Preparing the Heat Shrink Tubing

The image above shows the parts needed to prepare the heat shrink tubing for using between the IREDs and the photo devices.

The tubing is a little larger than needed and is curved or even bent when taken out of the bag. A screwdriver and a lighter is used to get the diameter of the tubing correct and straightened out.

The piece above is used between the Crystal Filter and the Phototransistor between the VFO Amplifiers. It is cut 5" long. The ends are trimmed 1/8" after finishing.

The pieces used between the Bandpass filter/VFO and the Crystal Filter/Crystal Oscillator are prepared the same way but are much shorter than the piece above.

The best dimension for the screwdriver shaft is 3/16", but anything close will work. Any smooth tubing can be used, it doesn't have to be a screwdriver.

The tubing is slipped over the screwdriver and heated in sweeping motions. Do not keep the heat at one place or it will distort the tubing.

Feel where the end of the screwdriver is located and do not heat that part of the tubing. The piece will be turned over to get the part that is missed. Leave plenty of room from the end of the screwdriver so the end will not be closed shut from the heat.

The tube after the first heating is finished.

The tube is turned around and the end that was missed is heated.

The tubing after the second heating is finished. It is straight and the exact size to fit over the IRED and Phototransistor.

The tubing after being slipped off the shaft of the screwdriver. Trim about 1/8" off both ends. The ends will be slightly distorted and a cut will clean them for a tight fit on the photo devices.

The IRED will be a tight fit inside the tubing which will keep the tubing from slipping off the IRED when moving the receiver around.

The Phototransistor will not be quite as tight as the IRED, but some resistance should be felt when inserting the Phototransistor. Be careful if trying to reheat the tubing to get a tighter fit, the Phototransistor can be damaged and the tube can close up from the heat.

A loose fit on the tubing will not effect the performance of the device. Also, the bottom edge of the Phototransistor can be pushed up into the tubing for a really tight fit if desired.

Please note that the tubing is installed after the devices are installed on the board. The images above are for illustration purposes only.

Back to Testing Board 1 - Bandpass Filters

Back to Testing Board 1 - Crystal Filters

Back to Testing Board 2 - Crystal Oscillator