Re: Slightly OT. Stacking wideband TV yagi's

Robin wrote:
"Marky" <bigfathairybiker@xxxxxxxxxxx> wrote in message news:43172284$0$13706$4d4eb98e@xxxxxxxxxxxxxxxxxxxxxx

"harrogate2" <harrogate2@xxxxxxxxxxxx> wrote in message news:RJIQe.3305$x4.1501@xxxxxxxxxxxxxxxxxxxxxxx

1.     If you have a 12dB antenna, then going to a stacked pair of 48
eles you will only get about 17-18dB gain, and that is
      unlikely to give you a decent picture unless you have a
ghosting problem.
2.    You stack only if vertically polarised - you bay if horizontal.
3.    I assume we are talking TV aerials here and not 70cms?


Since when did ghosting get resolved by better gain!?


Higher gain, so the beamwidth will be smaller,
Call the multipath reflections noise. The higher gain will result in a higher signal to noise ratio.

With Loads of "wanted" signal at the antenna, an attenuator can then be fitted to reduce the multipath reflections to a level that is lower than the noise floor of the receiver, then the ghosting will disappear.

The ghosting is caused by the fact that UHF RF gets reflected, the path for the reflected signal is longer than the direct signal, so takes longer to reach the RX. hence the ghost image slightly to the right of the direct image, hope this helps.

Robin


In some locations the reflected signal can be stronger than the direct signal. The direct signal will then appear as a 'pre-ghost' image slightly to the left of the reflected image.
--
;-)
73 de Frank Turner-Smith G3VKI - mine's a pint.
http://turner-smith.co.uk
.

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