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#1
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Hi-Fi AM Radio.
rar+p and rats:
Okay, here's the answer directly from the Radiotron Designer's Handbook, fourth edition, pages 1226 and 1227: "Section 3: The Synchrodyne" [...] "and hence the synchrodyne is likely to be most popular for high-quality local-station reception." There you have it. Are we done. This is a 3-tube design for local stations. One RF amp, 2 12au7s. Use an IC or two in the oscillator loop and its perfect, almost a Costas Loop. Build it; they will come. Steve. -- Steven D. Swift, , http://www.novatech-instr.com NOVATECH INSTRUMENTS, INC. P.O. Box 55997 206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA |
#2
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Steven Swift wrote: rar+p and rats: Okay, here's the answer directly from the Radiotron Designer's Handbook, fourth edition, pages 1226 and 1227: "Section 3: The Synchrodyne" [...] "and hence the synchrodyne is likely to be most popular for high-quality local-station reception." There you have it. Are we done. No we are not. Mr Noring will be submitting test results on the prototype receiver he is nutting out. This is a 3-tube design for local stations. One RF amp, 2 12au7s. Use an IC or two in the oscillator loop and its perfect, almost a Costas Loop. The synchrodyne never became commercially viable for home radios in the old tube era, just twice as expensive to make and adjust. But when PLLs became easy with chips there were a few synchrodynes made but I have never seen a synchrodyne AM radio yet. I tried to make one with RF amp and 6BE6 but it was a poor performer. The selectivity depends on the audio filter, and when two stations are 9 or 10kHz apart, and both are strong, you get some weird monkey chatter. But they should be good for locals which are at least 45 kHz apart; If they were only 27 kHz apart, the unwanted station modulation appears at the detector as a 27 kHz carrier modulated by its audio signal, and if the audio filter has a pole at 12 kHz, and a steep roll off, the other station is thus filtered out by the audio filter, not the RF or IF filter. This may sound strange, but the wanted station's carrier is locks a local oscillator's F to its own F, and so you get the modulation imposed on an "exalted carrier". A station 27 kHz away beats with the oscillator F. RDH4 says very very little about synchrodynes. But Wireless World ran some very big articles on them and some very complex (and mostly incomprehensible) circuit designs were published. Its all there in the right libraries. Build it; they will come. Maybe not many :-/ Patrick Turner. Steve. -- Steven D. Swift, , http://www.novatech-instr.com NOVATECH INSTRUMENTS, INC. P.O. Box 55997 206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA |
#3
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"Steven Swift" wrote in message ... rar+p and rats: Okay, here's the answer directly from the Radiotron Designer's Handbook, fourth edition, pages 1226 and 1227: "Section 3: The Synchrodyne" [...] "and hence the synchrodyne is likely to be most popular for high-quality local-station reception." I think the fact that the synchrodyne never became at all popular as an AM radio detector in the tube era means something. If I recall correctly, I read that synchrodyne detectors would howl until they sync'd. Also, the phasing would have to be perfect to get good demodulation from normal double sideband AM. There you have it. Are we done. This is a 3-tube design for local stations. One RF amp, 2 12au7s. Use an IC or two in the oscillator loop and its perfect, almost a Costas Loop. Build it; they will come. Steve. I suppose it's something worth experimenting with, but diode detectors aren't bad. Even in the solid state era, sync detectors aren't particularly popular. The add on sync detectors are expensive. It still doesn't seem to be easy. Frank Dresser |
#4
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"Frank Dresser" writes:
I think the fact that the synchrodyne never became at all popular as an AM radio detector in the tube era means something. If I recall correctly, I read that synchrodyne detectors would howl until they sync'd. Also, the phasing would have to be perfect to get good demodulation from normal double sideband AM. Frank Dresser Yes, they howl. But his channel concept eliminates that problem. In a private email, I asked Jon if his design can use ICs. If you use a couple of ICs to generate the "synchronized" signal, I think you can get around the complexity. Jon has a lot of work. Block diagrams are pretty simple. Details are hard. Steve. -- Steven D. Swift, , http://www.novatech-instr.com NOVATECH INSTRUMENTS, INC. P.O. Box 55997 206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA |
#5
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Steven Swift wrote:
"Frank Dresser" writes: I think the fact that the synchrodyne never became at all popular as an AM radio detector in the tube era means something. If I recall correctly, I read that synchrodyne detectors would howl until they sync'd. Also, the phasing would have to be perfect to get good demodulation from normal double sideband AM. Frank Dresser Yes, they howl. But his channel concept eliminates that problem. In a private email, I asked Jon if his design can use ICs. If you use a couple of ICs to generate the "synchronized" signal, I think you can get around the complexity. Jon has a lot of work. Block diagrams are pretty simple. Details are hard. AM stereo radios use sync detectors to demodulate the L-R signal (broadcast in quadrature). Not strictly in quad, but close. The Sony SRF42 has a sync detect chip that doesn't do the "envelope" detector correction on the quad signal, and thus I could shift by 90 degrees the AM carrier signal feeding its PLL section. Thus creating sync demodulated main channel (true mono on non-AM stereo stations). See http://home.earthlink.net/~wa2ise/im...syncdetmod.jpg http://home.earthlink.net/~wa2ise/images/cxa1758n.jpg and 3/4 the way down this page: http://pw2.netcom.com/~wa2ise/radios/amstmod.html |
#6
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"Frank Dresser" ) writes:
