27th Jan 2017, 7:26 pm | #21 |
Dekatron
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Re: All about CB radio
I can remember buying that Sharp 40 channel AM CB some time around 1981and it involved a covert meeting with someone on a street corner in a dodgy part of Bradford... "are you the bloke with the Sharp CB?" "Yes, have you got the cash?" "Show us the radio first"... and the deal was eventually done!
I've still got my very first DV27 aerial plus a few others up in the loft and I think I still have my first power pack up in the loft somewhere. It was an ex computer PSU that I bought from M&B Radio in Leeds some time around 1981/2. It was a decent little 6.5A linear (not switch mode) PSU with controllable voltage and current limit. Much better than a regular CB PSU and it only cost a tenner. Normally stuff from M&B was very pricey but these were on special offer just as you walked in the door. I think they used to put the cheap stuff near the door to keep the curious and the clumsy away from the expensive test gear on sale Before I bought the PSU I used to use a spare and very tired 12V battery from my motorbike.
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27th Jan 2017, 7:36 pm | #22 | ||
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Re: All about CB radio
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I've had a 1000 in my collection for a while - there are a couple of things which often go wrong with them, one is failure of the trimmer capacitor in the PLL VCO circuit, and for some reason the nice green 7-segment channel displays are prone to going intermittent - possibly a weakness in the design of the more compact channel switch which, as on most radios of that period, directly generates the segment data for the channel display as well as the binary or BCD channel code for the PLL. |
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27th Jan 2017, 7:38 pm | #23 | |
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Re: All about CB radio
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27th Jan 2017, 8:31 pm | #24 |
Heptode
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Re: All about CB radio
I remember well the coming of legal CB. The previous US spec models usually had PLL chips which could be accessed via almost any digital code to get channels way out of the legal band (some working better than others - going too far brought other limits into play). Most (or maybe all) legal UK rigs had limits (internal ROM) so an invalid code could not be used. I found the whole idea very useful though as, for a college course project, I fitted a socket on the rear of a Midland 2001 then intercepted the logic lines to the PLL chip with switching buffer chips so that I could change channel via an external computer.
It was more an academic exercise rather than of great value with a 40 channel legal rig but the resultant noise free operation when controlled by a simple microprocessor system as compared with the fairly high level of noise when controlled by a standard PC of the time taught me quite a bit about the noise emissions from consumer computer equipment. I remember a brush with the law when our next door neighbour reported me to the police. They were not really interested but as they left, had a chat with the neighbour, then still sat outside in their car we had the experience of the police radio coming in on the stereo (playing a record at the time). It took me by surprise, in fact I was shocked LOL |
27th Jan 2017, 8:47 pm | #25 |
Octode
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Re: All about CB radio
There was a good technical case for FM - it is much less likely to be demodulated by cheap audio equipment and non-linear junctions (rusty bolts). But I'm sure I remember a major reason for the UK specification being incompatible with everyone else's was the result of intensive lobbying of the government by "British Industry".
The idea was to make it as difficult and expensive as possible for Far Eastern and USA manufacturers to provide the kit. Thus UK companies would be able to take advantage of a lucrative new consumer market, free of competition from imported equipment. This happened to play well with the political climate of the time. |
27th Jan 2017, 9:10 pm | #26 |
Hexode
Join Date: Mar 2012
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Re: All about CB radio
Does anyone remember a 120 channel illegal rig? We had one, I think it was Formac 120 or something like that. It had 120 channels and an AM/FM switch, the first 40 channels were the normal FCC ones; not sure what to remaining ones were. I do remember there was some overlap with 27/81 as we used to talk to people that had the new CB's, the channels didn't coincide with the official ones, and I seem to remember we got better results when switched to AM, even talking to people on the new FM rigs.
