Integrating a Noise Source

One of the nice features of the HP70K design is the ease by which custom components can be integrated into the system. Cabling pass-through ports, filters, power sensors, noise generators, attenuators, directional couplers, bias tees, and other components can easily be integrated with minimal effort, all the while retaining a professional appearance.

To illustrate how this is done, we’ll assemble an wide-band noise source that can be coupled with a 70620B or 70621A Preamplifier. We’ll show in a later article how this can then be used to characterize filters.

When modules are not installed, a blanking panel is attached to the front of the system. These plastic panels are perfect for mounting connectors and components.

The first step is to mark a centre line, and mark where any drill holes will be made. In this case, we have two connectors, a BNC connector for the +28 VDC noise source drive, and an N Connector for the noise source output.

Distances from the top were measured based on the HP70K mechanical guidelines for the placement of connectors.

Before drilling, clamp the blanking panel to a sacrificial piece of wood, front side down. This provides the cleanest hole.

Start with a small drill bit aligned with the centre mark, and use progressively larger bits until the desired hole size is reached.

When sizing the holes, try to ensure that the size is as close as possible to the thread size of the connector, as this prevents connector movement when cables are connected and disconnected.

Once the holes are drilled, the blanking panel is ready for the mounting of the connectors.

Once attached, the connectors are tightened and ready for component mounting.

At this point, if the goal was to pass cables through from the rear of a 70001A or 70004A, the project would be complete, but since we are creating an integrated noise source, there is one more step, attaching the noise source:

An HP 346B noise source, mounted to the HP70K blanking panel.

And here’s how it looks, installed in a system and connected to the preamplifier:

As can be seen, all that is needed to finish the project is to add lettering to indicate the +28VDC IN and the NOISE SOURCE OUT connectors, and a module title: “HP 346B NOISE SOURCE”.

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