Thursday, December 5, 2019

A 500 Watt HF PA, Part 7: Back Panel, Interconnects, and Miscellaneous

This post is the seventh post in my series describing my 500 watt HF power amplifier project:


In this post I will describe the back panel, the various interconnecting cables, and any other miscellaneous topics that come to mind:


Here's a shot of the Back Panel:


And the its other side...



Back Panel Schematics:

There's really only one circuit on the back panel, and it is for the connectors to control the PA.  Here is its schematic:



My FPGA-SDR transceiver uses the RJ-45 connector (shielded!) to control the PA.  If I want to use the PA with a different receiver/transmitter combo (or transceiver), I've included a traditional RCA jack for the T/R conrol.

The diode to the RCA blocks any positive DC voltage that might be on the RCA jack's T/R signal so that it does not blow up my control circuitry.


Interconnect Cables Schematics:

The various assemblies within the PA require cables to interconnect them.  These cables are shown in the two schematics, below:

Control:


(Control cables with one end soldered to a board are not shown in the drawing, above.  Instead, they are shown on the appropriate schematic).

RF:


Miscellaneous:

Mechanicals:

Some time ago I decided to standardize on using the carcasses of old HP gear for my project builds.  You can see an example of this here with my Automatic ATU, FPGA-SDR transceiver, and ancillary equipment (apart from the Tek scope and microphone):


For this project I chose another HP chassis, but while trying to fit the switching power supplies, the PA, LPF, Supervisory, T/R Switching, and other assemblies into it, I realized I had created a "blivet."

What is a "blivet"?  It's what you get when you try to squeeze 10 pounds of manure into a five pound bag.

The Blivet-to-be...

(Shown with an analog Vdd supply that I later discarded for switchers).

Back to the drawing board, or, in this case, a search of my attic, where I found another chassis.  At the time it seemed a little too large (but in hind sight the size is perfect!).  And, best of all, it was essentially a "virgin" HP chassis -- there were neither holes nor labels on the front panel.

In other words, apart from some holes in a back panel, it appeared unused.

Where did it come from?  I suspect a local HP engineer (this area is where HP started, after all) decided to use the chassis for a project but did not get too far with it.  Later it must have appeared at the local swapmeet where I picked up, long ago in the dim past.

Here is that HP chassis, now containing my new PA...


I had to purchase a 12"x12" 0.1" thick aluminum plate (from OnlineMetals) upon which I mounted  the various assemblies.

And I had to drill (and, for the bottom cover, punch) holes for ventilation:


But apart from that, the mechanical build was relatively painless.

And the case even included these very convenient carrying handles!



Overall weight of the entire Power Amplifier is about 27 lbs.



And that's it for miscellaneous topics and this blog post!    Continue on to the other posts in this series via the links, below...


K6JCA HF PA Posts:

Standard Caveat:

I might have made a mistake in my designs, schematics, equations, models, etc.  If anything looks confusing or wrong to you, please feel free to leave a comment or send me an email.

Also, I will note:

This design and any associated information is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without an implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


No comments: