Tips for building into VU3SUA enclosure

Dave, N8SBE completed a build of the µBITx last night in one of Sunil’s µBITx enclosures, and he has helpful observations for others using this case.

Front panel PCB

In spite of the pictures, the main board must fit OVER the front panel PCB, so that you can mount the LCD display up close to the front panel.

Dave put vertical male pins on the ends of the front panel PCB, which meant that there was insufficient clearance.   If you want to put male pins on the front panel PCB, you should use the right-angle ones (and then the mic connector will be a tight fit against the chassis mount four-pin mic connector, but I was able to just make it work).

He ordered a Dupont kit of male pins, female sockets and housings from Amazon and a suitable crimp tool:


The crimp tool works fine, but Dave spoiled a few female sockets before I got the hang of it.

If you are crimping female sockets on the ends of the original wires that come from the Relimate sockets on the µBITx (trim them to 8 inches first, then you can use the extra for other wiring, see below), then it seems the wire gauge is about 22 gauge, but the crimp die in the centre of the tool that is marked for 22 gauge is too large and won’t crimp the wire properly. He ended up using the crimp position for the smallest wire size, and it worked fine.

It is also important to insert the female socket in the tool first (Dave found that by clicking the tool 3 clicks it closed the jaws just enough to make it easy for me guide the socket into the tool), then push the female socket in far enough so that the box that encloses the male pin is completely outside the dies on the back side of the tool.

Then lightly pressing the handles to keep everything in place, insert the stripped wire into the back of the female socket, and crimp.

The wire should be stripped only about an 1/8″ of an inch, and the insulation should be inserted into the back of the female socket such that the bare wire bundle is crimped with the smaller crimps, and the insulation is held by the larger diameter crimp at the back end of the female socket.  If you strip off to much insulation, you will either fail to get the insulation into the back crimp, or you will force wire into the female socket area, and that will interfere with the male pin when it is inserted.  If you’ve done everything correctly, tugging on the wire shouldn’t make it come out, it will seat correctly on a male pin, and you should not have to resort to soldering anything.

Soldering crimp joints is a BAD idea, not only because the clearance in the female connector bodies is very close, but the solder that wicks into the wire bundle will stiffen the wires past the crimp, and create a stress point that will eventually break the wire if subjected to vibration and movement.

Dave ended up using Dupont housings/connectors on the Audio, Digital (both 8 pin), Mic (three pin), Volume (three pin), encoder (4 pin) and speaker connectors (2 pin). 

When you cut the ubitx supplied analog and digital wire bundles to the recommended 8 inches, you end up with enough left over that you can make all the other front panel connections with using the left over wire.  You can even select the appropriate colours, as documented in the wiring instructions on the HFSignals website.

Small PCB for Encoder

Dave completely missed that there was a small PCB board included for the encoder switch.  He ended up tack-soldering the ends of the four-wire bundle coming from the front panel PCB to the actual switch pins.  It works fine.

Wiring the volume control

Dave somehow got the wiring backward on the volume control (hi end vs. low end), and was “surprised” by a VERY loud noise when he first powered it up.  If you mount the control with the soldering tabs on top so you are viewing them directly when looking down at the rig with the top off, then the correct colours from left-to-right (with the front panel closest to you) are yellow, orange, green (given the wiring colors shown in the wiring section on the HFSignals website).

Power supply wiring

The power supply wiring was an issue, due to the power on/off push-push switch.

It is NOT meant for soldering, as the tabs are practically impossible to solder to (don’t know the material, but it does NOT accept solder), and the body melts in an instant. The tabs are meant to be used with push-on tab crimp connectors (You can find suitable ones at the local auto store in the electrical section).

Dave still wanted to use the PCB board, so he ended up inserting the power switch tabs through the board, pushing the auto tab crimp connectors on, and then tack-soldering the crimp connectors to the board.Ugly, but effective.
Before Dave figured that out, though, he had partially melted and loosened one of the power switch tabs.   
The rest of the power PCB board wiring went OK.  Dave put a three pin header and connector on the end of the board going to the ubitx supply wiring.  Originally he used a right angle male header, but discovered that this interfered with the mounting bracket (and likely the board when installed) for the digital interface PCB.  The solution was to bend up the pins from the board at a 45 degree angle.  Ugly, but effective.
Check the actual wiring of the DC power plug.  The diagram supplied with the enclosure kit shows using a pin for ground that was found to have a no-connect.  The other unused pin turned out to be ground (the sleeve on the DC plug). 
Double-check your wiring in this area with a multimeter to ensure that 1) You have continuity where you expect it from power supply to the µbitx board, and 2) You haven’t inadvertently reversed anything or shorted anything out. 
Don’t forget the chassis ground to the solder tab that comes with the SO-239 socket.

Wiring up the Antenna connector

Dave used the supplied antenna 2 pin connector and wiring that was supplied with the ubitx, but it was not possible to keep it only 2 inches long in this enclosure.  It’s more like 4+ inches. You could use a short piece of RG-174, instead, to lessen any possible pickup of birdies.

Digital interfaces on rear panel

Dave hasn’t used the digital interface for the back panel or the front panel RX/TX LED.