Tuesday, June 16, 2015

A masterpiece - I0QM real BALUN for Yagi Antennas

As You probably know, there is lot's of projects, descriptions and models of more less real balance-unbalance transformers on the web.
Below You can see my example of I0QM real balun for monoband pure resistive Yagi's.
This solution has been widely tested by me with various 6m and 4m Yagis with perfect results compared to so called "choke baluns".

General idea

First implemented in my 6m YU7EF yagi 10yrs a go, still in use with EME antenna. No any overheating, stable SWR/RL and probably (as tested) lower out of band spurs from Russian video's. Pics show resonance in 6m band, and increasing SWR out of band edge below 50MHz, as well as above 51MHz. Look below.

A hint: Various manufacturers of coaxial cables ensure You that their cable has known velocity factor. The fact is, that's a lie.
Nowadays almost all cables are manufactured you know where :-)
In this example ordinary RG213 type with known Vf~0,66 was used.
Calculated lenghts were out of space, with resonance at 48Mhz. Do we need to have R1 TV frequency resonant balun? Certainly not! :-) Try it and measure before final sealing. Cut small part's each end, and trim the lenght until You get perfect 6m band response. That's it!

Coaxial end sealing box - both shields were tinned, and soldered together (gently!) N connector was set in the box, and inner conductor soldered. To get proper shield with N connector small strip of Cu track was soldered as seen on pics. After cooling, box was sealed with epoxy resin.

SWR sweep - balun terminated with ordinary 50Ohm resistance, measurements taken with AA-170 Analyzer :

Almost perfect R/X response :

All parameters :

This simply works! Thank's and compliments to I0QM for this "must have" design.

Good luck with your designs.

No comments:

Post a Comment