Hello Eric,

1. The back section is fixed by four screws through the side plates. Remove
those screws and bend the back section as far as the wiring allows. You will
see the screw heads when the top and bottom cover of IC490 have been removed.

2. 470 nF = 0.47 æF  The capacitance could be higher, but there are space
limitations inside the rig underneath the IC490 Main Unit print.

For the time being you will not need the connection with varactor D3 for
any satellite, but you may need it for a 9600 baud terrestrial net. It will,
however, be feasible to prepare that connection as well when the AF/FM and
AF/SSB connections are being built.

3.                      +12V ÄÄÂÄÄÄÄ¿ 4.7 k
                               ³    ²
                               ³    ÃÄĺÄÄ> SSB out to 9-pin connector
                         850 k ²    ³ 0.47 æF
   #3/IC3                      ³   /
   SSB in ->ÄĺÄÄ---*cable--ÄÄÄÅÄÄ´ BC337 or similar NPN transistor
            0.47 æF            ³   \
                         150 k ²    ³
                               Á    Á
*cable from 0.47 æF condenser on the Main Unit to the amplifier located
 at an empty spot within the rig

You will need the above amplifier only when SSB signal level at #3/IC3 will
not be sufficient for your TNC. I am not familar with TAPR 1200 baud psk
modem.

4. As you know doppler shifts UO-14 frequency downwards only from rise to
set. Often 435.077 ---> 435.058 MHz. Consequently IC490 needs down commands
only. It will get such a command each time the calculated frequency drops by
1 kHz. My program calculates the current frequency, not doppler shift only.
I initally tune my Rx to the frequency I know UO-14 has, when rising above
horizon. I dont need to hear UO-14 at that moment. In fact I know UO-14
frequency any time without listening, just by looking at the monitor. When I
tune my Rx at that frequency I know that UO-14 is there. The control system
then steps the frequency down as frequency calculation tells it to do.

I think you will not need the diagram for the circuitry since your tracking
program apparently does not tell the above things.


You would find Finnish speaking fellows at the subsidiaries of Finnish
companies, like EPL-Kone Pty, in your country. That would unfortunately not
solve the program problem.

Pate OH2SN @ OH2RBI

Hello Eric,

Re your questions concerning IC490

I replaced some of the less important original connections at the 9-pin
connector on the back of IC490 by the the following ones.

Each of the three extra connections described below is made via 740 nF
condenser with the following points shown on the IC490 wiring diagram
A. SSB audio output: IC3  terminal 3 (hot end of R86)
   I built a small one transistor amplifier to boost SSB audio to
   G3RUH 1200 baud PSK modem. I inserted that inside IC490.
B. FM audio  output: IC12 terminal 9 (junction C160/C161)
   FM audio level from IC12 terminal 9 is sufficient for G3RUH 9600
   baud modem.
C. Tx audio to FM modulator: junction C16/D3 (varactor)

A is connected with Rx audio input of the 1200 baud PSK modem.
B is connected with Rx audio input of the 9600 baud modem
C is connected with Tx audio output either of the 1200 baud PSK modem
  or the 9600 baud modem.

The microphone and speaker connections cannot be used instead of the
above since those AF channels would spoil the signal.

I have included in my tracking program a section that calculates at 3 seconds
time intervals the current receiving frequency, inclusive doppler, of UO-13.
The frequency (e.g. 435.077 MHz) is displayed at 1 kHz accuracy on the monitor.
I initially tune IC490 on the receiving frequency UO-14 has when moving above
the horizon. When the calculated frequency changes (drops) by 1 kHz, the
program causes the PC speaker to give a sound. It is then a simply matter to
know when and how much the Rx ought to be retuned. The calculated frequency
matches at any time better than well with the true reciving frequency.

I then made the frequency tracking automatic. AF to the speaker is connected
as input to an auxilary two transistor device. That connects terminal no 3
of IC490 microphone connector via 470 ohms resistor to ground when AF will
appear at the speaker. That steps the Rx frequency down by 1 kHz.

My tracking program REALSATC.COM includes automatic antenna control and
runs on my PC/XT. I use another micro, PC/AT, as packet radio terminal.
From your point of view my tracking program has the draw back that its
text is in Finnish. Maybe you have a contact with someone who would be
willing to include the above features in another tracking program.

73 Pate  OH2SN @ OH2RBI