Satgen425  Apartment Operating  by GM4IHJ   (BID SGEN425)    17 May 97

The resident of a flat or apartment who wishes to operate on the
satellite bands has lots of problems. What can he do about it ? The 
following reviews a few point, using as an example one of the worst
case situations - operating Ao16 or Ao19 2m up 70 cms down AFSK PSK.

First to clear up a misconception whereby several apartment dwellers
have read my sgen 423 and assumed they can get by with a single tilted
colinear unattended on the roof. This misses the point that the
colinear has to lean in a different azimuth plane for different orbits
This scheme is OK for a backyard op who sets the colinear tilt and
azimuth plane of tilt,before each high elevation pass. But it is no go
on top of an apartment where the would be operator does not have
regular access. But flat dwellers should not despair. 70% of all
Ao16/19 orbits can be received on a vertical colinear. All you miss is
the central parts of the high elevation passes when signal reception
is irregular.

But 2m Tx desenses the 70cm downlink. So you must have a 70 cm cavity
filter directly on the back of the receive antenna.

It also helps to convert the 70cms to 29 MHz immediately after the
receive filter to reduce the effect of 2m feed across to the receive
coax. The combination of a filter followed by a converter to HF has
proved to be much more effective than the 70cm mast head pre amp which
some authorities recommmend. At IHJ blocking and ringing in the pre
amps tried , made them a hindrance rather than a help.

If you can get a 70cm converter with low mixer noise that also helps
because the PSK downlinks seem to be inherently noisy due to imprecise
0/180 degree phase shift. So any signal to noise boost you can get, is
useful.

Reception is the most important part. Please do not attempt
transmission until you have reasonable reception, and , when you do
transmit be aware that your poor location may need a lot more uplink
power than an open field site. QRP from an apartment is a non starter.
You may be able to put a colinear on the roof for 2m . If you can get
it ,both your Tx and reception feeder lines should be of the highest
quality coax you can get your hands on, particularly if you have to
bring 70cm receive right down to the operating position , because you
have not got a 436/29 MHz converter at the masthead.

At IHJ in the old Oscar 8J days, roof top antennas were simply not
possible . Even so 2m up 70cm down working was achieved using a pair
of simple 2m yagis pointing, one through a south facing window and,
the other through a north facing window - through the glass !
Alongside the 2m yagis, 70cm reception was via home brew short back
fire antennas, one at each window . Simple coax switches were used to
change from north to south antennas as desired. Note for potential
house builders. IHJs retirement home has large roof skylight windows
facing north and south , which allow comfortable operating even with
fragile homebrew GHz band equipment, what ever the Scottish weather.