Excuse my ignorance on CB radio, this was just a memory from back in the day. I think the radio is still buried in a cupboard at my parents house. |
27th Jan 2017, 9:14 pm | #27 | |
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Re: All about CB radio
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27th Jan 2017, 9:20 pm | #28 |
Hexode
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Re: All about CB radio
I've just googled the Formac and the memories came flooding back. It had a H, M, L switch, and I remember it had a roger bleep which used to irritate people. I also remember in our mispent youth we were making pests out of ourselves and pretending to be 2 different people on the channel, we used to kill the roger bleep by switching off before unkeying the mic.
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27th Jan 2017, 9:36 pm | #29 |
Rest in Peace
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Re: All about CB radio
In the early days I used to listen in on an old CR100 receiver then, as people started to bring their broken sets in for repair (remember you couldn't take them to a high street dealer in the illegal AM days), I eventually managed to cobble a decent set together from "write offs" and I was hooked. The whole concept of being able to talk to your friends over the radio was new and exciting! Common faults as expected were audio amp chips, caused by s/c external speaker wires, blown front ends, being too near someone with a high power RF amp, and blown RFPA transistors, caused by bad aerials. Power supply reverse protection diodes blown up were also common, and the failure of the little back to back protection diodes on the front end coil. I seemed to be the only one in the area who had an SWR meter and who knew how to use it, so I used to do quite a few mobile installs.
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27th Jan 2017, 9:54 pm | #30 | |
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Re: All about CB radio
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However, I could often tell what radio someone was using just by the nature of the audio response and the illegal 120 channel radios often sounded quite harsh and band limited on FM. Easy to spot them on the band! I don't think the FM quality was as good. Some of these early export radios weren't designed as well for FM and some of them rather crudely modulated a crystal rather than a PLL. Some of the ones that did modulate the PLL did it with the wrong loop bandwidth for FM. The mk1 Cobra 148GTL-DX was a classic example of this. For various reasons the transmit audio on FM was quite poor on these multimode export radios. But then again some of the UK40FM radios had obvious issues too. It was easy to spot anyone using a Communicator 440 or Planet 2000 model for example because the PLL had a very dirty lock characteristic when switching to transmit. So the radio would give out a trademark 'squidge' sound at the start of every transmission. The Uniden/Audioline UK40FM radios always sounded a bit muffled and the cybernet radios always sounded quite bright. Probably the worst sounding radio on transmit was the Economy 40 UKFM CB and this cheap and nasty CB didn't even have an s meter.
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Regards, Jeremy G0HZU Last edited by G0HZU_JMR; 27th Jan 2017 at 10:01 pm. |
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28th Jan 2017, 1:31 pm | #31 | |
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Re: All about CB radio
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Did anyone ever see a UK CB radio made by Pye / Philips? Or Storno? Or Dymar? Or Marconi? Or Plessey? Or Thorn? Neither did I. There were Rotel and Motorola badged UK radios, but they were 'Cybernet inside'. Amstrad were always just importers / badgers and their CB rados were no exception. |
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28th Jan 2017, 2:27 pm | #32 | |
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Re: All about CB radio
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Today's quiet flash programmable microcontrollers with no external data / address buses - and no external clock circuit if you don't mind the timing being a bit arbitrary - would have made a huge difference to our efforts at the time. |
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28th Jan 2017, 3:12 pm | #33 |
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Re: All about CB radio
The Magpie Autoscan 5000 was a UK designed and built CB radio for the UKFM band. It was a class apart from anything from the far east in terms of build quality and receiver performance and features but they were very expensive.
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28th Jan 2017, 3:55 pm | #34 |
Nonode
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Re: All about CB radio
My first CB Radio was a Harrier CBX I think, bought from Rumbelows where I worked at the time at a discount.
