Published in Electron October 1998
Packet trx Nokia MD59LS PA3GCO
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Introduction 
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This is a description of the conversion of a second hand carphone into a packet transceiver in the 70 cm band. Needed are a controller and an rf switch circuit with pindiodes. Pcb's have been designed for both circuits. Part 1 handles about conversion for speeds up to 9600 Baud, part 2 describes a wideband upgrade which enables packet speeds up to 100kB. Numbers in the text between square brackets, for example [03], refer to details in one of the pictures. Click on this number to view the particular detail. Click on the picures for super size! Both pcb layouts and schematics are available in PDF. 
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Considerations
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Nokia carphone MD59LS is well known. Several hams have already published articles of how to use them in our 70 cm amateur band. I wanted to use the Nokia as a packet-only transceiver. Really a black box, without display, knobs, lf amplifiers, etc. My goals were: 
    Very wide frequency range, not only 430-440 MHz
    No programmable parts like processors of eproms
    No expensive or special parts
    Packet radio only
    Short tx-delay and short dead-time
    Every Nokia MD59LS must be suitable
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Controller
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The main part of the controller pcb is used for programming the pll, type 145156. Only three lines are needed: Clock, Data and Enable, all ttl-level. Databits are transferred serially and determine the frequency. Databits are read on the rising edge of Clock. When all Databits have been sent, Enable becomes active (high) which concludes the pll programming. This pll needs 19 bits: 2 controlbits, 10 bits for the N counter and 7 bits for the A counter. For this controller the controlbits are always 1, the 10 bits N counter determines how many MHz, the 7 bits A counter determines how many times 12.5 kHz is added. An overview:
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Bit Meaning Remarks
C1 control-bit preset to 1
C2 control-bit preset to 1
N9 512 MHz  preset to 0
N8 256 MHz preset to 1
N7 128 MHz preset to 1
N6 64 MHz 0 or 1 (dipswitch)
N5 32 MHz 0 or 1 (dipswitch)
N4 16 MHz 0 or 1 (dipswitch)
N3 8 MHz 0 or 1 (dipswitch)
N2 4 MHz 0 or 1 (dipswitch)
N1 2 MHz 0 or 1 (dipswitch)
N0 1 MHz 0 or 1 (dipswitch)
A6 64 times 12.5 kHz 0 or 1 (dipswitch)
A5 32 times 12.5 kHz 0 or 1 (dipswitch)
A4 16 times 12.5 kHz 0 or 1 (dipswitch)
A3 8 times 12.5 kHz 0 or 1 (dipswitch)
A2 4 times 12.5 kHz 0 or 1 (dipswitch)
A1 2 times 12.5 kHz 0 or 1 (dipswitch)
A0 1 times 12.5 kHz 0 or 1 (dipswitch)

 
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The overview shows N9, N8 and N7 are preset. This results in a frequency range of 384.0000 MHz (all dipswitches open) - 511.9875 MHz (all dipswitches closed) in 12.5 kHz steps. 

Why this very wide frequency range? This way you can choose where you want your local oscillator above or beneath the frequency your working on. When this Nokia is used in the 23 cm band with a tripler (also on my homepage), you need a flexible controller with a wide frequency range.

The controller (Schematics controller in PDF) uses four shift registers, type 74HC165. 8 bits parallel into every 74HC165. With 4 of these shift registers a bitstream of 32 bits can be made. More than enough for this application. The first 13 bits are not used and are preset to 0. Bits 14 until 18 are C1, C2, N9, N8, and N7 and are preset, as described before. The remaining 14 bits are adjustable: 7 bits for the MHz, 7 bits for 12.5 kHz.

U6A and U6B make a SR-flipflop. As soon as the Nokia is connected to a power supply unit, this flipflop will start counter U5. Databits are now sent to the pll. When this is completed, the flipflop is reset via U6C and counter U5 stops. This all takes place within 1 second. The rest of the time, flipflop, counter and shif registers don't do anything. Only the first second after " starting up" your Nokia.

