Re: X Beam aerials


"charles" <charles@xxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:4f28cbed22charles@xxxxxxxxxxxxxxxxxxxxxxxxxx
In article <46fb5ceb$0$313$4d4eb98e@xxxxxxxxxxxxxxxxxxx>,
'X-beam' aerials as you call them, often called 'High Gain' aerials, tend
to have a narrower forward lobe than a conventional Yagi. However, to
compensate, they tend to have odd rear lobes which vary from channel to
channel. If there are strong reflections from the rear, high gain aerials
can show ghosting sometimes only on one channel. If, on the other hand
the
reflection is from the front and to the side of the main signal, the
narrow
front lobe can often reject the 'ghost'.

I've always found the performance of large complex yagi-derived designs to
be pretty poor as far as directivity is concerned, especially in Gp A.


A carefully set up pair of aerials can be arranged to null out reception
in
any given direction, but again this will vary from channel to channel.
It's a very time consuming business.
It's not that bad when you get used to it. IF the ghosting or CCI is coming
from a specific direction the inter-aerial spacing can be worked out for the
centre frequency. If there are a lot of sources of ghosting or CCI I usually
put the two aerials a couple of foot apart and hope for the best. This can
be surprisingly effective. It seems to work better than logic says it
should.


Another way of rejecting signals from the rear is to use a log periodic or
a grid (or bow-tie) aerial. Of course, these have the drawback of low
gain, but it's always possible to amplify a low, but clean, signal.
Vertically polarised grids seem to reject well from the sides. Other than
that I don't like 'em at all. They all seem to have very poor gain about
ch60.

Bill


.

Relevant Pages

  • Re: Snap Crackle and Pop
    ... The aerial was a top of the range High Gain something or other with a CAI test certificate, can't remember what make just now, but it was the best one they had and it said suitable for loft installation. ... As it is in the roof I bought a new 25db gain amp from a local installer that I know, I've been using amps on loft based aerials for years with terrestrial signals without any problems whatsoever. ...
    (uk.tech.digital-tv)
  • Re: Snap Crackle and Pop
    ... The aerial was a top of the range High Gain something or other with a CAI test certificate, can't remember what make just now, but it was the best one they had and it said suitable for loft installation. ... As it is in the roof I bought a new 25db gain amp from a local installer that I know, I've been using amps on loft based aerials for years with terrestrial signals without any problems whatsoever. ...
    (uk.tech.digital-tv)
  • Re: Joining 2 aerials
    ... Set aerial at 200 degrees pointing to Bluebell Hill,thing is i ... don't get channel 5 on the 3 freeview boxes and on our 'ordinary' TV its ... Anyway my 2 old aerials where semi decent and i'm wondering if i can put ... According to Freeview site CP broadcasts fewer channels, ...
    (uk.tech.digital-tv)
  • Re: Slightly dumb aerial questions
    ... the inner core to the element ... it doesn't matter which terminal I connect ... Some early aerials sold locally were peaked for the part of the channel ...
    (uk.tech.broadcast)
  • Re: Snap Crackle and Pop
    ... You have problems with Dave which is on channel 42 Mux C at c 642Mhz ... The different muxes are broadcast from aerials on the mast at different ... peeping round the gable of your house while the old analog aerials may ... and some being poor or terrrible. ...
    (uk.tech.digital-tv)