Log-Periodic Antenna Design

[Dave]

My current UHF antenna is a 14" Radio Shack clip lead clipped from the
center of my coax to the venetian blind. I have to hand-adjust it
for the channel, weather conditions, phase of the moon, etc. I can
do this because I can _see_ an indication of signal strength.

Well, with this new Fascist "No More Free TV" crap, I'm gonna need
a real UHF antenna. My budget is exceedingly limited, but I have
a supply of materials (GTAW filler rod, with some coppery-colored
coating, so it solders like a dream, and is as stiff as piano wire)
to build an antenna with.

But I've been searching the web for some weeks now, and I can't
seem to find any kind of formula, except there was this program
I downloaded - LPDA.EXE, which runs on DOS. Unfortunately, it's
in Russian or Polish or Uzbekistani - one of those East Yurp
languages. Here's a screen snap:
http://mysite.verizon.net/richgrise/images/LP-Prog-Output.gif

Which I went through pretty much by-guess-and-by-gosh - can
anybody read that stuff?

There are a lot of factors I don't know about, like "Tau", and
all of the specific designs on the web are flat - something is
telling me I want one of those pyramid-shaped ones, but I really
don't know the difference (between that and flat) - it's probably
something to do with bandwidth or F/B ratio or whatever.

My local library has no ARRL Antenna Book (!), and did I mention
I have a seriously limited budget?

So, how do I pursue this? It'd be nice to have a program that will
calculate the whole thing for me, but am I dreaming? If I want to
send myself to Log-Periodic School, where should I start?

Or, does anyone have a UHF-TV log-periodic design that they'd share?

Thanks,
Rich

Log periodics are not necessary for sub-octave operation.

 

[GregS]

My current UHF antenna is a 14" Radio Shack clip lead clipped from the
center of my coax to the venetian blind. I have to hand-adjust it
for the channel, weather conditions, phase of the moon, etc. I can
do this because I can _see_ an indication of signal strength.

I did the same thing and I was surprised how many digital chanels I got.
I was at a dollar store and saw the RCA UHF/VHF loop/ears for $5 and
that gave me considerable better reception.

greg

 

[GregS]

My current UHF antenna is a 14" Radio Shack clip lead clipped from the
center of my coax to the venetian blind. I have to hand-adjust it
for the channel, weather conditions, phase of the moon, etc. I can
do this because I can _see_ an indication of signal strength.

Well, with this new Fascist "No More Free TV" crap, I'm gonna need
a real UHF antenna. My budget is exceedingly limited, but I have
a supply of materials (GTAW filler rod, with some coppery-colored
coating, so it solders like a dream, and is as stiff as piano wire)
to build an antenna with.

But I've been searching the web for some weeks now, and I can't
seem to find any kind of formula, except there was this program
I downloaded - LPDA.EXE, which runs on DOS. Unfortunately, it's
in Russian or Polish or Uzbekistani - one of those East Yurp
languages. Here's a screen snap:
http://mysite.verizon.net/richgrise/images/LP-Prog-Output.gif

Which I went through pretty much by-guess-and-by-gosh - can
anybody read that stuff?

There are a lot of factors I don't know about, like "Tau", and
all of the specific designs on the web are flat - something is
telling me I want one of those pyramid-shaped ones, but I really
don't know the difference (between that and flat) - it's probably
something to do with bandwidth or F/B ratio or whatever.

My local library has no ARRL Antenna Book (!), and did I mention
I have a seriously limited budget?

So, how do I pursue this? It'd be nice to have a program that will
calculate the whole thing for me, but am I dreaming? If I want to
send myself to Log-Periodic School, where should I start?

Or, does anyone have a UHF-TV log-periodic design that they'd share?

Thanks,
Rich

Ever hear of the BOW TIE. Its a sort of Fractal antenna. Having a wide band.
It could be improved by making it a full fractal.

greg

 

[John Smith]

I bought one, a Phillips MANT310/MNT310F - didn't work
as well as the non-amplified RS one I already had.

Actually, I had to construct my own with a broadband MMIC device, to get
decent functionality ... however, my mother has an el-cheapo unit she
purchased from some yard sale, it/they work surprisingly well!

Location, reflections, etc. can vary ones experience greatly--but hey,
they usually beat a wire coat hanger!

Regards,
JS

 

[[email protected]]

My current UHF antenna is a 14" Radio Shack clip lead clipped from the
center of my coax to the venetian blind. I have to hand-adjust it
for the channel, weather conditions, phase of the moon, etc. I can
do this because I can _see_ an indication of signal strength.

