HP 5100B frequency synthesizer DC-50MHz in 0.01Hz steps
A frequency synthesizer is an instrument which translates the frequency
stability of a single frequency to any one of many other possible frequencies
usually over a broad spectrum. It s
single frequency generator is usually of frequency standard quality; thus, the
synthesizer may be called frequency standard capable of furnishing a large
number of frequencies. The two basic
approaches to frequency synthesis are known as Direct and Indirect. Direct synthesis performs a series of
arithmetic operations (multiplication, division, and mixing) on the signal from
the frequency standard to achieve a desired output frequency. The indirect method uses tunable oscillators,
phase-locked to harmonics of a standard frequency, to derive a desired output
frequency.
One advantage of HP direct synthesis type of instruments is that they can be
switched (frequency changed) much faster than indirect synthesis where the
switching speed is governed by the phase-locked circuitry. With direct synthesis the limitations on
switching speeds are set by the time constants in the filtering circuits on the
control lines to the switches and by the circuit bandwidths. Direct synthesis is also fail-safe in that
if any part of the circuitry becomes inoperative the output signal is not
present.
On the other hand, the indirect method of synthesis can be less costly for
an equal frequency range as less circuitry is normally required in the
synthesis process. It then follows that
for an equivalent cost the indirect synthesizer can include modulation and
attenuation functions that the direct synthesizer does not.
Hewlett-Packard direct synthesizers are particularly noted for the
following:
1. Complete guaranteed specifications on tested noise and
stability characteristics for all instrumentsspurious signals, phase noise,
a.m. noise, rms fractional frequency deviation, long term stability, and
harmonic signals.
2. Frequency switching speeds of 4 ms for 2 digits and
typically 20 ms
for a change of many digits.
3. Rugged and modular construction designed for reliable, long
life operation.
4. Customized modifications for special requirements often to
achieve a cost savings.
The basic principle that conducts the 5100 development was the following:
"The sources that provide the highest frequency stability are single
frequency sources, commonly called "Frequency Standards." Having
these high quality standards to hand, it is natural to look for some method to
translate their stability to other desired frequencies. This translation when
the operation is something more than a single arithmetic operation, is commonly
know as frequency synthesis. Hence, a variable frequency synthesizer is an
instrument that translates the frequency stability of a single frequency standard,
to any one of many other possible frequencies, usually over a broad
spectrum."
The 5100B is of the "Direct Synthesis" type
which simply performs a series of arithmetic operations on the signal from the
frequency standard to achieve the desired output frequency. The direct
synthesis approach has the pronounced advantages of permitting fine resolution
and fast switching (lower than 1 millisecond for any frequency change), as well
as an extremely clean output signal.