"Steven Swift" wrote in message ... rar+p and rats: Okay, here's the answer directly from the Radiotron Designer's Handbook, fourth edition, pages 1226 and 1227: "Section 3: The Synchrodyne" [...] "and hence the synchrodyne is likely to be most popular for high-quality local-station reception." I think the fact that the synchrodyne never became at all popular as an AM radio detector in the tube era means something. If I recall correctly, I read that synchrodyne detectors would howl until they sync'd. Also, the phasing would have to be perfect to get good demodulation from normal double sideband AM. The quote is about the synchrodyne detector, not synchronous. While Radiotron mentions "sync'ing" I'd not treat that as a basic of the synchrodyne. At its basic, it's what we'd now call a direct conversion receiver, ie beat the incoming signal down to audio. The "high fidelity" derives from the fact that selectivity comes at audio, and one can build good audio filters. Because one is translated the RF signal to audio, any front end selectivity is there to prevent mixer overload. And the translated signal goes from DC to daylight (a slight exageration), so putting the filter there is not just a "tone control" but acts the same way as a good filter further up. The immediate problem is that such a receiver can do nothing of the audio image (which is the same thing as the image in a superheterodyne receiver). This is not a problem with AM, since the audio image (ie the signal on the other side of the carrier) is the other sideband. And of course, the lack of anything to sync the local oscillator to the incomining carrier means that off-tuned receivers will provide a beat note, and worse, a caucophony of sound as the two sidebands translate to different audio frequencies and beat against each other. While obviously there were schemes along these lines, to get better AM reception, I don't think the synchronous detector was described until 1958 or so. At least, that's when it first hit CQ magazine, and if it wasn't by Costas himself, it was by a guy named Webb who worked for GE (who were the commercial proponent of DSBsc). Michael There you have it. Are we done. This is a 3-tube design for local stations. One RF amp, 2 12au7s. Use an IC or two in the oscillator loop and its perfect, almost a Costas Loop. Build it; they will come. Steve. I suppose it's something worth experimenting with, but diode detectors aren't bad. Even in the solid state era, sync detectors aren't particularly popular. The add on sync detectors are expensive. It still doesn't seem to be easy. Frank Dresser |
#7
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Frank Dresser wrote: "Steven Swift" wrote in message ... rar+p and rats: Okay, here's the answer directly from the Radiotron Designer's Handbook, fourth edition, pages 1226 and 1227: "Section 3: The Synchrodyne" [...] "and hence the synchrodyne is likely to be most popular for high-quality local-station reception." I think the fact that the synchrodyne never became at all popular as an AM radio detector in the tube era means something. If I recall correctly, I read that synchrodyne detectors would howl until they sync'd. Also, the phasing would have to be perfect to get good demodulation from normal double sideband AM. Most synchrodynes do howl and whistle while a station is tuned because the oscillator beats with the wanted station carrier until the the station carrier is the same F as the oscillator. PLL wasn't used in many early synchronous applications. Locked osillators were. These used a sample of the station's carrier to trigger the oscillator's F to be the same when the two frequencies became close enough. To get over the howling, muting circuits were devised to block reception until the station was tuned, so it was there, or it wasn't, it was either tuned, or not tuned. By the time you built all the necessary things to make the old style synchrodyne livable withable, you have used twice the tube count, and that's a lot more that could go wrong as tyhe set aged. Chip technology changed all that, and I have a couple of simple synchronous, or otherwise known as direct conversion circuits. Mr D.G.Tucker's synchrodyne circuit of 1947 is a tantalising circuit, but it needs extremely careful layout and preparation to get the darn thing to work as suggested. I couldn't get the balanced demodulator with a 3 winding tranny to work properly with its 4 diodes, and the oscilations wouldn't lock properly, or became unlocked when the modulation % became so high there wasn't enough carrier left to trigger the locking. If it wasn't one thing, it was another, so I built a superhet. There you have it. Are we done. This is a 3-tube design for local stations. One RF amp, 2 12au7s. Use an IC or two in the oscillator loop and its perfect, almost a Costas Loop. Build it; they will come. Steve. I suppose it's something worth experimenting with, but diode detectors aren't bad. Even in the solid state era, sync detectors aren't particularly popular. The add on sync detectors are expensive. It still doesn't seem to be easy. It isn't easy with discrete components. Probably far easier with a chip like the NE602, or LM2111. The application notes might give info about their radio use; I have two circuits with each of the above within, but its OT for a tube group. It should be possible to apply an locked oscillator signal at 455 kHz to the IF signal, and recover the audio from a mixer circuit where the product is the audio. The synchrodyne is similar to a superhet in that the difference between the a stations F and the ocsillator F is not 455 kHz, its simply the audio signal, so its audio that comes out of the frequency converter instead of a 455 kHz IF signal. One tube design uses a the same tube type as one would use for a normal F converter, the 6BE6. A PLL isn't all that easy to do with tubes, since changing an oscillator's F with a varying DC level isn't easy, since rigging a reactance tube up results in little F change. This function is much easier with chips, and varicaps, which were not around in 1947. I even made a 6AU6 RF amp to synchronize the oscillator on a very low threshold of station carrier, by means of using a limiter amp like in an FM set where the last IF amp is run in seriously over loaded conditions to stop any AM of the IF signal getting into the discriminator, but it never really worked properly at 100% modulation; one needed a phase locked set up with a slow time constant driving the voltage control of oscillator F, so that momentary absenses of station carrier signal didn't let the oscillator F drift off the station F. Does anyone have a good phase locked loop schematic using tubes for between 500kHz and 1,700kHz? I vaguely remember one in Electronics Australia in the 1960s, but I became uninterested in electronics about then. Patrick Turner. Frank Dresser |
#8
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Frank Dresser wrote:
I think the fact that the synchrodyne never became at all popular as an AM radio detector in the tube era means something. If I recall correctly, I read that synchrodyne detectors would howl until they sync'd. Also, the phasing would have to be perfect to get good demodulation from normal double sideband AM. Now appearing on alt.binaries.pictures.radio Syncrhodyne three tube receiver from the April 1951 edition of Radio News. Jeff -- "They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." Benjamin Franklin "A life lived in fear is a life half lived." Tara Morice as Fran, from the movie "Strictly Ballroom" |
#9
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In message , Jeffrey D Angus
writes Frank Dresser wrote: I think the fact that the synchrodyne never became at all popular as an AM radio detector in the tube era means something. If I recall correctly, I read that synchrodyne detectors would howl until they sync'd. Also, the phasing would have to be perfect to get good demodulation from normal double sideband AM. Now appearing on alt.binaries.pictures.radio Syncrhodyne three tube receiver from the April 1951 edition of Radio News. Jeff Many years ago, there was a series published in 'Wireless World' (might even have been by John Linsley Hood) about the design of an AM synchrodyne using transistors and linear ICs. It actually stripped off the carrier from the incoming signal, and then limited and filtered this to use as the source of the local oscillator. I believe the concept was called 'Homodyne'. As far as I know, the audio quality was excellent, but it couldn't tune a weak signal close to a powerful one as the powerful one always succeeded in becoming the LO for the demodulator. Here in the UK, AM audio is filtered to 5kHz before it gets to the modulator, so you wouldn't get any increase in audio bandwidth. -- Chris Morriss |
#10
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Chris Morriss writes:
Many years ago, there was a series published in 'Wireless World' (might even have been by John Linsley Hood) about the design of an AM synchrodyne using transistors and linear ICs. It actually stripped off the carrier from the incoming signal, and then limited and filtered this to use as the source of the local oscillator. I believe the concept was called 'Homodyne'. -- Chris Morriss Did a "proof-of-concept" bench test of this homodyne. I took a signal generator set to 1MHz, 400Hz AM at 30%. Took that output to the RF port of a diode ring double balanced mixer. Also fed it to Cmos gate to get a "limited" carrier. I feed the square wave from the Cmos gate to the LO port on the mixer. The IF port went to a low-pass filter. This is the block diagram of a "homodyne" receiver. Okay, I used a big signal from a clean generator, but the results were perfect. We knew it would work, because I blocked out the real world. If Jon allows himself an IC, I suggest using an FM radio chip to get a limiter, then the audio path can be all tubes. If he puts in a decent pre-selector, and perhaps a "strong signal" trap, it can be made to work. My lash-up is limited by the fact that I need a big signal to get the square wave from the CMOS. But as Turner, et al, have said "it is still a lot of work and engineering." My new (1980+) radio books say that this will give superior performance to an envelope detector, but is too complicated for "consumer" receivers and therefore, never caught on. I wonder if you can get enough limiting on local signals to make this work with all tubes. Steve. -- Steven D. Swift, , http://www.novatech-instr.com NOVATECH INSTRUMENTS, INC. P.O. Box 55997 206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA |
#11
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Okay, I used a big signal from a clean generator, but the results were perfect. We knew it would work, because I blocked out the real world. If Jon allows himself an IC, I suggest using an FM radio chip to get a limiter, then the audio path can be all tubes. If he puts in a decent pre-selector, and perhaps a "strong signal" trap, it can be made to work. My lash-up is limited by the fact that I need a big signal to get the square wave from the CMOS. My new (1980+) radio books say that this will give superior performance to an envelope detector, but is too complicated for "consumer" receivers and therefore, never caught on. I wonder if you can get enough limiting on local signals to make this work with all tubes. Maybe build a local oscillator that runs at the carrier frequency, and rig it so it "locks" on the received carrier thru a buffer stage. Color TV set chroma detector circuits do something like this to lock a local oscillator to feed a pair of synchronous detectors to get the U (in phase) and V (quad) chroma signals. There's also "phsydo-synchronous" detectors. Those are usually an IC with a high gain "limiter" to amplify the hell out of the received carrier and then use that to run a synchronous detector. RCA used such in TV sets about 20 years ago. TV signals use a form of AM for the video, and FM for the sound. |
#12
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Chris Morriss wrote: In message , Jeffrey D Angus writes Frank Dresser wrote: I think the fact that the synchrodyne never became at all popular as an AM radio detector in the tube era means something. If I recall correctly, I read that synchrodyne detectors would howl until they sync'd. Also, the phasing would have to be perfect to get good demodulation from normal double sideband AM. Now appearing on alt.binaries.pictures.radio Syncrhodyne three tube receiver from the April 1951 edition of Radio News. Jeff Many years ago, there was a series published in 'Wireless World' (might even have been by John Linsley Hood) about the design of an AM synchrodyne using transistors and linear ICs. It actually stripped off the carrier from the incoming signal, and then limited and filtered this to use as the source of the local oscillator. I believe the concept was called 'Homodyne'. Ppl should read all the old WW magazines on all articles about radio and audio. There is a lot to read. As far as I know, the audio quality was excellent, but it couldn't tune a weak signal close to a powerful one as the powerful one always succeeded in becoming the LO for the demodulator. This might be unlikely with local stations, and if there was some selectivity in the RF front end ahead of the real business. So a two gang cap and double tuned pair of LC at RF is usefull Here in the UK, AM audio is filtered to 5kHz before it gets to the modulator, so you wouldn't get any increase in audio bandwidth. Yuk, Patrick Turner. -- Chris Morriss |
#14
