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Old 3rd Sep 2018, 2:51 pm   #1
Scott37
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Default Historic AM audio quality

A question that has intrigued me for some time: I think I read somewhere that pre-1978 when the 9 kHz separation was introduced, some medium wave transmitting stations operated at a much greater bandwidth than is permitted today. I have also read that old valve radios were better quality than the AM tuner included in modern radios. Does this mean that medium wave / AM radio sounded much better in the old days than it does now?
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Old 3rd Sep 2018, 4:45 pm   #2
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Default Re: Historic AM audio quality

I can't specifically answer your question but I can tell you that in the 60's Joe public (me) was much less critical than today. The only decent source of "pop" music in those days was Luxembourg and later on, the "pirates". The reception from Luxembourg was often very poor but we listened and enjoyed many hours of it. Also most folk had no experience of the high quality FM stereo broadcasts we went on to enjoy later.
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Old 3rd Sep 2018, 5:01 pm   #3
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Default Re: Historic AM audio quality

Yes to all of the above

We were mostly less critical, but we certainly enjoyed it when things were working well. We weren't unaware. Live music was available and ears were as good then as today.

Transmitters were allowed to have more extensive sidebands, so more audio frequency extent at the top end. Transmissions were not compressed to hell and beyond so you got good dynamic range on the good stations and poor attempts at audio processing on the poor ones (but they often had the material you wanted as John said, so you listened anyway)

Simpler receivers back then had wider selectivity. Less good for avoiding adjacent stations, nicer on the wide stations with no one noisy next to them. Modern receivers were engineered for the narrower channels of today and the tendency to use ceramic block filters made them quite narrow.

It was a good time to be listening. It was never boring even if I didn't know what the infra-draw system was.

FM seemed a bit too good, too predictable. It felt like there was something missing.

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Old 3rd Sep 2018, 5:58 pm   #4
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Default Re: Historic AM audio quality

I have an off air prom recording made from one of the Radio 3 MW transmitters in 1969 (not by me). It's not obvious that it's not from an FM source and the only giveaway is the occasional burst of interference from passing thunderstorms. Obviously it's mono, but the audio bandwidth is as good as you could expect from a domestic 3.75ips recording from 1969.

AM coverage in hifi tuners from the 70s onwards is generally a bit of an afterthought and not intended for serious listening.
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Old 3rd Sep 2018, 5:58 pm   #5
kalee20
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Default Re: Historic AM audio quality

Quote:
Originally Posted by Scott37 View Post
I have also read that old valve radios were better quality than the AM tuner included in modern radios.
That's probably true in general! I don't have access to a modern hi-fi tuner, but certainly in the late 1930's there were some astonishingly good AM radios, in terms of sensitivity, selectivity, signal-to-noise ratio, immunity to overload, and AGC action. Even the middle-of-the road sets seem to be able to still put up a better performance than a modern set.

I have a 2-year-old, quite posh car, with DAB, FM, and AM radio. AM tuning is in 9kHz steps, but performance in terms of sensitivity and sound quality is lousy.
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Old 3rd Sep 2018, 6:24 pm   #6
Peter88gate
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Default Re: Historic AM audio quality

Quote:
Originally Posted by Radio Wrangler View Post

It was a good time to be listening. It was never boring even if I didn't know what the infra-draw system was.
Ah! Memories of good old Horace Batchelor, a stalwart advertiser on Radio Luxembourg with his infra-draw Pools prediction system. He was based in Keynsham, Bristol and he always spelt out the address - K-E-Y-N-S-H-A-M every time!!

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Old 3rd Sep 2018, 6:40 pm   #7
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Default Re: Historic AM audio quality

I used to work in Eynsham and got some very funny looks occasionally from younger colleagues when I said "That's Eynsham, spelt E-Y-N-S-H-A-M"
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Old 3rd Sep 2018, 6:44 pm   #8
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Default Re: Historic AM audio quality

Boris Ratular and his Infra Kecks method as we used to say.

