Just wondering, what frequency response did FCC need for proof for AM stations from the 40s to 60s? Also, what could you get for audio from 5 tube AM radios of the 50s? Also, as a little kid , remember that you shoud not listen to a car radio with motor off for any period of time, for fear of killing the battery.
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AM Radio in 40s to 60s.
- Thread starter mgpt6
- Start date
mgpt6 said:
As one of those "little kids" I remember the hum of those old AM radio's as they warmed up. I also remember the heat they produced and amount of energy they consumed. But remember, cars of the day, especially early in the decade, tended to have six-volt batteries which were small by today's 12-volt thin-wall versions. Those old cars also had generators (versus today's alternators) which did not have large generation capacities nor did they charge with the engine at idle. It is unlikely you would completely discharge the battery with the radio unless left on for a prolonged period but it was possible to drain it enough that starting the engine might not be successful.
Interestingly enough, my current ride, a 2011 Hyundai Santa Fe has a much larger charging system but still has a warning displaying on the nav system about leaving the radio on with the engine not running.
You ask a good question about the AM frequency response of the day. I want to say it was 20 - 7500hz but I don't recall the +/- db range. Seems it wasn't 1db, but 3 seems too extreme. Could it have been 2? The noise spec was -45 or -50db. Distortion limits were pretty high by today's standards...seems that the distortion limits were different at different frequencies? Maybe 3.5% at the low-mid frequencies and a little higher on the higher frequencies? Hopefully someone who was more into the AM side of things than I will recall the specifics. There was also a spec called Carrier Shift. I want to say that the carrier could not vary more than 5% between unmodulated and modulated conditions--chances are that rule still stands. Been a long time since I did an AM proof. Now what were people getting in real life? With an all tube transmitter into a dummy antenna at 1010 WCSI Columbus,Indiana in 1977, I was pretty proud of the numbers I was getting, so I remember them well : Frequency response was within +/1db 30 - 11000hz and -3db at 15000hz. Distortion was 0.5% at 400hz with 95% modulation and the noise level missed the FM spec by 1 db at -59db. It was a daytime station and I had the distortion analyzer on the transmitter every 2 weeks and kept these numbers consistently. And if I slacked off, the PD could hear the distortion starting to creep up...I had him spoiled.
The old 5 tube radios had far better high frequency response than today's AM radios...it seems 5khz response was pretty common with some getting closer to 8khz. There were a few AM tuners with a Wide/Narrow switch and in the Wide mode, they passed plenty of 10khz audio as evidenced by the 10khz whistle and/or the need for a 10khz whistle filter.
The car radios you speak of that ate the battery in the car had tubes in them and needed a couple hundred volts for the plates in the tubes. Getting 200 volts from a car battery was quite a challenge. The method of choice was to use a vibrator that reversed the polarity of the DC power into the transformer many times per second, effectively presenting the transformer with something that resembled AC power that it could use. Inefficient method, but it worked. Adding the filament power to that and you can see why the radio was quite power hungry. I was way too young to own a car in the 50's (and before) when these types of radios were common, but in the early 60's when I was getting interested in radio, I bought a few of them at auction sales for 25 or 50 cents and with the help of a car battery (thanks dad!), I got them to work. You could hear the vibrator purring if you listened closely to it.
Thanks for reminding me of some fond memories from the very dawn of my interest in radios that eventually led me to my broadcast engineering vocation!
The old 5 tube radios had far better high frequency response than today's AM radios...it seems 5khz response was pretty common with some getting closer to 8khz. There were a few AM tuners with a Wide/Narrow switch and in the Wide mode, they passed plenty of 10khz audio as evidenced by the 10khz whistle and/or the need for a 10khz whistle filter.
The car radios you speak of that ate the battery in the car had tubes in them and needed a couple hundred volts for the plates in the tubes. Getting 200 volts from a car battery was quite a challenge. The method of choice was to use a vibrator that reversed the polarity of the DC power into the transformer many times per second, effectively presenting the transformer with something that resembled AC power that it could use. Inefficient method, but it worked. Adding the filament power to that and you can see why the radio was quite power hungry. I was way too young to own a car in the 50's (and before) when these types of radios were common, but in the early 60's when I was getting interested in radio, I bought a few of them at auction sales for 25 or 50 cents and with the help of a car battery (thanks dad!), I got them to work. You could hear the vibrator purring if you listened closely to it.
