How to Build a 3 Element Yagi Antenna and Analyze It with Free SDR Software

[houlahound]

Just sharing, to explore EM theory you can build a highly directional 3 element yagi antenna and usecfree SDR software to analyse it. The only cost is a SDR receiver if you want quantitative data.If someone wants to edit me I will write a detailed method and parts list including a tone generator and RF transmitter diagram etc with about 10 parts, no soldering needs.

Super cool non trivial physics made easy.

 

[berkeman]

highly directional 3 element yagi antenna

I wouldn't call a 3-element Yagi antenna "highly directional". They are usually around 6dBi-7dBi or so...

http://www.dx-antennas.com/Yagi3.htm

http://www.wc7i.com/3_element_yagi.htm

 

[houlahound]

At 90 degrees he n was -120 at zero degrees gain was -70 at 180 degrees gain was -80... That is highly directional in my opinion.

The goal of the project is to optimise that and or add more elements.

Angles are rel to omnidirectional VHF transmitter at very low power.

 

[berkeman]

At 90 degrees he n was -120 at zero degrees gain was -70 at 180 degrees gain was -80... That is highly directional in my opinion.

The goal of the project is to optimise that and or add more elements.

Angles are rel to omnidirectional VHF transmitter at very low power.

Directionality is not so much about comparing forward power to orthogonal power -- most Yagis will have good cancellation at 90 degrees. But as you add more elements, you get more directionality:

 

[davenn]

Directionality is not so much about comparing forward power to orthogonal power -- most Yagis will have good cancellation at 90 degrees. :

indeed. even a plain dipole has near zero radiation off its endsDave

 

[houlahound]

The forward to back ratio was the key parameter in this project.
Curious, is it valid to take the ratio of two db measurements at different angles to give a measure of gain or just use the difference?

What the measurement tool reads is in reference to what is unclear.The -120 db is just the noise floor which changes every other day, -120db relative to what??

 

[davenn]

The -120 db is just the noise floor which changes every other day, -120db relative to what??

you missed the important reference -120dBm not -120dB
actually its quite easy to get a receiver sensitivity to -120dBm

have a look at this site ...
http://www.radio-electronics.com/info/rf-technology-design/rf-noise-sensitivity/noise-floor.php

and this one ...
http://cp.literature.agilent.com/litweb/pdf/5952-8255E.pdf

there are dozens of others

here's a diagram I drew up many yrs ago using various references, when I was deep into
microwave band communications

Dave

 

[houlahound]

Theoretical and measured rarely agree in practical antennas. I would like to see your measured values.

The point of the project is this can be done for under $30 with household equipment.

Correction under $10 and that cost is for the coax connectors.

 

[houlahound]

Dave I do appreciate the links, will read them.

 

[berkeman]

Theoretical and measured rarely agree in practical antennas.

Not when you use quality antenna simulation software.

Are you by chance located in Northern California? Pacificon is coming up soon (amateur radio annual conference for NorCal), and the Friday seminar is a great antenna seminar. I highly recommend it and the ARRL Antenna Handbook...

www.pacificon.org

.

 

[houlahound]

not in US, would love to go tho. any recommendations on design software?

 

[houlahound]

sample data, hope you can view it;

SDR interface;

noise