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John Byrns wrote: In article , wrote: Frank Dresser wrote: I think the fact that the synchrodyne never became at all popular as an AM radio detector in the tube era means something. If I recall correctly, I read that synchrodyne detectors would howl until they sync'd. Also, the phasing would have to be perfect to get good demodulation from normal double sideband AM. Now appearing on alt.binaries.pictures.radio Syncrhodyne three tube receiver from the April 1951 edition of Radio News. Looks more like the article came from Radio Electronics than from Radio News, no way of confirming the April 1951 date. The synchrodyne schematic never appeared on ABPR when I looked out for it. Patrick Turner. |
#15
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In article , Patrick Turner
wrote: John Byrns wrote: In article , wrote: Frank Dresser wrote: I think the fact that the synchrodyne never became at all popular as an AM radio detector in the tube era means something. If I recall correctly, I read that synchrodyne detectors would howl until they sync'd. Also, the phasing would have to be perfect to get good demodulation from normal double sideband AM. Now appearing on alt.binaries.pictures.radio Syncrhodyne three tube receiver from the April 1951 edition of Radio News. Looks more like the article came from Radio Electronics than from Radio News, no way of confirming the April 1951 date. The synchrodyne schematic never appeared on ABPR when I looked out for it. Too bad, it's an Australian design from "down under". Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
#16
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Jeffrey D Angus writes:
Now appearing on alt.binaries.pictures.radio Syncrhodyne three tube receiver from the April 1951 edition of Radio News. Jeff Did anyone actually see this schematic? I can't find it. Steve. -- Steven D. Swift, , http://www.novatech-instr.com NOVATECH INSTRUMENTS, INC. P.O. Box 55997 206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA |
#17
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"Steven Swift" a écrit dans le message
Did anyone actually see this schematic? I can't find it. Right he http://techpreservation.dyndns.org/b...files/?C=N&O=A Synchro-1 and -2.jpg Syl |
#18
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HiFi AM is stretching the definition of HiFi! Designing and building a good
receiver is not a trivial task. When I was a kid in Jr High and didn't know any better I used whatever was at hand or I could scrounge and most projects usually worked, and even worked better when certain parts were substituted by trial and error. But in reality none compared to the war surplus receivers I converted. Later in when I was in the RCAF radar school and had more knowledge and parts I did much better. But still not as good as commercial units. After college I made a few attempts getting into the details of characteristic curves for tubes and transistors, load lines and calculating component values. It's a very big task to select the best tube or transistor for each stage and decide on stage gain, distortion, etc. But once that's done, physical layout is very important. After design and layout the unit is built and it's generally not a proto-type, it's the final prize. After changing part values to optimize performance one finds that many things should have been done differently. And I know guys who have built several re-designs till they were satisfied but again I never saw one that outperformed a commercial unit. It's a lot of fun to take an idea from concept to a working unit but anyone who thinks they're going to build something better than what's available should learn how to engineer by going to school or get a job around a lot real smart designers. These days I know the challenge but I still pick up project parts at hamfests knowing full well that I may never get around to using them. Mind games are entertaining but not as much as plugging a project in to listen for the crackle of static and hoping like hell the smoke stays in. It's long road from concept to enjoyment with lots of disappointment and surprises in between. I've resisted the temptation to post this to the shortwave group so Telamon could gripe. -- 73 Hank WD5JFR .. "Steven Swift" wrote in message ... rar+p and rats: Okay, here's the answer directly from the Radiotron Designer's Handbook, fourth edition, pages 1226 and 1227: "Section 3: The Synchrodyne" [...] "and hence the synchrodyne is likely to be most popular for high-quality local-station reception." There you have it. Are we done. This is a 3-tube design for local stations. One RF amp, 2 12au7s. Use an IC or two in the oscillator loop and its perfect, almost a Costas Loop. Build it; they will come. Steve. -- Steven D. Swift, , http://www.novatech-instr.com NOVATECH INSTRUMENTS, INC. P.O. Box 55997 206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA |
#19
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It's a lot of fun to take an idea from concept to a working unit but anyone who thinks they're going to build something better than what's available should learn how to engineer by going to school or get a job around a lot real smart designers. But so many so called engineer designed radios were inspired mostly by accountants, who hate the parts in radios because they cost money to put there. Engineers had pitched battles with accountants in company staff offices all the time. So it isn't too hard to build an AM radio with at least 10 kHz BW and low thd, but it usually uses a couple more tubes the engineers of yesterday were forbidden to use. A superhet isn't rocket science, its schoolboy electronics, and any determined person could build such a radio if they had the will, the tools, workshop, etc. Sure, the old junk from hamfests does help the ability to experiment more easily, since things like IFTs can be tweaked and tried, and who cares if you stuff one up? Patrick Turner. |
#20
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HiFi AM is stretching the definition of HiFi! Designing and building
a good receiver is not a trivial task. When I was a kid in Jr High and didn't know any better I used whatever was at hand or I could scrounge and most projects usually worked, and even worked better when certain parts were substituted by trial and error. But in reality none compared to the war surplus receivers I converted. Last year I sold an old (but never-used) Sony stereo AM radio (for seven times what I paid for it). Checking it out, I located a local stereo AM station. Tuning was tricky -- you had to find _just_ the right spot. But had I not known it was AM, it might very well have thought it FM. The sound was _that_ good. Certainly hi-fi in the subjective sense of low distortion and coloration. FM has a major advantage over AM that can be summed up in one word -- limiting. You can get perfectly flat response without having a perfectly flat IF strip. |
#21
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How about frequency respoonse?
