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Author Topic: TAK-tenna...Really that good/  (Read 4295 times)
AJ4DW
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Posts: 130




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« Reply #15 on: April 08, 2008, 08:46:27 AM »

I won't defend the Tak-Tenna because I haven't tested it. Folks make a good point about the utility of the reviews... I like using them and depend upon them to help me make decisions, but I scan for the "less-than-5" reviews, like gymnastics scoring, you remove the highest and lowest scores and look at what's left. A consistently high score over 45+ plus reviews is hard to ignore.

I will defend experimentation, and I am not referring to modelling. (The model noted here was not of a Tak-Tenna but of a dipole with two capacitance hats, and the only comparison was at http://hometown.aol.com/n0lx/spirals.html which may or may not have properties similar to the Petlowany antenna in question).

Judging by the single 1/5 rating in the reviews, the builder, Steve, doesn't have any idea of the true characteristics of the antenna either (assuming we can be sure of THAT review, I don't know the reviewer and can't vouch for him).

There's another review at Ham Universe that's pretty interesting: http://www.hamuniverse.com/taktennareview.html
(again, although I've found Ham Universe a very useful site I can only go along with what the author claims). That review does NOT have any good comparisons either except in terms of *reception* of multiple bands. There are no objective measurements noted. He does mention that the antenna is NOT presented as a "miracle antenna" nor does it purport to break any laws of physics. It's represented as a small-footprint antenna that's effective and "10-14 dB at 90 degrees" directional.

So... we have an antenna that a lot of folks are enthusiastic about, which no one has model of, which theoretically won't do what it's reported to do, and we have no objective measurements, just a lot of opinion. Now that we have the theory it's time to test the theory, and that means actual measurements. I'll have to wait for that to make a decision. But again, I'd be willing to play around with one in the meantime.
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AA4PB
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« Reply #16 on: April 08, 2008, 11:25:52 AM »

If you look closely at the picture on their web page you'll see that each spiral has a feed line attached at about the half-way point. It looks like the two sprirals are the elements rather than capacity hats. The only numbers they give on the site is that it has a front to side ratio of 10-14dB (which isn't much compared to a yagi - but then this is a small antenna). My question would be how does it compare to something like a 2-ele yagi made from HamSticks?
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N3OX
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« Reply #17 on: April 08, 2008, 12:57:21 PM »

"(The model noted here was not of a Tak-Tenna but of a dipole with two capacitance hats"

Well, sort of.  The first model, the one I actually posted the file of, is a three foot horizontal radiator with spiral loading structures on either end.

It happens to resonate on 18.150 MHz and is awfully hard to make changes quickly to that model to make it resonate on 20m instead.  It's not an exact model of the actual TakTenna (and if you've got measurements, I'd be glad to take another stab at it!) but it is a similarly dimensioned end-spiral loaded antenna.

For those who just want to take a look at what I modeled ***the first time*** (which has about -4.3dB loss with respect to a 17m dipole), here's a picture:

http://n3ox.net/files/n3ox_tak.jpg

It's clear to me from the model that the spirals are simply end loading structures.  

Again, if someone has dimensions I'd be glad to try to build an accurate model of the real 20m TakTenna.  

- - - - - - -

Another approach would be to build MY antenna on 17m and measure a the real thing in comparison to a dipole.

You have to be careful with the measurement because if the model is correct, it's not actually that much worse than a dipole on the frequency it's tuned for, and that makes it hard to measure (and also pretty useful for home station use, honestly).  

So AJ4DW, if you're thinking of playing, why not build MY antenna here? We *DO* have a model of that.

The end spirals are #12 wire, about 8.5 turns at approximately 2" pitch... and start about 2" from the center of their form (I had to cut out some segments in the center because the wires were too short)  The horizontal wire is also #12 and is 3 feet long, split in the middle for a feedpoint.

This antenna has a predicted gain of -2.6dBi at the center frequency and a predicted 2:1 SWR bandwidth of 20-30kHz.  

The feedpoint resistance at resonance (about 18.150MHz) is 7 ohms.  If you bridge the feedpoint with a 0.18 microhenry inductor, this gives you a hairpin match that will give you a 50 ohm match to coax at 18.100 MHz (good for some PSK31 ? )

At 18.070 MHz, with the hairpin inductor in place, the impedance is 17+j47.  The additional loss in 30 feet of RG-8/X from the mismatch if you were to use a tuner to bring down the SWR for CW is just 0.5dB.   At 18.165MHz, the feed impedance is 3+j7 ohms, giving an additional coax loss of about 2.5dB in 30 ft of RG-8/X.

So there's a similarly dimensioned and potentially attractive antenna, similar to the TakTenna, that we can all build and try.

I've got predictions for gain and SWR bandwidth, and additional losses using reasonable coax feed and a tuner, and we can go ahead and test those.  

It's not identically a TakTenna but it's a very similar antenna that undoubtedly works on the same concept.  So let's try it out.  We can build this particular quite short version of a Petlowany/TakTenna type antenna for 17m and give it a test drive.  

