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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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29th Jan 2017, 12:16 pm | #41 | |
Dekatron
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Re: All about CB radio
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One oddball I do remember was the 'Shogun' which had separate 10-led digital S and RF meters. Not a bad radio, it had a FET receiver front end, or so I seem to remember. I was never sure who made that one either. (This is the early-eighties Shogun I'm talking about... I think there have been other unrelated models given the same model name since). |
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29th Jan 2017, 12:51 pm | #42 | ||
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Re: All about CB radio
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After the demise of 934Mhz, were any efforts made to move either of these to 1.2Ghz? I know absolutely nothing about them so I don't know if they had unresistricted or 'guarded' PLL ICs, for example. Quote:
It also annoys me when the ONLY repeater available in an area is a digital-only one. I can think of one not too far away from where I am now (not on Tyneside). If I could wave a magic wand I would banish all digital activity to its own frequencies, ie, the 'new' interleaved in-between channels, and pull analogue operation back onto the original 25Khz spaced channels, so that never the twain need meet. (As older original amateur transceivers were filtered for 25Khz spacing, more realistically, the two modes need to be moved into two blocks which are completely separate rather than interleaved). For the time being, I'm not aware of any digital traffic on CB bands, legal or otherwise. To be honest, I'm not too sorry about that. |
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29th Jan 2017, 1:06 pm | #43 |
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Re: All about CB radio
A few weeks ago I pulled my old ADI AT600 dual band handheld out of retirement. Once I'd restuffed the battery pack with new nicads it worked fine. Now whenever I'm in the workshop I switch it on and monitor the local 2 metre and 70 cms repeaters. I can honestly say that the number of contacts I've heard can be counted on the fingers of one hand.
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29th Jan 2017, 1:15 pm | #44 |
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Re: All about CB radio
I don't believe the 934MHz CBs were anywhere near as guarded as the 27MHz ones. There wasn't any attractive naughty frequencies nearby for the government to be afraid of.
934MHz stuff was so expensive (relatively) that it was pretty rare so it wasn't disposed of cheaply on the market so there was no interest in converting it to 23cm. 23cm was well enough served by transverter designs and coverage in big-3 Japanese transceivers is still unusual. My IC910 is still a virgin on that band. I'd not had 2m/70cm gear set up for some years, so I treated myself to a new set, stuffed in all the options, erected a shiny new antenna and met an almost complete lack of anything. I feel like a bit of a fool. David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done Last edited by Radio Wrangler; 29th Jan 2017 at 1:21 pm. |
29th Jan 2017, 2:28 pm | #45 | |
Nonode
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Re: All about CB radio
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After the initial rush for CB radios the demand dropped to zero, and most of the retailers had orders to flog them off at cost price or less. I bought loads of accessories for almost nothing when I worked for Rumbelows as we had orders to get rid of them at almost any cost. |
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29th Jan 2017, 5:07 pm | #46 | |
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Re: All about CB radio
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I think they used a two transistor amplifier followed by a doubler/detector for the S meter on these radios? The MC3357 didn't have an internal RSSI function so they fudged something externally. I never liked the cybernet 134 s meter system but it's 30 odd years since I last used one of these radios but I recall that the s meter was derived from the diode detector at the second 455kHz IF amplifier ahead of the AN240 chip. My memories of using this radio are fading now but I think the 134 radios had the same issues as the export radios. If you turned up the squelch on an export radio the squelch circuit loaded the AGC line and so the s meter reading dropped slightly. Not good! Also, the S meter range was limited. The squelch was operated from an AM detector and the squelch had that awful plop sound each time it activated because it interfaced to the AF chip in a way that caused this plop noise. Add to this the harsh distortion inherent in export radios and a cheap speaker and it all added up to a less than pleasant experience for a serious user. I tried multiple examples of all of the 134 radios. They usually had a very nice front panel with lots of features. The overload performance was quite good on them and the Tx audio was very bright and good for DX operation but it's hard to find anything else good about them except that people would pay lots of money for them even when scruffy and abused. I'm also a bit confused by your PYE stuff. I know nothing about those radios but I can't understand the connection between the AN240 in the PYE and the s meter system in the 134 radios? The AN240 is fitted to the 134 radios but it isn't involved in the s meter system. So I don't quite see the connection with PYE. Also, I didn't think the AN240 chip had an RSSI feature anyway?
