along the ecliptic is required.
Incidentally, I've seen ads for transparent DBS dishes, but only for
the UK.
http://www.maplin.co.uk/DiscontinuedModule.aspx?ModuleNo=47234
http://www.pulsat.com/satellite/site/details.php?product_id=330
Nothing available across the pond. What inspired transparent dishes
in UK?
--
Jeff Liebermann
Planning laws and building covenants can be very odd here. Many old
buildings in towns and villages are protected by a National Trust 'listing'.
Depending on the level of the listing, all sorts of provisions are made
about protecting the exterior appearance, and with high level listings, even
the internal features, down to decor in some cases. On buildings like this,
and indeed on some new buildings, the likes of satellite dishes are
expressly forbidden, particularly if they impact on the 'public' face of the
building. As far as I know, transparent dishes were developed to try to get
around this, and I believe some planners and listing inspectors, were
sympathetic to their use. I don't know how successful DBS has been over
there, but here, probably 60% or more of houses in any given street, have a
dish bolted on them, so disguise is quite a big issue in some areas. To that
end, I believe that there were some 'microwave friendly' paints developed as
well, to allow the dish to 'disappear' chameleon-fashion.
The coating on these transparent dishes is just a very thin vapour deposited
metalic coat as far as I recall reading somewhere long ago. I guess that
it's just the same sort of thing as the 'transparent' electrodes on LCD and
plasma screens.
As to the rotation of the LNB for linearly polarised skew correction, all of
the DBS dishes here are offset eliptical types, and have a fixed horizontal
attitude. Adjustment for azimuth and elevation is carried out by the X - Y
mounting bracket, but skew is carried out by rotating the LNB itself in its
clamp, which is a split circle around the waveguide throat, with a screw to
pinch it up. A right hand twist (looking from the front) of around 10 deg
is about right for the UK, but I guess with the USA being rather wider than
us, your range of required skew correction could be a lot more than that,
and even in both directions if your birds are located centrally.
In all of the LNBs that I have looked in, the probes are just pcb tracks at
90 deg to one another. There is then a 'steering' transistor, controlled by
the level of the supply voltage, in each probe channel, ahead of the RF amp,
to determine which polarisation is being listened to.
Arfa