best antenna

[abcd567]

... seems Coke might be phasing out the 355ml cans in favor of them but keeping the price the same

No need to be mad about this.
By reducing quantity with same price, they are wealthier.
By paying same money but drinking less coke, we are healthier.
Both will benefit.

[kucengemok]

is it possible to use sectorize antenna for 1090mhz? any idea about the construction?

[abcd567]

is it possible to use sectorize antenna for 1090mhz? any idea about the construction?

Do you mean like the cellular sector antennas?

sector antennas.PNG



http://en.wikipedia.org/wiki/Sector_antenna

[kucengemok]

yup..one of my friends is suggesting this new type of antenna to be used for 1090mhz..is it possible?

[STR_EDDS]

hey abcd567, its off topic, can i ask you something?

i needed a antenna for AIS, so i build this one but with a 75 ohm cable, http://nmearouter.com/docs/ais/aerial_mk1_technical.pdf

3 questions:

is it possible to build a Frankling AIS antenna?
is it possible to build the AIS collinear half length? this one is quite big, over 2 meters long.
how do i calculate velocity factor? how long are the segments with a 75 ohm cable?

[SpaxmoidJAm]

1) Yes it is http://www.qsl.net/va3iul/Antenna/Wi...%20Antenna.jpg see this image for dimensions (its still going to be large, bigger than the collinear)

2) Yes it only use two or three elements rather than the four in the PDF you linked wont be as good but it will be shorter.

3)Hopefully the cable you have will have some writing on the side, Google this and find the data sheet for it .This will tell you the velocity factor (far easier than trying to work it out) You then multiply that number by your half or quarter wave length. So for 162Mhz your wavelengths are Full 1850mm Half 925mm Quarter 462mm so if you have a cable will a velocity factor of 85% take you quarter wavelength and multiply it by 0.85 gives you a length of 393mm

Going from that PDF the RG58/U they are using has a velocity factor of 66%

[STR_EDDS]

Thank you!

My 75 ohm sat cable has 0,8 velocity factor.
So quarter length of the 4 segments is 369,6 mm each?

no wonder i have bad reception, i will build another one

[SpaxmoidJAm]

Yes that is the correct length
length.jpg

when your sections are soldered together the length should be measured at the yellow lines, excuse the mickey mouse paint drawing.

[abcd567]

hey abcd567, its off topic, can i ask you something?

i needed a antenna for AIS, so i build this one but with a 75 ohm cable, http://nmearouter.com/docs/ais/aerial_mk1_technical.pdf

3 questions:

is it possible to build a Frankling AIS antenna?
is it possible to build the AIS collinear half length? this one is quite big, over 2 meters long.
how do i calculate velocity factor? how long are the segments with a 75 ohm cable?

1) Yes it is http://www.qsl.net/va3iul/Antenna/Wi...%20Antenna.jpg see this image for dimensions (its still going to be large, bigger than the collinear)

2) Yes it only use two or three elements rather than the four in the PDF you linked wont be as good but it will be shorter.

3)Hopefully the cable you have will have some writing on the side, Google this and find the data sheet for it .This will tell you the velocity factor (far easier than trying to work it out) You then multiply that number by your half or quarter wave length. So for 162Mhz your wavelengths are Full 1850mm Half 925mm Quarter 462mm so if you have a cable will a velocity factor of 85% take you quarter wavelength and multiply it by 0.85 gives you a length of 393mm

Going from that PDF the RG58/U they are using has a velocity factor of 66%

Thank you!

My 75 ohm sat cable has 0,8 velocity factor.
So quarter length of the 4 segments is 369,6 mm each?

no wonder i have bad reception, i will build another one

Yes that is the correct length
[ATTACH=CONFIG]5703[/ATTACH]

when your sections are soldered together the length should be measured at the yellow lines, excuse the mickey mouse paint drawing.

