Stacking UHF TV yagis

[VK2KRR]

How would one determine the best stacking distance for a multi frequency UHF TV yagi ? In particular the Hills 91SFX ? Covers Channels 21 - 69 (480 to 816 MHz).

I've heard of different methods, like stack the length of the boom distance between antennas? Or 96% of the wavelength of the lowest freq?

May have to try experimenting with different distances myself perhaps and see how it goes.

[VK3RX]

Some years back Hills had a document titled something like "Stacking the odds in your favour" which I had a copy of but can't for the life of me locate it.

This might help: http://www.tesc.com.au/stagger.htm

[VK2KRR]

Thanks Damien, I have seen that page, and it also has stacking for gain, although fairly old info I think, but still gives ideas.

[VK2XSO]

I'm wondering if you're thinking in terms of them as a phased array acting as one antenna or as a spatial diversity system.
For spatial diversity systems it's a minimum of two wavelengths of the lowest frequency.

[VK2KRR]

Here is an interesting page I found with some antenna stacking test links - http://www.atechfabrication.com/reception_solutions.htm

VK2XSO I am just trying to get more forward gain and narrower main beamwidth for long distance reception and attenuating out signals Im not pointing at that may be on same freq.

[VK5PJ]

Leigh,
one word of warning, a lot of the driving force for stacking antennas for TV was to eliminate ghosting on analog reception on a single channel. To get GAIN the TV installers will just chuck in a masthead amp, which do a good job but have other problems for hams. If it was me, I would use a single yagi as you will not be able to predict the radiation pattern of a stacked pair over that wide a frequency range and you may end up with exactly what you did NOT want in the first place (a messy pattern) and it cost you twice the money for a radiation pattern like a porkupine.

my 2c's

Peter, vk5pj