A few Helical Antenna question
 

I am reading the 19th edition of the ARRL Antenna Book. I am unclear
which polarization to use if I want 2 Helical antennas to talk to each
other. In the book it says, ". . . when two stations use helical
antennas over a non reflective path, both must use antennas with the
same polarization sense.." I find this could be interpreted in
different ways and is not clear at all. It seems logical to me that if
both antennas had the same polarization that when they faced each other
they two helices would be in opposite directions and that would seem to
be bad. Am I right?

It says the circumference can be between 1.33 wavelengths and .75
wavelengths. From the gain formula it would seem that the 1.33 figure
would give the most gain for a given length of the antenna. Other than
mechanical considerations is there any reason I wouldn't want to use the
1.33 number?

Finally, I may have missed it, but I didn't see anything that indicated
how large of a wire or tube I should use for the helix. I am guessing
this is just a mater of how much power I plan on feeding it with?

PS I would like to build 2 of these one is for 2.4ghz wireless network
and one is 432 mhz amateur band EME and or satellite work. So the
2.4ghz version will likely never see more than 100 mW but could see as
much as 1 watt. The 432 mhz version could see as much as 1000 watts,
but if I did that it would be to an array of 4 of them so I guess each
one would only see 250 watts?

--
Chris W

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A few Helical Antenna question
 

Hi,

other. In the book it says, ". . . when two stations use helical
antennas over a non reflective path, both must use antennas with the
same polarization sense.." I find this could be interpreted in
different ways and is not clear at all. It seems logical to me that if
both antennas had the same polarization that when they faced each other
they two helices would be in opposite directions and that would seem to
be bad. Am I right?

On your first point, imagine you've constructed a long, long
helix that starts at your location and travels all the way to the
other station. It is logical that a wave launched by you would
then travel unimpeded along it to the far location. Now cut the
helix in the middle and turn one end around. What you will then
see is two helices rotating in the same direction, that is both
ends will have the same direction of rotation.

Can't help you with the rest unfortunately.


Cheers - Joe

A few Helical Antenna question
 

"Chris W" bravely wrote to "All" (26 Oct 05 12:07:11)
--- on the heady topic of "A few Helical Antenna question"

CW From: Chris W
CW Xref: core-easynews rec.radio.amateur.antenna:219311

CW I am reading the 19th edition of the ARRL Antenna Book. I am unclear
CW which polarization to use if I want 2 Helical antennas to talk to each
CW other. In the book it says, ". . . when two stations use helical
CW antennas over a non reflective path, both must use antennas with the
CW same polarization sense.." I find this could be interpreted in
CW different ways and is not clear at all. It seems logical to me that
CW if both antennas had the same polarization that when they faced each
CW other they two helices would be in opposite directions and that would
CW seem to be bad. Am I right?

"Same polarization sense" means with respect to the traveling
wavefront. When the transmitting antenna is nose to nose with the
receiving antenna, the combination will corkscrew in one sense only.

A*s*i*m*o*v

.... "Losing my virginity was a career movement." -- Madonna

A few Helical Antenna question
 

"Joe McElvenney" wrote in message
...
Hi,

other. In the book it says, ". . . when two stations use helical
antennas over a non reflective path, both must use antennas with the
same polarization sense.." I find this could be interpreted in
different ways and is not clear at all. It seems logical to me that if
both antennas had the same polarization that when they faced each other
they two helices would be in opposite directions and that would seem to
be bad. Am I right?

On your first point, imagine you've constructed a long, long
helix that starts at your location and travels all the way to the
other station. It is logical that a wave launched by you would
then travel unimpeded along it to the far location. Now cut the
helix in the middle and turn one end around. What you will then
see is two helices rotating in the same direction, that is both
ends will have the same direction of rotation.

Can't help you with the rest unfortunately.


Cheers - Joe

Hi Chris

I have some thoughts to share about how the CP antennas need to be
polarized, transmit and receive. But, I couldnt make any clearer than Joe
does.
Let me know if any additional text would be helpful.

Jerry

A few Helical Antenna question
 

On Wed, 26 Oct 2005 12:07:11 -0500, Chris W wrote:

I am reading the 19th edition of the ARRL Antenna Book. I am unclear
which polarization to use if I want 2 Helical antennas to talk to each
other. In the book it says, ". . . when two stations use helical
antennas over a non reflective path, both must use antennas with the
same polarization sense.." I find this could be interpreted in
different ways and is not clear at all. It seems logical to me that if
both antennas had the same polarization that when they faced each other
they two helices would be in opposite directions and that would seem to
be bad. Am I right?

