Coax Choke For Receiving Antenna ?
 

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

Coax Choke For Receiving Antenna ?
 

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

Coax Choke For Receiving Antenna ?
 

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

Coax Choke For Receiving Antenna ?
 

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.

Coax Choke For Receiving Antenna ?
 

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

Coax Choke For Receiving Antenna ?
 

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

Coax Choke For Receiving Antenna ?
 

On 31 Jan 2006 15:12:40 -0800, "bpnjensen"
wrote:

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.

I will disagree here. Although a single coax choke of specific design
won't solve all problems across all bands, a choke of the right size
will give you an obvious reduction in common mode noise at certain
minmum requencies and upward.

I installed one on my own antenna at home. I was hearing common mode
noise across all bands from zero to 30 mHz. i fashioned a coil choke
about 7" diameter on a piece of ABS pipe, wrapped neatly enough times
to get about 30 feet of the coax onto the coil, and mounted it just
below the antenna. This has made a noticeable difference for all bands
from 11 mHz and up...the background is considerably quieter than
before. A note here - this thing can get pretty hefty, fast, if you
use substantial coax of the 3/8' variety or larger. Messing with this
thing as an integral part of a relatively stiff run of coax can cause
minor cussing and swearing if you do not have some assistance (and
maybe even if you do ;-)

For lower frequencies, a larger coil able to hold a greater length of
coax would have been necessary; I didn't feel that the difficulty in
fashioning one of these and trying to get it up on top of the mount I
have would have been worth the trouble. I have since reconsidered this
decision many times and one of these days the neighbors just might see
big ugly coils of coax up under my two antennas. Whether my wife goes
along with this, I can't tell you.

Bruce Jensen

Wouldn't a ferrite work better?

Coax Choke For Receiving Antenna ?
 

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

Coax Choke For Receiving Antenna ?
 

You more or less made my point, i..e. these coax chokes are kind of
unwieldy in the HF range. However, if it works for you, you can't
argue with success.


bpnjensen wrote:
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.

I will disagree here. Although a single coax choke of specific design
won't solve all problems across all bands, a choke of the right size
will give you an obvious reduction in common mode noise at certain
minmum requencies and upward.

I installed one on my own antenna at home. I was hearing common mode
noise across all bands from zero to 30 mHz. i fashioned a coil choke
about 7" diameter on a piece of ABS pipe, wrapped neatly enough times
to get about 30 feet of the coax onto the coil, and mounted it just
below the antenna. This has made a noticeable difference for all bands
from 11 mHz and up...the background is considerably quieter than
before. A note here - this thing can get pretty hefty, fast, if you
use substantial coax of the 3/8' variety or larger. Messing with this
thing as an integral part of a relatively stiff run of coax can cause
minor cussing and swearing if you do not have some assistance (and
maybe even if you do ;-)

For lower frequencies, a larger coil able to hold a greater length of
coax would have been necessary; I didn't feel that the difficulty in
fashioning one of these and trying to get it up on top of the mount I
have would have been worth the trouble. I have since reconsidered this
decision many times and one of these days the neighbors just might see
big ugly coils of coax up under my two antennas. Whether my wife goes
along with this, I can't tell you.

Bruce Jensen

Coax Choke For Receiving Antenna ?
 

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

Coax Choke For Receiving Antenna ?
 

Wouldn't a ferrite work better?

I think ferrite is a good choice too, but based on some other posts
I've seen here, you apparently need a whole bunch of them to work
really well (like, dozens or more). Maybe a combination of both
methods would be workable for some. For me, and considering that it
didn't really need additional weatherproofing, the coax coil worked out
as a good solution for 11 MHz and up. Cost a bit less too.

Bruce Jensen

Coax Choke For Receiving Antenna ?
 

"bpnjensen" wrote in message
oups.com...
Wouldn't a ferrite work better?

I think ferrite is a good choice too, but based on some other posts
I've seen here, you apparently need a whole bunch of them to work
really well (like, dozens or more). Maybe a combination of both
methods would be workable for some. For me, and considering that it
didn't really need additional weatherproofing, the coax coil worked out
as a good solution for 11 MHz and up. Cost a bit less too.

Bruce Jensen

Hi Bruce,
The coax loop is a good solution for HF- particularly if you have G.D.O. and
can select the number of turns that achieves self resonance in the middle
of the freq of interest.

And remember on the ferrites- if they are big enough, you can make multiple
passes through them- the reactance goes up as the square of the number of
turns- saves on ferrites.

Dale W4OP

Coax Choke For Receiving Antenna ?
 

And remember on the ferrites- if they are big enough, you can make multiple
passes through them- the reactance goes up as the square of the number
of
turns- saves on ferrites.

Dale W4OP

Hi Dale - I've done this with standard electrical cords (like zipcord),
but that's much smaller stuff and works OK with little snap-on types of
ferrites. Your comment suggests that one would benefit from one of
those great big toroids about 4 to 6 inches across, threading the coax
through it many times - is that right? If so, is it best to wind it
tightly, or does that risk messing up the construction of the coax?

Thanks,
Bruce Jensen

Coax Choke For Receiving Antenna ?
 

On 2 Feb 2006 07:05:31 -0800, "bpnjensen" wrote:

And remember on the ferrites- if they are big enough, you can make multiple
passes through them- the reactance goes up as the square of the number
of
turns- saves on ferrites.