This one comes with dimensions, a model, and performance predictions, and actually, for an antenna you can probably throw in the trunk of your car or stick in the corner of your apartment, isn't so bad aside from the narrow bandwidth.

I see no reason why you couldn't use the TakTenna's approach of attaching the spirals using fly leads to change the resonant frequency.   It undoubtedly will need some tweaking with such a narrow 2:1 SWR bandwidth.

You need about 39 feet of wire, and a handful of PVC pipe, bamboo, or wood supports.  An antenna analyzer is helpful.

The inductor across the feedpoint would be, say 4 turns of #12 wire on a 3/4" form spaced out over 1.25" .  It will be self supporting and can be compressed or stretched for best SWR at your center frequency.



73,
Dan


















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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
AA4PB
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Posts: 12685




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« Reply #18 on: April 08, 2008, 01:42:52 PM »

Dan, take a close look at the picture on their web page. Doesn't it look like the feed line goes to a "T" and then off to the center of each spiral? The boom between the two spirals looks like PVC or something. It doesn't appear to be anything more than a support structure. I expect the directivity is off the end of the support boom.
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N3OX
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« Reply #19 on: April 08, 2008, 02:01:51 PM »

"Doesn't it look like the feed line goes to a "T" and then off to the center of each spiral?"

I thought each of those was a single wire.

They do call it an "electrical half-wave dipole antenna" and this:

http://www.tak-tenna.com/Balcony%20Pix.pdf

suggests that it radiates broadside to what they're calling the "boom", to quote:

"Note: Simple 90* rotation....
From horizontal propagation...
to vertical propagation!!!"

So, that's my take on the design.  You might be able to feed a spiral element midway and get it to resonate somewhere but the field cancellation would be huge.


Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
N3OX
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« Reply #20 on: April 08, 2008, 02:15:17 PM »

Bob,

Just for kicks I fed a single spiral coil at a random spot on the coil that I eyeballed to about halfway in an arc-length sense.

It resonated at 22.456MHz, very narrow, and had a radiation resistance (lossless impedance) of about 0.09  ohms with a total resistance at resonance including copper loss of about 1.3 ohms.  Overall efficiency is about 7% and the pattern is like that of a bad magloop, vertically polarized, shallow nulls along the axis perpendicular to the plane of the coil.

Gain was something like -11dBi.

Dan
 
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
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« Reply #21 on: April 08, 2008, 02:35:27 PM »

It appears to me that each spiral is a 1/4 wave of wire and the feedline if being around 30" joins the spiral minus that distance from the start of the spiral and is the tap point. This makes the wire a 1/4 wave from the feedline attachment. Any thoughts. Bill
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N3OX
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« Reply #22 on: April 08, 2008, 03:11:21 PM »

"This makes the wire a 1/4 wave from the feedline attachment."

It's a quasi-coincidence.

You can't, in GENERAL, coil up half of a dipole and have it stay half of a dipole.

There's actually a 180 degree phase flip and amplitude minimum in the current at about turn five of eight going outward each of the spirals in my model.  

That's pretty weird.  There's some transmission-line resonance type effect going on with the spirals.  They do seem to support standing waves.

However, the overall effect is nothing exotic.  The radiating bit of the antenna is the central 30" section, at least by comparison with the pattern and performance of an ordinarily loaded short dipole.

This sort of smacks of accidental empirical discovery.  Given a total length of wire of any random length in the range 0.4 to 0.9 wavelengths or so, there are several structures you could build with any one piece of wire that will resonate at a given frequency.

If you had a half wavelength of wire you could stretch it out into a half-wave dipole... or you could twist it and see what else you can come up with, and that may be what happened here.

My 17m antenna happens to resonate right in band with a total wire length of about 3/4 wavelength... each coiled up leg totals 3/8ths wavelength of wire.  

If I had a 0.4 wavelength wire, I could potentially wind small tight coils near the center to give enough inductance to resonate what was left.  If I had 0.7 wavelengths of wire, I could just ball up the ends like a ball of string until it resonated like a half-wave dipole.... or I might come up with some fancy structure like this that happens to resonate.

You pick a different spiral pitch and overall size and it won't resonate on 20m anymore, even with 1/4 wavelength total wire on each side.

Conversely, you pick 1/4 wavelength of wire for each side and there are clearly at least two very qualitatively different structures you can build with the same resonant frequency, and there are countless others that we'd have to argue over whether they were different or not ;-)

73,
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
AA4PB
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Posts: 12685




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« Reply #23 on: April 08, 2008, 03:21:11 PM »

There's a more extensive review at http://www.hamuniverse.com/taktennareview.html

The claim is that the spirals are each 1/4 wave long and that you adjust the tap point for minimum SWR. Obviously there will be some radiation from wires feeding them that run along the boom. I'm not sure what the pattern looks like. It appears that the coils will be more than simple capacity hats since they are in a spiral form and based on the SWR changing by adjusting the tap points.
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N3OX
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« Reply #24 on: April 08, 2008, 08:25:49 PM »

"It appears that the coils will be more than simple capacity hats since they are in a spiral form and based on the SWR changing by adjusting the tap points. "

If I were to try to describe them in familiar terms, I'd say they're loading coils and capacitance hats rolled into one.