-- 73 Hank WD5JFR "William Sommerwerck" wrote in message ... HiFi AM is stretching the definition of HiFi! Designing and building a good receiver is not a trivial task. When I was a kid in Jr High and didn't know any better I used whatever was at hand or I could scrounge and most projects usually worked, and even worked better when certain parts were substituted by trial and error. But in reality none compared to the war surplus receivers I converted. Last year I sold an old (but never-used) Sony stereo AM radio (for seven times what I paid for it). Checking it out, I located a local stereo AM station. Tuning was tricky -- you had to find _just_ the right spot. But had I not known it was AM, it might very well have thought it FM. The sound was _that_ good. Certainly hi-fi in the subjective sense of low distortion and coloration. FM has a major advantage over AM that can be summed up in one word -- limiting. You can get perfectly flat response without having a perfectly flat IF strip. |
#22
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"Henry Kolesnik" wrote in message m... How about frequency respoonse? Of what? AMS radios have nearly identical freqeuncy response to FM radios. Noise being the primary drawback... and even that isn't an issue in a high signal area such as a large city. Back in the heyday of AMS, I used to actually prefer to listen to KGW-AM over any of our local FM stations because the signal was strong and clean and every bit as good sounding as FMS, with the added advantage of not having to deal with multipath or picket fencing. FM does have the advantage in distance over AMS for clean signal, but only because of the reason William brought up.. limiting. You can amplify an FM signal far beyond clipping without affecting the intelligence contained therein. I don't believe early FM receivers had any designed-in limiting, they just didn't have any gain. |
#23
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AMS radios have nearly identical freqeuncy response to FM radios.
This is unlikely. Stereo FM is essentially flat to 15kHz, and rolls off (sharply) above that only because filters are used at the transmitting end to keep HF program material from messing up the 19kHz pilot tone. To match that response, an AMS radio would occupy a 30kHz band. |
#24
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Brenda Ann Dyer wrote: "Henry Kolesnik" wrote in message m... How about frequency respoonse? Of what? AMS radios have nearly identical freqeuncy response to FM radios. Noise being the primary drawback... and even that isn't an issue in a high signal area such as a large city. Back in the heyday of AMS, I used to actually prefer to listen to KGW-AM over any of our local FM stations because the signal was strong and clean and every bit as good sounding as FMS, with the added advantage of not having to deal with multipath or picket fencing. FM does have the advantage in distance over AMS for clean signal, but only because of the reason William brought up.. limiting. You can amplify an FM signal far beyond clipping without affecting the intelligence contained therein. I don't believe early FM receivers had any designed-in limiting, they just didn't have any gain. It was very quickly realised that huge gain and limiting became necessary fro reliable FM reception, since signal strengths vary so much, even in the same room, so they were designed to make a constant output signal to the discriminator once the input signal was over a ver low threshold of signal level. Increasing signal level 60 dB makes little difference to the reception. AM signals would have to rely on very complex AVC if the stations's Fs were placed between 88 and 108 MHz. FM is a much easier way to get a good result at 100 MHz. But AM works fine at 1 MHz, and it potentially can sound equally good to any FM signal. Most AM receivers are poor quality with low audio bandwidth and high distortion. Patrick Turner. |
#25
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"Brenda Ann Dyer" wrote in message ... [snip] I don't believe early FM receivers had any designed-in limiting, they just didn't have any gain. Limiting was a requirement of the Armstrong license. Philco sold a few early FM radios without any limiting, but Armstrong ran newspaper ads warning people not to buy the cheapened up radios. Armstrong also sued Philco. As far as gain goes, I think it was there, if people wanted to pay for it. For example, the Stromberg-Carlson 925 prewar FM band radio had a RF amp, seperate oscillator and pentode mixer (rather than a noisy converter tube), two IF stages and two limiters. Frank Dresser |
#26
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How about frequency respoonse?
