how to make twin staked dipole

[YellowFM]

I found a detailed guide how to make a dipole http://jugglingpirate.net/dipole-aerial ... broadcast/ , and here is how to combine them in a stack ?

[LockingNut]

Are you asking or telling lol cos juggling don't tell you how to make a double.

[SOTS 87 7]

Are you asking or telling lol cos juggling don't tell you how to make a double.

Hmmm, I noticed that. Would be interesting to see other peoples methods on how to make a double and what the most effective is.

[LockingNut]

Are you asking or telling lol cos juggling don't tell you how to make a double.

Hmmm, I noticed that. Would be interesting to see other peoples methods on how to make a double and what the most effective is.

That's exactly what I was thinking, would be interesting to hear some peoples different formulas...this formula is defo a good starting point for the dipoles themselves as the measurement allows room for shaving down the elements if need be rather than being to short and having to attach things on the ends to see if the swr rises or drops...but as we know the part that makes the double is the length of the feeder cables so...answers/formulas on a postcard gents!!!

[s2000]

Never built one myself, prefer building slim jims but I found this page:

http://hevirred.blogspot.co.uk/2013/11/ ... vider.html

I'm just wondering, is there any technical reason why the guy appears to have insulated the mast from the boom arms (with the chopping block)?

[pjeva]

There are many different ways to do stacking, i will try to find some study about different possibilities and field forming later. Basic thing is that you make two exactly same antennas, with same impedance and resonance. If you have two identical antennas, lets say gamma matched dipoles, both 50 ohm impedance, if they both have same feeder cables, they will represent 25 ohm impedance to transmitter if you connect them in parallel. So, you need some impedance transformer to change antenna system impedance of 25 ohm to 50 ohm which you have on output of transmitter. In professional systems, it is common to use lambda/4 impedance transformer. It means that you use coaxial conductor of aome impedance and lenght of lambda/4 to transform impedance. Formula to calculate its impedance is:

ImpedanceX=squareroot(txImp × antennaImp)

In numbers:

ImpedanceX = squareroot(50ohm × 25ohm)

ImpedanceX = squareroot(1250)= 35,35ohm

Since you cannot buy coaxial cable with impedance of 35,35 ohm, you must build it. Two parallel cables of 75ohm and lambda/4 lenght will do the job, but you can also make one more close to 35,35ohm using square aluminium tube with INTERNAL dimension of 1" and copper tube of appropriate diameter. If you need to make it more broadband, you can make transformation twice (50ohm to 40ohm and then 40ohm to 25ohm for example). To calculate diameters of copper tube use AppCAD software. I will try to upload pictures later...