I remember buying a mains supply and setting it up in my bedroom along with a K40 Mag mount and sitting it on a metal filing cabinet to get a good ground plane and trying to get a low SWR of 1/1 . I still have both units to this day, along with 20 or 30 other cb radios I've collected over the years. |
28th Jan 2017, 4:20 pm | #35 | |
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Re: All about CB radio
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By contrast, the design roots for the 134 cybernet radios go back to the AM/FM/SSB export radios. You can see this in the schematic where the 455kHz IF strip is really a legacy AM receiver strip (with AGC) with an FM chip added at the back end. That's exactly the same way they did AM and FM on some of the AM/FM/SSB export radios. Take a look at a Superstar 2000 schematic to see the similarities. The Fidelity 2001FM had a fresh approach for the whole receiver strip with a JFET first RF amplifier and a dual gate mosfet for the first mixer and used less components in the 455kHz stage presumably because it was a dedicated FM design. I disliked the channel change knob/action on the Fidelity 2001FM and I didn't like the look of it either but I bought one because it was so cheap and I did prefer it to the 134 based radios. It was far from perfect but it was definitely one of the better CB radios and I've still got one here somewhere.
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28th Jan 2017, 4:23 pm | #36 |
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Re: All about CB radio
I can remember rushing out to buy one of these from Dixons in the 1980s when they sold off all their CB stock at bargain prices. The word soon got around and I managed to get there in time to buy the last Harrier CBX in Dixons in Hinckley for just £10. It was new and boxed and unopened and I sold it soon afterwards for a decent profit
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28th Jan 2017, 10:16 pm | #37 | |
Heptode
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Re: All about CB radio
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I think the same idea could be used with a non legal CB (ie those using PLL chips like the PLL02A) but for my college project I thought it prudent to stay legal. I did think about data transmission myself but never came across anyone with a similar mind to work with. In the past week or two I have thought about testing the CB with the Arduino microcontroller I am now 'playing with', as I still have it, but have not got round to it yet. I would be interesting as it is straightforward to connect my laptop to the Arduino and maybe get a result of less noise from the radio. |
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28th Jan 2017, 10:22 pm | #38 |
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Re: All about CB radio
For those who missed the chance to try 934MHz, there is always 1296MHz available.
Changes to the amateur radio exam have made it relatively trivial for anyone who mucks about with radios. With it split into three exams and a project etc for the full thing, it is more of a perseverance test. The VHF bands are almost empty, so the business of re-jigging everything for 12.5kHz channels turned out to be a bit of a waste. The HF bands have plenty of vacant space. Contacts seem to (as mentioned) be utterly boring rubber stamp jobs for the purpose of collecting post-cards and filling in all the squares on a map, though you do run across some discussions of recent surgical procedures. It would be quite good fun to unleash a bunch of people actually doing things with radios onto the bands David
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28th Jan 2017, 11:36 pm | #39 |
Heptode
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Re: All about CB radio
They can't (or won't) cope. nuff said
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29th Jan 2017, 12:00 pm | #40 | |
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Re: All about CB radio
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The great thing about the FM receiver being made the way it was was that the S-Meter (derived from the AGC line, which would not be present in a 'pure' FM receiver design), actually worked properly. Contrast that with the various pure FM chassis (especially Maxon) which used the ubiquitous MC3357 FM I.F. / discriminator IC. The earliest place you could find a signal to derive a meter drive signal from was at the 10.7Mhz I.F. point, and by the time it got there it had already been ramped up to the maximum by the IC's internal limiter. The upshot was that most UK radios using the MC3357 had horrible, cranky s-meters which would show FSD on any incoming signal which was in reality anywhere between S3 and S30. Examples: the UK versions of the Midland 2001, 3001, 4001 and Cobra 19X. When I got into amateur radio I took an interest in the Pye MX290 PMR radio series, some examples of which had originally been on early cellphone-like systems. The MX290 series used the MC3357 as well. One requirement of a cellular-like system is that it can detect the comparative signal strength of signals on different channels, and I was interested to note that in those radios, an extra parallel IF strip had been added in purely for the purpose of deriving a signal strength reading. The IC used on the add-on PCB was none other than the AN240P FM discriminator IC used in all of the Cybernet designs. I saw this as proof of my suspicion that it was impossible to derive a decent s-meter signal from any receiver using the MC3357, since even Pye/ Philips had not managed to do it. I often wondered if the Pye / Phillips engineer who came up with that add-on was familiar with CB designs and those of Cybernet in particular. |
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