Length of antenna elements depend on frequency/wavelength.
For ADS-B the wavelength is about 1/3 of a meter (275mm), hence antenna are small.
For AIS the wavelength is 1.85 meters (1850mm), six times that of ADS-B. Hence AIS antennas are 6 times taller.

Yes, you can make Franklin for any frequency/wavelength. The element length for AIS = 1/2 wavelength = 925 mm.
A 4 element Franklin will be 4 x 0.925 m = 3.7 meters (3700 mm) high.

CoCo can be made of 2, 4, 6, 8 etc elements. If you want short antenna, use only 2 elements, but gain will be low. Normally 4 or more elements are used for reasonable gain.

CoCo elements are 1/2 wavelength x Velocity factor, NOT 1/4 wavelength x Velocity factor.

The velocity factor does NOT depend on cable impedance (75 ohm or 50 ohm).
It depends on type of insulation.
The RG58 cable normally has PE (PolyEthylene) insulation, which has a velocity factor of 0.66
AIS 162 MHz has a wave length of 1850 mm.
The length of element = 1/2 x 1850 x 0.66 = 611 mm
If you check pdf document, they have used element length (end of braid to end of braid) = 611mm, which matches with the calculations.

You have found your cable has a Velocity Factor of 0.8. Normally cables with FPE (Foamed PolyEthylene) have Velocity factor in the range 0.8 to 0.85. It looks your cable has FPE insulation.

For your cable, the CoCo element length = 1/2 x 1850 mm x 0.8 = 740 mm (end of braid to end of braid). Your CoCo element is longer than the element in pdf document.

[abcd567]

yup..one of my friends is suggesting this new type of antenna to be used for 1090mhz..is it possible?

Please ask your friend to give a link to the manufacturer's/seller's web page for this type of antenna for 1090MHz.

[STR_EDDS]

thank you abcd567, one last question.

i need to tilt the antenna 35° because its to long for my attic.
any bad effects on reception when i do this?

[abcd567]

thank you abcd567, one last question.

i need to tilt the antenna 35° because its to long for my attic.
any bad effects on reception when i do this?

Yes, tilting antenna reduces range & output, but you can minimize the loss by:
(1) Tilting in the direction shown in the attached sketch.
(2) Keep the tilt as small as practically possible.

Antenna Tilt.PNG

[JLD]

In search for inspiration for improving co-linear antennas, I finally bumped into this thread.

http://forum.flightradar24.com/threads/3831-best-antenna?p=53161&viewfull=1#post53161

The "super Antenna" made by 1090 MHZ is indeed interesting.
If you can approximate the corrugated shape of the outside shield to a sine, the additional length you get is 1.22 compared to a straight line.
Guess what, 1/1.22 ~ .82 which is very close to the velocity factor for this type of cable.
This means corrugated cable might be the "perfect" solution to solve the dilemma to achieve at the same time a half wave resonant frequency on the outside shield and a 180 phase shift between extremities.
As soon as I can find some corrugated cable, I will verify with my VNA if the resonant frequency is indeed around 1.22 below the physical length.

The other critical point is the decoupling which very often make co linear antennas very unpredictable when the cable becomes part of the antenna radiation.
Seems the decoupling is also working well here.

JLD

[abcd567]

....snip....

This means corrugated cable might be the "perfect" solution to solve the dilemma to achieve at the same time a half wave resonant frequency on the outside shield and a 180 phase shift between extremities.

......snip.....

As soon as I can find some corrugated cable, I will verify with my VNA if the resonant frequency is indeed around 1.22 below the physical length.

.....snip.....

JLD

Greate! Very promising. Looks like the CoCo puzzle is about to be solved. Waiting for your VNA measurement results.

[JLD]

Well, started to search where to find corrugated coax in EU but does not seem easy!
Any input is appreciated!

Until I find some corrugated, an alternate way to increase electrical length compared to physical length is to use larger diameter tube / coax.
I will measure today what is the correction factor to be used with a few different size of copper tubes and coaxial.
I will start with 11mm coax cable.

JL