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Regards, Jeremy G0HZU Last edited by G0HZU_JMR; 29th Jan 2017 at 5:35 pm. |
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29th Jan 2017, 6:25 pm | #47 | |
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Re: All about CB radio
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There was a dual 27/934 version built as well. I never ever saw any in real life though. I think there was a transverter made by Grandstand but I never saw one of these either. I did use a Reftec 934 briefly in the CB shop in Hinckley (but didn't manage any contacts) and also saw the Cybernet Delta 1 model there. I did 'win' a Reftec 934MHz CB radio at a formal ham rally auction back in the 1990s but the owner snatched it from reach when it didn't fetch what he expected. There was much embarrassment from the auctioneer because it was sold with no reserve. I think I won it for just £10 so I have some sympathy but it was very annoying to see the owner snatch it away like that.
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29th Jan 2017, 7:05 pm | #48 |
Nonode
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Re: All about CB radio
This may be of interest to you.
It does have a list of 934mhz manufacturers,and is a short history of the band. http://934mhz.com/index.php/complete...radio-reviews/ |
29th Jan 2017, 7:12 pm | #49 | |
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Re: All about CB radio
Thanks!
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29th Jan 2017, 7:49 pm | #50 | ||
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Re: All about CB radio
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If we start again from the agreed premise that the MC3357 just didn't have an intentional RSSI circuit so the meter circuit always had to be some kind of external fudge, maybe that's why they tended to be so bad. Quote:
(MX290 series radios equipped with this mod also had electronic channel control so the microprocessor based control board could change channel at will). I've got the full service manual for the MX290s (not where I am now) so I'll take a closer look at exactly what the AN240 does in that particular circuit. Is it possible that the AN240P doesn't have an integrated limiter? |
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29th Jan 2017, 9:13 pm | #51 |
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Re: All about CB radio
I'm not sure about the inner workings of the AN240 chip. My memories of it are not fond ones as every FM CB radio I ever used with one of those in sounded harsh and a bit distorted to me. I think it must have some form of limiter and a fairly crude FM detector (maybe a differential peak detector?)
Back in the day I tried to explain this to other radio users but they seemed to like the harsh punchy sound of the 134 radios. This was a complete mystery to me... I couldn't tolerate the narrow, distorted audio they produced for very long. The awful squelch system just made it worse. If you were to compare this AN240 detector chip to the one in the little Fidelity 2001FM, the 2001FM chip had a fairly decent onboard RSSI system so it could output a DC voltage to the s meter depending on how hard the amps/limiters were working. Not the best s meter in terms of range/response but well above average. It also had a proper quadrature FM detector producing fairly clean sounding FM. Not the best sounding radio but well above average. I think that is why I liked these radios. They were above average at all the things that mattered to me.
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29th Jan 2017, 11:27 pm | #52 |
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Re: All about CB radio
I looked up the AN240 datasheet and it appears that it was used a lot in TV sound systems. It should be capable of decent performance in this respect. Certainly good enough for a CB radio at 455kHz. It doesn't appear to have an RSSI feature built in though.
It does have a limiter stage and a differential peak detector and I think this chip is similar to the old CA3065 chip? The pinouts and features look the same.
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30th Jan 2017, 12:54 am | #53 |
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Re: All about CB radio
Big Oops. I was so puzzled by our foregoing discussion that I buried myself in the MX manuals as soon as I got home and found what I was looking for, the optional 'Carrier Level Detector' module AT28832. The circuit description says...
"IC1 is a comprehensive FM I.F. system integrated circuit, only the IF amplifier and tuning meter sections of which are used in the carrier level detector module" The only problem is... the IC is a CA3089, widely used in domestic FM tuners. That IC does of course have a meter output. No idea how I got it so thoroughly stuck in my head that it was an AN240P, sorry about that. Also, the same manual has a block diagram of the MC3357 (also used in the MX290 series) and you're right (as you knew you were) about the limiter stage coming late on in the MC3357, so you could theoretically derive a signal meter feed by tapping off from the 455Khz I.F. But nobody ever seemed to manage it very well. Maybe Maxon should have adopted the 3089 instead? |
30th Jan 2017, 1:05 am | #54 |
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Re: All about CB radio
Great link, thanks, electronicskip. There was a lot in that that I didn't previously know, including the 'afterthought' channel frequency changes. Nor had I been aware that Grandstand had ever planned a transverter. Fascinating stuff.
