On 07/04/2015 10:33, Capitol wrote:
Martin Brown wrote:
On 06/04/2015 23:59, tony sayer wrote:
In article , Capitol
scribeth thus

Does anyone have any experience of these? The plots I've seen seem to
have very variable gain/frequency responses.

Whatever are you up to with that sort of thing?..

A difficult to manufacture DIY aerial?


I am currently building a pigeon proof TV aerial, a double biquad.
I can mount this under the eaves so the bloody pigeons can't perch on it
and fight. Our pigeons IMO resemble small turkeys which I blame on the
deranged neighbour who feeds them. They destroyed the last new log
periodic TV aerial in 3 months and next doors a few months later.

Unless you are a big fan of Dave why not install FreeSat? I doubt if
pigeons can do much harm to a dish beyond adding "dielectric coating".

next doors weedy looking replacement 6 months at the outside. I pigeon
proofed the original Yagi with spikes, this worked within limits until
they destroyed the feeder cable at Xmas. They also crap all over the
roof causing more moss growth and the patio, which she complains about.
Preliminary tests on the double biquad are promising. I haven't
attempted to measure the gain bandwidth yet but may get round to it this
week in a very crude manner. I came across fractal antennae so
investigated the theory and discovered there really wasn't a predictive
one. As this group has a wide range if interests, I thought I'd ask here
to see if there was any hands on experience. NEC programs require that
you start with an empirical geometry and then you can calculate the
performance. On fractals the geometric limits are infinite, so you end
up doing the calculations for ever. Aerials always end up as cut and try
IME, it's just like trying to lay out frequency synthesisers in UHF radios.

How well it works depends on local signal levels. Where I live a foot of
random wire will do almost as well as a real Yagi antenna.

--
Regards,
Martin Brown