I doubt the "respoonse" went much higher than 8kHz. But the sound wasn't "obviously" dull, muddy, or rouned-off. It lacked the "air" of a good FM signal, but given the program material, it wasn't the sort of thing you'd much notice. |
#27
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William Sommerwerck wrote: HiFi AM is stretching the definition of HiFi! Designing and building a good receiver is not a trivial task. When I was a kid in Jr High and didn't know any better I used whatever was at hand or I could scrounge and most projects usually worked, and even worked better when certain parts were substituted by trial and error. But in reality none compared to the war surplus receivers I converted. Last year I sold an old (but never-used) Sony stereo AM radio (for seven times what I paid for it). Checking it out, I located a local stereo AM station. Tuning was tricky -- you had to find _just_ the right spot. But had I not known it was AM, it might very well have thought it FM. The sound was _that_ good. Certainly hi-fi in the subjective sense of low distortion and coloration. FM has a major advantage over AM that can be summed up in one word -- limiting. You can get perfectly flat response without having a perfectly flat IF strip. I am not sure you know what you mean here. The FM IF limiting is done to remove all AM from the 10.7 mHz IF signal. The only information is the frequency modulation. Foster Seeley FM discriminators are sensitive to AM which causes distortion. So makers use limiters prior to the FSD. Ratio Detectors are less prone, but slightly higher thd. The 300 kHz BW of the 10.7 mHz IF channle is needed because max deviation in 10.7 mHz is 75 kHz each side of 10.7 mHz. Such bandwidths allow carrier modulation F up to around 100 kHz, so several multiplexed signals can be applied to the FM carrier. The receiver can filter out L+R , 19 kHz pilot, 38 kHz L-R subcarrier, and another two carriers at 67 kHz and 96 kHz, each of which may have 10 kHz of audio BW. Patrick Turner. |
#28
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FM has a major advantage over AM that can be summed up in one word --
limiting. You can get perfectly flat response without having a perfectly flat IF strip. I am not sure you know what you mean here. The FM IF limiting is done to remove all AM from the 10.7 mHz IF signal. The only information is the frequency modulation. Foster Seeley FM discriminators are sensitive to AM which causes distortion. So makers use limiters prior to the FSD. Ratio Detectors are less prone, but slightly higher thd. I did know what I was talking about, and you gave excellent confirming examples. |
#29
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William Sommerwerck wrote: FM has a major advantage over AM that can be summed up in one word -- limiting. You can get perfectly flat response without having a perfectly flat IF strip. I am not sure you know what you mean here. The FM IF limiting is done to remove all AM from the 10.7 mHz IF signal. The only information is the frequency modulation. Foster Seeley FM discriminators are sensitive to AM which causes distortion. So makers use limiters prior to the FSD. Ratio Detectors are less prone, but slightly higher thd. I did know what I was talking about, and you gave excellent confirming examples. I wasn't sure you did at the time. No offense meant. I am not always a man of brevity, and postings about radio need to be somewhat concise if possible because its a complex subject, and I sure don't know everything. Patrick Turner. |
#30
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William Sommerwerck wrote:
HiFi AM is stretching the definition of HiFi! Designing and building a good receiver is not a trivial task. When I was a kid in Jr High and didn't know any better I used whatever was at hand or I could scrounge and most projects usually worked, and even worked better when certain parts were substituted by trial and error. But in reality none compared to the war surplus receivers I converted. Last year I sold an old (but never-used) Sony stereo AM radio (for seven times what I paid for it). Checking it out, I located a local stereo AM station. Tuning was tricky -- you had to find _just_ the right spot. But had I not known it was AM, it might very well have thought it FM. The sound was _that_ good. Certainly hi-fi in the subjective sense of low distortion and coloration. FM has a major advantage over AM that can be summed up in one word -- limiting. You can get perfectly flat response without having a perfectly flat IF strip. May I assume that the station was actually playing music on AM? Funny thing, the original Mopar radio in my car had AM stereo. Back before I replaced it (2001, cassette deck went dead), there were several stations boadcasting in AM stereo, all of them talk or news. Perhaps there was music on some of the foreign language stations, I didn't check them. IIRC, the one station that was broadcasting music in English at that time, was in mono. In any event, I think clearly that the thing that killed AM stereo is the lack of music being broadcast on AM by the time it became available. Weather, traffic and Terror (TM) reports, are just fine in mono. Regards, DAve |
#31
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DaveW ) writes:
William Sommerwerck wrote: HiFi AM is stretching the definition of HiFi! Designing and building a good receiver is not a trivial task. When I was a kid in Jr High and didn't know any better I used whatever was at hand or I could scrounge and most projects usually worked, and even worked better when certain parts were substituted by trial and error. But in reality none compared to the war surplus receivers I converted. Last year I sold an old (but never-used) Sony stereo AM radio (for seven times what I paid for it). Checking it out, I located a local stereo AM station. Tuning was tricky -- you had to find _just_ the right spot. But had I not known it was AM, it might very well have thought it FM. The sound was _that_ good. Certainly hi-fi in the subjective sense of low distortion and coloration. FM has a major advantage over AM that can be summed up in one word -- limiting. You can get perfectly flat response without having a perfectly flat IF strip. May I assume that the station was actually playing music on AM? Funny thing, the original Mopar radio in my car had AM stereo. Back before I replaced it (2001, cassette deck went dead), there were several stations boadcasting in AM stereo, all of them talk or news. Perhaps there was music on some of the foreign language stations, I didn't check them. IIRC, the one station that was broadcasting music in English at that time, was in mono. In any event, I think clearly that the thing that killed AM stereo is the lack of music being broadcast on AM by the time it became available. Weather, traffic and Terror (TM) reports, are just fine in mono. Regards, DAve Of course what you really mean is that AM has ceased to be for entertainment. I suspect old time radio (if done in stereo), any "radio theatre", and comedy skits like Cheech and Chong would benefit from being broadcast in stereo. Michael |
#32
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May I assume that the station was actually playing music on AM? Funny
thing, the original Mopar radio in my car had AM stereo. Back before I replaced it (2001, cassette deck went dead), there were several stations boadcasting in AM stereo, all of them talk or news. Perhaps there was music on some of the foreign language stations, I didn't check them. IIRC, the one station that was broadcasting music in English at that time, was in mono. Yes, it was C&W. Like most non-orchestral music, you're not going to miss the uppermost octave very much. In any event, I think clearly that the thing that killed AM stereo is [sic] the lack of music being broadcast on AM by the time it became available. Weather, traffic and Terror (TM) reports, are just fine in mono. This is possible. There's also the fact that stereo FM had been around almost 20 years by the time stereo AM systems were approved. I also suspect converting a transmitter to stereo AM is significantly more expensive than a stereo FM conversion. By the way, it's stereo AM, not AM stereo. |
#33
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"William Sommerwerck" wrote in message ...