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30th Jan 2017, 1:59 am | #55 | |
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Re: All about CB radio
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By the way, I looked up how differential peak detector circuits work and it threw up one odd thing. I think some of these FM chips that use this detector type were designed for use in 4.5MHz TV systems. The AN240 (CA3065?) is one example. I think the chip uses an internal active LPF at 5MHz just ahead of the detector and this is designed to remove the harmonics from the square wave output of the limiter and this then feeds the detector section with a sine wave. So if you use the chip at 455kHz then the internal LPF is almost useless and the detector will be hit with a square wave. I don't know how significant this is but it obviously didn't cause any major issues with CB radios at 455kHz. I think the upc1028 used in the Uniden radios may be similar in this respect? However, I think it is designed for use at 10.7MHz so it presumably has a 10.7MHz internal LPF. But the radios run these chips at 455kHz? It probably doesn't matter much because the distortion in the AF stages and the speaker will be greatest and also the station being received will probably have some significant distortion in the FM modulation system as well. But these chips do seem to be designed for a specific IF frequency that is much higher than 455kHz. The little MC3357 uses a quadrature detector and is fine at 455kHz but as we all know, it had a very weedy internal mixer that did the 10.7MHz to 455kHz conversion so any radio that used this chip that had a wide 10.7MHz ceramic filter ahead of it was a bleedover box across most of the band. I'm sure you must remember when the crystal filter mods appeared in the early/mid 80s. These filters transformed a lot of these radios that used the 3357 chip.
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Regards, Jeremy G0HZU Last edited by G0HZU_JMR; 30th Jan 2017 at 2:09 am. |
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30th Jan 2017, 2:37 am | #56 |
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Re: All about CB radio
I found this link that allows online viewing of some old UK CB magazines.
Sadly, the list of available magazines starts in 1987 by which time CB was dying but it's worth a quick look at one or two of them. I'd really like to see some from 1981 or 1982 just to read the adverts and jog a few memories https://archive.org/details/CitizensBandMagazine
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30th Jan 2017, 6:34 pm | #57 |
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Re: All about CB radio
I have taken the 455KHz signal off before the limiter on MC3357/9 chips before for S meter purposes but you can get weird meter readings if there is an adjacent channel carrier, or something fairly close can sometimes do it. I know some of the early Pye stuff used a complete FM IF strip added on just for the squelch circuit. Were the MX290 sets you refer to Sirius used on NB3 systems? We had Motorola MC Micro NB3 versions (T340's?) which sensed two levels of signal for cell handover. I presume the first level was maybe to pre-empt pending handover (to make the set look around for a better cell transmission), then the lower signal level sensor would actually trigger the switch to the next available cell. We used an add-on to the Marconi 2955 (2960) test set to run tests on NB3 trunked radios. It used to run through all the testing automatically, once you programmed it with all the traffic and voice channels which was a bit of a task. I can still remember all those unmistakable data bursts now. Why didn't they mute them? Apologies, I am wandering off topic again.
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30th Jan 2017, 7:21 pm | #58 | |
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Re: All about CB radio
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Although I've clearly been labouring under a false impression about that, the fact that Pye / Philips put a whole second IF strip into the MX series just to get an RSSI signal suggests to me that even they could not manage to derive a decent RSSI signal from the already-present MC3357. NB3: Briefly, not sure. I never worked in general radio communications for someone like (for example) Apex or North East Radio Communications so I only ever encountered this type of equipment when it had been withdrawn from service and the networks it worked with no longer existed. My interest was in reprogramming the now defunct microprocessor based control PCBs to make them behave in more useful ways - to make them function as frequency readouts / channel selectors (for amateur radio) so they could be left on the MX radios instead of being taken off and discarded as had previously been the case. |
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30th Jan 2017, 7:42 pm | #59 | |
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Re: All about CB radio
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Some years after I stopped buying both magazines regularly I happened to see an issue of Citizen's Band and bought it on impulse but I was saddened by how thin and dumbed-down it had become. There was a reader's letter in which the writer explained that he had managed to make his CB PSU run cooler by putting a smaller value fuse in it. The error went uncorrected by the editorial team, who just printed it at face value. Maybe they did so in anticipation of the storm of letters which would follow. Or maybe they really didn't know. No, it wasn't the April issue. I never bought Citizens Band magazine again. At the height of its powers it had some decent quasi-technical articles, like how to make a 27Mhz inverted-V aerial, how to make a handheld 27Mhz DF loop, and so on. I would imagine some of the contributions came from writers who also worked on the mother ship ('Hobby Electronics' magazine). Talking about this is making me want to read them all again. |
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30th Jan 2017, 11:05 pm | #60 |
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Re: All about CB radio
I recently serviced an old base station radio for an old acquaintance - he'd got it of the
net. It featured a nice large bright heatsink for the power supply pass transistor, but this was obviously not good enough for the previous owner, who had obtained some aerosol black matt paint and sprayed it (and the whole regulator board components too) as black heat sinks are more effective. Fortunately the rest of the set was unmangled albeit with a few paint spots. |