alanh Posted May 28, 2008 Posted May 28, 2008 All, The Log Period Antenna was originally designed in 53 years ago so it is hardly a new design! Description of the LPA Build your own Band 4-5 antenna to Australian channels 28 - 69 Construction article by Alan Yates If you want something deep, try How to become an antenna guru AlanH
digitalj Posted May 28, 2008 Posted May 28, 2008 I can see how a Log Periodic is made, starting at the back: element 1 = 100% element 2 = 80% of element 1 element 3 = 80% of element 2 = 64% of element 1 element 4 = 80% of element 3 = 64% of element 2 = 51.2% of element 1 etc... spacing 1 = 100% spacing 2 = 80% of spacing 1 spacing 3 = 80% of spacing 2 = 64% of spacing 1 spacing 4 = 80% of spacing 3 = 64% of spacing 2 = 51.2% of spacing 1 etc... Does this mean that I can expand the bandwidth by either adding an element to the transmitter side that is 80% of the previous element with a spacing of 80% of the previous spacing or add another element to the back of the antenna that's 125% of the previous element with a spacing of 125% of the previous spacing?
Thornton Melon Posted May 28, 2008 Posted May 28, 2008 All,The Log Period Antenna was originally designed in 53 years ago so it is hardly a new design! Description of the LPA Build your own Band 4-5 antenna to Australian channels 28 - 69 Construction article by Alan Yates If you want something deep, try How to become an antenna guru AlanH Thanks so much for this post Alan,I have been interested in antennas for many years,and have built a few from electronics magazine plans. This post is most helpful in understanding some basics. Now back to my matchmaster problem,I am now recieving every digital station except CH 7,which displays "no signal" whilst all other stations have reasonably strong reception and a good picture. I was getting CH7 before. I am going to check my antenna connections again to-day. Cheers Thornton
alanh Posted May 29, 2008 Author Posted May 29, 2008 Digitalj, If you wish to change the bandwidth, the starting length and spacing of the rear reflector will change, as it will if the lowest frequency required changes. There is not a simple statement I can make to quantify this. Log Periodic Arrays are designed to be repeating patterns. AlanH
wahroonga farm Posted May 29, 2008 Posted May 29, 2008 Not sure why anyone thinks a log periodic is new (except that it has an excellent reputation for digital reception in the correct circumstances). If you truly wish to study antennas and their characteristics; get hold of the ARRL Antenna Handbook, currently in it's 21st edition. I must update mine
beeblebrox Posted May 29, 2008 Posted May 29, 2008 Does this mean that I can expand the bandwidth by either adding an element to the transmitter side that is 80% of the previous element with a spacing of 80% of the previous spacing or add another element to the back of the antenna that's 125% of the previous element with a spacing of 125% of the previous spacing? As Alanh says it's not actually that simple. The antenna design is proportional on Length, Diameters and positions of the dipoles... in the ARRL handbook there's 28 pages on LPDA design. If you're interested I can email you a couple of pages from a recent IEEE Antennas and Propagation Society Magazine that talks about improving LPDA design with Particle Swarm Optimization and has all the basic equations for LPDA design.
Mr.Bitey Posted May 29, 2008 Posted May 29, 2008 You guys arnt about to start talking about the fingerprint of god, gods donuts or time traveling 386 pc's or anything in here are you ? Cheers, Scientificey
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