Service manual

7
The position of channel 23 is odd and the effect is as if the channel switch goes ---26-23-
25-24--, so this arrangement in most FCC and European rigs must be taken into account
when any new codes are calculated*. This comment applies especially when you are
programming a straight sequence of channels without any "hops". The Eprom contents
would then look like this :-
020 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF 3C
021 3D 3E FF 3F 40 41 42 FF 43 44 45 46 FF 47 48 49
022 4A FF 4B 4C 4D 4E FF 4F 50 51 53 54 52 55 56 57
023 58 59 5A 5B 5C 5D 5E 5F 60 61 62 63 FF FF FF FF
The switch does not produce codes for the "hops" and can not access these Eprom
locations. Also, channel 23 position is effectively moved. Nevertheless, with correct
programming of the 40 Eprom LOCATIONS which ARE addressed by the switch, the
result is a "straight" 40 channels selected by a channel switch which was never intended to
give such a sequence! For the early UK channels and for the Amateur 10 meter band, this
ability to produce a band of channels without gaps is especially useful.
You can understand, now, that an Eprom will allow you to use the standard codes, from a
channel switch, to select Eprom LOCATIONS which contain any codes which your PLL
will accept. The only limitations on frequency coverage would then be the actual "N" code
set available in the PLL and the restricted bandwidth of the rig itself. Even the restriction of
the "N" code set can be alleviated by changing the PLL for one with a larger set of codes.
An interesting point, in considering the use of an alternative PLL, is that you would be
wise to choose one which will run on a higher supply voltage than the original because this
will widen the voltage range of the PD output and automatically give an increased VCO
frequency range. The MC145106P, for instance, can use a Vcc supply of up to 12 volts,
whereas a uPD858, for example, can use only 5 volts, maximum.
* The hiistory of this odd channel arrangement is that, originally, only 22 channels were
allocated. Subsequently, however, channel 23 was also authorized, 30kHz higher than 22.
When, finally, the full 40 channels were permitted, channels 24 and 25 were allotted to the
gap between 22 and 23 wiith channels 26 onwards falling in line above 23.
Note: In most counttries it is illegal to possess a transmitter which is capable of operating
on CB frequencies as well as Amateur Radio frequencies.