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Balun and dipole antenna testing questions

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liletian

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Suppose I want to measure a dipole antenna with an espected impedance of 10+50j. Can I still use regular 50 ohms balun and network analysizer to measure the antenna impedance? Could anyone comment on the measurement?

One more question to use balun as a transformer. Does there exist a balun to transform an unbalance impedance of 10+50j device into a balunced impedance of 10+50j. If there does, could anyone please give me the link of the product?

thanks
 

It just transforms the reference impedance. For example if a 4:1 balun is used to transform 50 ohms to 200 ohms then interpret results on a Smith chart as if reference Z is 200 ohms.

You have got to make sure balun does the unbalance to balance transformation and the dipole doesn't get coupled to feed line or other objects too close to antenna. Keep transmission line right angle to dipole.
 

Attached is a drawing for a matching balun made from 0.141 inch semi-rigid coax and shrink tubing.

Each coax is insulated with shrink tubing then the two are shrink tubed together to make a parallel transmission line with Zo of about 80 ohms and velocity factor of 0.8.

Make open stub (capacitive reactance) and parallel shorted stub (inductive reactance) as required to match 50 ohms to antenna impedance.

It is targeted at balun for UHF and above. I have made one for VHF but it is hard to pull the center conductor partially out to get the open stub length. I had to cut into outside coax shield at open stub point to cut center conductor and pull excess out. Then patch over shield cut opening.

The connection of two center conductor at end adds about 2-3 nH in series with open stub capacitance if you want to add that to calculations. Measured loss is quite low, about 0.05 db at 1 GHz. I made reference dipoles up to 2.4 GHz with this that are within 0.1 db of theoretical performance.

In is also good for testing input Z and general measurement on a balanced input amplifier or mixer.
 

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  • Semi Rigid balun.pdf
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So a 4:1 balun will transform the impedance of 10+10J into 40+40J?
What is a balun? For example,
**broken link removed**

What is this balun made of? It looks like a wideband balun. How do they made it? What is the principle of wide band balun?
Thank you

---------- Post added at 01:34 ---------- Previous post was at 01:30 ----------

I plan to use a very short transmission line to connect the balun to the dipole antenna since the transmission line impedance will be 50 ohms and does not match to the antenna. Do you think it is right?
 

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