Interesting tunable TV antenna (2)

This is probably one of the most interesting but impractical antennas I’ve come across. It might have been very useful in the days when TV had only one or two channels but how on earth would men be able to channel hop when each time you first have to get up and tune your antenna? Maybe in those days they did’?t know how to design wideband UHF antennas with > 6 dB gain?

However, it is still a very fascinating idea – having a tunable antenna, so after some investigation I think I might have figured out how it works.

I made a model and simulated the antenna with different tuning positions and the resonant frequency increased as I increased the tuning stub (similar to pulling it upward) as shown in the graph below.

S11 vs Frequency for different tuning lengths. The frequency increased as the antenna arms were shortened.

S11 vs Frequency for different tuning lengths. The frequency increased as the antenna arms were shortened.

Radiation pattern of the antenna tuned to 600 MHz with maximum gain of 6.2 dBi.

Radiation pattern of the antenna tuned to 600 MHz with maximum gain of 6.2 dBi.

The gain of the antenna is +- 6 dB as shown in the image above. This is quite high for a folded dipole but it seems like a very clever cross between a folded dipole and a V-dipole. Another interesting observation was that almost no currents flowed on the tuning stub which means it has almost no effect on radiation.

The length of the loop is about 3 lambda at the resonant frequency thus instead of using a standard folded dipole with one wave length circumference it operates in a different resonant mode with a V-dipole-like angle making it more directive.

If I had no choice but to use this antenna I would have probably built a remote control stepping motor to tune the antenna to the right frequency on each channel hop. Maybe I must still do this and invite a couple of friends over to come watch TV and channel hop at my house!

Read the previous interesting tunable TV antenna post here.

Author: Robert Kellerman

Leave a Reply

Your email address will not be published. Required fields are marked *