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
. For remote
control on the back there is a wire for
each of the buttons on the front. That's a lot of wires!
HP Memory Project: The
First Commercial Application of Frequency Synthesis
Journal May 1964
: A 0-50 Mc Frequency Synthesizer with
Excellent Stability, Fast Switching, and Fine Resolution
: Frequency Synthesizers Jan 1969
The 5100A A1A4 assembly takes in 1
and after amplifying 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 assembly (E1) consisting of the
heater and a temperature sensor. Q2 drives the heater.
Running the Step Recovery Diode hot increases its lifetime and
hence the output. 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 Synthesizer no longer works.
The A1A4 Printed Circuit Board holds the Step Recovery Diode in
lower right (off white circle).
One fix is to find a stud mount varactor diode and wire it in
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
transistor circuit generates a lot of harmonics. In the
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
feeds the 1 MHz signal to the base. The base has a 10k
to ground. The emitter has a parallel circuit consisting of
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
The transistor is off during the negative input half cycle and
only during the positive half cycle generating a narrow pulse rich
harmonics. The output of the module consists of harmonics at
12 Mhz and so is not directly suitable for use in the 5110 which
out 30 to 40 MHz.
Brooke's Home, Time
& Frequency, Electronics
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