Satgen346  Operating Fo20  Mode JA  Pt1   by GM4IHJ           11th Nov 95

Back in 1978 Amsat launched Oscar 8, which in addition to a Mode A
transponder, carried the very first mode J transponder 145 up 435 down.
Mode J had a dificult start , there were no commercial 435 MHz
transceivers or receivers for CW or SSB, but gradually a core of real
satellite DXers conquered its much more demanding operational features,
and in a year or so , this Japanese built transponder became a firm
favourite with many Amsat stalwarts. For most satellite operators however,
Mode J resided firmly in the "too difficult " category.
Has this situation changed 17 years later? With Fo20 mode JA ( A for
Analog) available every day in a relatively high altitude orbit from which
it is capable of providing excellent DX contacts between stations more
than 8000 kms apart , Eg Western USA and Canada to Western Europe .
No it has not. JA still attracts very few users. Which is surprising when
one notes that JA should be the training route for all those wishing to go
from the simple RS birds up to the much more difficult mode JD digital
Pacsats and Uosats. Equally obvious Mode B 435 up 145 down is being slowly
destroyed by 145 MHz, crowding and miscellaneous noise from every kind of
electronic gadget. While mode J is much cleaner , and might be a secure
band for the future if ordinary satellite operators could be told how to
overcome some of its "apparently unforgiving features" such as high
doppler, difficult reception ( compared with 2m ) and need for much more
accurate antenna tracking.

Mode J operating problems start at the receiver. Here at IHJ 5 different
combinations have been tried. The simple FRG 9600 Rx lacks good
performance and must have a good pre amp in front of it if it is to hear
anything useful. The 435 transceivers are better ( but not much ) and
worse still they are very expensive. Best results at IHJ have been
achieved using 435/28 converters connected to a good HF communications
receiver. With a Microwave Modules converter there is good weak signal
performance and this is enhanced by the smooth tuning of the HF receiver,
and if like IHJ you are lucky enough to still have one of the original
Jamsat converter from 1980, you can get even better results. Then if you
are rich enough to add a good LANDWEHR pre amp at the antenna you should
have the best possible reception.
All the JA user then needs is a good antenna. Purists will suggest that
something like a 10 XY yagi providing switchable polarisation with 
azimuth and elevation training rotators on the mast, is the perfect kit.
But this is not really necessary unless you are going for mode J on a
Phase 3 long range orbiter that stays at high elevation for long periods.
Fo20 spends 80% of it time in range of your station at low elevation .
Indeed the best DX is always at low elevation. Therefore an elevation
rotator is something of a luxury. 
So the compromise at IHJ has been, Jamsat converter and HF Rx fed by a 20
element long yagi with horizontal polarisation only , plus a Landwehr pre
amp. This may need more precise antenna pointing, but with modern tracking
software using the computers available in 1995, being a clear improvement
over the 1978 manual perspex overlay of track from EQX, above a polar gc
map, a narrow antenna beam is not a problem.