N2PK Vector Network AnalyzerAn inexpensive Vector Network Analyzer of a Lab quality
A good looking and easy to assemble enclosure for the v4.1 dual detector VNA board
No project can be considered complete without shaping a good enclosure around it. Enclosures make both you and your project happy, and the complete unit has much more chances to sit proudly on your desk next to the commercially made hardware, then the one looking like a rat nest. I recognize this is not always possible to find a suitable enclosure, which at the same time has a good appearance. That is why at some point I decided - whenever possible, find an enclosure first, and only then start collecting parts and make PCBs.
With such approach in mind, the VNA board was sized right to have a standard 16-cm (6.3-inch) length. I have had a positive experience with the extruded aluminum enclosures made by Hammond, so I checked the catalog again and picked one that had a 16-cm width (available from Mouser, P/N 546-1455T1601). These enclosures are very good for the homebrew instrumentation projects, as they have removable side panels, and a sliding top cover. Here is the exploded view of the one I got for the N2PK VNA, and which the board was designed for:
The slots in the enclosure's interior make it very easy to mount a 0.062-inch thick board - it simply slides into the slots from the front. As one can see, it is extremely easy to put the board at a different level, and even stack multiple boards. I believe for this particular project this enclosure is perfectly sized - there is enough room below and above the board for the Molex header and RF SMA connectors, and behind the VNA board for a small elephant to fit in. Those who do not have a pet elephant could utilize this free space to mount the power supply. Simply make your power supply board 16 cm in length, and it will nicely slide into the slots behind the main board. Make sure you are using 0.062'' thick PCB material.
What I especially like in these enclosures - the removable top belly plate. No screws are required here; nothing sticks out of the top of your instrument. When you slide the plate in, and put the side panels in place, you can hardly tell where is the top and where is the bottom of the box - so nicely the belly plate fits in. Look - here is the appearance of the assembled box. Now tell me what is wrong with the box top. Apparently nothing.
Now leave the emotions behind and go back to practicality. The parallel port connector should be mounted on the rear removable panel, no questions here. The removable panels are made from a soft aluminum, and this helps in shaping the hole for the DB-25 type connector. The RF connectors is something that you like - some people prefer using N-connectors throughout the shack, some like small SMA ones, some do not mind medium-size BNCs. Your connector type could be any of those - we all know N- and SMA ones a very good for the RF, but not all of us know BNC type is also nice at high frequencies. My 22GHz HP spectrum analyzer has both N and BNC type connectors. So it is up to you, install whatever type you prefer. I would only stay away from the UHF type, which is commonly used in the amateur radio equipment. I believe, however, because it does not maintain the impedance with frequency, it should not be used in the RF instrumentation.
The connectors could be mounted on the second removable panel, which in this case becomes the instrument's front panel. Up to 10 BNC connectors could fit in two rows in this configuration. This is what I personally prefer, and I may go that way. If one wants N-type, the normal 1 inch connectors would fit tightly in two rows, and it would be better to use the ones that have a smaller base plate. In front of the panel you can see the Greenlee punch I use to make accurate holes for N-type connectors.
Alternatively, the connectors could be mounted on the bottom of the box, which becomes the top of the instrument, and the belly plate then becomes the instrument bottom. There is much more panel space available in this case, and access to the connectors is easier. Also the Reflection Bridge is easier to connect and disconnect in this configuration.
Whatever option one may like, the enclosure is easy to assemble and disassemble. Slide the belly plate in, install the front and back panels, put 8 screws in place, and here it is - your beautiful instrument just got a beautiful home!
You can use the email address below to send me your questions or comments.