Thoughts about the tape measure 3 element direction finding Yagi
 

(repost updated)
All started because I could not get the PVC tubing which the many
internet sites propose. The plumber shops where I live can only supply
heavy massive material suited as killing weapon in the hands of a
desperate fox transmitter hunter.

So I had to look for an alternative design and that lead me
to the aluminium boom with the movable slider.

With the PVC tubes it should be possible to make the middle "T"
moveable, or not? Would have to drill through the T with
a larger diameter wood-drill.
http://tinyurl.com/3vygo9f


I am here now:
https://sites.google.com/site/tapemeasureantenna/
This allows for future changes, updates and additions.

The old stuff is still the
http://img839.imageshack.us/img839/1...oxhuntyagi.pdf

What's missing is a list of ready-to-build recipes.
Am still struggling with the tape-measure correction factors
for the antenna simulator (4nec2)
Anybody having already tried simulating tape measure antennas?

3 element Tape measure direction finding antennas are a bit larger
than their 2 element competitors like the MAY1000
http://www.rfparts.com/diamond/MAY1000.html
A simple two element ARDF antenna must be carefully adjusted
in element spacing, else it will be totally worthless. This often
applies to the portable HB9CV antennas from the junk box
which are being used off their design frequency.
I cannot imagine running through underbrush thicket with the MAY1000.
It will quickly fold into it's sales package size :-)

w.











Regards,
w.

Thoughts about the tape measure 3 element direction finding Yagi
 

On Sun, 28 Aug 2011 22:09:00 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote:

Am still struggling with the tape-measure correction factors
for the antenna simulator (4nec2)
Anybody having already tried simulating tape measure antennas?

Not tape measures, but I have done stamped sheet metal, which is
somewhat similar. See the plots at:
http://802.11junk.com/jeffl/antennas/mfj1800/index.html
The NEC2 deck is under:
http://802.11junk.com/jeffl/antennas/mfj1800/slides/mfj-1800.html

The problem is that the common "wire" rod antenna elements aren't
close enough. So, I had to use the actual dimensions from the sheet
metal. You'll probably need to do the same, with the added
complication of including the arc in the cross section. It's not as
horrible as it might seem as all your elements are the same cross
section. Use the "Geometry Builder" program that comes with 4NEC2.

I cannot imagine running through underbrush thicket with the MAY1000.
It will quickly fold into it's sales package size :-)

Have you considered an inflatable version?

http://www.scouting.org/filestore/jota/pdf/TURNER.pdf
Hmmm.... they use a WB2HOL tape measure antenna.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Thoughts about the tape measure 3 element direction findingYagi
 

On Sun, 28 Aug 2011 22:09:00 +0200, Helmut Wabnig wrote:
All started because I could not get the PVC tubing which the many
internet sites propose.

Hi. I foxhunt regularly with the Melbourne ARDF community,
and we have the design of 2m sniffer antennas down to a fine art.

The best material for the shaft is 12mm square or u-channel aluminium.

The common antenna element length and spacing recommended with the
tape-measure antenna is wrong - very wrong. For a start, the lengths
vary by too much (in the hope of a wider effective bandwidth), and
the reflector is too close to the driven, the director too far away.
This causes large rear side lobes, which makes sniffing incredibly
frustrating.

For effective sniffing, you *don't* want maximum F/B ratio, and you
don't want maximum gain - what you want is a cardioid pattern with
just one lobe - the front one. Anything else will give you a bum
steer.

The best pattern we've found so far is the VK3VT beam:
http://www.vk3vt.net/VTbeam.html. Most of the recent ones use a
gamma match instead of the one shown.

We build this using elements made up from 3mm fiberglass rod and
co-ax braid, covered by heatshrink. The element goes through a
short copper tube before the heatshrink goes on.

These elements are sufficiently stiff to keep their shape, but
whippy enough to run with through a tree.

Clifford Heath.

Thoughts about the tape measure 3 element direction finding Yagi
 

On Mon, 29 Aug 2011 08:51:12 GMT, Clifford Heath wrote:

On Sun, 28 Aug 2011 22:09:00 +0200, Helmut Wabnig wrote:
All started because I could not get the PVC tubing which the many
internet sites propose.