Thanks for reminding me of some fond memories from the very dawn of my interest in radios that eventually led me to my broadcast engineering vocation!
All the AM proofs I've seen before the NRSC came into being were done from 50 cycles to 15,000 cycles. Hz and KHz for you young whippersnappers’ (what DOES that mean anyway?!?).
The only limit to the high frequency would have been the 15 KHz low-pass filter on the Moseley/Marti STL or phone line. Don't remember a low pass on the CBS Volumax/Audimax pair.
The only limit to the high frequency would have been the 15 KHz low-pass filter on the Moseley/Marti STL or phone line. Don't remember a low pass on the CBS Volumax/Audimax pair.
Carrier shift has become something desirable these days. It's at the heart of the "Dynamic Carrier Control" algorithms which can cut power consumption by somewhere between 18% and 37% depending on the algorithm chosen and the format. It's been used in Europe for a decade or more and only recently accepted by The FCC. Doesn't require prior permission; only notification that a station has adopted it. Of course most modulation monitors become useless when DCC is in use but they're no longer required so checking things with an oscilloscope periodically is good practice.
I used to have a car radio hooked up to a 6v car battery that I used out in the middle of nowhere as a 'portable'. When the battery ran down I used to swap the battery with one in a manual shift car (remember sticks ???). Then a push start and a short hill got the engine going to re-charge the battery. Anyway, I used to get about three days of 6 hour use before the battery would no longer run the radio.
N
nocomradio
Guest
One thing I seem to recall about early radios in vehicles, was that before the vibrator came along, there was a sort of generator in the form of an electric motor that made the plate voltage. Something along the lines of a phase generator as is commonly used to generate 3 phase power where it isn't available. That unit was located under the rear seat or other out of the way location and it required a fair amount of power just for itself.
I also think that some of the "you'll flatten the battery" was just rumor and conjecture. Most radios would go for hours on battery power.
I also think that some of the "you'll flatten the battery" was just rumor and conjecture. Most radios would go for hours on battery power.
"One thing I seem to recall about early radios in vehicles, was that before the vibrator came along, there was a sort of generator in the form of an electric motor that made the plate voltage"
I believe the unit was called a "Genmotor."
I believe the unit was called a "Genmotor."
Genmotor might have been a trademarked name, but the generic term is dynamotor.
Commonly used up into maybe the early 1950s in mobile transmitters.
Commonly used up into maybe the early 1950s in mobile transmitters.
I remember seeing those in transmitters but can't say I recall one in a car radio...but those could well have been gone from the auctions by the early/mid 60's.RadioFan2J3 said:
N
nocomradio
Guest
Couldn't remember the name, but that is it!
Seems they fall under the whole category of motor-generators. Same as rotary phase generators for three phase as I mentioned above. Using a motor to generate higher or different power for various uses. A quick web search reveled that many of them used for radio were implemented in aircraft radios. I do seem to recall seeing them mentioned in some old automotive catalogs from the 30's, so maybe they were surplus, or not very widely used. I can see how they would pull a battery down in short order though.
Seems they fall under the whole category of motor-generators. Same as rotary phase generators for three phase as I mentioned above. Using a motor to generate higher or different power for various uses. A quick web search reveled that many of them used for radio were implemented in aircraft radios. I do seem to recall seeing them mentioned in some old automotive catalogs from the 30's, so maybe they were surplus, or not very widely used. I can see how they would pull a battery down in short order though.
As I recall, the AM proof back in the '60s required measurements between 50 and 7500 Hz. I think the +/- was 1 dB (not positive!) for most of the band, with a loosening at the ends. This topic sure brings back memories (good and bad!) of hours spent in the middle of the night in grungy mouse-infested conditions, trying to get the proof done before morning drive. I did have an AM that I was proud of back then -- pretty much flat from 50 to 13k. Technically, AM was a far better service than it is now.
