Log-Periodic Antenna Design

LOL ...

Darn, you just can't get decent psychiatric help with your food stamps, can you? :-(

Regards, JS

That's interesting. In what way(s) is it improved by making it fractal? How much is the improvement? Can you point me to a reference about this which gives some quantitative data?

Roy Lewallen, W7EL

No, that's "Best Regards's". It's the possessive, not plural, form of "Best Regards". I think the grammar is part of the same dialect as the verb "destinate" (as in "I've just destinated"), but you'd have to ask Richard about that -- he's the one with the English Lit degree.

Roy Lewallen, W7EL

It may not take too much antenna. I picked up one of the converter boxes and hooked it to a 432 mhz beam at 70 feet and got 21 stations on the auto tune. Then to a 9 element M2 2 meter bem and it picked up 29 stations. This was at the end of about 130 feet of low loss rg-8 size coax and then 25 feet of rg-6. Several of the stations were the same transmitter,but differant chanels on the TV.

Standard, indeed; this antenna is known as a biconical. It has excellent wideband response making it ideal for EMC testing. Most good antenna texts such as that by Krauss give a detailed analysis of the biconical antenna. I see no relationship between its design and a fractal design other than both are wide bandwidth antennas.

The bowtie antenna which Rich and others have mentioned is a "flattened" form of the biconical. If the bowtie is bent along its major axis, it makes an excellent wideband driven element for a corner reflector antenna.

73, Barry WA4VZQ

I read it in a QST or so back in the 1960's. :-)

Thanks! Rich ex-WN0GJS

Hope This Helps! Rich

Sorry, it doesn't. Among the claims, trolls for investors, and testimonials, where is the quantitative data showing that a fractal antenna is in any way better than a bow tie, in what ways, and how much? In other words, exactly where is the evidence on which you based your statement?

Roy Lewallen, W7EL

Hi Rich,

Tacking the new-age term of "fractal" to antenna does not automatically bring:

1. Widebandedness;
2. Gain;
3. Small size.

The link above fairly confirms it in the fog of offering.

I could expand upon this - but the interest of those who become suddenly engaged with the topic rarely translates into a meaningful discussion, and never leads to an actual construction.

73's Richard Clark, KB7QHC

< snip >

It doesn't.

I have two converter boxes, one Magnavox, one Zenith. I just now tried my local stations with them using a straight 24-inch alligator clip lead as the antenna. Location is a residential garage in the San Diego suburbs. Stucco walls, metal garage door closed, overhead fluorescent lights on. Transmitters in three different locations.

All the UHF locals came in, 10 transmitters with about twenty total programs. The one low-power VHF did not. Looping the clip lead back and clipping the end to the F-connector produced about the same results. (Lost one TJ station.)

When I "upgraded" to a POS 2-bay bowtie in the rafters (about 8 feet up), all eleven locals came in, plus KCBS from LA . On the Zenith box, arguably a better unit, I got two more LA channels, although one of them had some intermittent freezing and tiling.

If even poor antennas work well, why all the whining?

"Sal" (KD6VKW)

My Webster's unabridged dictionary gives the following examples of the correct way to pluralize numbers.

"figure 8's", "the 1890's", "the 20's"

73 is a number that stands for "Best Regards" 73's would be "Lots of Best Regards".

--
73, Cecil  http://www.w5dxp.com

?arnumber=1610336

If you are a member of IEEE, you can access this paper:

Multiband behavior of wideband Sierpinski fractal bow-tie antenna Yamini, A.H.; Soleimani, M. Microwave Conference, 2005 European Volume 3, Issue , 4-6 Oct. 2005 Page(s): 4 pp. - Digital Object Identifier 10.1109/EUMC.2005.1610336

--
73, Cecil  http://www.w5dxp.com, IEEE

I've not had any problems with the UHF circular loop that comes with standard rabbit ears. The only problem I've had is with VHF channels on the dipole. I need a weatherproof version of my RS rabbit ears. Unfortunately, ABC is Channel 7 here in Tyler, TX.

--
73, Cecil  http://www.w5dxp.com

I don't have time to search for it, but there's also a dual quad UHF TV antenna that's easy to build with the same kind of materials. I prefer steel tie wire to coat hangers because it's easier to work with.

Now that the FCC has given a green light to whitespace device deployments (particularly those that rely solely on spectrum-sensing technology), you may find you need a better antenna than a simple loop, bowtie or coat hanger.

For those of you who are not following the issue, a quote in this week's TV Technology pretty much sums it up:

"MSTV (Maximum Service Television) told the Commission Oct 31 that the least the FCC could do is subject the devices to rigorous testing beforehand and ensure fair and reliable tests to prevent interference to DTV. In a filing, MSTV also attacked the FCC proposal that a device should be able to detect signals as low as -114 dBm, a level MSTV equated with setting a smoke detector to only be able to detect a raging fire."

Whitespace devices will also cause great harm to wireless microphones, particularly older models.

-mpm

I don't have data. I think the home made TV antenna in the video, is very much like a bow tie, and could have better bandwidth by making the elements different lengths. The gain factor is going to be narrow band since the feed length is constant. I would have also used 12ga copperweld or solid copper. You can also get closer to fractal by using many more different sized elements.

greg

Well, they work if you have a good, strong, signal, but if you don't fuhgetaboutit!

Here in the desert, all the stations are co-located only about 6 miles from here, but there are two little problems. One, 80% of the valley population is located to the south, so they have configured the antennas with their major lobes that direction, and second, there is a Edmom Hill between us and the antennas! You can't even get analog broadcasts here, much less digital!

Charlie

And if you aren't a member, you aren't in on the joke?

With all the added capacitance to the elements, I have little doubt that there would be lots of resonance's, and it would be cool to choose the geometry to bring about the proper feed point impedances, but these things can never be gainful with all the losses introduced.

Neat idea for specific applications like little pocket toys, but certainly not the answer to everything.

I wonder how the Limo's will deal with DTV in motion.

much like a bow tie,

Comparable to a 4 bay bowtie. Maybe 6db gain. Brazing rod would be a little lighter and wouldn't rust. Would work much with a reflecting plane and above the house clutter.

Twin lead could make a comeback since there won't be such a worry about the low band interference issue. Actually much less loss than coax. I may yet change over to 300 ohm window line on my bigazz deep fringe at 40ft and switch it to the ham shack for 6/2m SSB work and DTV DX. TV DX won't be dead, you will just have to know where to find it