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General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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24th Oct 2019, 3:07 am | #21 | |
Nonode
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,943
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Re: AM Broadcast Signal
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The original BBC FL4/55 filter, of 1973, steep cut from 5 kHz combined with a 3 dB lift at 5 kHz: The IBA ILR curve, from 1977: And according to this, by 1993, the BBC had eased up slightly on the “brickwall”, with the steep cut -3dB point moved out to 5.8 kHz: Cheers, |
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24th Oct 2019, 9:42 am | #22 |
Nonode
Join Date: Jan 2004
Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area.
Posts: 2,965
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Re: AM Broadcast Signal
Thanks Synchrodyne, very interesting.
So it looks like the sound quality of some of the AM transmitters has improved slightly since the 1970's especially with the improved compression techniques. On some of my best radios including my Hacker Hunter RP38A, its now just a joy to listen to BBC R4 on 198Khz. I notice there is still quite a difference between the commercial stations with Absolute on 1215Khz sounding quite reasonable but some of the Smooth stations sound harsh and flat with the top end of the Audio cut off with to much compression. I wonder if this would be shown on an SDR.
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Simon BVWS member |
24th Oct 2019, 10:19 am | #23 |
Octode
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 1,320
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Re: AM Broadcast Signal
I was lucky enough to work in La Paz in the Andes about 20 years ago doing a media survey. I took with me an HF225 receiver amongst other things.
One local station I heard on MW sounded almost like an FM station. I opened the rx bw to maximum (can't remember now but probably 15kHz) and it sounded excellent! A good strong, not too limited or compressed AM station on a wide-band IF setting sounds excellent. One reason why our so-called 'pantry transmitters' can sound so good. In Europe the bands are (or were) very crowded and bw restriction is absolutely essential to limit adjacent channel interference, particularly at night. But in less densely populated areas this is much less important, and dare I say it, regulation is probably more casually enforced... |
24th Oct 2019, 1:06 pm | #24 |
Dekatron
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 3,684
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Re: AM Broadcast Signal
I've just dug out my pre-1997 (last time I had anything to do with domestic MF) notes and performance spec for BBC TX AM broadcasting: 60Hz - 5kHz plus/minus 1db (WRT 1kHz at 40% mod).
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Regds, Russell W. B. G4YLI. |
26th Oct 2019, 2:51 am | #25 | |
Pentode
Join Date: Sep 2018
Location: Devon, UK.
Posts: 151
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Re: AM Broadcast Signal
Ian G4JQT:
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I gather that Monique used an Optimod processor, thus demonstrating that they didn't have to be set up for maximum impact. I believe the Orban Optimod 9100 had a day/night switch, for less bandwidth at night. |
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