Spektrum DSM RX Antenna Coaxial Cable Extension

A few pics describing the method I used to extend the rx antenna. The cable used is RG178. Overall diameter is 1.8 mm (0.07"). The overall length is a matter of whatever is enough to get the antenna at least foot or so above deck. I chose 1 m for my IOM extension as this allows the rx to remain in the pot but the antenna itself can be placed about 600 mm up the backstay. I read somewhere that someone was concerned about the weight of such an extension. The weight of 1m of this cable is approximately 8 grams. Not what I would consider an issue.

Standard rx antenna connection. Note the two surface mount pads next to the black antenna wire (labeled J2). Use these pads to connect the coaxial cable shield. Remove the top pcb from the bottom pcb to access the underside of the top pcb. When handling the receiver pcbs, take precautions against ESD (electrostatic discharge). Simply apply the soldering iron tip to the antenna wire pad on the underside and pull the existing wire out. Then carefully remove the glue from the top side. The glue can be seen as a clear blob next to the black wire.

RX end of the coax prepared for attaching to the pcb. a small amount of the shield braid is parted and tinned with solder ready for connection to the pcb.

New cable attached to the pcb. Pass cable through existing hole in the top pcb. (bottom right in pic) Using this hole will give strain relief for the joints.

Antenna end of the coax. The outer cover and shield is stripped back far enough so that either 3.6" or 8.5" of the centre conductor is exposed. It's the centre conductor which will become the new antenna. Leave the insulation on the centre conductor.

Finished job. The antenna portion of the cable is covered with heat shrink to protect the shield from water and also to stiffen the antenna such that it will stand on its own. There's 3 layers of heat shrink used here to make it nice and stiff. The last inch or so of antenna is uncovered in this example simply because that's all the heat shrink I had at the time. The tip of the antenna was sealed with a tiny drop of glue also for moisture protection.

The coax leaves the rx case at the alternative antenna opening in the case. I recommend using this opening rather than the top (standard) hole. If the top hole is used, there's no strain relief so I can see the connection of the coax to the pcb failing before long. This hole will need to be drilled out for the 1.8mm cable diameter. Do take the pcb out before poking a drill bit into the case!