U7A is used as an inverter. When the packet modem wants the transceiver to transmit, ptt is drawn to ground. The output of U7A will then go high and transistor Q1 becomes active. The voltage on the emitter of Q7 is now available for the pa and the pinswitch.
Q7B is also used as an inverter. This voltage is used to prevent the tx-oscillator from oscillating during reception. An idea from PA3EKO, and it shall be discussed later in this document.
 

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... ... The double sided pcb for the controller has been designed in such a way that it can replace the original Nokia processor pcb. It fits exactly and no additional wires are needed. Pay attention to connector JP5. Solder it in such a way that the colors of the wires correspond with the original situation. 
 
 

Layout pcb bottom side controller in PDF
Placing of parts controller in PDF
Layout pcb top side controller in PDF














 

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Pinswitch 
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A pinswitch is used because it's a fast rf switch, reliable and it doesn't make annoying clicking sounds like a relay. Mitsubishi makes pinswitch modules for 70 cm, but they are expensive. Furthermore, they can't be repaired when something should go wrong.

Schematics pinswitch in PDF

It works as follows: during reception no voltage is applied. The diodes will not conduct and have a high impedance. An rf signal arrives from the antenna. On its right side, it will experience the high impedance of D5, a barrier. The signal can travel to the left side, via the two coaxial lines, to the receiver. How about tx? Voltage is applied and all diodes will conduct and have a low impedance. Rf power from the power amplifier goes via D5 and C1 directly to the antenna. Why does the rf power doesn't go directly into the receiver? Diodes D1, D2, D3 and D4 conduct and can be seen as shortage to ground. These low impedances are transformed by the coaxial transmission line into a high impedance, because the line has an electric length of a quarter of a wavelength. So the rf power from the pa experiences a high impedance and will not reach the receiver. By adding an extra quarter wave line with two diodes, extra separation between pa and rx is created. 
 

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The top side of the double sided pcb has all the tracks, the bottom side is a ground plane. Don't forget to drill all the holes and solder the connections between top and bottom side.

The coaxial cable for the antenna port was removed from the original Nokia duplexfilter. Connectors for tx and rx are SMB. Don't forget to remove copper around the center pin of J1 on the bottom side of the pcb.
 

 

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The pinswitch is placed where the original duplexfilter used to be. One wire connects this switch with the controller. Use a shielded cable.

Placing of parts pinswitch in PDF
Layout pcb top side pinswitch in PDF















 

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Modify Nokia itself 
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The official Nokia MD59LS service doc is not necessary. For those who do have it, I'll use references according to the original documentation, like L19, L23, etc.
Open the Nokia. On one side you find duplexfilter, audio pcb and processor pcb. Remove these three. The two compartments will be used for the new controller and the pinswitch. The other side of the Nokia: Power amplifier, synthesizer and receiver module. 
 
 

 

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Receiver board 
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On one end of the rx module you'll find a brown connector with 5 pins. Pin 1 [10] is close to the potentiometer. Cut the track on the bottom side that goes to this pin [21]. Now make a connection [20] from pin the earlier mentioned pin 1 to pin 8 of the demodulator TDA1576. Replace the hexlixfilter [09] by a 70 cm filter, for example the pin compatible 252MX1549A. No tuning needed. This completes the modification of the receiver. 
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Synthesizer board
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Pin 1 of the 145156 is grounded via a 3R9 smd resistor. Remove this smd resistor and place it back in such a way that pin 1 is connected to pin 5 of the 145156 via the 3R9 smd resistor. Remove the smd resistor on pin 19 of the 145156. Pin 19 is not connected now. Make a connection between pin 19 of the 145156 and pin 3 of the 7474. Pin 1 [07] of the brown connector with 7 pins (pin 1 closest to the pa) has on the bottom side an smd C and smd R to ground. Remove both. Seen from pin 1 of the brown connector, the next part is a plastic C [06], directly beside the square adjustable inductor [06]. Shortcut this condensator. Replace the original 31.4 MHz crystal [06] by a 21.4 MHz standard crystal. If it's difficult tot get it working on 21.4 MHz exactly, try using shortcutting the square adjustable inductor [06] on the bottom side of the pcb. This works fine with low cost 21.4 MHz crystals.
 