"As I recall, the AM proof back in the '60s required measurements between 50 and 7500 Hz. I think the +/- was 1 dB"
It was +/- 1dB between 50 and 7500 Hz. 7500 Hz to 10000 Hz, +/- 3dB.
Many AM transmitters could pass 30-15,000 Hz.
It was +/- 1dB between 50 and 7500 Hz. 7500 Hz to 10000 Hz, +/- 3dB.
Many AM transmitters could pass 30-15,000 Hz.
No truer words have ever been spoken in this forum.local oscillator said:
AM back in the day was superior to nowadays. No NRSC limitations then. Receivers for the band were better. Less man made electrical noise. We need to go back to no NRSC curves and allowing at least response to 10 Khz analogue. And outlawing HD Radio on AM. How about opening up Long Wave and allowing HD Radio there as a new domestic broadcast band? Better yet, make the new band Digital Radio Mondial.
No kidding Ken...back then, kids in school would talk about listening to skywave signals on their transistor radios on a routine basis. No one thought anything was unusual about listening to Chicago stations in Georgia or New York City stations in Ohio...it was the norm. What was once the norm is now impossible in many areas due to the above mentioned reasons. And they call this progress.Kent T said:
K
kenglish
Guest
Did anybody see the movie, "Pirate Radio"? It was amazing to see depictions of teens listening to an offshore AM station, on transistor radios inside school dorms, or in hospitals.
I'm taking a radio with me the next time I go to the hospital for any reason....I'll let you know if it hears a station :
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I'm taking a radio with me the next time I go to the hospital for any reason....I'll let you know if it hears a station :
.BobOnTheJob said:
Who needs the ionosphere when streaming works better? Those of us (like me) who want to listen to distant radio stations can do so, and much more reliably than in the old days. TuneIn, Radio.com, and iHeartRadio made the ionosphere obsolete.
It's not about the transmission method; it's about the programming. Being a ex-Chicagoan in Phoenix, I can listen to The Score or ESPN Chicago any time I want to listen to Chicago sports talk, either on my PC or my phone. I can't do that on an Ancient Modulation radio. Then-WMAQ, WGN, WBBM, and WLS were barely audible here on winter nights at one time, but that time was before the mid '70s. Not possible today, with the rare exception of WBBM.
Many stations' marketing departments and/or management folks get it and acknowledge that they are available nationwide, even if the sales department doesn't care. All stations that stream are national or world-wide (unless the streams are blocked from access outside the US) broadcasters by definition. But they can still provide local content that interests their own area, or people from their own area. This is much better than hoping that the ionosphere cooperates for a few hours a night.
Bottom line: Except for hams, the ionosphere is a liability in 2012, not an asset. And streaming is still broadcasting.
Sorry, but listening on line is not the same as skywave. Although I do listen on line on occasion. Skywave is cooler.
And, you can't do that in the car yet. And don't tell me I can do it on my smart phone. That can run into money. And, for tha matter, I don't have a smart phone.
And, you can't do that in the car yet. And don't tell me I can do it on my smart phone. That can run into money. And, for tha matter, I don't have a smart phone.
KeithE4 said:
Well, yes, but not more fun (unless content is your only reason for listening).
In the 50's I had a little AM transistor radio which I carried pretty much everywhere and listened for stations in "exotic" places which then seemed far, far away. I even had a little notebook where I logged all my DX's. When I was in my bedroom I had a great big old combo shortwave/AM radio and long wire antenna and did the same thing. I can only remember listing to one distant program (some sort of music program from a station in S.F.) regularly as my primary purpose was DXing.
To pass those long overnight shifts while in the navy I did the same DXing but using RTTY or Morse instead of AM.
Nowadays I use the Internet to find streams of content (herewith a shameless plug for the best Oldies station in the universe KODS out of Carnelian Bay, California). The Internet, with its streaming stations, means I don't have to settle for local stations whose formats are not to my liking.
I still DX occasionally and most recently was able to reliably bring in a S/W station from Australia every afternoon. While their accents and adverts were somewhat interesting the subject matter (gardening) was not. ;D
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