Monthly Archives: March 2012

The NS-40 kit and custom enclosure

This was my first experience building a kit that came with a circuit board but no enclosure. I learned first-hand how challenging and time-consuming it can be to precisely machine an aluminum enclosure for a kit. In this case the kit provider only suggested a possible enclosure for use with the kit. Fine, except that the builder is left to his own devices when it comes to placement and drilling of holes to accommodate an antenna port as well as connections for power and a key.

I was stumped for a while on how best to implement antenna, power and code key connections until I remembered a Ten-Tec 1340 QRP CW kit I had built in 2010 that resulted in failure (I mistakenly applied power with the polarity reversed and fried unspecified components). Now that failure was about to help solve my challenge of how to set up connections to the circuit board.

From the Ten-Tec kit I removed the strip used to connect power and a key. I also removed the SO-238 antenna connection and at the same time realized the mini RG-174 coax was just what I needed for my antenna hook-up. However, that still left me with the challenge of how to mark the holes I needed to drill in order to mount the power and key connection strip. I decided to simply lay the Ten-Tec enclosure with its pre-drilled holes against my case, then use a marker to indicate where my holes needed to be drilled. Simple!

Once I had the markings in place for the holes I needed to drill I realized I did not have a 5/8 bit to make the hole for the chassis-mounted SO-238 connector. I decided to simply use the largest bit I had (a 1/2″ bit) then use a half-round file to enlarge the hole to the dimension I needed. Buying the 5/8 bit would have cost $15-$20 bucks anyway.)

It worked pretty well. Drilling the holes accurately for the multi-port strip proved more challenging, not because my marking were imprecise but because I did not have a good jig to hold the case steady on the drill press pedestal. For a first effort it came out pretty well, although it won’t win any beauty contest. One other very important thing I learned in machining this case is that this kind of work cannot be done without a good drill press. Using a simple hand drill is simply too hard because it is very difficult to hold the drill bit steady on the marking for each hold. (Hat tip to my brother-in-law, Tom, for the use of his drill press!) That said, I later learned that I should probably have been using a step drill bit.

Now for the acid test. Would the NS-40 work? To this point I had not even fired it up as I had no connections in place for power, antenna or key. So I really had no idea whether it was even going to work or whether the xtals I purchased would work based on the modification I implemented which allows me to switch xtals as needed vs. having a single xtal soldered to the board.

I hooked my 8 AA power supply up to the NS-40, connect my straight key to the rig, fired up my trusty Hallicrafters SX-130 receiver and voila! The NS-40 came through loud and clear.

Completing this project gave me a new appreciation for the skills needed to machine an enclosure for a kit. This may give me the courage to try future projects where part of the challenge is preparing an enclosure for the kit.

Exterior view of the NS-40.

Interior view of NS-40 as seen from the front of the unit.

Side interior view of NS-40.