The HP 70420A module provides a modular platform for measurement systems, and was used in the HP E5500 series of Phase Noise Test Systems. The 70420A module supports measurements from 50 kHz to 1.6 GHz, with option 201 extending the frequency range to 26.5 GHz.
The 70420A functioned as a component in a much larger test system. For example, a diagram of an E5501A system is shown on the left. Often these phase measurement systems would require an entire rack.
Today, similar measurement capabilites can be found in a USB-connected instrument the size of a paperback book.
There main configurations were supported:
- 70420A STD: 50 kHz to 1.6 GHz
- 70420A OPT 001: 50 kHz to 26.5 GHz, High Power Input and AM detector. Optional 70421A, 70422A, or 70427A Downconverter
- 70420A OPT 201: 50 kHz to 26.5 GHz. Optional 70427A Downconverter
Due to the ability to support high frequencies, the E5500 has remained in use far beyond the discontinuation of the MMS product line (e.g. 2008). Below we see an example of the E5500 system being used to measure the single-sideband phase noise performance of a PSG signal generator:
The output signal from the PSG is connected to the “SIGNAL” input. A reference signal generator is also connected, and the 70427A handles frequency downconversion.
The untuned source for which phase noise is to be measured is input to a phase detector, along with a second voltage-controlled reference signal (from the reference signal generator). A phase lock loop adjusts the tune voltage output allowing the two signals to lock. The oscilliscope is used to manually monitor the beat note output.
As this system requires significant manual and automatic controls, this module is not functional without the associated software.
For example, an input signal must not be applied until the software has correctly set the input attenuator for the desired configuration.
Once the test is all set up and manually tuned, the output from the test set is analyzed using a spectrum analyzer, along with a digitizer under the control of the E5500 software.
So, understanding the context in which the 70420A was used, let’s take a look inside.
Inside the 70420A
As we can see, this is one of the more complex modules, but is largely empty. There are six internal modular bays, each of which can contain two boards or RF modules.
In the 70420A OPT 201, as shown, the top right bay is occupied by the phase detector, as illustrated by the below diagram:
The middle right bay is half-occupied by a low-frequency signal routing and processing board.
A 70420A OPT 001 would have additional modules installed to support AM detection and support for high power input.
The power supply and control boards are shown at the bottom. Seven unoccupied ribbon cable connectors can be seen that would connect to other modules, depending on the configuration.
Here we can see the main MC68000 processor, with the 5064–3945 ROM on the left.
Module Resources
Unfortunately, none of the module-level documents have been able to be located.
Some details on this module can be found by looking at the E5500A/B documentation.
