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Newsgroups: rec.video.satellite
Date:         Sun, 15 Nov 1992 23:04:38 MST
From:         Bob Wier <rrw@SUNSET.CSE.NAU.EDU>
Subject:      Janiel Bandwidth mod

Note - Here is my PRELIMINARY version of the Janiel
Bandwidth Lock mod. Unfortunately, I don't have my
satellite system here, so I won't be able to actually test
it until I go home for the Thanksgiving holidays - but all
of the test equipment in the lab says that it's working
properly (switching, etc).

The inside of the Janiel is pretty nice - certainly worth
the $40 - $50 they are currently running if you can find
one.  The layout is tight on the analog board, but not to
the extent of current VLSI tranceivers.  Things are not too
tight on the digital board.

The analog board looks well laid out, although there are a
LOT of zero ohm resistors (also known as jumpers :-) on the
digital board.  But a double sided board probably would
have been a lot more expensive.

Someone asked about computer control.  The unit actually is
computer controlled by the built in microprocessor.  I note
there is a single line going out to the "remote" jack on
the back panel. Obviously a serial communications line.  I
think it would be  difficult to mod the processor directly
to run via computer control, but if one could get the data
format to send commands to the micro...

Unfortunately, this is information which would probably
come from the AP 2000  antenna positioner.  If anyone has
the code information on this, I'd love to have it!

---enjoy! --Bob W.

----------------------------------------------------------------------------





Selectable Bandwith Lock Modification for the Janiel
SP2000/2000.B Stereo Processor

by Robert R. Wier, WB5KXH

The Janiel unit features automatic selection of the proper
bandwidth for satellite subcarrier audio reception.
Unfortunately, it can be "faked out" by unusual program
content or by somewhat non standard transponder formats,
such as are heard on the Canadian birds.

The following modification enables the manual selection of
either the narrow (150Khz ) or wide (400 Khz) IF filters.
Original automatic selection of the appropriate bandwidth
is also retained as an option.

This modification has a number of features:

- Simple and cheap: only 6 wires, 4 resistors, and a switch
are needed, with an approximate cost of $5.

- Unambigious indication of narrow versus wide bandwidth
selection in both manual and automatic modes.

- Bandwidth display indicator requires no supplemental
display hardware.

- Modification is applied to the component side (top) of
the PC board, eliminating the removal of the board from the
chassies (easy access).

- no PC foil traces are cut and only 2 resistors need be
opened from the top side of the board.  If the display
option is not required, no removal of any components is
required.

- low frequency signals are used, eliminating possible RF
circuitry problems.

- no adjustments or modifications to the tricky stereo
discriminator circuits is required (or encouraged!).

The modification adds resistors in parallel with the
existing bias voltage resistors on the two bi polar
transistors which control the switching selection of narrow
or wideband circuitry.  By shifting the bias voltage,
either transistor can be forced on causing that particular
mode to be selected.  By switching out the added resistors,
normal operation (automatic) is restored.

In order to display which bandwidth has been selected, the
decimal point in both channel frequency displays are used.
By driving them from the bandwidth selection flip / flop a
visiual indication is given as to which is being used.
This  display option operates both in stereo and monaral
modes, locked and automatic.  Since the frequency range is
about 5.00 to 8.50 there is essentially no reason for the
decimal point to be displayed execpt for cosmetic reasons.
Thus its use as a bandwidth indicator does not produce any
loss of tuning information.

NOTES:

A close reading of the service manual point out that
automatic bandswitching is performed only  on the basis of
the signal being received on channel "A".  Normally this is
not a problem, since if monaural is selected channel "A" is
used. However, if channel "A" is not on station, and
channel "B" is used to tune a signal then the automatic
bandwidth will NOT function even if deep modulation is
heard.  The use of channel "A" versus channel "B" is not
important when the frequency selection is  locked by the
added selection switch.