Wind the two in the same "screw sense" (i.e., both clockwise out to
the far end, or both CCW out to the far end) and they will be same
sense.


It says the circumference can be between 1.33 wavelengths and .75
wavelengths. From the gain formula it would seem that the 1.33 figure
would give the most gain for a given length of the antenna. Other than
mechanical considerations is there any reason I wouldn't want to use the
1.33 number?

The higher gains give higher sidelobes too. For earth-earth paths
that probably isn't a major issue. For satellite work it can be
significant.


Finally, I may have missed it, but I didn't see anything that indicated
how large of a wire or tube I should use for the helix. I am guessing
this is just a mater of how much power I plan on feeding it with?

Not really, any more so than with building a dipole. A popular
material for 70cm is 1/4" copper tubing, which you can easily get in
50' lengths at the hardware store. Look for refrigerator tubing in
the plumbing supply section.


PS I would like to build 2 of these one is for 2.4ghz wireless network
and one is 432 mhz amateur band EME and or satellite work. So the
2.4ghz version will likely never see more than 100 mW but could see as
much as 1 watt. The 432 mhz version could see as much as 1000 watts,
but if I did that it would be to an array of 4 of them so I guess each
one would only see 250 watts?


True.
But for EME/Satellite work, helices are not ideal for reception.
Transmit is fine, but the sidelobe levels cause weak signal noise
problems. If the satellite has plenty of downlink power it may not be
a problem, but EME would definitely be an issue. Not to mention that
you really need switchable polarization for EME, and to do that
effectively with a helix requires two of them!

--
Chris W

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give the gifts they want
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from anywhere, for any occasion!
http://thewishzone.com

A few Helical Antenna question
 

Just an extra comment Chris.

The "non reflective path" is also real important. As a circular
polarised signal reflects off objects, it changes polarisation to the
opposite sense. You'll find that "opposite polarised" in circular has
far more (in practice) attenuation than for plane antenna cross
polarisation.

If your path has an odd number of reflections you have to use the
opposite polarisation at each end.

Cheers Bob VK2YQA

Chris W wrote:

I am reading the 19th edition of the ARRL Antenna Book. I am unclear
which polarization to use if I want 2 Helical antennas to talk to each
other. In the book it says, ". . . when two stations use helical
antennas over a non reflective path, both must use antennas with the
same polarization sense.."

A few Helical Antenna question
 

PS I would like to build 2 of these one is for 2.4ghz wireless network
and one is 432 mhz amateur band EME and or satellite work. So the 2.4ghz
version will likely never see more than 100 mW but could see as much as 1
watt. The 432 mhz version could see as much as 1000 watts, but if I did
that it would be to an array of 4 of them so I guess each one would only
see 250 watts?

--
Chris W

EME on 432 is linearly polarized (although switching polarities to make up
for Faraday rotation can be advantageous) - you'll be throwing away a huge
3dB, have higher sidelobes than a well designed Yagi (nullifying the low sky
temp advantage of deep space) and less gain per boom length than a good
Yagi- all in all, a dismal choice for EME.

Dale W4OP

A few Helical Antenna question
 

Dale Parfitt wrote:

PS I would like to build 2 of these one is for 2.4ghz wireless network


and one is 432 mhz amateur band EME and or satellite work. So the 2.4ghz
version will likely never see more than 100 mW but could see as much as 1
watt. The 432 mhz version could see as much as 1000 watts, but if I did
that it would be to an array of 4 of them so I guess each one would only
see 250 watts?

--
Chris W



EME on 432 is linearly polarized (although switching polarities to make up
for Faraday rotation can be advantageous) - you'll be throwing away a huge
3dB, have higher sidelobes than a well designed Yagi (nullifying the low sky
temp advantage of deep space) and less gain per boom length than a good
Yagi- all in all, a dismal choice for EME.