May I assume that the station was actually playing music on AM? Funny thing, the original Mopar radio in my car had AM stereo. Back before I replaced it (2001, cassette deck went dead), there were several stations boadcasting in AM stereo, all of them talk or news. Perhaps there was music on some of the foreign language stations, I didn't check them. IIRC, the one station that was broadcasting music in English at that time, was in mono. Yes, it was C&W. Like most non-orchestral music, you're not going to miss the uppermost octave very much. In any event, I think clearly that the thing that killed AM stereo is [sic] the lack of music being broadcast on AM by the time it became available. Weather, traffic and Terror (TM) reports, are just fine in mono. This is possible. There's also the fact that stereo FM had been around almost 20 years by the time stereo AM systems were approved. I also suspect converting a transmitter to stereo AM is significantly more expensive than a stereo FM conversion. Not necessarily, but you have to replace equipment a lot sooner than FM stuff which makes broadcasters grumbly. By the way, it's stereo AM, not AM stereo. It's a Compatible Quadrature Amplitude Modulation stereophonic transmission system as originally developed by Motorola (patents have expired)...Roma, beefsteak, Big Boy. Ketchup, catsup? |
#34
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"Henry Kolesnik" HiFi AM is stretching the definition of HiFi! ** Not in the slightest - at least as as far as the receiver is concerned. A flat response from 20Hz to 15 kHz +/- 1 dB with low THD ( 0.5% or less) and low background noise is a genuine "hi-fi" signal - better by far than the reproduction from a typical cassette deck which is riddled with audible defects AM does not have. Designing and building a good receiver is not a trivial task. ** A receiver capable of recovering the transmitted audio signal faithfully is not very difficult - many amateurs have successfully built them. The inhibitions to hi-fi that most associate with the AM band are not inherent in AM as a technique. ........... Phil |
#35
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"Henry Kolesnik" wrote in message . .. HiFi AM is stretching the definition of HiFi! Designing and building a good receiver is not a trivial task. When I was a kid in Jr High and didn't know any better I used whatever was at hand or I could scrounge and most projects usually worked, and even worked better when certain parts were substituted by trial and error. But in reality none compared to the war surplus receivers I converted. I'm fond on my 1957 RCA's frequency response on the "broad" setting. I made some recordings of it he http://www.scaptura.com/radio/audio/...radio_Samples/ -- Jon Scaptura http://radio.scaptura.com |
#36
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Looks like an envelope detector can perform well. See my post
over in a.b.p.radio with diagrams. Below is the text without the diagrams: After reading Brian's web page on modulation acceptance http://n2.net/k6sti/ma.htm I decided to try some simulations of the AA5 envelope detector and got results similar to Brian's page before any mods. Then I decided to try using that second diode 12AV6's and 12SQ7s come with. That second diode will do the AVC function, thus leaving the first diode doing only the audio envelope detection. As Brian described, the AVC filter cap tends to back bias the envelope detector in convential AA5 circuits, causing clipping at low valleys of the modulation. Moving the AVC to its own diode gets rid of that problem. Also reducing the envelope detector resistance value to 150K from 500K also helps (you will lose about 3dB of audio, which isn't that much). And with the AVC now separate this will only mildly affect the AVC (by about 1dB). And when you move the AVC pick-off cap to the plate of the IF tube, this drop goes away. This was observed in a real radio I tried this mod in. If I can believe my simulation results, I get distortion products nearly 50dB down at 95% modulation index. IIRC, 95% is an FCC rule for AM stations. The simulation circuit tried to factor in the loading of the AVC detector on the source 455KHz signal on the envelope detector performance. Also the circuit simulates a little "contact potential" on the vacuum tube diodes with the 1V source and 10meg resistor. To modify an AA5 style AM receiver, unground the extra diode in the 'AV6. Disconnect the AVC resistor (usually 2.2 to 3.3 megs) from the detected audio line. Add a 220K resistor across the half meg volume control to get a load of 150K on the envelope detector. Now connect the free end of the AVC resistor to the newly freed diode plate. And connect that diode plate to ground via a 470K resistor. And from the diode plate to the IF tube plate goes a 30pF cap. See diagram. This would cost 2 extra parts in production, the 470K resistor and 30pF cap. 'AV6's shipped with the extra diode already. This should make for better sound from consoles and bigger table sets. And AM sections of tube AM/FM receivers where AM was an afterthought. It probably won't much help that tiny Japanese AA5... |
#37
