Practical
1
Tony Jones G7ETW
charles.jones125@yahoo.co.uk
his piece is about a CB radio I was given,
a Midland (Alan) 78 Plus. Now don’t
scoff please; a radio is a radio and 11m
technology has come a long way since the
eighties.
This radio, now called a ‘Pro’, is a premium
product costing around £80. As Fig. 1 shows,
it doesn’t look much different to the CBs we
had when (and sometimes slightly before) Mrs
Thatcher did her sums and realised legalising
CB would bring in a lot of VAT.
T
CB Radios Today
So have CBs changed? Well, yes and no. Power
remains 4W and the channel knob still clunks
round in sets of 40 channels 10kHz apart. (Or
so I thought. More later.) UK legal modes are
AM and FM, even SSB (but not on this set). The
speaker is still pathetic, but you now get a nice
LCD display.
This is a ‘multi-norm’ CB for use in different
countries. With ‘UK’ selected – a power-up
option, Fig. 2a – it has two sub bands toggled
by the AM/FM button. ‘UK’ on the main display
now (Fig. 2b) gives the UK-only channels
starting 27.60125MHz. ‘EC’ brings up the CEPT
(original USA ‘mid’ 40) channels starting at
26.965MHz.
10m on a CB
Tony Jones G7ETW ‘repurposes’ an old CB radio for the
amateur 10m band.
I do hope you’re still with me, because now
it gets interesting from an amateur radio
perspective. Among the selectable country
modes are two that offer 4MHz of coverage
from 26.5MHz up. ‘PX’ (Poland Export) does
the ‘zeroes’ (frequencies in tens of kHz) and
‘RU(ssia)’ does the ‘fives’.
This is amazingly useful, but an unwary
operator could break the law just about
anywhere! However, for (trusted) us, this makes
available the entire 10m band.
Implementing 10m
Implementing PX mode gave me ten sets (‘a’ to
‘l’, no ‘k’) of 40 channels. So far, so good. But
despite the display indications, transmit was
disabled.
Googling, I saw on the Rigpix site that this
radio has three relevant jumpers. My board did
not match the one pictured but more Googling
led me to a CB blogger called ‘Simon the Wizard’
who kindly sent me a link to one of his ‘mods’
pages where my board was featured.
Fig. 3 shows my board with the jumpers
as standard. To enable ‘PX’ mode, jumper 3
(marked as ‘OPT 3’) needs to be opened (ie no
connection made). OPTs 1 and 2 are one big
blob on my board, but I didn’t need to change
them so I left well alone. See Fig. 4 for the
completed job.
Evaluating the Mod
First the good news: the mod works, see Fig. 5.
In a dummy-load test transmission across the
club shack the radio sounded good on the Icom
IC-756.
AM/FM selection works and power out on FM
is 3W. If I turned up the ‘regulator’ control (see
Fig. 6, potentiometer RV1), I daresay I’d get a
bit more, but running any radio at the absolute
maximum is never a good idea.
Tuning up and down I noticed something
odd. Each 40-channel block took up 450kHz.
Systematic testing revealed that some
channels jumped 20kHz and others were out of
sequence.
Puzzled, I put the radio back in UK mode and
checked the standard, un-modified EC channels
only to see precisely the same thing. Channel
3, for example, should be 26.995MHz but is
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PRACTICAL WIRELESS July 2023
Practical
2a
2b
3
4
6
actually 27.005MHz. 26.995MHz is allocated
to CB, but as a hidden or ‘alpha’ channel. And
channel 23 is 27.255MHz, 30kHz above channel
22, with channels 24 and 25 lower in frequency!
This is a hangover from when CB was
extended from 23 to 40 channels in the 1970s.
Most CB sets still don’t have frequency displays
so the user would never know.
Conclusion
An Alan 78 Plus (and many other similar CB sets
I expect) is modifiable to do 10m, QRP with AM
and FM. I found it an easy job, with no need for
modifications to RF circuitry or firmware. 3W is
5
Fig. 1: The Midland 78 Plus. Fig. 2: Select UK (Fig. 2a), and the UK channels (Fig. 2b) are available. Fig. 3: Board
before modification. Fig. 4: Board after modification. Fig. 5: It works! Fig. 6: Location of potentiometer RV1.
not a lot to play with, but for a QRP man like me,
that’s OK.
I can’t deny this channel mishmash is a bit of
a nuisance. But for the few frequencies around
29.2MHz I could use I’ve made up a channel
table and stuck it on the radio. It’s no different
to using old-school PMR sets with just channel
numbers after all.
Not bad, I’d say, for a radio that cost me
nothing! PW
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