best antenna

[abcd567]

Simulation Results Franklin 4-element by 4nec2 software gives Gain =6.19 dBi & SWR=1.17:

Wire dia = 3mm
Gap between stub wires =6 mm (center-to-center distance between stub wires = 1.5 mm + 6 mm + 1.5 mm = 9 mm)
Optimum cable tap position = 45 mm from open end (or 69 mm -45 mm = 24 mm from shorted end)

franklin-4 element-3mm wire 6mm gap - pattern gain swr-R1.png . franklin-4 element-3mm wire 6mm gap - Sweep for Tap position-R1.png . franklin-4 element-3mm wire 6mm gap - input data-R1.png

[abcd567]

Same wire data as above, simulated in software MMANA-GAL, gives Gain = 7.35 dBi, & very high SWR = 133 !!!!!!

Which software to trust????

Wire dia = 3mm
Gap between stub wires =6 mm (center-to-center distance between stub wires = 1.5 mm + 6 mm + 1.5 mm = 9 mm)
Optimum cable tap position = 45 mm from open end (or 69 mm -45 mm = 24 mm from shorted end)


franklin 4element 3mm wire 6mm gap layout - mmna-gal.png. franklin 4element 3mm wire 6mm gap pattern mmna-gal.png . franklin 4element 3mm wire 6mm gap wire data mmna-gal.png

[peterhr]

The guys at http://forum.flightradar24.com/threa...-Over-The-IRAN would like a solution ... an easy to build reliable antenna, that doesn't need esoteric bits.

[abcd567]

Another Simple Antenna:
http://qsl.net/py4zbz/adsb.htm#e

One more here:
http://www.lesaunier.com/htm/franklin1_eng.htm

cable tap arrangement: http://www.lesaunier.com/images/radi...franklin_8.jpg

[abcd567]

Another, similar to one above
http://adsbradar.ru/antenna-franklin-1090mhz

[SpaxmoidJAm]

What about a strait forward dipole, it doesn't get any easier than that.

With collinear aerial yes you do need to be exact with your measurements and know your exact velocity factor to do that. How ever of all the ones i have made and haven't been exact and just thrown them together they still work quite well and generally better than you think. Certainly for the cost of the coax worth ago.

[abcd567]

…

What about a strait forward… dipole, it doesn't get any easier than that.......

My very first antenna was a 1/2 wavelength Dipole.
Gain 2.2 dBi, impedance=75 ohms, hence SWR=1 : )

Because of it's low gain (2.2 dBi) & long run of coax (50 feet/15m as antenna & desktop are in different rooms of my apartment), I had to add an inline amplifier (13 - 18 dB).

[Forum Error]

Thank you all for a very interesting thread!

I would like to add some quotes from some of the material I've been reading recently:

LENGTH AND PHASING.—Although the 1/2 wavelength is the basis for the collinear element,
you will find that greater lengths are often used. Effective arrays of this type have been constructed in
which the elements are 0.7 and even 0.8 wavelength long. This type of array provides efficient operation
at more than one frequency or over a wider frequency range. Whatever length is decided upon, all of the
elements in a particular array should closely adhere to that length. If elements of different lengths are
combined, current phasing and distribution are changed, throwing the system out of balance and seriously
affecting the radiation pattern.

SPACING.—The lower relative efficiency of collinear arrays of many elements, compared with
other multi-element arrays, relates directly to spacing and mutual impedance effects. Mutual impedance is
an important factor to be considered when any two elements are parallel and are spaced so that
considerable coupling is between them. There is very little mutual impedance between collinear sections.
Where impedance does exist, it is caused by the coupling between the ends of adjacent elements. Placing
the ends of elements close together is frequently necessary because of construction problems, especially
where long lengths of wire are involved.

The effects of spacing and the advantages of proper spacing can be demonstrated by some practical
examples. A collinear array consisting of two half-wave elements with 1/4-wavelength spacing between
centers has a gain of 1.8 dB. If the ends of these same dipoles are separated so that the distance from
center to center is 3/4 wavelengths and they are driven from the same source, the gain increases to
approximately 2.9 dB.

A three-dipole array with negligible spacing between elements gives a gain of 3.3 dB. In other
words, when two elements are used with wider spacing, the gain obtained is approximately equal to the
gain obtainable from three elements with close spacing. The spacing of this array permits simpler
construction, since only two dipoles are used. It also allows the antenna to occupy less space.
Construction problems usually dictate small-array spacing.

