Nokia R58/B58 series repeater modifications

Version 1.3 by Pentti Gronlund OH3BK 26th March 2007


Firmware

There have been two different versions of repeater firmware available
for the Nokia RB58/RC58/RD58 mobiles. 

The early version was written by the hams at Nokia R&D. The firmware
contains parts of the Nokia PMR binary and therefore it is not public
domain and not available on our server. This firmware is not
recommended for new installations anymore because it works only on the
later processor board (P8E) and adjustments to the parameters is done
through quite a tedious process.

The OH5NXO ham firmware has now a versatile repeater mode with total
FFSK remote control of the parameters from an R58 mobile. We recommend
using the latest version on our server. It works both on the P8N and
P8E processor boards. The more recent P8E board is recommended, as it
is more stable in environments with no uninterrupted power. 

You can also use this firmware in the BB58/BB58/BD58 base stations by
substituting the mother board with the A8N audio board and P8N/P8E
processor board taken from a mobile set.


Audio modifications

The simple way is just to connect the ERP pin (9) to the MIC pin (3) 
on the handset D25S connector. The relay gain and maximum deviation 
are then set with the mic gain and limiter adjustments. The drawback
in this setup is that you will be doing one extra de-emphasis/pre-
emphasis round with some inadequacies from the ideal 6 dB/octave
curve, and add these in the repeater audio transfer function. You
will also be getting some excess noise from the microphone amp.

Another way to do it is the way the factory people made the direct
relay audio ath the A8N board:

Remove D4 and D6 (can be D4, D5 and D6 in some versions of the board)
Change C21 4n7 ---> 1 n
Change R36 470k ---> 27 k (we'll start with this value)
Draw a wire from the C25 minus lead to test point TP3

This mod does not use the deviation limiter. Adjust R36 with a test
set close to 1:1 relay gain but so, that there is no splatter to
adjacent channels with a noisy received signal.

We would be thankful for an audio modification with a direct non
de/pre-emphasized path and with the least amplifier stages needed,
but with a ~5 kHz brickwall limiter.


Squelch board

The RD58/BD58 UHF vesions do not have a noise squelch, but they rely
only on RSSI for the squelch input. They have to be equipped with a
similar noise squelch detector circuit that the VHF versions have on
the RX board. The processor handles both modes:

http://oh3tr.ele.tut.fi/~ftp/modifications/mobira/r58/salpa2.gif 


Other connections

Ground pin 11 of the handset connector to switch on the power. Ground
is available at pins 1, 2, 4, 8 or 10.

If you are making a repeater of a R58 series mobile, remove the original
duplexer or the PIN diode switch/antenna filter board (AF8D). On a
very, very quiet site you can possibly manage with only the ham band
duplexers. In real life you need to install a bandpass filter between
the duplexer and the receiver and a lowpass filter in the transmitter
line. This also applies to the B58 base station version, as external
filters are used also in the original base station rack.

You should also install the real noise detector by OH6MF and OH6HAM in
the UHF version (RD58 or BD58) and use it instead the RSSI squelch. The
other band versions already use a noise squelch.

IC25 (FX003 CCIR decoder) should be installed on the A8N audio board,
to decode the 1750 Hz access tone used e.g. in Europe.

Remove both EPROMs (IC15 and IC16). Program the firmware on a 27C512
chip and install it at IC15.

The webmaster@oh3tr.ele.tut.fi wishes to receive more instructions of
making a repeater out of an R58 mobile.