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Robert Casey wrote: Looks like an envelope detector can perform well. See my post over in a.b.p.radio with diagrams. Below is the text without the diagrams: Unfortunately I cannot see the ABPR post you say you posted. ABSE seems a more reliable place to post a schematic perhaps. Patrick Turner. After reading Brian's web page on modulation acceptance http://n2.net/k6sti/ma.htm I decided to try some simulations of the AA5 envelope detector and got results similar to Brian's page before any mods. Then I decided to try using that second diode 12AV6's and 12SQ7s come with. That second diode will do the AVC function, thus leaving the first diode doing only the audio envelope detection. As Brian described, the AVC filter cap tends to back bias the envelope detector in convential AA5 circuits, causing clipping at low valleys of the modulation. Moving the AVC to its own diode gets rid of that problem. Also reducing the envelope detector resistance value to 150K from 500K also helps (you will lose about 3dB of audio, which isn't that much). And with the AVC now separate this will only mildly affect the AVC (by about 1dB). And when you move the AVC pick-off cap to the plate of the IF tube, this drop goes away. This was observed in a real radio I tried this mod in. If I can believe my simulation results, I get distortion products nearly 50dB down at 95% modulation index. IIRC, 95% is an FCC rule for AM stations. The simulation circuit tried to factor in the loading of the AVC detector on the source 455KHz signal on the envelope detector performance. Also the circuit simulates a little "contact potential" on the vacuum tube diodes with the 1V source and 10meg resistor. To modify an AA5 style AM receiver, unground the extra diode in the 'AV6. Disconnect the AVC resistor (usually 2.2 to 3.3 megs) from the detected audio line. Add a 220K resistor across the half meg volume control to get a load of 150K on the envelope detector. Now connect the free end of the AVC resistor to the newly freed diode plate. And connect that diode plate to ground via a 470K resistor. And from the diode plate to the IF tube plate goes a 30pF cap. See diagram. This would cost 2 extra parts in production, the 470K resistor and 30pF cap. 'AV6's shipped with the extra diode already. This should make for better sound from consoles and bigger table sets. And AM sections of tube AM/FM receivers where AM was an afterthought. It probably won't much help that tiny Japanese AA5... |
#38
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Patrick Turner wrote:
Robert Casey wrote: Looks like an envelope detector can perform well. See my post over in a.b.p.radio with diagrams. Below is the text without the diagrams: Unfortunately I cannot see the ABPR post you say you posted. ABSE seems a more reliable place to post a schematic perhaps. Hi Pat, just posted it over in ABSE. "Improving envelope detector...." |
#39
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Robert Casey wrote: Patrick Turner wrote: Robert Casey wrote: Looks like an envelope detector can perform well. See my post over in a.b.p.radio with diagrams. Below is the text without the diagrams: Unfortunately I cannot see the ABPR post you say you posted. ABSE seems a more reliable place to post a schematic perhaps. Hi Pat, just posted it over in ABSE. "Improving envelope detector...." I see no schematic visible at ABSE with title "Improving envelope detector..". I see only :- '''''''''''''''''''''''"Robert Casey" wrote in message ... [snip] This should make for better sound from consoles and bigger table sets. It probably won't much help that tiny Japanese AA5... I admire your improvements but it seems that since most all toob sets are collecibles, changing the circuitry in any way would cause them to be no longer "stock from the factory", i.e. they'd be modified. And if you did modify a collectible radio without telling the buyer, it would be grounds for calling you a dishonest seller. And as you said, there's probably not much point in it for most cheaper radios.''''''''''''''''''''''''''''''''''''''''''' '''' I have to agree with the sentiments here about collectables, but one reason I don't bother collecting many AM radios is their poor sound, and to improve them, you have to modify them, and I do just that if there is no other way to repair them, and if an owner is happy about it. Hopefully they'll run well for another 50 years, and the next repairist will have to make similar decisions I have. I refuse to allow a major slice of my brief time on our dear little blue planet be entirely taken up with collections of anything, unless they are part of my work earning a living. Patrick Turner. |
#40
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I admire your improvements but it seems that since most all toob sets are collecibles, changing the circuitry in any way would cause them to be no longer "stock from the factory", i.e. they'd be modified. And if you did modify a collectible radio without telling the buyer, it would be grounds for calling you a dishonest seller. True to some extent, though it would be an easily reversed mod. The real reason manufacturers didn't install this circuit was that it would cost one resistor and one capacitor extra, plus the labor of wiring it in. In a consumer product, every fraction of a penny you can shave becomes significant after millions of units made. And most people didn't seem to mind the extra distortion. And as you said, there's probably not much point in it for most cheaper radios.'''''''''''''''''''''''''''''''''''''''''' ''''' I have to agree with the sentiments here about collectables, but one reason I don't bother collecting many AM radios is their poor sound, and to improve them, you have to modify them, and I do just that if there is no other way to repair them, and if an owner is happy about it. Hopefully they'll run well for another 50 years, and the next repairist will have to make similar decisions I have. This same technique should help the AM section of a tuner sound better, in those receivers where AM was an afterthought ("Oh, just throw in a 6BE6, make that 6BA6 FM IF amp also do the AM IF, and use the diodes of that 6AV6 over there..."). |
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