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.
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.
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.
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.
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.
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.
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