log periodic antenna calculator
I search trough internet and can't find any good manual
how make simple log periodic VHF dipol for TV 4 chanel
frequency 62.25 Mhz.
i only find log periodic antena for VHF/UHF from
6 to 69 chanel.
The purpose of log-per antenna is wideband, at cost of a lower gain. It's completely useless for a single frequency/TV channel. A regular yagi is just fine.
I don't know how to make a simple dipole periodic, by the way. Log-per always involves a larger number of coupled dipoles.
FvM I'm little bit disapointed with your answer.
First of all I know that Yagi is better then log periodic antena
and I have one factory maded and work ok.
But on my area in Croatia there is no need for Yagi-WHY?
Becose I see transmitter on the hill which is 20 km air line.
Transmiter is 150kW power and log periodic is better and chiper choice then yagi.
So i need log-per for 4 chaneel VHF which is 62.25 Mhz.
So L/2 is 2.28 m or each dipol part(wire ) must be long 114 cm.OK
I only need measures for conection koax cable , in another words how calculate
distance between uper and lower part of qadrat aluminum tubes.
And distance between wires.
I hope that i'm clear enough.
Log periodic antenna is made from multiple dipoles placed in a logarithmic distribution, and its main characteristic is broadband frequency.
Because the log distribution, just small difference from the calculated distances between dipoles, can dramatically affect the gain of the antenna, when is not the same case for a Yagi.
Anyway, is more complicated to make a log-periodic compared to a Yagi antenna.
Yagi at the same dimensions and number of elements can give greater gain at single frequency.
Yes, execpt for the confusing title and the term log-per antenna. I see, that you want a simple dipole, not a log-per antenna.
The most simple dipole is made from two wires (1,2 m each) connected unsymmetrically to the coax cable center respectively outer conductor, if you have no 1:1 balun. You can coil up 0.5 m of the cable end to reduce the effect of the unsymmetrical connection.
FvM...
Ok i'm ask wrong question.(little bit)
I need log periodic dipol for 4 ch 62.25 = 1.14 m
Is now clear enough.
So without asimetric part(ferit transformer).
On this log periodic dipol i will conect 75 ohm coax cable directly
like on any other log periodic antene.
So how calculate this measures?
Here is my drawing how look like log dipol.
I only need L1 and L2 length?
No doubt,that this design can work as an antenna, somehow. But I don't see any advantage compared to an usual simple dipol, as everyone uses it.
As I mentioned before, the term log-periodic antenna implies a periodic structure, e.g. an array of dipoles with different length.
P.S.: To repeat my previous suggestion, omit the feed rods (L1 = 0) and connect the dipole rods directly to the cable.
advantage is obvious - simple construction
there is no need for asimetric transformer 300- 75 ohm
so every component has price and also affect on recived signal
i think that every asimetric transformer has about 0.5 - 0.7 db damping.
This shape of dipol antena is also very good for FM.
Ps. I made some experiments and build one or two this dipols.
Even on UHF is very good reception.
Added after 1 hours 30 minutes:
HI...
I made some calculation and here is my results.
Simple construction !? From my side looks three times more complicated than a simple dipole.
When in VHF/UHF the usual allocation for fade margin or multipath propagation is 10 up to 30dB’s range, I don’t think that gaining 0.5dB (not using a balun) is actually a real gain.
As far as I understand, impedance matching is your only argument for using this construction. As i said before, a simple straight dipole is fairly matched to a coax cable without a balun. I think, that it's properties are similar, possibly better than your design. Your design is very asymmetric and can't have an optimal direction pattern.
All log-per antennas, I know have an open end feed transmission line, not shorted as yours. I don't think, that this is an improvement.
maby looks complicated but when you start build it is very simple.
Yes main advantage is impedance transfer from antenna to cable.
And of course without asimatric trafo.
Gain of each dipol only is 0 dB if you dont know?
However this dipol has very good results in my area.
Hmm.
Just simple open dipole direct connected to coax will work better.
Try to look for "Iskra" log-periodic for channel 2-4, 4 or 5 elements I forgot.
I used it long time ago on 50Mhz band and some ameteur rtx with good results.
So, if you live near TX-Psunj then you dont need any antenna !
;)
Darko I'm Zlatko...
Are you from Croatia or from Slovenia?
I know for log Iskra dipol I want make my own
Hrvatska .. :)
Use this calculator:
http://changpuak.ch/electronics/lpda.html
for example min freq. 40Mhz, Max 70Mhz boom len. 1500mm
And you have good TV-I band antenna for summer DXing ..
:)
De èovjeèe reci mi na hrvatskom...:D
ma ja o?u napravit svoju ne?u namjerno da kupujem .
Imam dvje tri napravljene i hvataju signal OK.
Okolica Nove Gradi1ke..