 

 

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C38 [16] [18] is a 1p8 smd condensator. It's the coupling C between varicap and the frequency determining LC circuit. By increasing this C, not only the frequency goes down but also the caption range of the pll goes up. Place 2p2 smd on top of the 1p8 condensator, which results in a new 4 pF coupling C.
Beside the 12.8 MHz TCO is a 78L05 voltage stabilizer which sometimes oscillates spontaneously [08]. Place a 10uF elco on the output of the 78L05 to ground, as close as possible tot the 78L05. Unwanted oscillations result in loud noise on the local oscillator signal.
 
 
 
 

 

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Schematiscs fast-ptt-mod in PDF












The PA3EKO-fast-ptt-mod: Solder a diode 1N4148 with its cathode to the emitter of smd transistor Q6[17] on the bottom side of the pcb. Drill a hole at the emitter [19]. Diode 1N4148 [11] is placed on the top side with its cathode through the drillhole, after removing copper around the hole. Connect a 1 nF ceramic condensator from the anode of the 1N4148 to ground [11]. On the top side, near the brown 7 pin connector, you'll find 2 inductors which look like resistors, L19 [13] and L23 [14]. Desolder one side of L19, the side closest to the brown 7 pin connector. Now bend the loose end of L19 in the direction of L23, and solder them together [15]. Because one end of L19 has been desoldered, a free hole remains. Solder a 4K7 resistor in this free hole [12]. The other side of the 4K7 resistor is connected to the node of the 1N4148 anode and the 1 nF ceramic condensator [11]. Explanation: Usually the MD59LS transmits by applying a voltage to the 21.4 MHz crystal oscillator. The same oscillator is being modulated with the 9K6 packet signal. It appeared that the first 50 ms the oscillator couldn't be modulated well enough, which resulted in high tx-delays. PA3EKO had the following idea: Don't remove the voltage during reception. Problem: The receiver hears the 21.4 MHz oscillator during reception. So let the oscillation stop during reception, without removing the voltage. During reception diode 1N4148 conducts. Then the 1 nF ceramic condensator becomes connected to the emitter of the oscillator transistor Q6, which stops the oscillation. During tx this voltage is removed which results in a very fast packet transceiver that can be modulated within 10 ms after keying it.
 
 
 
 

 

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Tuning and using 
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Set the local oscillator (LO) frequency using the dipswitches on the controller board. Dipswitch SW1 is for MHz, SW2 for 12.5 kHz. Mf for both tx and rx is 21.4 MHz. 

Example: The working frequency should be 430.6625 MHz. This means the LO should be at 430.6625 + 21.4 = 452.0625 MHz. So MHz is 452, and number of times 12.5 kHz is 5 ( 5 times 12.5 kHz equals 62.5 kHz). SW1 already has a preset of 384. So set SW1 to 452 - 384 = 68. Set SW2 to 5. To do so, close switches 64 and 4 of SW1 (together 68), close switches 4 and 1 (together 5) of SW2.
The original DIN connector is used for both packet modem and voltage. 

 

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Color of wire Signal
red +12 to 15 Volt
black ground
yellow ptt from modem
blue tx-audio from modem
brown rx-audio to modem

 
 
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Connect a power supply unit and verify that the pll locks. Use a receiver which is tuned to the LO frequency. Measure the pll control voltage at the test point [04] besides the adjustable condensator [03]. If it is in lock already, adjust the voltage at the test point [04] to 5 Volt by adjusting the variable condensator [03]. If it doesn't lock, there are two possiblities: 
    The pll control voltage is at its lower limit, around 1 Volt.
    Solution: Turn the variable condensator clockwise so the capacity increases. 
    This results in a higher control voltage. 
    Adjust it to 5 Volt.

    The pll control voltage is at its upper limit, around 9 Volt.
    Solution: Turn the variable condensator counter clockwise so the capacity decreases. 
    This results in a lower control voltage. 
    Adjust it to 5 Volt.

