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General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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17th Feb 2023, 10:12 am | #21 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
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Re: AM broadcast bandwidth?
Re Post #17
In the 1920s it was a factor in choosing Brookmans Park that it sat next to the Great North Road and some of the best quality landline circuits from central London. Last edited by Jon_G4MDC; 17th Feb 2023 at 10:21 am. |
17th Feb 2023, 11:54 am | #22 |
Nonode
Join Date: Mar 2010
Location: Dukinfield, Cheshire, UK.
Posts: 2,033
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Re: AM broadcast bandwidth?
Our local Asian Sound on 1377 kHz is flat out to +/-6 kHz, with a steep drop to noise level over the next 1 kHz.
Meanwhile, Manx Radio on 1368 kHz (not a strong signal by any means) is visible at +/-8 kHz.
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17th Feb 2023, 6:27 pm | #23 |
Heptode
Join Date: Jul 2018
Location: Worthing, West Sussex, UK.
Posts: 983
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Re: AM broadcast bandwidth?
For those interested, here is a user manual for an Orban Optimod 9100A.
AM multi band audio processor, it features a block diagram and description https://usermanual.wiki/Document/Orb...3511111063.pdf
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17th Feb 2023, 7:20 pm | #24 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
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Re: AM broadcast bandwidth?
Interesting brochure.
"Operate at 5kHz at all times to meet EBU or other international specifications" Otherwise it can be set for 12kHz if you are the only station on the dial for a few hundred miles. Swap between day and night! |
18th Feb 2023, 9:56 am | #25 |
Octode
Join Date: Jul 2009
Location: Carmel, Llannerchymedd, Anglesey, UK.
Posts: 1,497
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Re: AM broadcast bandwidth?
Here on Anglesey, Manx is the strongest kid on the block during the day. An interesting station, whose programme content varies between complete rubbish and first class. They certainly cater for all tastes! Sadly we have lost the radio Wales MW transmitter at Penmon, which was quite loud on my crystal set.
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18th Feb 2023, 11:39 am | #26 |
Octode
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 1,320
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Re: AM broadcast bandwidth?
I have a note from the Engineer in Charge, Brookmans Park dated Jan 1995:
Lowest transmitted frequency about 40Hz. Virgin Radio +/- 6.5 kHz Radio Five +/- 4.5 kHz Sunrise +/- 6.5 kHz Talk UK +/- 4.5 kHz That's old info, but shows there was room for variability depending on general programme content - i.e. speech or music. I've just checked Radio Norfolk 873 kHz +/- 6.5 kHz Five Live 909 and 693 kHz still +/- 4.5 kHz. (My pantry tx 1350 kHz +/- 9 kHz.) In my dealings with OFCOM setting up AM RSLs only a few years back, the specification was simple and clear; all radiation beyond +/- 9 kHz of the carrier should be at least 40 dB down on that carrier. I can confirm that no broadcaster would use a channel on an adjacent channel to the same or adjacent target zone, so in practice splatter onto adjacent channels doesn't matter - at least with daylight service areas. Night time is (or was) a different matter. Stations to the same MF UK target area would be at least three channels apart. I doubt any of this is significant these days as no one is routinely monitoring what's left of AM broadcasts in the UK, let alone pursuing transgressors... This non-interference coordination also took place on HF where 'friendly' broadcasters, (BBC, VOA, RCI, DW, etc. etc.) had quarterly co-ordination meetings to ensure there were no adjacent frequency or target zone clashes. We also had to keep in our heads the transmission schedules of 'friendly' broadcasters who didn't attend (RFI and Spain for example) and of course all the 'hostile' broadcasters, Radio Moscow, Radio Beijing, and the East European HF stations. This was in the 1980s - all a very long time ago now... Last edited by Ian - G4JQT; 18th Feb 2023 at 12:04 pm. |
18th Feb 2023, 8:02 pm | #27 | |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
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Re: AM broadcast bandwidth?
Quote:
Keeping tightly within your allocation should be a matter of pride for any TX operator.
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18th Feb 2023, 8:34 pm | #28 |
Banned
Join Date: Dec 2022
Location: Peterborough, Cambridgeshire, UK.
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Re: AM broadcast bandwidth?
Worth noting that BBC transmitter equipment in wartime had an audio filter that boosted the HF by 4dB at 10kHz wrt 440Hz.
See http://www.bbceng.info/ti/early/TT6_...0Equipment.pdf |
18th Feb 2023, 9:36 pm | #29 |
Heptode
Join Date: Jul 2018
Location: Worthing, West Sussex, UK.
Posts: 983
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Re: AM broadcast bandwidth?
Worth noting that BBC transmitter equipment in wartime had an audio filter that boosted the HF by 4dB at 10kHz wrt 440Hz.
Thanks Cathovisor, the Americans do similar with their NRSC Curve, which I think Virgin AM used in some form. Here is more info. for all https://www.nrscstandards.org/standa...rsc-1-1988.pdf
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18th Feb 2023, 11:13 pm | #30 | |
Nonode
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,943
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Re: AM broadcast bandwidth?
Quote:
True, but the rub is in the actual definition of “allocation”, and the associated rules for maxima outside of that allocation. As covered above, a common misperception is that MF AM channel widths are directly related to carrier spacing, thus ±4.5 kHz for 9 kHz spacing. In practice, that tends not to be the case. As an example, here is part of the response I received to a question I asked of the ABC (Australia) back in 2005: “The ABC MF AM transmissions have audio bandwidth that is restricted by the licensed spectrum (20kHz total per service, i.e. +/- 10kHz), in order to avoid interference to adjacent channels. Thus, at the time, the MF channel allocation was ±10 kHz, even though the channel spacing was (and as far as I know, still is) 9 kHz. But the ABC was clearly serious about staying within its allocation. That situation would indeed make it problematical for someone wanting to DX an adjacent channel, but I imagine that from a broadcaster viewpoint, transmission quality in the primary service area took precedence over DX’ing possibilities. I can recall a case in NZ, I think it might have been in the 1970s, but possibly a bit later, when RNZ (or it might still have been NZBC) added a new transmitter, down south I think, to expand the coverage of one of its services. It used a frequency that was in the established plan (coordinated with Australia) for that area, but hitherto unused. The local DX society got seriously bent out of shape, claiming that it inhibited DX reception of distant stations (such as Auckland from Dunedin, or somesuch.) I think the response was polite and empathetic, but of the nature that the needs of the listeners in the service area of the new transmitter did carry enough weight to take precedence over the needs of a relatively small number of DX’ers. Cheers, |
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20th Feb 2023, 11:45 am | #31 |
Pentode
Join Date: Nov 2007
Location: Cork, Ireland
Posts: 134
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Re: AM broadcast bandwidth?
Regarding DXing MW stations on frequencies 9kHz away from local ones, receivers with USB or LSB selection can be used to very good effect to audibilise the DX. All the online SDRs I have used allow this selection on MW.
Lets say for example someone's local signal on 648kHz (Caroline or anything else using the frequency) was seen as barrier to DX on the adjacent 639 or 657 - just use LSB on 639, or USB on 657. Considering the planning mentioned above (stations serving the same area usually at least 27kHz apart) , its highly unlikely one would have a strong/local signal on BOTH sides of a DX frequency, so single sideband reception can nearly always be used to good effect in these conditions. Last edited by colourking; 20th Feb 2023 at 11:51 am. |
22nd Feb 2023, 12:12 am | #32 | |
Pentode
Join Date: Sep 2018
Location: Devon, UK.
Posts: 151
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Re: AM broadcast bandwidth?
Quote:
Radio Monique were the only station AFAIK to set up their Optimod processor in this way. |
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22nd Feb 2023, 10:20 am | #33 |
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 bandwidth?
I have the official AM audio response curve, from the BBC, which show its flat from 30Hz to 5 KHz then drops off fairly rapidly after that with 6Khz at -20db down. This is quoted as limiting out of band radiation without degrading audio quality to much. This would indicate a total bandwidth tailing off at 12Khz.
I do remember many portable and car radios from the late 1970's and the 1980's which did sound awful on AM as they used something called brickwall ceramic IF filters which cut off sharply just after 4 KHz, This did eliminate the adjacent channel interference problem at night but at a terrible cost of appalling audio quality.
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22nd Feb 2023, 10:59 am | #34 |
Banned
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Re: AM broadcast bandwidth?
*Official* OFCOM spec for audio bandwidth (and other matters) here:
https://www.ofcom.org.uk/__data/asse...3/code2013.pdf AM transmission is covered in sections 3.2 and 3.5. |
23rd Feb 2023, 2:08 am | #35 | |
Octode
Join Date: Feb 2009
Location: Bletchley, Buckinghamshire, UK.
Posts: 1,205
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Re: AM broadcast bandwidth?
Quote:
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23rd Feb 2023, 11:00 am | #36 | ||
Banned
Join Date: Dec 2022
Location: Peterborough, Cambridgeshire, UK.
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Re: AM broadcast bandwidth?
Quote:
No? I'm not looking at your computer though. |
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8th Mar 2023, 8:45 pm | #37 |
Diode
Join Date: Mar 2022
Location: Shepperton, Surrey, UK.
Posts: 2
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Re: AM broadcast bandwidth?
My recollection (and it is some time ago!) was that the tv VHF transmitter sound was limited to 10 kHz, UHF 625 line sound (fm) was in theory 15kHz. The actual transmitted bandwidth was limited by the distribution links. The link to Crystal Palace was 15kHz, so London was good quality, but by the time the signal had travelled to Kirk o Shotts in Northern Scotland you were lucky to get 6.5 kHz (and the signal to noise was nothing to write home about). In the early 1970's on 625 line channels the separate audio links were replaced by the Sound in Syncs system, where the sound was pcm digital incorporated into the television sync pulse. This gave CD quality 15kHz sound throughout the country (and on the Eurovision links).
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9th Mar 2023, 12:23 am | #38 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,798
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Re: AM broadcast bandwidth?
Remember also that the apparent bandwidth of all stations being received will be widened by the phase noise of the receiver's LOs.
It isn't just a matter of occupied BW of the TX and selectivity of the RX. THere have been some awful receivers. David
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