Hi. I foxhunt regularly with the Melbourne ARDF community,
and we have the design of 2m sniffer antennas down to a fine art.

The best material for the shaft is 12mm square or u-channel aluminium.

The common antenna element length and spacing recommended with the
tape-measure antenna is wrong - very wrong. For a start, the lengths
vary by too much (in the hope of a wider effective bandwidth), and
the reflector is too close to the driven, the director too far away.
This causes large rear side lobes, which makes sniffing incredibly
frustrating.

For effective sniffing, you *don't* want maximum F/B ratio, and you
don't want maximum gain - what you want is a cardioid pattern with
just one lobe - the front one. Anything else will give you a bum
steer.

The best pattern we've found so far is the VK3VT beam:
http://www.vk3vt.net/VTbeam.html. Most of the recent ones use a
gamma match instead of the one shown.

We build this using elements made up from 3mm fiberglass rod and
co-ax braid, covered by heatshrink. The element goes through a
short copper tube before the heatshrink goes on.

These elements are sufficiently stiff to keep their shape, but
whippy enough to run with through a tree.

Clifford Heath.



Do you think the matching affects the cardioid or F/B pattern?
So far I have neglected any influence from that.

With the YAGICAD optimizer I could not come to a positive end.
This program finds 100 different "optimums" therefore
I turned to 4nec2 now.
The patterns which YAGICAD calculates look good to me.
When I compare the F/B patterns, of course the 4nec2 has a more
detailed "resolution" showing minor side lobes where YAGICAD
is just approximating.

I wonder how important matching is for a pure
direction finding antenna, methinks rather it should not.
Only the coax cable currents are not considered
in the simulator diagrams, there might be an influence.
Therefore matching is important :-)

Thank you for the vk3vt link.

w.
http://www.qsl.net/oe8uww/

Thoughts about the tape measure 3 element direction finding Yagi
 

On Sun, 28 Aug 2011 14:24:01 -0700, Jeff Liebermann
wrote:

On Sun, 28 Aug 2011 22:09:00 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote:

Am still struggling with the tape-measure correction factors
for the antenna simulator (4nec2)
Anybody having already tried simulating tape measure antennas?

Not tape measures, but I have done stamped sheet metal, which is
somewhat similar. See the plots at:
http://802.11junk.com/jeffl/antennas/mfj1800/index.html
The NEC2 deck is under:
http://802.11junk.com/jeffl/antennas/mfj1800/slides/mfj-1800.html



Thank you for the examples!

w.
http://www.qsl.net/oe8uww/








The problem is that the common "wire" rod antenna elements aren't
close enough. So, I had to use the actual dimensions from the sheet
metal. You'll probably need to do the same, with the added
complication of including the arc in the cross section. It's not as
horrible as it might seem as all your elements are the same cross
section. Use the "Geometry Builder" program that comes with 4NEC2.

I cannot imagine running through underbrush thicket with the MAY1000.
It will quickly fold into it's sales package size :-)

Have you considered an inflatable version?

http://www.scouting.org/filestore/jota/pdf/TURNER.pdf
Hmmm.... they use a WB2HOL tape measure antenna.

Thoughts about the tape measure 3 element direction finding Yagi
 

On Tue, 30 Aug 2011 09:03:33 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote:

I wonder how important matching is for a pure
direction finding antenna, methinks rather it should not.

You are right, not at all.

Only the coax cable currents are not considered
in the simulator diagrams, there might be an influence.
Therefore matching is important :-)

You should have stopped writing at the first thought. CHOKING is
supremely important, and is a benefit found in good matching design.
Choking can be achieved without matching, however. And choking will
be needed at least at the feed point, and again a quarterwave down the
line.

73's
Richard Clark, KB7QHC

Thoughts about the tape measure 3 element direction findingYagi
 

On Tue, 30 Aug 2011 09:03:33 +0200, Helmut Wabnig wrote:
I wonder how important matching is for a pure direction finding antenna,

I don't think it affects sensitivity, which is not really at a premium
anyhow.

