Hello:

Will be putting up a receive-only antenna (30 MHz) in my backyard.

The antenna will terminate in a Balun, and then a lightning arrestor,
immediately before the coax (8X probably)
run back to the house some 30 feet away.

Have read in one or two places a brief comment that it is a good idea to
make a few turns of the coax
right before the start of the antenna. Termed a "Choke".

If so, what is the purpose ?
Needed even if there will also be an arrestor ?

If a good idea, how many coax turns, of what diameter ?

Also a good idea at the other end, by the receiver ?

Thanks,
Bob

I don't think a coax choke is suitable at HF frequencies. I've seen
them used as low as FM broadcast pirate stations. The length of coax is
proportional to the frequency in use.


Robert11 wrote:
Hello:

Will be putting up a receive-only antenna (30 MHz) in my backyard.

The antenna will terminate in a Balun, and then a lightning arrestor,
immediately before the coax (8X probably)
run back to the house some 30 feet away.

Have read in one or two places a brief comment that it is a good idea to
make a few turns of the coax
right before the start of the antenna. Termed a "Choke".

If so, what is the purpose ?
Needed even if there will also be an arrestor ?

If a good idea, how many coax turns, of what diameter ?

Also a good idea at the other end, by the receiver ?

Thanks,
Bob

wrote:

I don't think a coax choke is suitable at HF frequencies. I've seen
them used as low as FM broadcast pirate stations. The length of coax is
proportional to the frequency in use.

Coax chokes are quite common in HF antenna designs.

dxAce
Michigan
USA

On Tue, 31 Jan 2006 15:22:33 -0500, "Robert11"
wrote:

Hello:

Will be putting up a receive-only antenna (30 MHz) in my backyard.

The antenna will terminate in a Balun, and then a lightning arrestor,
immediately before the coax (8X probably)
run back to the house some 30 feet away.

Have read in one or two places a brief comment that it is a good idea to
make a few turns of the coax
right before the start of the antenna. Termed a "Choke".

If so, what is the purpose ?
Needed even if there will also be an arrestor ?

If a good idea, how many coax turns, of what diameter ?

Also a good idea at the other end, by the receiver ?

Thanks,
Bob


A choke passes DC unimpeded and blocks higher frequecy AC. Unless
your SWL antenna is mounted on an FM transmitter tower I don't see any
advantage. Lightning wouldn't notice it.

Most Baluns are actually autotransformers and all parts are at DC
ground (provided your coax outer conductor is grounded and the
termination is properly affixed). This is the best solution to
protecting you from anything other than a direct hit. A lightning
arrestor will keep your house from burning down but won't save your
radio's front-end.

On Tue, 31 Jan 2006 15:22:33 -0500, "Robert11"
wrote:

Hello:

Will be putting up a receive-only antenna (30 MHz) in my backyard.

The antenna will terminate in a Balun, and then a lightning arrestor,
immediately before the coax (8X probably)
run back to the house some 30 feet away.

Have read in one or two places a brief comment that it is a good idea to
make a few turns of the coax
right before the start of the antenna. Termed a "Choke".

If so, what is the purpose ?
Needed even if there will also be an arrestor ?

If a good idea, how many coax turns, of what diameter ?

Also a good idea at the other end, by the receiver ?

Thanks,
Bob


If transmitting, a choke can keep stray RF off the outside of the coax
shield. There's not much point to one on a receiving antenna.

bob
k5qwg

If transmitting, a choke can keep stray RF off the outside of the coax
shield. There's not much point to one on a receiving antenna.

bob
k5qwg

How about for keeping common mode noise from the house reaching the antenna?
Of course this is better accomplished by a 1:1 isolation transformer nearer
the RX.

Dale W4OP

On Wed, 01 Feb 2006 03:01:58 GMT, "Dale Parfitt"
wrote:



If transmitting, a choke can keep stray RF off the outside of the coax
shield. There's not much point to one on a receiving antenna.

bob
k5qwg

How about for keeping common mode noise from the house reaching the antenna?
Of course this is better accomplished by a 1:1 isolation transformer nearer
the RX.

Dale W4OP


You're absolutely right. Somethimes my fingers get ahead of my
brains...

bob
k5qwg

In article ,
"Robert11" wrote:

Hello:

Will be putting up a receive-only antenna (30 MHz) in my backyard.

The antenna will terminate in a Balun, and then a lightning arrestor,
immediately before the coax (8X probably)
run back to the house some 30 feet away.

Have read in one or two places a brief comment that it is a good idea
to make a few turns of the coax right before the start of the
antenna. Termed a "Choke". If so, what is the purpose ?

You are looking at the Ham stuff, which is geared for transmitting. The
transmitting situation needs to take a few more things in account that
are not as important in receiving. The main idea here is to prevent
common mode RF current on the outer shield coupling to/from the antenna
as you may end up with a hot radio and shack. If you are burrowing the
coax on the way to the BALUN there is no need for this and the BALUN
already performs this function.

Needed even if there will also be an arrestor ?

Not needed in your situation.

If a good idea, how many coax turns, of what diameter ?

As an example if you were to do this for a dipole up a mast 3 to 10
turns about a foot diameter depending on the frequency.

Also a good idea at the other end, by the receiver ?

If the coax has a run through the walls of your place and 30 feet
through the air instead of 30 feet through the ground then yes both ends
and also spaced at intervals along the run.

This is easier done with a ferrite clamp on choke as opposed to coiling
the coax.

--
Telamon
Ventura, California