Well, with this new Fascist "No More Free TV" crap, I'm gonna need
a real UHF antenna. My budget is exceedingly limited, but I have
a supply of materials (GTAW filler rod, with some coppery-colored
coating, so it solders like a dream, and is as stiff as piano wire)
to build an antenna with.

But I've been searching the web for some weeks now, and I can't
seem to find any kind of formula, except there was this program
I downloaded - LPDA.EXE, which runs on DOS. Unfortunately, it's
in Russian or Polish or Uzbekistani - one of those East Yurp
languages. Here's a screen snap:http://mysite.verizon.net/richgrise/images/LP-Prog-Output.gif

Which I went through pretty much by-guess-and-by-gosh - can
anybody read that stuff?

There are a lot of factors I don't know about, like "Tau", and
all of the specific designs on the web are flat - something is
telling me I want one of those pyramid-shaped ones, but I really
don't know the difference (between that and flat) - it's probably
something to do with bandwidth or F/B ratio or whatever.

My local library has no ARRL Antenna Book (!), and did I mention
I have a seriously limited budget?

So, how do I pursue this? It'd be nice to have a program that will
calculate the whole thing for me, but am I dreaming? If I want to
send myself to Log-Periodic School, where should I start?

Or, does anyone have a UHF-TV log-periodic design that they'd share?

Thanks,
Rich

I have used the procedure in the following paper:
http://www.urel.feec.vutbr.cz/ra2008/archive/ra2004/abstracts/116.pdf

I slightly modified the design (e.g. I used several different
diameters for the elements), but basically I used the same formulae.
I did not use their formula for deciding the right spacing between the
support tubes to get the right characteristic impedance, because I
suspect that maybe it is only valid over a limited range of spacing.
Instead, I measured the characteristic impedance of just the tubes
with no elements attached on a VNA that could plot impedance vs
distance in a sort of TDR mode, and I adjusted the spacing until it
was right. I epoxied some very small (roughly 1mm cube) spacers
between the support tubes to keep the distance right, once it was
adjusted properly. It is important that the space between the support
tubes is mostly filled with air, not epoxy or any other dielectric,
because the wave needs to propagate at the right speed between the
tubes so that the elements are fed in the right relative phase, and
this won't happen if there is something with a higher dielectric
constant in there. I used those brass tubes that you can get in hobby
shops, but unfortunately brass is fairly resistive and I did not
silver plate it. I would have used aluminium if it were easier to
solder in a reliable way.

The finished antenna had a good return loss over the desired frequency
range (sorry, can't remember the numbers) and it did the job for which
it was intended although I don't have a measured gain value etc.
because I don't have an antenna range.

I have a spreadsheet for calculating the element lengths (in
Openoffice.org format) if you are interested.

Chris

 

[Rich Grise]

Rich Grise wrote: ....

Looking for a cookbook design, or the theory to do it yourself?

Cookbook, if at all possible. Like, element lengths and spacing,
and the angle between the booms - which brings up a question - what
effect does it have when you take a flat L-P and "open it up", like
to a pyramid shape - I was doing a thought experiment with this and
when it's completely "flattened out", (180 degrees between the booms),
it looks like a <drum roll please> Bow Tie!

Thanks,
Rich

 

[Rich Grise]

Upisi najnizju radnu frekvenciju : enter lowest frequency Upisi najvisju
radnu frekvenciju : enter highest frequency

Duzina antene: length of antena
Broj elemenata: number of elements

Pritisni taster za proracun antene: press a key to calculate antenna

Duzina 1. elem. length of first element

Pritisni taster za nastavak Press any key to continue

Duzina zavrsnog kratkospojenog odsecka: length of final shorted section
Upisi precnik dipola: enter diameter of the dipole

Upisi ulaznu otpornost (ohm): Entry resistance (weird in original)

Impedanca napojnog voda: feeder impedance (not sure what this is)

Upisi precnik napojnih provodnika: diameter of feeding leeds (my guess
these are two bars that hold elements)

razmak izmedju napojnih provodnika: distance between feeder leeds (and
distance between two bard holding elements)

You owe me a beer. BTW, its Croatian or Serbian. I kind of understand some
90%.

Thanks!
Rich

 

[Rich Grise]

LOL ... talk about trolls! That HAS TO BE THE BEST TROLL OPENING LINE I
HAVE EVER SEEN!

Hey, "John Smith", why don't you go outside and play
hide-and-go-****-yourself?

Cheers!
Rich

 

[Rich Grise]

Someone else has already provided the translation, so that will take care
of some of the wholes in data entry and reading.


