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Author Topic: Tak-Tenna, MFJ 80/40V/ or HI-Q 6/80 mobile / vertical for Townhouse?  (Read 9055 times)
KT0DD
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Posts: 277




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« on: August 29, 2011, 08:33:37 AM »

Hello, first of all, I know that these compromise antennas radiate poorly in all directions...lol. I'm trying to decide which way to go for my townhouse. I wish to operate on 75/40/20/17/10m. I can probably get wire up for 20-10m. I just read about the TAK-tenna and was impressed and am considering it. I own a Hi-Q  6/80 mobile antenna I could mount vertically, or would a MFJ 80/40 or hy-gain vertical be the best way to go. My intended operating is SSB, 500 to 1000 mile radius on 75/40m, with occasional moderate DX hunting. I use a Kenwood TS480HX 200 watt rig w/ ext. tuner.

Any suggestions are appreciated.

73, Todd - KT0DD
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N3OX
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« Reply #1 on: August 29, 2011, 10:22:46 AM »

The tuning procedure for the Tak-Tenna basically ensures that it's end-loading and matching the coax shield.  If you were trying to make a tiny loaded dipole radiate like a dipole, you would specify that the coil taps at the ends should be symmetric and you'd need a balun at the feedpoint.  Look through the reviews and notice how many people with a 40m Tak-Tenna have it installed atop a 20 foot mast with a vertical coax run... you can build a heck of a good top loaded 20 foot vertical and even if it doesn't have radials it will work pretty okay Cheesy

I think a Tak-Tenna can work okay for its size on its own, in the sense that even if it wasn't causing the feedline to radiate, it might work about the same as a magnetic loop of its size.  The loading is somewhat more lossy, but it doesn't have the radiation cancellation inherent in the magloop design, so the radiation resistance is higher and you can make it out of inexpensive wire.

I have a model of an antenna similar to a Tak-Tenna:

http://n3ox.net/files/N3OX_spiral.jpg

The model throws some warnings because of the really short segments at the inner part of the spiral but doesn't seem to have errors that are too serious, and it's suggesting about 10% efficiency on 40m and 6kHz 2:1 VSWR bandwidth (with respect to the 2.7 ohm impedance at resonance)

The reported bandwidth is much wider than that.

K4SAV modeled something a little closer to the real thing :

http://lists.contesting.com/archives//html/Towertalk/2008-04/msg00339.html

I can get a lot of current going down the feedline if I add one to my model and tap the two coils differently but am having a hard time getting a 50 ohm match on 40m (I can get a 100 ohm match with lots of feedline radiation, and a gain only a few dB down from a 40m quarter wave vertical !!!)

Of course, the real easy test of the feedline radiation is to clamp on a calibrated current meter (http://www.w8ji.com/building_a_current_meter.htm) onto a real installation's feedline and see what happens.

What I can say for sure is that it would be hard or impossible to avoid feedline radiation if you don't use a good balun and symmetrical tapping.  And you probably wouldn't WANT to avoid the feedline radiation, because that's how you get a wide usable bandwidth and better performance.  But I personally would rather put up a 20 foot mast, maybe with some kind of top loading structure, and just match it from the BOTTOM where I can fiddle with the matching network more easily and can more likely install a multi-band network.  I'd also add some radials!

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

Monkey/silicon cyborg, beeping at rocks since 1995.
KT0DD
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Posts: 277




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« Reply #2 on: August 29, 2011, 11:25:35 AM »

So, something like the MFJ 80/40 antenna with coils at the top and a capicitance hat would be better? How noisy would it be compared to the Tak?
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WB6BYU
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« Reply #3 on: August 29, 2011, 01:30:57 PM »

Quote from: KT0DD
...My intended operating is SSB, 500 to 1000 mile radius on 75/40m...

A vertical should for the outer part of that range, but for for closer stuff you'll want a horizontally
polarized antenna.  That's a problem, because you probably don't have much horizontal space to
string it out.  There are a number of shortened horizontal antennas on the market, including the
Tak-Tenna, Buddi-Pole, and various sorts of dipoles made from mobile antennas.

Whenever you shorten a dipole from a full half wavelength, you encounter a range of effects:

(1) the antenna is no longer resonant.  You have to add loading coils, capacity hats, or some
combination of those or similar methods to make it resonant.  Loading coils have losses.

(2) the radiation resistance decreases.  This has two effects - first, the SWR will be high unless
you employ some sort of matching and/or the antenna has high losses.  Second, the currents
are higher at the center (leading to higher losses for the same diameter wire) and the voltages
are higher at the ends than a straight wire dipole.

(3) The bandwidth narrows.  This is a side effect of (1) and (2), because there is more reactance
in the system and less resistance, therefore a higher loaded Q.  Tuning becomes more critical, and
even a nearby branch blowing in the wind will cause the SWR to vary.

