Wright's Aerials
Playing about with a DAB aerial

Digital Audio Broadcasting uses roughly the same frequencies as some of the old 405-line VHF TV transmissions.

For some time I have been on the lookout for an old Band III TV aerial so that I could experiment with DAB. Yesterday I found one. It was a 9-element yagi and it had spent the last forty years in a loft, so it was in good condition. I connected it to a length of coax, and believe me it seemed funny working on a Belling-Lee ITV aerial. The last time I did that would be about 1967, I should think. I took the aerial to the high point in my back yard, where I have good views in several directions, and tried it out. It didn't work. It was awful. Time for a rethink.

The aerial was originally for channel 10, which was around 200Mc/s* I think. Anyway, that suggested that the elements and spacing would be about 10% too long, which is a lot really. I worked out the proper dimensions for 222MHz and the result was that I shortened the elements by 70mm. I reduced the spacing between the reflector and dipole by 25mm and between the dipole and first director by 30mm. I didn't bother altering the other directors. After that the aerial worked pretty well, with about 6dB more gain than a four element Antiference DAB aerial. The latter is wideband of course, in case the full DAB band ever gets used, so the gain isn't very good really.

Although the new home brewed aerial brought in a Winter Hill multiplex at quite good strength according to the spectrum analyzer, reception on the DAB tuner was little better than with the Antiference because we have a DAB transmitter 1km away and the tuner couldn't discriminate. Not surprising really because the local is 80dB above Winter Hill!

Time to stack two DAB aerials to discriminate against the local Transmitter. After all, I really need to listen to a load of inane commercial radio stations from Lancashire!

*I did that for effect. Don't write in.

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