Dale W4OP

Hi Dale - I've done this with standard electrical cords (like zipcord),
but that's much smaller stuff and works OK with little snap-on types of
ferrites. Your comment suggests that one would benefit from one of
those great big toroids about 4 to 6 inches across, threading the coax
through it many times - is that right? If so, is it best to wind it
tightly, or does that risk messing up the construction of the coax?

Thanks,
Bruce Jensen

There's no electrical reason to use anything thicker than RG-58/U for
HF receiving. You can get 6 loops through your standard Radio Shack
ferrite.
http://www.wr6wr.com/newSite/article...ndyou0598.html

http://www.radioshack.com/product/in...tId=2103979&cp

Coax Choke For Receiving Antenna ?
 

"bpnjensen" wrote in message
oups.com...
And remember on the ferrites- if they are big enough, you can make
multiple
passes through them- the reactance goes up as the square of the number
of
turns- saves on ferrites.

Dale W4OP

Hi Dale - I've done this with standard electrical cords (like zipcord),
but that's much smaller stuff and works OK with little snap-on types of
ferrites. Your comment suggests that one would benefit from one of
those great big toroids about 4 to 6 inches across, threading the coax
through it many times - is that right? If so, is it best to wind it
tightly, or does that risk messing up the construction of the coax?

Thanks,
Bruce Jensen

Scarmble winding will be as good as a neat winiding.

Dale W4OP

Coax Choke For Receiving Antenna ?
 

David wrote:
There's no electrical reason to use anything thicker than RG-58/U for
HF receiving.

I'll agree with that for short runs, but RG-8X is only slightly larger in
diameter and less than half the loss per foot.

--
If John McCain gets the 2008 Republican Presidential nomination,
my vote for President will be a write-in for Jiang Zemin.

Coax Choke For Receiving Antenna ?
 

On Sun, 05 Feb 2006 01:03:44 -0600, clifto wrote:

David wrote:
There's no electrical reason to use anything thicker than RG-58/U for
HF receiving.

I'll agree with that for short runs, but RG-8X is only slightly larger in
diameter and less than half the loss per foot.
That's flat out factually inaccurate.

http://users.erols.com/rfc/attenrat.htm#RG8MINIX

Coax Choke For Receiving Antenna ?
 

I'll agree with that for short runs, but RG-8X is only slightly larger in
diameter and less than half the loss per foot.

That's flat out factually inaccurate.

http://users.erols.com/rfc/attenrat.htm#RG8MINIX

The latter seems correct - this table indicates that the difference in
loss between the two at 10 MHz is only 0.1 dB, very small. I was,
however, under the general impression that RG-8X is somewhat more
durable...can't say where I heard that, however.

Bruce Jensen

Coax Choke For Receiving Antenna ?
 

bpnjensen wrote:

I'll agree with that for short runs, but RG-8X is only slightly larger in
diameter and less than half the loss per foot.

That's flat out factually inaccurate.

http://users.erols.com/rfc/attenrat.htm#RG8MINIX

The latter seems correct - this table indicates that the difference in
loss between the two at 10 MHz is only 0.1 dB, very small. I was,
however, under the general impression that RG-8X is somewhat more
durable...can't say where I heard that, however.

Yep, get the non-contaminating version with the black jacket, which is suitable
for direct burial.

dxAce
Michigan
USA

Coax Choke For Receiving Antenna ?
 

Yep, get the non-contaminating version with the black jacket, which is suitable
for direct burial.

In this case, what does "non-contaminating" mean? Does it refer to the
inert chemical makeup of the jacket, or does it refer to some
electrical property in which signal is able to pass through unaltered
(as compared to the "contaminating" type :-/ )?

Thanks,
BJ

Coax Choke For Receiving Antenna ?
 

bpnjensen wrote:

Yep, get the non-contaminating version with the black jacket, which is suitable
for direct burial.

In this case, what does "non-contaminating" mean? Does it refer to the
inert chemical makeup of the jacket, or does it refer to some
electrical property in which signal is able to pass through unaltered
(as compared to the "contaminating" type :-/ )?

Chemical makeup, I believe.

dxAce
Michigan
USA

Coax Choke For Receiving Antenna ?
 

dxAce wrote:

bpnjensen wrote:

Yep, get the non-contaminating version with the black jacket, which is suitable
for direct burial.

In this case, what does "non-contaminating" mean? Does it refer to the
inert chemical makeup of the jacket, or does it refer to some
electrical property in which signal is able to pass through unaltered
(as compared to the "contaminating" type :-/ )?

Chemical makeup, I believe.

See http://www.smeter.net/daily-facts/4/fact29.php which gives a brief explanation.

dxAce
Michigan
USA

Coax Choke For Receiving Antenna ?
 

See http://www.smeter.net/daily-facts/4/fact29.php which gives a brief explanation.

dxAce
Michigan
USA

Excellent explanation, thanks.

BJ

Coax Choke For Receiving Antenna ?
 

"bpnjensen" wrote:


In this case, what does "non-contaminating" mean?

It means water won't cross through the jacket and contaminate the
dielectric and damage the conductors. Even the best coaxes, short of
hardline, "breathe" a little, which is where the contamination comes
from.

--
Eric F. Richards

"Nature abhors a vacuum tube." -- Myron Glass,
often attributed to J. R. Pierce, Bell Labs, c. 1940