5110A Synthesizer Driver & 5100A
© Brooke Clarke 2005
This is a synthesizer based on add,
subtract, multiply NOT on PLL
It is big and heavy, but has very fast coherent switching and good
noise. This model was used by BR communications to develop their
. For remote control on the back there is a wire for
each of the buttons on the front. That's a lot of wires!
What Goes Wrong
The 5100A A1A4 assembly takes in 1 MHz
and after amplyfing the signal with Q1 drives Step Recovery Diode
CR6. In order to get the diode to deliver more output
power it has been built into an assebmly (E1) consisting of the SRD, a
heater and a temperature sensor. Q2 drives the heater.
Running electronic components
hot causes their lifetime to be shortened and in this case the SRD
fails. When that happens the 10 outputs die and the whole 5100
Synthizer no longer works.
|Comp side of
The A1A4 Printed Circuit Board holds the Step Recovery Diode in the
lower right (off white circle).
One fix is to find a stud mount varactor diode and wire it in place of
the SRD and leave the heater disconnected.
Another possible fix is to use the circuit
PRC-25 A15 /
module. This module has a 1 MHz crystal oscillator and using a
transistor circuit generates a lot of harmonics. In the PRC-25
the transistor is a PNP 2N2273 and in the newer PRC-77 it's an
NPN 2N918. A 10 pF capacitor (typo in the PRC-77 manual)
feeds the 1 MHz signal to the base. The base has a 10k resistor
to ground. The emitter has a parallel circuit consisting of a 1k2
resistor and a 0.05 uF cap to ground. The collector is
transformer coupled to the output with the top of the transformer
primary connected to +9.5 volts and decoupled to ground with 0.05
uF. Positive supply isolating by means of a 200 uH choke.
The transistor is off during the negative input half cycle and turns on
only during the positive half cycle generating a narrow pulse rich in
harmonics. The output of the module consists of harmonics at 1 to
12 Mhz and so is not directly suitable for use in the 5110 which puts
out 30 to 40 MHz.
Brooke's Home, Time
& Frequency, Electronics
page created Oct 15, 2005.