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Author Topic: HB9CV antenna  (Read 14663 times)

KC0SHZ

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HB9CV antenna
« on: May 27, 2006, 08:08:48 PM »

(sorry for the cross post to home brew)

There are a lot of European hams that use this antenna and there are mentions of it in the VHF range.

I would like to build a 2 meter version. I have a print out, but as it was written by someone who has obviously built a bunch and uses English as a second language, it is not clear to me.

I have three questions:

1. Anyone able to share a schematic of this antenna with me that has one that was in English to start?

2. From the PL259 connector, a capacitor is attached that goes to the feed line. The ground of the connector is attached to a metal cross beam. Is it absolutely necessary to use a metal cross beam?

3. The distances of the feed line to the director and reflector are given, but at 2 meters, are the same distance. This would have one feed point very close to the cross beam and the other a ways out on the director. Should those distances be that similar? The geometry I am seeing is that there is a 2 element beam with a feed point that has a capacitance match and this connects to two lengths of wire, one goes across the beam to the reflector and one goes to the director so that the connections between the feed wire and the director and the feed wire and the reflector are on opposite sides of the cross beam. Is that correct?
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WB6BYU

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HB9CV antenna
« Reply #1 on: May 30, 2006, 12:30:00 PM »

There are some good descriptions of this antenna (and some
of the variations you may encounter) on W4RNL's web site:

http://www.cebik.com/phase/hb.html
http://www.cebik.com/phase/ph.html

(and browse any other articles on phased arrays you find there)

One of the common designs uses a metal boom with a wire
running along it as the phasing line between the two
elements - in this case you either need to use a metal
boom or replace this with a standard coax phasing line.
Balanced versions need not use a metal boom.

Note that the HB9CV is the same basic antennas as the
"ZL special", though the latter is generally built with
direct feed in the center of the elements and the HB9CV
generally uses gamma or "T" matching to the elements,
which gives more flexibility in setting the impedance
to match the available phasing line.

I have two commercial versions from VK4BRG at home for
2m DF use.  These actually feed the antenna at the rear
element rather than at the front, and have a rather poor
front/back ratio.  I modified one of them to feed it at
the front element, and it only changed things a little
bit.  Based on the W4RNL articles, I think this antenna
was designed for maximum gain rather than good F/B, but
I've seen some other designs around that might be better.

I know many of the European foxhunters use the HB9CV
because it gives a reasonably good pattern in a small
antenna, but remember that they use horizontal polarization
which will have a much sharper pattern than hunting a
vertical signal with the same antenna.  (The same is
true of the Moxon:  I use it for horizontal signals but
it is not sharp enough for good bearings on vertically
polarized signals unless you know the characteristics of
the rear null at the frequency you are hunting.)  But
they also stress the importance of using a balanced
version, as the unbalanced ones may have a skew of several
degrees in the pattern.

I don't know if these notes plus the linked articles have
answered all of your questions - if not, feel free to
ask some more.

KB4EMF

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HB9CV antenna
« Reply #2 on: June 04, 2006, 08:29:15 PM »

I can only answer your question 2.  No, the boom does not have to be metal.  The braid of the coax goes to the MIDDLE of the element.  You can use any materials you want, such as PVC or wood.

If you use metal boom, be sure to keep the phasing line AWAY from the boom.



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KB4EMF

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HB9CV antenna
« Reply #3 on: June 04, 2006, 08:34:39 PM »

I have trouble understanding what you are trying to ask on question 3.  So, I'll just explain what it SHOULD look like.

The driven element and the reflector element looks identical except -

1)  The reflector element is longer
2)  The matching stub is on opposit side of each other

The phasing line twists at the middle, and one side connects to the center of the element.  The other side connects to the inner end of the matching rod.  The distance of the shorting bar from the boom is usually identical between the driven element and the reflector.  I recall, the center conductor of the coax attached directly to the inner end of the matching rod on the driven element, and the braid attached to the middle of the driven element.  I did not have to use any capacitors for my 15 meter version.

I have a schematic of the antenna but mine is written in Japanese...

If you like, you can e-mail me at <my-call-sign>@yahoo.com and I can try to draw one for you.
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WB6BYU

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HB9CV antenna
« Reply #4 on: June 06, 2006, 10:04:13 AM »

The HB9CV can be used for hunting vertically polarized
signals if you design it for maximum front/back ratio and
hunt using the rear null (which can be quite sharp) rather
than the front peak (which is rather broad).  The same goes
for the Moxon.

Having used both, I think the Moxon is easier to build and
to get repeatable performance, especially with the articles
and calculator on the W4RNL web site.

In general I prefer to hunt the peak of an antenna as it
tends to be more reliable, but if you don't have a good
receiver/attenuator it may be easier to use the null.
Be sure to adjust the antenna for optimum null at the hunt
frequency.
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