precise gap he should be using? My dim recollection is
of a chart for the transmitter power in use.

Antenna ground or rig ground?
 

JB wrote:
enough to avoid problems with the transmitter. Multiple series gaps
only
raises the firing voltage, but the breakdown voltage will be set by the
largest gap in the series. A gap at .035 will fire at about 2-10kv
depending on humidity. You only want it wide enough so that it won't
arc
Humidity doesn't change the breakdown voltage very much. In fact,
increasing humidity increases the breakdown voltage. One correction
table for a "rod gap" with 1/2" square electrodes has a 10% correction
going from 15 torr to 30 torr water vapor pressure and a -16%
correction going from 15 to 2.5 torr, which is nowhere near the 5:1
variation cited above. Interestingly, on this basis water vapor is a
better insulator than nitrogen, since density of the humid air is
actually less. Typical breakdown voltage tolerance on a rod gap is +/-
8%.
That was off the top of my head so I stand corrected but there ARE
variations based on other real world stuff like air pressure and dirt on the
insulators. 5-20kv for inside an engine is real world but that depends on
other stuff too, like what kind of spark-plug, compression, resistors,
mixture, timing, but I digress. The point is the gap may have to be
adjusted for best results and might be too wide for protection. I invited
him to read up on the subject because I have other projects I have my head
into

So what are your experiences with spark gap transmission line arresters?
Perhaps you have the precise gap he should be using? My dim recollection is
of a chart for the transmitter power in use.

A good rule of thumb for small gaps with large radius of curvature
electrodes is 30kV/cm (e.g. a 1cm gap between 10cm diameter spheres).

In strongly non uniform field gaps (e.g. needle gaps), the breakdown is
typically 1/3 or less.. that is, 10kV/cm


70kV/inch or 25 kV/inch, respectively.

A sparkplug with a 0.035inch gap would breakdown around 1-2kV in normal
air. In an engine, where the density at firing is probably 5-10 times
higher, the voltage is 10-20kV as you've given.

The usual way to set spark gaps for this kind of thing would be to make
it adjustable, fire up the transmitter at worst case max power and
reflection, and set the gap to be somewhat bigger than causes the gap to
break down. A good worst case would be 2x peak RF voltage (i.e. 2.8
Vrms), since that's what you'd get with a 100% reflection at just the
wrong phase. (unless the source can supply reactive power.. then it's a
lot more complex, because of the potential for resonant rise) You could
use a current limited DC power supply or something like a neon sign
transformer to set the spacing.

But making things practical..

say 2 kW and a 450 ohm transmission line. Erms = sqrt(2000*450) = about
950Vrms.. call it 1350V peak. With sharp ended electrodes (like the
sheet metal V shapes shown in old ARRL handbooks) one might want a
spacing of 0.050 inches?

Antenna ground or rig ground?
 

OK, thanks again for all the good advice. After concidering all the
suggestions and re-reading 3 different ARRL antenna manuals I have
decided to go with a buried cable (uninsulated of course) all around
the house and extending out to my vertical antenna base. I will run
ground straps from the electrical service box, my bedroom receiver,
and the entrypoint for my feed lines to the buried cable. I am going
to go with the spark plug (non resistor type) protection combined with
knife switches to disconnect the rig -and- ground the ballanced
antennas to the buried cable. All co-ax will have commercial gas type
protectors grounded to the cable. There will be a copper bus on the
back of the shack bench with -all- gear grounded through it to the
buried cable.
I will also put spark gaps on the base of the tower grounded to the
cable. There will be a large expensive surge protector in line with a
power distributing strip on the bench which will be unplugged at the
first indication of electrical storms.
The inspiration for all this is a large Oak tree out back with the top
15 or 20 feet blown off by a lightning strike.
If there is anything I have missed please call it to my attention.
Thanks Gary N9ZSV






On Sat, 11 Oct 2008 22:12:20 -0500, Gary Pewitt
wrote:

Here's a simple question. I want to connect my transceiver to several
antennas using 450 ohm ladder line and a balanced tuner. I found a
couple of small double pole double throw knife switches for the ladder
line. There are only two ways to hook these up. I can hook the tuner
output to the center with the ground on the bottom and the antenna on
the top connectors. This will allow me to connect the transceiver to
the antenna or to ground. The second way is to connect the
transceiver to the top contacts, the antenna to the center, and ground
to the bottom contacts. This will let me connect the antenna to the
radio or to ground. Is it better to ground the radio and let the
antenna float? Or to ground the antenna and let the radio float?
Of course if I leave the switch handle sticking straight up nothing is
connected to anything.
I am inclined to think grounding the antenna is better but I have been
wrong before.

Thanks and 73 Gary N9ZSV