Satgen 646  S Band SatReception by GM4IHJ   (BID SGEN646) 2001-08-11

AO40 is proving to be an interesting target for testing reception of
its S Band downlink in a variety of somewhat restricted locations :-
indoors and out; with local near line of sight obstructions,  static
and mobile; and, weather factors.

Indoor operation is never easy, but sometimes there is no
alternative. However tests show that it can be done with inobtrusive
small antennas, over a sizeable part of the orbit . At IHJ a simple 
pair of 6 turn helixes gives a rough match to a 50 ohm cable, and
when aimed through a double glazed south facing window , useful
reception is possible over an arc of about 50 degrees either side of
the plane normal to the window , provided the squint angle is modest
and local buildings do not obstruct the line of sight. 

It is appreciated that this always south facing sitution does not
apply to station much nearer the equator than IHJ. Here in Scotland
AO40 appears in the southern sky between Az 100 round through south
to Az 260, at elevations generally in the bracket 10 to 30 degrees.
Not everyone else will have this simple situation , but they should
be able to see some part of the satellites orbit through a window ,
and if they can, they should get adequate reception for QSOs.

There will be some multipath interference if your window faces
buildings near the line of sight or, much worse as at IHJ, moving
traffic on the road 20 ft beyond the antenna. Moving the antenna
outdoors onto the garage roof north of the house provided immediate
relief from this problem , but at the expense of losing all contacts
below 15 degrees elevation.

No attempt has been made to provide antenna rotators in either
elevation or training. It simply is not necessary. AO40 usually moves
quite slowly across the sky and is easily tracked, if the simple
antenna is realigned every half hour or so.

As yet it has not been possible to check the full effect of Scottish
weather patterns on AO40 S Band reception. There is clearly some
signal depreciation in heavy rain , but at other times the signal in
rain appears to be enhanced. Indeed comparisons with attenuation on
signals from 10 Ghz Direct TV sats , watching both signals on FFT
displays, suggests that weather is less of a problem at S Band than
it is at higher frequencies. But this is clearly an experiment which
needs to be followed over all the seasons of the year and all the
varied weather patterns.

All things considered, it would seem that S Band AO40 is not outside
the reach of apartment dwellers. At IHJ access on the uplink is being
examined with a colinear 70 cm antenna disguised as a flag pole and
placed outside the window. So, provided she who must be obeyed, does
not object to a small antenna on the window sill among the knick
knacks and china ducks, plus a smart external mini flag pole. AO40
may be in reach of all, even if we never hear from the lower
frequency bands.