[TowerTalk] Wire log periodic antenna

[Scott MacKenzie]

In the ARRL Handbook, 8th edition, Chapter 10, pages 10-12, describes just
such an antenna.  I built one for Field Day and it worked extremely well. It
was nice to be able to rotate it around by moving the stays.  

As this was about 10 years ago, I don't have any records of the SWR or
anything like that.  But as built, without making any changes, I had an SWR
of 1.5:1 - good enough for my TS-820 tube rig.

Scott

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of LA6FJA/K3RAG Stein
Roar Brobakken
Sent: Tuesday, December 16, 2008 12:58 PM
To: n8de at thepoint.net
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] Wire log periodic antenna

Hi Don

Yes, but I found this now about LPDA, but really wonder if it is possible to
do it as INV-VEE formation.
Because all I have seen have been straight, first antenna I saw with wire
was this army antenna.

I will do some research 

73s Rag LA6FJA

****************************
http://www.supernec.com/lpda.htm 

Geometry of an LPDA

The relationship between element spacing and element length are given by the
scale factor tau, as shown in equation 1.

tau = Ln+1/ Ln = dn+1/ dn
..................................................1


Truncating coefficents are used to find the minimum value for L1 (longest
dipole element) and the maximum value for LN (shortest dipole element) as
shown in equations 2 and 3. 

L1 = 0.5 lambda max
.........................................................................2


LN = 0.25 lambda min
......................................................................3


Tau can be calculated using the following equation, if the length and
spacing of individual elements is required.

tau = (LN /
L1)1/(N-1)............................................................4


The Form Factor (FF) is defined as:

Form Factor = Boom Length / lambda max ................................5


-----Opprinnelig melding-----
Fra: n8de at thepoint.net [mailto:n8de at thepoint.net]
Sendt: 16. desember 2008 18:51
Til: LA6FJA/K3RAG Stein Roar Brobakken
Kopi: towertalk at contesting.com
Emne: Re: [TowerTalk] Wire log periodic antenna

Rag,

The spacing between adjacent elements in a LPDA is NOT a function of
highest/lowest frequency.

Do some research on LPDA design and you will discover that the 'graduation'
of spacing and element lengths is dependent on CHOICE of 'sigma', the factor
which determines bandwidth and boom length.

When Dr. Duhamel of Collins Radio 'discovered' Log Periodics waaaaay back,
his design information was published in a few texts, but most of it goes too
far for ham radio uses.

K4EWG {I believe] designed and built a nice LPDA that was printed in the
ARRL Antenna Handbook and one edition of the Antenna Compendium.

A little searching should prove fruitful.

Good luck.

Don
N8DE

Quoting LA6FJA/K3RAG Stein Roar Brobakken <s-roabr at online.no>:

> With correct picture link !!
> Hi
>
> I am planning to put a wire yagi for 40m to NA, but suddenly I came 
> over a picture for a wire log periodic antenna.
>
>
> I have seen some pictures of wire log periodic antennas on internet, 
> Just like this one
>
http://www.antenna.it/military/images%20military/disegno%20lp1530-w%20copy.j
> pg
>
> One guy have made one like this
> http://www.radiosky.com/super_cheap_log_periodic_antenna.html
>
>
> He have used spacing between 40 cm - 75 cm(2'5.8" - 1'3.8") for 17mhz 
> -30 Mhz.
>
>
> My spacing calculation gives:
>
> 40 cm is 1/35 wave on 17 Mhz, for first driver * is this optimal
calculation
> ?
>
> 75 cm is 1/40 wave on 30 Mhz,? for Rear Reflector * is this optimal 
> calculation
>
>
> so my question is then have anyone tried something like this version
before?
>
>
> My idea is to make one for 7 to 21 Mhz ?
>
> should I just put my first driven element on 6 Mhz and then calculate
until
> 21.5 Mhz for reflector?
>
>
> I don't know what will happen when I get up one as Inverted-Vee in a 
> Log periodic formation ?
>
> Anyone have a idea to figure the length of elements etc? correct spacing ?
>
>
>
> 73s Rag LA6FJA
>
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