UK CB Radio 40th anniversary (2nd Nov 2021)

[G6Tanuki]

One of the banes of CB operators in the 80s and 90s was cheap mains power-supplies.

There were plenty of "regulated 3-5A" supplies out there - typically a transformer, bridge-rectifier, rather underspecified electrolytic smoothing capacitor and a simple series-pass transistor [2N3055 or similar] as the regulator.

Problem was - the off-load DC voltage across the electrolytic was typically something like 23V - and could go higher - lots of these power-supplies were specced for 220V supplies and when you fed them from 250V ...

If the electrolytic didn't fail and melt-down the transformer/rectifier, the series-pass transistor [which was invariably provided with only the smallest heatsink] went short and shoved 24V into the unfortunate radio, causing sufficient destruction to render a repair uneconomic.

"Buy cheap, buy twice" as my uncle would say.

[SiriusHardware]

Mustang-3000 that (like Amstrad's, Fidelity 2001 & Harvard HomeBase), used the PCMA002F board - Suspicious similar number to Cybernet PCMA001S in the later Nato-2000 Multi-mode (which could be internally-set to operate to UK 27/81 standard) 'export' model. So I always thought it was a later design by Cybernet, even though it looked rather different to the classic PTBM134 / 135 designs.

You're not the only person to have suggested this, but hand on heart, the PCMA... designation common to the PCMA001 and PCMA002 is the ONLY similarity I can see between them. The building style, the circuit diagram drawing style, all are very different from the signature Cybernet style. If you bear in mind that the Amstrads were available alongside all of the common Cybernet 134 / 135 chassis sets, it's hard to see why they would have chosen to make a third , contemporary chassis not in their signature style and not built their way. For example, every Cybernet set with FM that I have ever seen used an AN240 FM demodulator IC. Why would they suddenly switch to the LA1230 for the Amstrad chassis?

Re: Cybernet vs. Uniden, there always were those two factions, you were either a Uniden Man or a Cybernet man, and your preference was usually slanted by whoever's works were inside your first set. Cybernet man through and through here - they did have their quirks, like the heavy 'BOK' produced by the squelch opening / closing due to the rather brutal method of muting the audio amp, ie, by slamming one of its input terminals down to GND so that the output followed suit, producing a large pulse through the output capacitor.

[bionicmerlin]

My minds a bit fogged after all these years but probably something like 6 months before legalisation there was a Volkswagen Audi dealer in town that was offering I think 22 channel CB FM radios free when you bought a new car with the view that they would be legal on nov 81 . I only ever seen one . It was a odd ball make and yes some of the channels were the same but not all of them . The one I seen was removed from his Audi and replaced with a proper legal 40 channel not to long into 82 . Andy

[ortek_service]

I do also remember Ford-badged Cybernet's. But not sure you could get a new vehicle with one ready-fitted like it seem somes USA vehicles had with Cobra 148's
I wouldn't have expected any 22-Ch set - Which some EU countries had as a sub-set of the CEPT / FCC 'Lo' (and later more commonly known as 'Mid' when an extra 'Low' block got added below on some 120ch CB's) of 26.965-27.405MHz to have covered any of the original UK-Only 40 27/81 (27.60125-27.90125) channels - Which were apparently deliberately specified to make legacy illegal AM etc. sets incompatible (after a few brief tests had shown they usually caused more interference than FM) and was thought to originally make the PLL's very expensive until some 'bodges' allowed cheaper ones to be within the tolerances across 40 channels.
Some reduced CEPT-channels sets were also only 1W, as it seems some other EU countries had only adopted a sub-set of the CEPT standard.
The Ironic thing was that the UK did eventually adopt the CEPT 40 Channels (originally agreed to in the early 70's?) and then tried to phase out the original 27/81 channels, so was nearly back full circle to pre-27/81 systems apart from move to FM-Only until more recently.

Of course, 27MHz was never a great choice for local communications, but was chosen for ease of making these at lowest-cost (which had meant very few could use / afford 934MHz). And had involved giving alternative 35MHz & 459MHz to R/C modellers, even though the same channels hadn't been used (but half were on FCC / CEPT frequencies).
446MHz, as now used by short-range licence-free PMR radios, would have been much more suitable, but wasn't low enough cost back then.