Dale W4OP




The calculation in the ARRL Antenna book say that a 12 foot boom with a
circumference of 1.33 wavelengths will give me a 19.9 dbi gain this
should make up for the 3 db loss I think. I haven't seen a yagi that
gives that much gain in with a 12 foot boom. The book also says that
the side lobe problem can be significantly reduced by creating an array
of 4 helical antennas. That should up the gain to 25.9 db. That's
pretty good for EME isn't it? Take it to 16 and you get over 30 db
gain. And the only need to be spaced at 1.5 wavelengths, that's only
3.4 feet.

--
Chris W

Gift Giving Made Easy
Get the gifts you want &
give the gifts they want
One stop wish list for any gift,
from anywhere, for any occasion!
http://thewishzone.com

A few Helical Antenna question
 

Jerry Martes wrote:

"Joe McElvenney" wrote in message
.. .


Hi,



other. In the book it says, ". . . when two stations use helical
antennas over a non reflective path, both must use antennas with the
same polarization sense.." I find this could be interpreted in
different ways and is not clear at all. It seems logical to me that if
both antennas had the same polarization that when they faced each other
they two helices would be in opposite directions and that would seem to
be bad. Am I right?


On your first point, imagine you've constructed a long, long
helix that starts at your location and travels all the way to the
other station. It is logical that a wave launched by you would
then travel unimpeded along it to the far location. Now cut the
helix in the middle and turn one end around. What you will then
see is two helices rotating in the same direction, that is both
ends will have the same direction of rotation.

Can't help you with the rest unfortunately.


Cheers - Joe



Hi Chris

I have some thoughts to share about how the CP antennas need to be
polarized, transmit and receive. But, I couldnt make any clearer than Joe
does.
Let me know if any additional text would be helpful.

Jerry




No it makes perfect sense, I don't know what I was thinking. I mean if
you take 2 right hand threaded bolts and have them face each other they
are still right hand threaded and a nut will go of one and right on to
the other spinning the same way. It's obvious now that I think about it.

--
Chris W

Gift Giving Made Easy
Get the gifts you want &
give the gifts they want
One stop wish list for any gift,
from anywhere, for any occasion!
http://thewishzone.com

A few Helical Antenna question
 

"Chris W" wrote in message
news:ku88f.1019$ZP1.519@dukeread11...
Dale Parfitt wrote:

PS I would like to build 2 of these one is for 2.4ghz wireless network

and one is 432 mhz amateur band EME and or satellite work. So the 2.4ghz
version will likely never see more than 100 mW but could see as much as 1
watt. The 432 mhz version could see as much as 1000 watts, but if I did
that it would be to an array of 4 of them so I guess each one would only
see 250 watts?

--
Chris W


EME on 432 is linearly polarized (although switching polarities to make
up for Faraday rotation can be advantageous) - you'll be throwing away a
huge 3dB, have higher sidelobes than a well designed Yagi (nullifying the
low sky temp advantage of deep space) and less gain per boom length than
a good Yagi- all in all, a dismal choice for EME.

Dale W4OP


The calculation in the ARRL Antenna book say that a 12 foot boom with a
circumference of 1.33 wavelengths will give me a 19.9 dbi gain this should
make up for the 3 db loss I think. I haven't seen a yagi that gives that
much gain in with a 12 foot boom. The book also says that the side lobe
problem can be significantly reduced by creating an array of 4 helical
antennas. That should up the gain to 25.9 db. That's pretty good for EME
isn't it? Take it to 16 and you get over 30 db gain. And the only need
to be spaced at 1.5 wavelengths, that's only 3.4 feet.

--
Chris W

The closest optimized Yagi I found was a K1FO on a 14' boom- 17.9dBi which
compares quite well with your 19.9dBi on a 12' boom once we adjust for the
polarization loss making the helical 16.9dBi linear for the helix vs. 17.9dB
for the K1FO My experience with EME is at 23cM where we use dishes- but I
can tell you that 1dB is to kill for..
The circularity could be an advantage as it would be insensitive to Faraday.
Another advantage is that they are non critical to build- at least from a
gain standpoint. But I think the real issue will be weight and weight
ditribution. Between the helical tubing, non conductive boom and the
reflector screen a helix is going to be a clydesdale compared to a Yagi.
Another problem might be the necessity to mount the array from behind the
reflector- that's going to be quite a moment arm.

Bottom line is, 432 MHz EME is well explored- I am not aware of the use of
helices for EME there- although, again I am not active on 432 EME. If they
are not being use, there's probably a reason.

Dale W4OP