Conect a spectrum analyser or a mW power meter tot the rf output of the synthesizer board. On this board you find a 6 times helix filter [05] which has to be tuned to 430 MHz. Key the transmitter by the connecting the yellow wire (ptt) to ground. Start by turning the 6 screws clockwise until only 0.5 mm of them remains visible. For real fine tuning you need the spectrum analyser or mW power meter. More than 20 mW output power is possible, 15 mW is enough for the power amplifier. Now connect the synthesiser board to the power amplifier, connect the output of the power amplifier to a Watt meter and a 50 Ohm dummy load. Key the transmitter. You won't have any output at all. 
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On the pa board is a transistor BFR96S, with a variable condensator at its collector [01]. Adjust this variable condensator to get output. It only has 1 correct position. Now tune the rest of the trimmers of the power amplifier. Maximum power can be obtained by turning the three potentiometers [02] fully clockwise.
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Performance

 

Performance
frequency range of vco 384.0000-511.9875 MHz
output 430-440 MHz after pinswitch > 20 Watt
surpression of harmonics > 60 dB
tx-delay < 10 ms

 

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In part 2 a wideband upgrade is described, which makes it possible to upgrade your packet speed up to 100kBaud. 

 

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Parts lists
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To be absolutely sure which parts I have used, I include order numbers and supplier. I'm aware of the fact that non dutch readers have no use for this information. Please drop me an e-mail if you're not sure what is meant in the following parts lists.
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Number Reference Part for controller Supplier
1 C1 10 uf / 35V radial miniature Display 81.02.10U.35
1 C2 68 nF Wima 5mm Display 81.40.68N.63
12 C3..C14 10 nF ceramic 2.5mm Display 81.10.10N
2 JP1, JP3 header 5 positions female right 1x36 .
1 JP2 header 7 positions female right 1x36 Display 05.88.1536
1 JP4 header 2 positions male right 2x36 Display 05.88.1236
1 JP5 connector print right 4.8mm Display 04.11.1K136
1 JP6 5-pin housing socket connector 3.96mm Display 05.59.105
1 . 5-pin header socket connector 3.96mm Display 05.59.205
5 . shrinkcontact socket connector Display 05.59.001
1 L1 RFC 6-holes rfc Display 02.42.210
1 Q1 BC547B Display 01.40.BC547B
1 R1 4K7 Display 51.00.4K7
1 R2 10K Display 51.00.10K
1 R3 1K Display 51.00.1K
1 R4 470K Display 51.00.470K
1 R5 8K2 Display 51.00.8K2
2 SIL1, SIL2 7X100K, 1 common Display 51.71.100K
2 SW2, SW1 dipswitch 7 Display 03.48.007
4 U1..U4 74HC165 Display 01.26.HC165
1 U5 4060 Display 01.30.4060
1 U6 74HC132 Display 01.26.HC132
1 U7 4011 Display 01.30.4011
1 U8 78L05 Display 01.00.78.41
1 U9 7810 Display 01.00.7810.50
5 . Preci-Dip contactstrip 32 pens solder Display 71.08.B032

 
Number Reference Part for pinswitch Supplier
1 R1 270R Display 51.00.270R
1 C1 1 nF smd Display 81.50.1N
2 C2, C3 100 nF smd Display 81.51.100N
5 D1..D5 pindiode MI308 or low-cost BA682 Barend Hendriksen
1 LINE1, LINE2 30 cm RG316 for LINE1 en LINE2 Barend Hendriksen
2 J1, J2 SMB male print square Barend Hendriksen
1 L1 20 cm emailled copper wire 0.5 mm for L1 Display 05.96.KLD50.2
1 . 20 cm shielded cable for connection controller Display 05.22.101

 
Number Part for Nokia itself Supplier
1 helixfilter type 252MX1549 Barend Hendriksen
1 crystal 21.4 MHz Barend Hendriksen
1 1N4148 Display 01.60.1N4148
1 1 nF ceramic Display 81.10.1N
1 4K7 Display 51.00.4K7 
1 2p2 smd Display 81.50.2P2
1 10uF/35V tantal Display 81.05.10U.35

 
 
 
Closing remarks
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Some types of 7810 oscillate spontaneously. Place a 10 uF elco between output and ground pin of the 7810, as close as possible to the 7810. This prevents unwanted oscillations.
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