Nokia MD59LS on 23 cm PA3GCO
...
Introduction
...
The last few years I've been active on 23 cm, using a transverter and an all mode 2 m transceiver.I got the idea to make the Nokia MD59LS suitable for 23 cm FM, so I could be qrv portable on the local 23 cm repeater PI6SHB. In FM I'm only interested in the lower part of the 23 cm band (PI6SHB transmits on 1242.3500 MHz). So I chose a transverter with a local oscillator of 810 MHz. So 430-440 became 1240-1250 MHz. The result was ok, but there are disadvantages: You need an oscillator on 810 MHz (101.25 MHz times 8) with a non standard crystal. Unless this oscillator is temperature controlled, the frequency stability is not sufficient, even for FM.

I only used one single frequency. That's why I tried something else: Tripling from 70 to 23 cm. Using this concept no extra oscillator signal is needed and the stability is (because of the TCO in the Nokia) perfect for FM. The MD59LS uses 12.5 kHz steps on 70 cm. After tripling that's 37.5 kHz on 23 cm. That's no problem because you use only one frequency. If this frequency is not exact, adjusting the 12.8 MHz TCO solves this problem. 

Both tx- and rx-module are based on the well known DB6NT 23 cm transverter. I took the parts that are useful for me.

Tx goes as follows: The MD59LS power amplifier isn't used anymore. The rf signal from the synthesizer board goes directly tot the tx-module. It is housed in a standard 37X55X30 mm cabinet and contains a BFG93A as tripler, followed by a 23 cm helixfilter and a 23 cm power module 67715.

Rx: The LO signal that normally feeds the Nokia rx board, goes to the rx-module. Then it is tripled by a BFG93A followed by a 23 cm helixfilter. This new LO signal is applied to mixer SMD-C2. This mixer is also connected to a 23 cm frontend: MGF1302, helixfiler, MAR-6. As IFoutput I've chosen 21.4 MHz, so it can be injected in the original Nokia rx board. Or if you use a wideband 31.4 MHz IF, that's also possible. This module is also housed in a standard 37X55X30 mm cabinet. 

For using the MD59LS on verey 23 cm frequency, a controller is needed to program the pll over a wide range. The one on this internet site can be used for this purpose. It can program the pll between 384.0000 and 511.9875 MHz.

In the original situation one VCO is used for tx and rx. Using the MD59LS on 23 cm, that's still the case. The frequency stays the same. That's why this concept can also be used full duplex in a repeater or a packet trx.

Only one crytal has to be fabricated, to replace the original 31.4 MHz crystal on the synthesizer board. This new crystal only determines the SHIFT between tx and rx. So when going qsy and keeping the shift the same, no new crystal is needed..
 

 ...
...

23 cm tx-module
...
The rf signal on 70 cm is applied tot smb connector J1. Why smb? Because smb is also used in the Nokia. Around 20 mW is needed for the tx module. Transistor T1 creates a lot of harmonics. The helixfilter selects only the 23 cm signal. Via C7 the signal is applied tot the power amplifier 67715.
There's only 1 tuning point: The helixfilter. It is tuned to maximum output. Despite the fact this tx-module operates on 8 V only (7808), 2 Watt output on 23 cm is no problem.
The pcb I designed (epoxy 1.6 mm) is double sided. 
.		 ...
Click on picture for schematics tx-module in PDF

...
...
...
Click on pictures for layouts tx-module in PDF
........
...
...
Cut the pcb so it fits exactly in the cabinet. Now drill the holes for the feedthrough capacitor and the 2 smb connectors. The holes for the smb connectors 8 mm from the cover of the cabinet. Then drill a 3 mm hole for the 7808. Finally drill the 2 holes for the 67715. Now solder the pcb in the cabinet. Solder the pcb all around, both sides of the pcb. The smb connectors I use are originally for pcb mounting: 1 inner pin, and 1 on each corner.		 ...
... Remove the 4 corner pins, as short as possible. Now you have an smb connector that can be soldered tightly to the outside of the cabinet. ...
....
...


...
Now place all necessary parts on the pcb. Place the BFG93A upside down! Mount the cabinet to the MD59LS housing for cooling.
...		 ...

 
......
...
...
...
...
...
...
23 cm rx-module
...
The rf signal on 23 cm arrives on J1. Then there's the frontend with T1, 23 cm helixfilter F1 and amplifier U1. Then the signal is at the mixer M1.

The LO signal on 70 cm is applied to J3. 10 mW is enough. T1 triples this signal to 23 cm, F2 filters the 23 cm component. The rx-module has 2 tuning points: Both filters. Both are tuned to optimum rx.The whole module operates on 6 V (78L06).
The pcb I designed (epoxy 1.6 mm) is double sided. 
 

 ...
Click on picture for schematics rx-module in PDF

...
...
...

Click on pictures for layouts rx-module in PDF
......
...
...
Cut the pcb so it fits exactly in the cabinet. Now drill the holes for the feedthrough capacitor and the 3 smb connectors. The holes for the smb connectors 8 mm from the cover of the cabinet. Now solder the pcb in the cabinet. Solder the pcb all around, both sides of the pcb. On the groundplane the holes for C2 and C3 are covered (see picture). 
...		 ...
...


...
Now place all necessary parts on the pcb. Place the BFG93A upside down! 
...		 ...

 
......
...
...
...
...
...
...
Connection between 23 cm tx-module and Nokia MD59LS
...
J1 is the input of the  23 cm tx-module and is connected via coax cable to the rf output of the Nokia synthesizer board. Finding 12 V in the Nokia shouldn't be a problem.
...		 ...
...

Connection between 23 cm rx-module and Nokia MD59LS
...
J3 is the connector the 70 cm LO signal is applied to. Via a coax cable it is connected to the LO output of the Nokia synthesizer board. On J2 there's the 21.4 MHz (or any other frequency you wish) IF signal. Via a coax cable this signal can be injected in the Nokia receiver, directly behind the SBL-1 mixer. While tuning you can use the RSSI output of the TDA1576: Connect a Voltmeter to pin 13 and you have a nice signal strength indicator.
...		 ...
...
Example rx in 23 cm repeater PI6SHB
...
PI6SHB receives on 1270.3500 MHz. As LO frequency I use 1270.3500 + 21.4000 = 1291.7500 MHz. 1291.7500 is made by setting the vco to 430.5833 MHz (430.5833 times  3 is 1291.7500 MHz). By programming hte vco on 430.5875 MHz, and adjusting the 12.8 MHz TCO, this can be done easily.
...		 ...
...
Example tx in 23 cm repeater PI6SHB
...
PI6SHB transmits on 1242.3500 MHz. The vco is set to 430.5833 MHz (see the example abovez). From the MD59LS a signal on  414.1167 MHz is needed ( 414.1167 times 3 is 1242.3500 MHz). The new crystal on the synthesizer board shoulde be 430.5833 - 414.1167 = 16.4667 MHz.

So the 16.4667 MHz crystal results in a 28 MHz shift on 23 cm. In this case: ( RX IF + SHIFT ) / 3 = frequency crystal 
 

 ...
...
Remarks
...
If the crystal frequency in your application becomes so low that filtering in the Nokia becomes a problem, there are two solutions: Use separate MD59LS units for tx and rx. It saves a crystal and filtering problems are over.
Or use a uhf mobile phone that uses other concepts to generate teh tx signal, like Siemens and Motorola. Both are very suitable for 23 cm use.
...		 ...

Back
www.pa3gco.com