Lawrence.
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Old 3rd Sep 2018, 6:59 pm   #9
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Default Re: Historic AM audio quality

I remember so well!(H.Batchelor)
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Old 3rd Sep 2018, 7:08 pm   #10
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Default Re: Historic AM audio quality

There are some pertinent earlier threads including:

https://www.vintage-radio.net/forum/...ad.php?t=70496

https://vintage-radio.net/forum/showthread.php?t=120815

These contain some information on historical AM transmitted bandwidths and receiver bandwidths.

I have a large file on this subject (accumulated over many years); I’ll look through to see if there is anything significant not already posted, and add it to this thread.


Cheers,
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Old 3rd Sep 2018, 7:11 pm   #11
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Default Re: Historic AM audio quality

I also remember HB, I used to tune in to Radio Luxembourg to listen to “Italy Sings” which regularly featured Mario Lanza, my favourite singer.
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Old 3rd Sep 2018, 7:27 pm   #12
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Default Re: Historic AM audio quality

Not to mention the constant switched mode power supply interference that ruins all but the strongest of AM stations these days.
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Old 3rd Sep 2018, 7:29 pm   #13
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Default Re: Historic AM audio quality

Quote:
Originally Posted by kalee20 View Post
I have a 2-year-old, quite posh car, with DAB, FM, and AM radio. AM tuning is in 9kHz steps, but performance in terms of sensitivity and sound quality is lousy.
Nearly off topic but some of us will remember putting a portable radio on the corner of the rear parcel shelf of our cars (before the days of hatchbacks) to listen to Luxembourg (didn't have the luxury of a fitted car aerial to plug in to it) and yes, the reception was even worse. Not so bad when "parked up" of course

In car entertainment in our Austin, pictured left, is a duet from the wife and myself.
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Old 3rd Sep 2018, 8:39 pm   #14
Scott37
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Default Re: Historic AM audio quality

Our radio had an external aerial socket and we had an aerial that clipped on to the glass and we could then close the window to hold it in place. I remember listening to 'Pick of the Pops' in that way. My Dad was distinctly unimpressed with Alan Freeman and very pleased when someone who could 'talk properly' (Tom Browne) replaced him.
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Old 3rd Sep 2018, 9:57 pm   #15
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Default Re: Historic AM audio quality

Old sets seem to make a much better job of AM reception, I was listening to a Murphy A186 at the weekend (from 1950 or so) and on the decent signal here from Absolute radio or Smooth radio it still sounded pleasant, it would have been interesting to hear how a top quality set could have worked before the Transmitters were restricted.

Anything with AM on it made in recent times seems very poor, the car radio I have got is virtually unusable on MW with very poor sound quality.
Steve.

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Old 3rd Sep 2018, 10:02 pm   #16
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Default Re: Historic AM audio quality

Has no one got tape recordings from the 70's? I have some from Caroline and Mi Amigo from then into the 80's, sound OK to me.
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Old 4th Sep 2018, 12:07 am   #17
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Default Re: Historic AM audio quality

From reading several magazines and threads there are a number of variables which had an effect on audio quality heard before and during the 50's.

First was the sound source. Ribbon microphones were available for live music but the final broadcast quality was subject to landline frequency response both from the theatre and to transmitter which often left a lot to be desired. Wireless World is a good source of the many complaints.

Record request shows even in the sixties often included a request for the 35mm film track rather than the record, so someone must have noticed the difference.

Second the set itself. Variable selectivity was a feature in the late 30's and 40's but both low IF frequency and heterodyne whistles were a problem; after then, it depended on how many IF stages the set had.

Loudspeaker design and the cabinet it was mounted in were known technologies in the 40's as indeed sound pressure levels but just how much the buyer was prepared to pay seemed may not be a problem for some but what the punter liked to hear is anyone's guess. The cost for a working man though was very high, typically £16 or 2 weeks wages.