Antenna length should be considered in wavelengths:  for the same physical length (say 10') the
electrical length is longer for 40m (0.07 wavelengths) than for 80m (0.035 wavelengths).  Many
of the shortened antennas that work reasonably well enough on 40m are extremely difficult to
get working in practice on 80m just because the size reduction is so great.

As N3OX pointed out if a Tak-Tenna really worked as advertised and did all the radiating itself it
would have a feedpoint impedance of 2.7 ohms (SWR = 18 : 1) and 6 kHz bandwidth on 40m.
Clearly, many of the smaller antennas rely on radiation from the coax for their performance:
this makes some sense, since in many cases the coax is longer than the antenna, but it also
means that the antenna tuning varies as the coax is rerouted between the antenna and the
shack.  Since the coax runs closer to most of the electronic devices in your home than the
antenna is, using the coax as part of the antenna tends to pick up more noise from those
sources.


While 40m and especially 75/80m operation is very difficult under such circumstances, it
isn't impossible in all cases.  The best antenna I've strung up for such use was a loop of
wire (insulation chosen to match the exterior colors) tossed over the roof and brought
down each side of the building, then in the ground floor windows to an antenna tuner right
at the rig.  True, it was coupled closely to the house electronics and was prone to various
RFI problems, but the transmitting efficiency on 40m and 75m was higher than what could
be achieve with any of the commercial shortened antennas on the balcony.

A high-Q tuned loop (sometimes called a "mag loop") can also provide high efficiency in
a small space using large-diameter conductors.  They also have a narrow bandwidth,
but are tunable to any spot in the band (or in some cases, across several bands in a
2 : 1 frequency range.)

Good luck!
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KH6DC
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Posts: 634




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« Reply #4 on: August 29, 2011, 01:56:41 PM »

I have a tak-tenna which I was experimenting around.  It's mounted on a wooden shovel handle on a tripod.  It's a pain to tune using the aligator clips and dinding your way around each coil for resonance (and low SWR).  It works fine, not great but it works.  The pain is I didn't move the clips, took the antenna down for the night and set it back up the next day, I had to retune the whole thing again.  It works.  I also have the Hi-Q Tune-a-dipole which was a set of 2 2.5/80 and a dipole bracket.  That works excellent and I can tune it from inside my shack with an antenna analyzer.

Good luck and 73, Delwyn KH6DC
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73 and Aloha,
de Delwyn, KH6DC
N3OX
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« Reply #5 on: August 29, 2011, 03:12:31 PM »

So, something like the MFJ 80/40 antenna with coils at the top and a capicitance hat would be better?

Yeah, if you've got somewhere to put a decent ground radial system.  I would stick with a self-contained antenna in a dipole style otherwise. 

I think the Tak-Tenna and it's Petlowany/Pancake/whatever cousins is an interesting thing in a lot of ways.  It has a couple things going for it as a self-contained antenna, most of all that it's an end-loaded dipole with big capacitance hats.  The capacitance hats and loading coils are all in the end structure.    But making it 30 inches long for 40m or whatever is strange.

Quote
How noisy would it be compared to the Tak?

I would say two things about that.  First of all, there aren't really inherently noisy antennas and less noisy ones.  There are several reasons why verticals get a bad rap, IMO.  A vertical has lots of response at low angles, and if you install that in the suburbs at ground level, it's "looking through" a bunch of houses full of plasma TV's and noisy wall warts.

There's a little bit of an effect from the way true ground-wave signals on the low bands propagate. 

There's the old saw that "man made noise is vertically polarized" but I think that's not really accurate when noise sources are close to you compared to "a ground mounted vertical will pick up lots of noise because it doesn't have a clear shot over the houses and stuff"   There's also the issue that, efficiency issues aside, a vertical's overhead null can be pretty detrimental for talking to people very close to you, and the signal-to-noise on high angle signals can be even worse because you're picking up lots of plasma TV and not as much one state over than if you were using a low horizontal antenna.

======

I think that many people find verticals to be noisier for local communications, and there are good technical reasons why that might be the case, but mostly it's all about how close your antenna is to the sources of bad noise and what its receiving pattern is compared to the arrival directions of desired ham signals and undesired noise signals.  Another important issue is whether or not the feedline going into the noisy house is well decoupled from the antenna, and "no-radials" verticals are terrible at that, whereas balanced horizontals are only really bad if the feedline is in a certain range of lengths.  So it's much more complex than "vertical vs. horizontal."

Comparing a vertical vs. a Tak-Tenna for overall use is extra tough.  If there's significant feedline current, then the Tak-Tenna+coax  up on a mast IS just a top loaded vertical with a bad ground system!  Then I think it would have the issues of a regular vertical plus poor decoupling of the feedline, unless you put a RF ground at the base of the vertical run of coax.   