[SiriusHardware]

Offering I think 22 channel CB FM radios free when you bought a new car with the view that they would be legal on nov 81

Tandy jumped the gun in a similar way, I seem to remember their 1979-80 or thereabouts catalogue featured a range of CB radios which you couldn't buy and ultimately never were able to buy from them in Britain, I think they had gambled that the UK would adopt the USA system as-was.

Even so, they did sell everything else to do with CB such as Aerials, SWR meters, 'How To' books and so on.

[Radio Wrangler]

Originally Posted by ortek_service

Of course, 27MHz was never a great choice for local communications, but was chosen for ease of making these at lowest-cost

27MHz is also an ISM band, populated with RF induction heaters etc., so it got given to the most non-essential services with no guarantees any frequency would be clear to use.

David

[ortek_service]

Originally Posted by G6Tanuki

One of the banes of CB operators in the 80s and 90s was cheap mains power-supplies.

There were plenty of "regulated 3-5A" supplies out there - typically a transformer, bridge-rectifier, rather underspecified electrolytic smoothing capacitor and a simple series-pass transistor [2N3055 or similar] as the regulator.

Problem was - the off-load DC voltage across the electrolytic was typically something like 23V - and could go higher - lots of these power-supplies were specced for 220V supplies and when you fed them from 250V ...

If the electrolytic didn't fail and melt-down the transformer/rectifier, the series-pass transistor [which was invariably provided with only the smallest heatsink] went short and shoved 24V into the unfortunate radio, causing sufficient destruction to render a repair uneconomic.

Yes, I do recall the rather-high off-load smoothed voltage often being a bit above the reservoir capacitor. Although never found one that failed, and also luckily virtually never found a PSU with the 2N3055(s) that had gone short-circuit. But I did manage to overheat a transformer that developed shorted-turns, due to too much sustained load (Admittedly, I was trying to use it for some electrolysis chemistry experiments, as a student!).
I do recall people trying to use battery-chargers to power CB's - Often without the essential battery to smooth the output and maintain regulation.

But most CB's got blown-up due to reversed powered connections and with the original inline-fuse no longer fitted. So the shunt 'suicide' polarity-protection diode usually went s/c - Always only a 1A 1N4001, so I used to replace with a 3A rated 1N540x etc. one. And if you were unlucky, the track to this diode burnt-out, so removing it's protection, although most of the time, only the Audio-Amp IC failed.
I was once given a CB, that had its power cable replaced by a directly-wire piece of mains-cable. And apparently a Physics teacher had connected it to the mains! I spent most of a night into next morning finding all the failed semiconductors - Virtually all the IC's, but also a few transistors etc. But did get it going at not too much expense as I had stocks of most CB semiconductors that I'd bought at reasonable prices / did have a box of scrap PCB's to raid.

[SiriusHardware]

even though the same channels hadn't been used (but half were on FCC / CEPT frequencies)

As far as I know the strange 20KHz jumps in the original USA channel set (as widely adopted everywhere else in the world) were to step over the pre-existing 27MHz Radio control frequencies which were already established by the time legal CB came along in the USA, so the 'original' CB channel frequencies were chosen to avoid direct clashes with the R/C frequencies.

That said, the RC receivers of the time probably weren't very sophisticated and might not have been able to cope with a strong local signal only 10KHz away - the R/C frequencies were probably spaced out as they originally were for that very reason.

There is an argument that the UK 27/81 frequencies with their weird offsets were chosen so that their harmonics would not land directly on 'round number' frequencies at two, three, four or five times the operating frequency. The same approach seems to have been adopted on PMR446 whose channel frequencies also have similar strange offsets.

There is another argument that choosing our own frequencies instead of adopting already widely used ones would allow the British electronics industry a head start to sell to their own market and discourage far east manufacturers from making products which they would only be able to sell in one small market (actually two, as Eire adopted our 'unique' frequencies at the same time as we did). As we know, that went well, as the vast majority of UK CB radios which hit the shelves in November 1981 were manufactured in the far east, even those which bore 'British' names like Rotel, Fidelity and Amstrad. The PMR manufacturers like Pye / Philips, Storno, Dymar, etc didn't get involved at all.