The above from: http://www.navymars.org/national/tra.../14182_ch4.pdf
More on element spacing at: http://www.w8ji.com/stacking_broadside_collinear.htm

It seems most people agree that a "free-space" tuned CoCo will be detuned by placing it inside a plastic tube. However, if this detuning makes the antenna "appear" too long, it might not be disastrous, because longer-than-λ/2 elements are not necessarily that bad? And with a "too long" antenna, the apparent element spacing would also be longer, which might actually be beneficial. All in all, to PVC or not to PVC might be a moot point?

Cheers,

A lurker

[peterhr]

A reasonable design target is 5DB antenna gain and an antenna amplifier like the one shown. The amplifier does two things, one is gives some compensation for impedence mismatching (presuming the amplifier has a fairly high input and low output impedance) and makes it possible to use a downfeed of somewhat unknown quality. I do 'like' the franklin designs (not that I have built one) because of their simplicity and repeatability ... but they would need DC voltage decoupling between the amplifier and antenna.

[abcd567]

A reasonable design target is 5DB antenna gain and an antenna amplifier like the one shown. The amplifier does two things, one is gives some compensation for impedence mismatching (presuming the amplifier has a fairly high input and low output impedance) and makes it possible to use a downfeed of somewhat unknown quality. I do 'like' the franklin designs (not that I have built one) because of their simplicity and repeatability ... but they would need DC voltage decoupling between the amplifier and antenna.

You have yourself solved the DC Blocking problem in an easy & cheap (£3.99) way in your post # 1282 on page 129

http://www.ebay.co.uk/itm/171258939281

DC Block-R.jpg

2 X F-THROUGH CONNECTOR - DC BLOCK

[abcd567]

@Trigger
@HermanZA

Here is your franklin with 3mm dia wire, 6mm gap by wrapping wire around 6mm drill bit
Good news Gain=6.86 SWR=1.52

NOTE: The impedance matching stub (middle one) is slightly bigger than phasing stubs (upper & lower ones)
Reason - to meet the following two conditions:

(1) Phasing stub:
Total wire length (two horizontal parts + round part) should be 1/2 wavelength = 138mm

(2) Matching stub:
Each horizontal length should be 1/4 wavelength = 69 mm.
Hence total wire length of horizontal parts alone should be = 2 x 69 = 138 mm.
The total wire length of matching stub (including round part) should be 138 mm +length of round part.
Length of round part = pi x round part diameter/2 = 3.14 x (1.5+6+1.5)/2 =14 mm.
Hence total wire length for Matching stub = 138 mm + 14 mm = 152 mm

Do not get confused by theory above. Ignore it and simply follow the dimensions given in the sketch I have drawn below, and it is done.

franklin 3mm dia wire-6mm gap stub-how-to.jpg . franklin-4E-3mm wire-6mm gap-round bend-gain-pattern.png . franklin-4E-3mm wire-6mm gap-round bend-swr sweep.png . franklin-4E-3mm wire-6mm gap-round bend-input wire data.png

[peterhr]

Indeedy!
I suppose I'll have to add your Franklin design + blocker + amp + downlead + voltage Injector + pigtail to a new 'Cheap antenna for FR24' thread - something I don't really want to 'own' since there are others much more interested in such things than I am. My interest is really in a simple cheap RPI based receiver and it could really do with a excellent simple cheap antenna design to go with it that doesn't require the reader to plough through over a thousand posts to get the info.

[abcd567]

Indeedy!
I suppose I'll have to add your Franklin design + blocker + amp + downlead + voltage Injector + pigtail to a new 'Cheap antenna for FR24' thread - something I don't really want to 'own' since there are others much more interested in such things than I am. My interest is really in a simple cheap RPI based receiver and it could really do with a excellent simple cheap antenna design to go with it that doesn't require the reader to plough through over a thousand posts to get the info.

Wait till more than one forum members built the latest Franklin (3mm wire dia, 6mm gap), put it on trial run, and report back results.

[abcd567]

I checked Home Depot and Canadian Tire in my area, they dont have 3mm dia (9AWG) wire. The largest they have is 12AWG (2 mm dia). I will search other stores on this weekend. If I get 3mm dia wire, I will make the Franklin. Uptill now I have been using core of RG6 cable, which is 18AWG (1 mm dia) to make wire antennas. Since my antennas are indoor, no wind, 1 mm dia wire is ok. Due to it being thin, it's bending, cutting & narrow gaps are easy to form.

[HermanZA]

I will attempt this coming weekend, to make a Franklin as per the latest specs. Will advise results, once I have to share. The 3mm rods I have, are 400mm in length, not sure if I will be able to find any longer 3mm wire/rods in this 1-horse-town of mine.