Service manual

So we need to switch in four diodes to add these bits to the appropriate inputs of the binary

adders. The end result will be codes of 241 to 241+

45 which is 286. In binary this

represents

Ch40- 1 0 0 0 1 1 1 1 0 = 286 = 1 1 E (HEX)

Ch 1- 0 1 1 1 1 0 0 0 1 = 241 = 0 F 1 (HEX)

A further complication can be seen here because the Most Significant Bit changes from "0"

to "1" somewhere in the range. This means that an inverter transistor must be used as

described earlier. Helpfully, the PB-010 chassis already has a position for a transistor,

which is TR28.

Eprom

thod

We have already done the hardest part, which was to work out the "N" codes. For the

Novice band these are 241 to 280 giving 40 channels from 28.105 to 28.495. Only 6

Eprom inputs are connected to the channel switch to select 40 locations. The remaining

Eprom inputs are not required and may be grounded to 0 volts. The

Eprom can hold only 8

BITs so the 9th BIT must be generated from the 8th by using the transistor inverter circuit.

The HEX code, therefore, omits the MSB and has just two digits, as you can see in the

following table.