A short dipole like the Tak-Tenna with a great balun and balanced coil-tapping will have a pattern like a horizontal dipole the same height above ground.  That might have some advantages for reception but if you choke off all the feedline current it will have a razor sharp bandwidth and very low transmit efficiency.  So it wouldn't be much good as your only antenna, and the narrow bandwidth might even make reception difficult well away from the frequency.

All in all, I'd think a decent ground mounted shortened 40/80 vertical would be better if you're not interested in primarily talking to your state and a one or two states over.    A shortened dipole might be better in that case, but an important principle about small antennas is that you shouldn't really make them shorter than is absolutely necessary, especially when they're already small.  A twelve or fifteen foot dipole with Tak-Tenna style loading structures on the ends would be WAY better than the 30 inch version.... but a 30 or 50 foot long 40/80 design might be even better. 

As far as noisy reception don't forget that you can always use a different antenna for listening, and sometimes it's better to build a  noisy but efficient transmit antenna and then build an inefficient antenna more isolated from things for listening.  There's a lot of surplus signal on 40m and 80m so all sorts of things that wouldn't transmit well at all can hear pretty well.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
WB6BYU
Member

Posts: 13045




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« Reply #6 on: August 29, 2011, 04:25:14 PM »

Quote from: N3OX

... if you're not interested in primarily talking to your state and a one or two states over... 



This really does need to be read in context, of course, depending on the size of the states surrounding you. Wink

Just including the adjacent states for me spans from Mexico to Canada, while two states over from MO
reaches from the Atlantic Ocean to west of the Rockies, and from Canada to Mexico and the Gulf.


But in general, a low horizontal antenna will work better than a vertical out to a couple hundred miles on
40/75m (when propagation supports the path.)  Beyond that it depends a lot on the height of the
horizontal antenna and the ground conductivity around the vertical.
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N3OX
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« Reply #7 on: August 29, 2011, 08:07:21 PM »

Quote from: N3OX

... if you're not interested in primarily talking to your state and a one or two states over... 



This really does need to be read in context, of course, depending on the size of the states surrounding you. Wink

Good point... Cheesy  If you're not  particularly interested in the first couple hundred miles would have been a better way to pu tit.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
KT0DD
Member

Posts: 277




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« Reply #8 on: August 31, 2011, 10:52:43 AM »

Thanks everyone. First, I guess I'll try to see how much wire I can throw on the roof and feed it with 440u ladder line. Next, I'll try A Tak or vertical if I cant do well with the wire. I know the wire will probably be 60-70 ft max. with about 20ft ladder line off of it. Probably not good for 75m, but worth a try.

73, Todd - KT0DD
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DJ0IP
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« Reply #9 on: September 17, 2011, 11:06:26 PM »

I have read a lot of good advice on this thread.
It is one of the better ones.

In my opinion, the monkey wrench in the works, is wanting to work 80m within 500 miles.
I suggest you consider this requirement separate from the other bands.  Build 2 antennas.
A vertical just isn't great for this, but of course a lot better than no antenna.

You didn't specify how much yard you have or if you have any yard at all.

Assuming you do, maybe this will work for you:
Put up an inverted L antenna, but rather in the shape of an inverted U.
Make the horizontal portion as long as you can.
Telescoping fiberglass poles are good for this.
Use one, preferably 2 elevated radials (quarter wavelength, bent however and whatever it takes to squeeze them in).
It's not a great solution but it will beat any vertical for less than 500 miles communications, and it doesn't really require a lot of space.

If you don't have any yard, then run it up the back side of the house, over the roof, and down the front side of the house.

If you have the room to make the radiator about 15 to 20% longer than a quarter wavelength on 80, do that, and then feed it through a capacitor.  This will help raise the feedpoint impedance.

GL es 73 - Rick, DJ0IP
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KA6KBC
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« Reply #10 on: December 29, 2011, 08:59:18 AM »

If you want to try the Tak Tenna - Here is my Homebrew version - As noted this is a Compromise Antenna, but it can get you on the air.

73's - Bill - KA6KBC

http://billbrwn.tripod.com/id3.html
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WX7G
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« Reply #11 on: December 29, 2011, 11:17:33 AM »

The Tak-tenna is actually a common-mode excitation device. It excites common-mode, or antenna current, on the feedline and apartment wiring which then becomes the real antenna. This can produce lots of RFI in the neighbor's electronics.

The mobile antenna suffers the same problem unless at least one resonant radial per band is used and a high common-mode impedance 1:1 current balun is installed in the coaxial feedline. But where to place the 80 meter radial?

A vertical mounted on the ground, away from the apartments, and with a current balun would work well and be less of an RFI problem.

And a dipole or G5RV might be the best even at a low height above ground. Possibly less RFI and good performance. An antenna tuner will be required.



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