From what I can tell, it's the connecting wires that do the lion's share of the radiating, just based on the pattern I get.

Take a look at the .jpg picture I posted back a few..h
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W8JI
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« Reply #25 on: April 09, 2008, 03:15:51 AM »

That's what they are.

Less than perfect capacitance hats that double as less than perfect loading coils that end load a very short dipole.

Since the feed impedance is fairly high we know what losses really are, don't we?

73 Tom
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K1CJS
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« Reply #26 on: April 09, 2008, 05:40:26 AM »

"Stick with full size dipoles, loops, etc. unless you HAVE to make do with something smaller!"

Good, sound advice.
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KG4RUL
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« Reply #27 on: April 09, 2008, 05:44:10 AM »

WA8MEA writes on April 8, 2008:
At the top of the stairs, without a care
it shoots signals so high in the sky.
It won't let you down, even in town
everyone knows its a BIG Slinky.

The best present yet, to give or get
that hams will all want to try.
Take a turn at bat, when you're ready to chat
everyone knows it's a BIG Slinky.

It's a BIG Slinky, it's a BIG Slinky,
for fun it's the best ham radio toy.
It's a BIG Slinky, it's a BIG Slinky
just a coil of ham radio joy.

Everyone needs a BIG Slinky....
You've got to get a BIG Slinky.

73, Bill

........

That is SO BAD that I LOVE IT!!!!!  If I laugh any harder I am going to pop some stitches!!!!!
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K1CJS
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Posts: 5879




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« Reply #28 on: April 09, 2008, 05:55:14 AM »

"It seems quite expensive for just what it is compared to what you would pay for a dipole."

It used to be about half the price it now is--which was a fair deal--the cost of the materials plus an equal amount of money for the fabrication, but it seems the manufacturer is looking to capitalize on his success.  So now its about thirty dollars worth of materials and ninety for the fabrication of the antenna.  

Hey, its his right to do so, but now this antenna CAN be compared to an Isotron--an expensive loading circuit.  I doubt he'll be selling as many of them as he would have if the price was left where it was.  
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K4SAV
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Posts: 1823




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« Reply #29 on: April 09, 2008, 07:29:40 AM »

When this antenna was being designed, he listed the requirements of this antenna discussion group for help in designing it.  This website has some description of the antenna, and a good picture.  Notice the unsymmetrical feeding of the coil, resulting in an off-center fed antenna.  Also notice that the coils are wound in opposite directions.  They called it a Princess Leia Antenna.
http://www.randstadamateur.net/index.php?option=com_smf&Itemid=41&topic=282.msg671

The first page of the TAC website implies there are four models, 40 meters, 20 meter, 11 meter, and 10 meter.  Another page of the website says there are only a standard model and a "More Portable Model".  I found pictures of the 40 meter and 20 meter models.  They look identical to me.

The website has a reference to the Tac-tenna expedition style in the Artic, OX60AD (OX3PG op) in Tule, Greenland.  I can't imagine they used a Tac-tenna when they have a Monster 95 ft boom log periodic at that location.  Maybe he just donated the QSL cards.
http://1.947group.org/gallery/displayimage.php?album=5&pos=1

The Tac-tenna website says the antenna was tested, proven and endorsed by Collins Radio Association, and there is a link given.  I could find no reference to the Tac-tenna on that website, and neither could Google when searching that site.  However, this is a users group for Collins Radio Equipment, not associated with Collins Radio Corp.  So the antenna was probably tested and approved by a member of this group.  You can guess who.

Notice that there is no common mode choke on this antenna,  That is for good reason.  It won't work well if you use one.  According to EZNEC, this antenna functions as an unbalanced load that injects large common mode currents onto the feedline.

With EZNEC I was unable to make the antenna resonate on 40 meters.  I was able to get the resonant point down to 8.8 MHz but no lower. I probably didn't have the right length feedline.  At that frequency with the antenna at 35 ft, using 80 ft of RG213 the gain was -7 dBi.  Adding a choke to remove feedline radiation, the gain dropped to -18 dBi.

Readjusting the taps for a resonance on 15 meters, with the antenna still at 35 ft, the max gain occurred at a very high angle, -1.5 dBi at 45 degrees.  At 10 degrees elevation the gain was -7 dBi.  Adding a choke to remove feedline radiation resulted in a gain of 0 dBi at 18 degrees.  The reason for the high angle radiation was the long vertical feedline radiating at a high angle.  The antenna was placed too high.  The gain would have been higher if the antenna was placed lower so that the vertical section of the feedline contributed some low angle radiation instead of mostly high angle.

You can see the feedline significantly effects the SWR and pattern of the antenna, so it is likely that everyone's experience with the antenna will be different because of different feedline lengths and routing of that feedline.  The antenna should placed a height such that the vertical section of feedline has a good length relative to the frequency of operation.  A long section of feedline on the ground will couple a lot of signal into the ground.  Some lengths of feedline operate much better than others.

Jerry, K4SAV
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