To make the mod:

The modification is not difficult, but it is somewhat tight
on the chassies (but not terribly so). You'll need nimble
fingers and about a 15 watt soldering iron.  You'll also
need:

Small diameter insulated wire (maybe 24 or 26 gauge wire -
no significant current is carried).

four 10K ohm resistors - exact value unimportant

1 DPDT CENTER OFF mini - switch (such as Radio Shack
275-620) - 1/4" drill bit required for drilling mounting
hole

Bandwidth modification:

Disassemble the cover unit. Be careful as the front panel
is plastic and the attachment tabs to the chassies might
easily be broken.

Determine where you will mount the switch - I put mine on
the back panel above and between the "audio subcarrier in"
jack and the "audio out" jacks. The back panel steel is
amazingly hard.

Cut two lenths of wire sufficient to run between
transistors Q216 and Q217 and the switch.  Wrap one wire
around the BASE lead of each transistor (labelled "B" -
these are in-line lead transistors - the base lead is on
the end - not in the center). Carefully solder the wire to
the base lead.

Run the wires to the center lugs on the switch, one
transistor base to one center lug.

Solder one end of a 10K ohm resistor to each of the 4
corner lugs.

Connect the other ends of the 10K ohm resistors together
which are on DIAGONAL lugs on the back of the switch.
Thus, if the switch is oriented vertically, the center lugs
would be at the East / West positions (where the wires to
the base of the transistors are attached) and also NW/SE
(attach the far end of the two resistors together) and
NE/SW (ditto). Thus, the NE/SW resistors would have their
ends away from the switch lugs twisted together (ditto
the NW/SE resistors).

Connect +8 volts to one set of the resistors (doesn't
matter which  - it will just change the position the switch
selects narrow vs. wide functions).  A handy place to get
this voltage is from the top end of L201. This inductor
looks like a large green transistor mounted up on end. It
is close to the front panel on the right hand circuit board
as viewed from the front. Q216 is to the immediate left of
L201 (about an inch).  Q217 is NW from Q216 about another
inch (as viewed from the front).

Attach ground to the other two resistors (a handy place to
get ground is from pin 7 of IC 201, immediately to the
right of Q217 - you'll need to find it for the display
modification anyway).  Chassies ground MAY be ok, but I
havn't verified that.

The idea here is to pull the base of one transistor high
thru a 10K ohm resistor while simultaneously pulling the
base of the other transistor low thru another 10K ohm
resistor.  When the switch is put in the opposite position
the transistor base pull up / pull down are reversed.

For the display mod (highly recommended so you can see what
the ##(&(*@@ is going on :-)

Locate IC 304 and IC 305 on the digital board behind the
LED number displays on the front panel.  To the left of
each, you'll find resistors R330 (right) and R 339 (left).
Cut the end of the resistor towards the BACK of the unit,
and bend them up (gently) so that you can solder a wire
onto them.

Connect a wire from cut end of the right resistor to pin 8
of IC 201 (just solder directly onto the leg of the IC
above the circuit board) - don't cut the leg of the IC.

Connect another wire from the left resistor to pin 11 of IC
201 (ditto).

That completes the modification.

USE:

When the switch is in the center (off) position, automatic
bandswitching will still be in effect.  One or the other of
the display decimal points will be lit (but not both)
indicating the bandwidth in use (left d.p. normally
indicates wide, but this may be reversed if you switched
any of the signals - it doesn't really matter).  In locked
mode, moving the switch off center in one direction will
select narrow, the other direction will select wide.

POTENTIAL PROBLEMS:

There MAY be some interaction between the locked bandwidth
setting and the MUTE function.  This has not been verified.

DISCLAIMER:

Although the above has been wired and tested, and is
believed to be accurate, R. Wier accepts absolutely no
liability for inaccuracies, typos, or equipment damage
resulting from these suggestions.  All responsibilities lie
solely with the owner, and there is no guarantee either
expressed or implied.  This limitation is effective from
the beginning of the world to the end of time, so there!

currently rrw@naucse.cse.nau.edu
longer term wier@red.cs.tcu.edu