A gamma match seems to skew forward-max location a bit to one side,
which matters if you're relying on accurate bearings from a distance,
but overall it doesn't matter much - in some ways it's better to
expect to spiral in on the fox a little anyhow, I reckon.

The gamma match also goes wonky if you put your hand on it, but I
guess that's not surprising. many of the top competitors use them
anyhow - we have a design that's easy to disassemble to put into a
suitcase for air travel.

One of the guys built a much-enhanced version of the NEC software for
the Mac, and he's automated it to automatically optimise (millions
of individual runs with different combinations) a 7-element boom
for 70cm, which is yielding very impressive DF results right across
the band.

Clifford Heath.

Thoughts about the tape measure 3 element direction finding Yagi
 

On Aug 28, 3:09*pm, Helmut Wabnig [email protected] --- -.dotat wrote:
(repost updated)
All started because I could not get the PVC tubing which the many
internet sites propose. ...
Regards, w.

While not adding to your solution I saw this posting and had to put in
a plug for my simplification.

I made a simplification to Joe's beam and want to let others know.

Instead of paying for those hose clamps, I simply use a short piece
of the tubing to hold the tape. It takes a little Dremel grinding to
remove the step inside, but makes a nice, clean design with the hair-
pin match inside.

Photos and videos on my site:

Photos:
http://k9dci.home.comcast.net/site/?/photos/

Videos:
http://k9dci.home.comcast.net/site/?...Radio_Control/

--
73, Steve, K9DCI USN (Vet) MOT (Ret) Ham (Yet)

More Details, Features and Downloads at:
http://k9dci.home.comcast.net/

Thoughts about the tape measure 3 element direction finding Yagi
 

On Aug 30, 11:17*am, Richard Clark wrote that :
On Tue, 30 Aug 2011 09:03:33 +0200, Helmut Wabnig [email protected] --- wrote:
I wonder how important matching is for a pure
direction finding antenna, methinks rather it should not.

You are right, not at all. ...
73's Richard Clark, KB7QHC

Matching, perhaps not so much, HOWEVER, the antenna pattern/phase/
characteristics are *THE* most important aspect of a DF antenna/
system. The DF antenna characteristics must be as close to ideal as
possible. I've been involved in DF since my stint in the Navy and they
went to great lengths to get the antenna sites ideal, for that reason.
Also...

But why I re-posted.... Thanks to Richard's post...
I forgot to mention a bead choke that I used with success on one of
these beams.
They also significantly improved the performance of a four dipole
Doppler type DF antenna
that one of the locals had and knew it was not right, but couldn't
decide what to do to fix it..

We used two cores on the coax to get well above the coax 50 ohms.

The following cores will fit inside the PVC pipe and around RG-58 size
coax.

Mouser: 623-2643540002
Fair-Rite (Mfr) # 2643540002
O.D. 0.562"
I.D. 0.25"
Len. 1.125
250 ohms @ 100MHz. [specs. I did not measure them as I recall]
171 ohms @ 25 MHz.

Finally,

Helmut,
You have quite a bit of reading there with that sliding element.
Can't wait to dig into it.

73, Steve, K9DCI Haven't read this group in ages.

Thoughts about the tape measure 3 element direction finding Yagi
 

On Thu, 8 Sep 2011 21:05:14 -0700 (PDT), Noskosteve
wrote:

On Aug 28, 3:09*pm, Helmut Wabnig [email protected] --- -.dotat wrote:
(repost updated)
All started because I could not get the PVC tubing which the many
internet sites propose. ...
Regards, w.

While not adding to your solution I saw this posting and had to put in
a plug for my simplification.

I made a simplification to Joe's beam and want to let others know.

Instead of paying for those hose clamps, I simply use a short piece
of the tubing to hold the tape. It takes a little Dremel grinding to
remove the step inside, but makes a nice, clean design with the hair-
pin match inside.

Photos and videos on my site:

Photos:
http://k9dci.home.comcast.net/site/?/photos/

Videos:
http://k9dci.home.comcast.net/site/?...Radio_Control/

Looks good.

I always wonder from where you people get the PVC tubes.
My local construction markets don't.


Since you have it, can you try to make the center elements movable,
this should work with the PVC tubes also.

w.