Tau is related to the shape of what you call the pyramid, or more actually
to the angle of the taper. This defines the smoothness of matching across
the span of frequencies you entered into the program. As you can see, it
also relates to the available gain. Another correlative is it also
relates to its length. All of these things are trade-offs that lend to
the rule of choosing what you want most and giving up on the rest.

I note elsewhere that you wanted something about 1 foot long. There is a
Tau that will give you this boom length, and you got it on the first
guess.


You should start building what your screen shot gave you IF that is the
span of frequency you need (already questioned by other correspondents).

73's

"Best Regardses"? ;-)

Anyway, thanks for this - I'm feeling a lot better about this project now
thanks to your help and that guy that translated it for me (forgot the
name, but he knows who he is - Thanks Again!);

I might even start cutting wire[1] and soldering this weekend! ;-)

Thanks!
Rich

[1] GTAW (Gas Tungsten Arc Welding) filler rod, with some coppery-
colored coating that solders even better than copper, about .030 dia.,
and as stiff as piano wire.

 

[Rich Grise]

You should start building what your screen shot gave you IF that is the
span of frequency you need (already questioned by other correspondents).

Apparently I'll only need up to ch. 52; have to look up the carrier freq.
on that.

Ch. 14 = 470-476 MHz
Ch. 83 = 884-890 MHz I think.

Now all I need to do is the algebra. ;-)

52 - 14 = 38
38 * 6 = 228
228 + 470 = 698
698 + 6 = 704

Cheers!
Rich

 

[Rich Grise]

Log periodics are not necessary for sub-octave operation.

Dude! Awesome! And this one doesn't even have a reflector!. I
wonder how far I should hang it in front of the venetian blind. ;-)

Thanks!
Rich

 

[Mark Zenier]

My current UHF antenna is a 14" Radio Shack clip lead clipped from the
center of my coax to the venetian blind. I have to hand-adjust it
for the channel, weather conditions, phase of the moon, etc. I can
do this because I can _see_ an indication of signal strength.

Your clip lead is too long. Try 1/4 wave.

I got good reception using a 4 1/2 inch length of 24 gauge solid poked
into the F connector for a (line of sight) 45 kW station, 20 miles away.
(Most of the local stations run in the 500-1000 kW range).

Mark Zenier [email protected]
Googleproofaddress(account:mzenier provider:eskimo domain:com)

 

[Rich Grise]

Ever hear of the BOW TIE. Its a sort of Fractal antenna. Having a wide
band. It could be improved by making it a full fractal.

Yes - somebody just pointed to a youtube of somebody making one out
of coathangers.

I think I'm gonna do that.

Cheers!
Rich

 

[Jim Lux]

You probably don't need a program, just a decent text book that covers the
topic adequately, which, undoubtedly is what the program writers worked
from, and they might not have got it right! 'Antennas' by John Kraus
contains enough detail to make a start and it's probably more general than
someone's program which might involve specific choices of some parameter
values. So my recommendation would be to find a technical library that
offers access to non-members and send yourself to Log-Periodic School as you
put it. The IET library in London does this, for free. Do you have an
equivalent institution (e.g. IEEE), or a local university that covers
electronic engineering? You might be surprised how much access you can gain
to libraries to which you have contributed through taxes, or which need to
maintain an 'altruistic' public appearance.

Orfanidis's book on electromagnetic waves and antennas is online, and
covers LPDAs.. Kraus is better, but you'll have to fork out at least
$20+shipping for a used copy. Kraus *is* my recommendation if you have
to have a single antenna book, though.

 

[Cecil Moore]

Kraus is better, but you'll have to fork out at least
$20+shipping for a used copy. Kraus *is* my recommendation if you have
to have a single antenna book, though.

Here's a new international 3rd edition available for less
than $10 plus shipping.

http://www.abebooks.com/servlet/SearchResults?an=Kraus&sts=t&tn=Antennas&x=0&y=0

 

[John Smith]

...
Hey, "John Smith", why don't you go outside and play
hide-and-go-****-yourself?

Cheers!
Rich

LOL ...

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

Regards,
JS

 

[NoSPAM]

I think a bow tie's design is actually motivated more by one of the
"standard" ultra-wideband antenna designs, that of a pair of opposing
cones touching each other at their narrow ends, being translated down into
2D.

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

 

[Rich Grise]

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.

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

Thanks!
Rich
ex-WN0GJS

 

[Rich Grise]

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?

http://www.google.com/search?hl=en&q="fractal+antennas"&btnG=Google+Search&aq=f&oq=

Hope This Helps!
Rich

 

[Sal M. Onella]

It may not take too much antenna.

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)