Moving on, it was some time during the 50's before Radiograms had to play microgrove records and 78's had surface noise so top cut was probably the norm. Those collectors with a number of sets will be a better judge.

Looking at the radio show reports in Wireless World will give those interested a good understanding of the high end market but my experience in Yorkshire working for Rediffusion cable relay, the extension speaker boxes supplied by them would sound just as bad as the picnic radios of the day but no one complained.

Chris
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Old 4th Sep 2018, 9:47 am   #18
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Default Re: Historic AM audio quality

I have many AM radio recordings from The BBC Third Programme "Jazz Record Requsts" (Charles Fox and Alexis Korner were the DJs) made in 1959 at 3 3/4 ips which reveal a lovely, smooth, somewhat extended, treble.
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Old 4th Sep 2018, 11:02 am   #19
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Default Re: Historic AM audio quality

I've recently remastered some material recorded off-air in 1951/52 - the presence of occasional atmospherics puts the matter beyond doubt - and the quality is such that it really is difficult to believe it is recorded off transmission. Mind you, the equipment used was the best available at the time - the recordings were made by Bob Monkhouse, who even then wasn't short of a few bob - but it does indicate what was possible. The recordings are issued in the Hancock Collectibles box sets.
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Old 4th Sep 2018, 12:34 pm   #20
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Default Re: Historic AM audio quality

I well remember building my own MW/LW tuner in the 1950s on the proverbial biscuit tin. I used Repanco coils, an EF91 RF stage, EA50 diode detector, and another EF91 audio stage. Its quality was certainly 'HiFi for the day' playing through a home-built 10W amplifer (p-p EL84s) and a reasonably wide range Stentorian HF1016 10-inch speaker in a reflex cabinet.

I lived then in Doncaster with a reasonable outdoor aerial running round our house gutter board and received strong signals from Moorside Edge (Home Service) and Droitwich (Light Programme). Interference wasn't a problem unless my mother was using the vacuum cleaner. The rather limited source of pop music was typically Family Favourites on the Light Programme over Sunday lunchtime.

I recall using some treble boost to bring the HF response up to a level comparable with LP records. The Droitwich bandwidth was clearly more limited than the Moorside Edge MW transmitter, but a little more treble boost improved matters. Unfortunately, as a schoolboy, ownership of a tape recorder was beyond my reach, but on the odd occasion when I did borrow a machine, I recall problems with heterodyne whistles from the beating of the bias oscillator. When, a few years later, I built myself an FM tuner, the main advantage was the elimination of those whistles. It would be great to have kept some of the AM tapes, but I didn't!

This subjective experience of AM quality is supported by a 1948 BBC Research Report by audio acoustics engineer Tom Somerville ( http://downloads.bbc.co.uk/rd/pubs/reports/1948-09.pdf ), long before the FM days:
"The circuit arrangements in the broadcasting chain, even under the present condition of medium wave broadcasting can be quite good up to frequencies of 10,000 cls if good landlines are available. This matter is receiving attention and the frequency range is being extended from about 6,000 c/s, the war-time condition,to 8,000c/s in the first instance, and subsequently to 11,000 c/s."

I understand that in practice in the 1950s MW transmissions could achieve a 10kHz audio bandwidth and LW 8kHz. It woud be good to see some corroboration of those figures.

Certainly the better receivers of the 1930s-40s could get close to exploiting this bandwidth. For example, BBC Research Department tests on a Murphy A40C ( http://downloads.bbc.co.uk/rd/pubs/reports/1945-11.pdf ) indicated a frequency response to 9kHz within 6dB.

I believe that the AR88 receiver used on its widest IF bandwidth approached this 'HiFi' level of performance. I must test mine sometime!

By comparison with the above 'golden era' of AM broadcasting, today's 4.5kHz brick wall filters in the transmission chain sound pretty grim. No wonder that modern AM receiver design takes so little care of fidelity.

Martin
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