[ortek_service]

Originally Posted by SiriusHardware

Re: Cybernet vs. Uniden, there always were those two factions, you were either a Uniden Man or a Cybernet man, and your preference was usually slanted by whoever's works were inside your first set. Cybernet man through and through here - they did have their quirks, like the heavy 'BOK' produced by the squelch opening / closing due to the rather brutal method of muting the audio amp, ie, by slamming one of its input terminals down to GND so that the output followed suit, producing a large pulse through the output capacitor.

Well I was kind of unbiased, as I never originally owned either - But I tended to wire all Mic's for Cybernet, as was more common than Uniden wiring on other chassis.
Yes, I do recall some annying sqelch bangs / the Cybernet etc. re-use as Mic. Amp reliant upon PTT switch to isolate Mic. So adding extra audio-processing circuitry involved relays etc. and I did prefer Uniden (& Mustang) dedicated Mic. amp stages.

Although the main thing which annoyed me most with many Cybernet's (apart from the more messing mass of different PCB points to front panel wiring) was the USA / export ones, that the main board only covered one block of 40ch's and so needed extra add-on multi-crystal boards. All the wiring to these made them rather sensitive to frequency pulling / drift, and it was difficult to get them to remain exactly on frequency (especially when crystals were pulled for LSB / UK offsets). Whereas, the variable-inductor for each mode / crystal on Uniden one's meant these tended to be much more likely to be on-frequency, once corrected aligned.
I think the UK40 Uniden's also had the best receiver overload performance of all the sets (Although the Cybernet's, like the Mustang/Amstrad ones, weren't too bad compared to the plethora of MC3357-based ones)

[SiriusHardware]

The Korean-made Maxons were the main offenders re: use of the MC3357. I also never saw a set with that FM IC produce a half way decent signal meter output. The Cybernets and Unidens were essentially ex-AM receiver designs with an FM demodulator hung on the end, so they still had a proper AGC line from which to derive a meter reading with the 'traditional' weighting / scaling.

Radios based on the 3357 (For example the UK spec Cobra 21, descended from the Cobra 19) had terrible meter scaling, always showing either between 1-3 or 9.

[ortek_service]

Originally Posted by SiriusHardware

As far as I know the strange 20KHz jumps in the original USA channel set (as widely adopted everywhere else in the world) were to step over the pre-existing 27MHz Radio control frequencies which were already established by the time legal CB came along in the USA, so the 'original' CB channel frequencies were chosen to avoid direct clashes with the R/C frequencies.

That said, the RC receivers of the time probably weren't very sophisticated and might not have been able to cope with a strong local signal only 10KHz away - the R/C frequencies were probably spaced out as they originally were for that very reason.

There is an argument that the UK 27/81 frequencies with their weird offsets were chosen so that their harmonics would not land directly on 'round number' frequencies at two, three, four or five times the operating frequency. The same approach seems to have been adopted on PMR446 whose channel frequencies also have similar strange offsets.

There is another argument that choosing our own frequencies instead of adopting already widely used ones would allow the British electronics industry a head start to sell to their own market and discourage far east manufacturers from making products which they would only be able to sell in one small market (actually two, as Eire adopted our 'unique' frequencies at the same time as we did). As we know, that went well, as the vast majority of UK CB radios which hit the shelves in November 1981 were manufactured in the far east, even those which bore 'British' names like Rotel, Fidelity and Amstrad. The PMR manufacturers like Pye / Philips, Storno, Dymar, etc didn't get involved at all.

The original FCC frequencies rather evolved over time, and original 9-Ch / some early 23-ch ones were all non-synthesised and just used crystals.
So they did jump over some R/C channels, but there were still a few R/C channels (presumably not often used) that were on the exact same frequencies. And when they went to 40Ch, even ended up with a backwards -30kHz jump! and ended up with a 450kHz-wide block due to all these 5 Alpha channels / holes (that then got repeated on upper and lower-blocks for simplicity).
Yes, early R/C receivers were quite basic single-conversion etc types and probably didn't have too great adjacent channel / blocking performance. So UK had to give new bands to them, before CB could be legalised to the masses.

