RADARC on Discord

Hope you are all keeping safe and also well hydrated in this heat!

Some members may not know that RADARC is now running a Discord server. Discord is an internet-based chat tool that runs quietly in the background, and is great for those times between meetings that you just remember something you want to discuss, either to someone specific at the club, or as an open discussion. It’s much more lightweight and quick turnaround than email is.

It’s available for Windows, Macs, iPhones and Android phones, is free, and pretty easy to use once you’re up and running. There’s been lots of interesting chat already on lots of different topics, and you can mute what you’re not interested in. The only thing missing is you!

If you’re interested, ping someone on the committee directly for an invite, or email committee @ radarc.org.

Motorola MC Micro Audio Connector

I have designed a 3D printable audio adaptor for the Motorola MC Micro radio. The design cab be downloaded on Thingiverse here :-

The design consists of 3 parts. The first is a grip which wedges between the internals of a 9 pin d-sub plug and the chassis of the radio. This isn’t strictly necessary but does help to avoid the plug vibrating loose. The internals of different plugs might vary so this grip might not always work but the design is made available in Tinkercad to tweak if required. I tried making a plug which would go all the way around but the minimum thickness of plastic most printers use is 0.4mm and there was insufficient space for this to work.
The second is a plate which holds the phono socket while making it easy to access the nut to do it up tight.
Finally there is a simple spacer piece to stop the end of the phono socket touching the d-sub contacts. This part is 20mm long and can simply be scaled to a different height when printing to compensate for a phono socket which has a much greater or shorter required depth.
All designs can be customised in Tinkercad :-

Parts Required :-
1* 9 pin d-sub plug
2* M3 * 30mm screws
1* phono socket

You will need to remove the metal surround from the d-sub plug. You might be able to snip it away using some cutters but I used a dremel type device with a small cutting disc to chop through it at the top and then peeled it back using a pair of pliers. If you do this please wear safety glasses as these small discs can shatter very easily if they catch and the sharp pieces can go flying off at quite a speed.

Step 1 is to push in the d-sub plug and then push in the grip behind it.

Next take the phono socket and solder wires to it and the solder ring. Make sure you do this before fitting as the heat will very easily melt the plastic.
Fit the phono socket. The plastic tends to deform a little under constant pressure so even with a spring washer it might loosen a bit after a while so I would suggest adding some silicone to fix everything in place and help stop the socket from rotating.

Feed the wires through the spacer and solder them onto the d-sub plug onto the speaker contacts.

Screw everything together and fit a phono plug onto the end of the speaker wires and it’s ready to test.

Motorola mc micro power connector

I have designed a 3D printable plug for the Motorola MC Micro radio. The design cab be downloaded on Thingiverse here :-

The design has a few close tolerance parts to ensure the pins fit well in the connector. Depending on the printer the holes may need to be enlarged or made a little smaller. The plug itself is not a snug fit inside the socket and relies on the connectors to provide the friction to hold it in place so there is a little room to enlarge or shrink it before printing but I have also made the tinkercad project accessible if anyone wishes to modify the design themselves :-

The crimps used inside the plug are Molex 5.08mm commonly used in PC power cables as in the photo below. So you can either buy a lead and remove the pins from it or purchase the crimps separately but these can be fiddly to assemble if you don’t have a crimping tool.

I bought the crimps on ebay and crimped them myself as I didn’t want to have to join the wires. I got them from https://www.ebay.co.uk/itm/Male-Female-PC-Power-Supply-Peripheral-Connector-Crimps-Molex-PSU-5-08mm/232573051969

Selecting the correct cable for the plugs is quite critical. In order to be able to have the crimps grip and hold the insulation properly you will want cable with an outside diameter of between 1.9 and 2.5mm. That is quite small considering the radio can draw in the region of 8-9A. In that size range you could get something like https://cpc.farnell.com/pro-power/14-0-2rbcopper50m/cable-figure-8-14-0-20mm-r-b-copper/dp/CB17492 which has a cross sectional area of 0.44mm. At 8A you are going to get a voltage drop in the power cable of 0.6V per meter (reference https://www.12voltplanet.co.uk/cable-sizing-selection.html) which is going to become significant at longer distances.
This is one of the reasons that you can see in the final photo that I chose to make an adaptor lead. The length of the adaptor is kept relatively short in order to minimise the voltage drop along the thinner cable.

The first step is to check that the pin crimp fits snugly. It is not quite round and in one direction it will be a loose fit and in the other it will be tighter. This orientation gives the best fit.

There could up to around 8-9A going through the contact when transmitting so it needs to be a good tight fit. It is probably a reasonable contact but of you flatten the end just a fraction it will be a lot better. Flatten in he orientation shown below so the naturally wider part becomes a little wider.

Next crimp the connectors. Start with the pin you have just squashed and crimp the ground wire to it. I had a crimping tool and found the ‘AWG 18-22’ setting worked well as you can see in the above photo. You could use a pair of pliers but it would be difficult to get the crimp as neat and small enough to fit in the back of the plug and you would probably want to add some solder.

Put the pin in first and then the socket. When pushing in the socket connector make sure it is orientated so that the pin naturally likes to twist into the correct orientation in order to make inserting the plug easier.

When the socket is inserted it will push in most of the way and them seem to stop in the position shown below. There are small barbs on the socket and you can grip the cable just behind the metal and then push it the rest of the way in and it will be a good tight fit.

That’s it pretty much assembled. When removing the plug the pin will tend to try to pull out of the socket. This isn’t a problem but you can add a bit of glue or put on some heat shrink (the stuff with adhesive if you have it)

Finally I prefer to have the plug almost a permanent fitting so I made it into a short adapter lead with a XT30 connector at the other end so if I wan’t to disconnect the radio I can just unplug the XT30 instead.