Satgen350  Operating Fo20 Mode JA Pt5   by GM4IHJ          9 Dec 95

Just what else is there to learn about operating Mode JA ? Before going on
to discuss operating procedures there is one technical point that must be
mentioned. Your Uplink 3rd harmonic on 145 MHz = 435 MHz, somewhere near
your receive frequency for the downlink. You can check whether you get
break through , by listening to your Rx whilst you key your transmitter on
several different frequencies. You may here a klick as you start to key,
that is not too important , but if your received noise level goes down
when your key is pressed even when the SAT IS BELOW YOUR HORIZON, you have
got break through. 

This can be corrected by fitting a 435 MHz narrow band filter in your
receiver antenna feed line. With a simple check you may find no break
through until you vary the azimuth of your antennas imitating a satellite
pass. At IHJ there are two bearings on which break through occurs reducing
Rx noise and sometimes producing actual spurious signals on some
frequencies. These two bearings feature two storey houses with their flat
walls facing the antennas, but again the problem is eliminated with a 435
filter in line permanently.

There are of course natural hazards which can affect Fo20 access. At IHJ
latitude 56N the polar auroral oval is above the station horizon on 3
nights out of 4 . This has the effect of introducing severe scintillation
of the downlink signal when ever the satellite is seen through the auroral
polar front. This can quite often disturb the early part of passes as the
satellite drops south over Canada, but by the time US stations come in
range the line of sight to the satellite is usually clear of the polar
front and good contacts are possible for about the last 5 minutes of the
pass as seen from Europe.

Another problem frequently encountered with mode JA, is failure to get the
2m uplink up to the satellite through Sporadic E. SpE is usually a summer
time phenomena and it can block the uplink to Fo20 for perhaps the first
third or half of a pass coming north over Europe or the Atlantic. But SpE
clouds above latitude 55N are rare, so the northern halves of passes are
rarely affected, with access to Fo20 returning as soon as the line of
sight to the satellite clears the SpE cloud or clouds.

So if you can overcome all the above minor problems , what can Fo20 JA
offer you by way of DX ? In practice this is not an easy question to
answer as Fo20s orbit was deliberately made elliptical so that part of
the orbit sees it at a height of about 912 kms , whereas at apogee its
height above the earth has risen to about 1745 kms. This means that DX
possibilities around the perigee low point extend only to about 6400kms (
max range with the sat half way between the two stations), while at the
apogee high point the DX range has extended to nearly 8450 kms . 

The satellite subpoint at apogee moves over a 5 month cycle. So a
particular station gets good long range DX ( apogee near his station for
about 6 or 8 weeks every 5 months or so). Best opportunities Europe W6
have been occuring recently, and will return again between end March and
early May in 1996.