I do recall Plessey had come up with a 4? IC reference PLL design circuit. But R&EW magazine had commented this was more expensive than what manufacturers had budgeted for the entire Tx circuitry, so I don't think anyone ever used their IC's.
And once Sanyo / Toshiba had come-up with a slight tweaked to their existing ROM-coded PLL's and it's 10.24MHz ref. xtal freq to get close-enough to the required frequencies, then there wasn't a need for more expensive / complex Motorola MC145xxx / PLL02 etc. Parallel PLL's which needed down-mixers due to low max. input frequency on these older process design IC's. (Although the few that did use these, made for some easier / cheap 10m band conversions
- Including an Icom 1050 model which it seems was basically a re-badge of the DNT / LCL / Jaws M2), so was about the only 'professional' transceiver manufacturer to venture into CB at the time. Although Maxon went on to produce many PMR 'Taxi' radios and Uniden to produce many 'Scanner' receivers.

[ortek_service]

Originally Posted by SiriusHardware

The Korean-made Maxons were the main offenders re: use of the MC3357. I also never saw a set with that FM IC produce a half way decent signal meter output. The Cybernets and Unidens were essentially ex-AM receiver designs with an FM demodulator hung on the end, so they still had a proper AGC line from which to derive a meter reading with the 'traditional' weighting / scaling.

Radios based on the 3357 (For example the UK spec Cobra 21, descended from the Cobra 19) had terrible meter scaling, always showing either between 1-3 or 9.

Yes, Midland models and the odd Colt / Cobra etc. clone of older AM models were amongst the common Maxon chassis manufacturers for the UK market.
Although the MC3357 was used in probably around half of all the different UK CB models, for low-cost - Including the DNT etc. (which had used higher-cost MC145106 PLL solution) And even some 10m 'Amateur radio' transceivers like the Uniden 2830 - It's main fault.
Some later ones went on to use the MC3359, which was probably a bit better - but still not as good as using a discrete mixer and FM-Demod IC.

I suppose once most just used 4 / 5 LED bargraphs, then S-Meter accuracy was no longer relevant. But it was usually a case of exactly where in the narrow '30+' region that all but the most-distant signals usually were.
I suppose there wasn't much QSL card exchanging amongst most CB-er's and with so many variable like the antenna you had / whether an ext. pre-amp was used that probably mostly just lifted noise floor, then most only wanted to know their signal relative to others on a group.

[SiriusHardware]

When I first got into amateur radio I remember lamenting that all the better (IMO) UK CB radios had 'difficult' PLL ICs, ones which were specifically designed to be hard to move onto other frequencies. The ones with freely reprogrammable PLLs were invariably ones you wouldn't even choose to use on CB.

The problem was eventually solved, my favourite of the various methods was a scheme which digitally removed one in every 'n' cycles of the signal coming out of the VCO before feeding it back into the PLL's divider input. This made the VCO frequency look lower than it was, so the PLL would raise the actual frequency of the VCO by the exact amount needed to bring the modified frequency into line. When I acquired the Rotel 220 in my collection it was modified for the 10m amateur band that way, but I have since reverted it to as-built.

[Restoration73]

During 1982 I repaired etc CB radios for a local retailer. The owner hads a link
with a ham retailer (Catronics, Wallington) and they came up with a scanning
base station using a steel chassis incorporating a Maxon radio and a psu. This
might have only been a prototype. The scanning pcb was made by them.

The KP77 mod from 22 channel EU to 27/81 was the worst bodge I've seen.
The LC7135 (EU) had the IC leads clipped on the component side. On the
solder side, a 7136 (UK) was fitted with the leads bent upwards - yuk ! The radio had no 27/81 ident.

The choice of 27/81 channel frequencies was unwise. Back then the local Met
Police cars were fitted with "P" band radios 83MHz transmit, 99MHz receive
with the carrier accessed repeaters using the reverse. 2 of the CB channels
3rd harmonic output could block the repeater inputs. The problem was only
resolved when the P band gear was decommisioned in 1989.