UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > General Vintage Technology Discussions

Notices

General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc.

Closed Thread
 
Thread Tools
Old 17th Feb 2023, 10:12 am   #21
Jon_G4MDC
Nonode
 
Jon_G4MDC's Avatar
 
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
Default 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.
Jon_G4MDC is offline  
Old 17th Feb 2023, 11:54 am   #22
Andrew2
Nonode
 
Andrew2's Avatar
 
Join Date: Mar 2010
Location: Dukinfield, Cheshire, UK.
Posts: 2,034
Default 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.
__________________
Andy G1HBE.
Andrew2 is offline  
Old 17th Feb 2023, 6:27 pm   #23
Cruisin Marine
Heptode
 
Join Date: Jul 2018
Location: Worthing, West Sussex, UK.
Posts: 983
Default 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
__________________
"Behind every crowd, there's a silver Moonshine"
Cruisin Marine is offline  
Old 17th Feb 2023, 7:20 pm   #24
Jon_G4MDC
Nonode
 
Jon_G4MDC's Avatar
 
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
Default 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!
Jon_G4MDC is offline  
Old 18th Feb 2023, 9:56 am   #25
lesmw0sec
Octode
 
Join Date: Jul 2009
Location: Carmel, Llannerchymedd, Anglesey, UK.
Posts: 1,498
Default Re: AM broadcast bandwidth?

Quote:
Originally Posted by Andrew2 View Post
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.
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.
lesmw0sec is offline  
Old 18th Feb 2023, 11:39 am   #26
Ian - G4JQT
Octode
 
Ian - G4JQT's Avatar
 
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 1,320
Default 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.
Ian - G4JQT is offline  
Old 18th Feb 2023, 8:02 pm   #27
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
Default Re: AM broadcast bandwidth?

Quote:
Originally Posted by Ian - G4JQT View Post
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..
But 'unnecesarily wide' transmissions are still deeply annoying to those of us DX-minded types who are trying to ID a weak station that's 40dB down to a station on an adjacent channel, and whose 'spitch' is really intrusive.

Keeping tightly within your allocation should be a matter of pride for any TX operator.
__________________
I'm the Operator of my Pocket Calculator. -Kraftwerk.
G6Tanuki is offline  
Old 18th Feb 2023, 8:34 pm   #28
Cathovisor
Banned
 
Join Date: Dec 2022
Location: Peterborough, Cambridgeshire, UK.
Posts: 418
Default 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
Cathovisor is offline  
Old 18th Feb 2023, 9:36 pm   #29
Cruisin Marine
Heptode
 
Join Date: Jul 2018
Location: Worthing, West Sussex, UK.
Posts: 983
Default 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
__________________
"Behind every crowd, there's a silver Moonshine"
Cruisin Marine is offline  
Old 18th Feb 2023, 11:13 pm   #30
Synchrodyne
Nonode
 
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,943
Default Re: AM broadcast bandwidth?

Quote:
Originally Posted by G6Tanuki View Post

Keeping tightly within your allocation should be a matter of pride for any TX operator.

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.

“The primary determinant in the transmitted bandwidth is a sharp-cutoff lowpass filter included in the audio processing prior to the transmitter. The actual cutoff frequency sometimes has to be varied in order to meet spectrum and operational requirements. In general however, a minimum realisable bandwidth would be about 7.5kHz, and some services (ABC Radio National in Sydney for example) have realisable bandwidth out to about 9.7kHz.

“Pre-emphasis is very widely used in AM transmission to compensate for the high-frequency rolloff inherent in most types of AM receiver. The characteristic used on ABC MF services is the US NRSC characteristic curve. This is basically equivalent to an R-C time constant of 75 microseconds, with an added shelving at about 8700Hz.

“Other factors in the program chain are generally controlled to allow the transmitted signal to achieve the potential performance. In particular as many program distribution paths can also be used for FM transmissions, their quality is not a limiting factor for MF services.

“Given the above, the use of a wideband receiver can yield an audible improvement in many cases.”


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,
Synchrodyne is offline  
Old 20th Feb 2023, 11:45 am   #31
colourking
Pentode
 
Join Date: Nov 2007
Location: Cork, Ireland
Posts: 134
Default 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.
colourking is offline  
Old 22nd Feb 2023, 12:12 am   #32
Pfraser
Pentode
 
Join Date: Sep 2018
Location: Devon, UK.
Posts: 151
Default Re: AM broadcast bandwidth?

Quote:
Originally Posted by Martin_Calva View Post
Here is my recollection from years ago... (so no guarantee that the information is correct although I think it is correct)

The AM channel spacing in Europe is 9kHz. The BBC broadcast AM with audio going up to 9kHz, so strctly speaking a total bandwidth of 18kHz. However there was generally no problem of interference between channels as the level of power at the extremes of the sidebands is very small in normal music signals. And frequencies were chosen so that stations in the same area did not use adjacent channels.

My dad told me that in the 1920's there had been discussion about this subject. P P Eckersley, the chief engineer of the BBC , had made a sarcastic comment that there would only be problems if the music consisted of a choir of bats accompanied by an orchestra of dog whistles.

The channel spacing in China is 8kHz. In the 1980's a Chinese student bought a digitally tuned AM receiver in Birmingham. I advised him to confirm before he bought it that it would be suitable for use in China. The salesman assured him it would be. Then he found that its channel spacing was not be compatible with Chinese channels. I advised him to take it back for a refund, as it was not suitable for the purpose for which it has been bought and which had been stated at the time of purchase, so under the Sale of Goods Act, the shop was obliged to accept the return.

A quick look at the Quad AM3 handbook shows that it provides control of the bandwidth of the IF amplifier. The manual states that, in the wideband position of the control, frequencies up to 10 kHz can be received.
I used a Sharp 'ghetto blaster' to enjoy the audio quality of Radio Monique on 963kHz. This receiver was the only one of many I then owned which fully reproduced the station's sweet, FM-like sound. I dimly recall a MW bandwidth switch on the back of the set. My Vega Selena B212 was nearly as good for this reception; it had no bandwidth switch.

Radio Monique were the only station AFAIK to set up their Optimod processor in this way.
Pfraser is offline  
Old 22nd Feb 2023, 10:20 am   #33
Hybrid tellies
Nonode
 
Hybrid tellies's Avatar
 
Join Date: Jan 2004
Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area.
Posts: 2,965
Default 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.
__________________
Simon
BVWS member
Hybrid tellies is offline  
Old 22nd Feb 2023, 10:59 am   #34
Cathovisor
Banned
 
Join Date: Dec 2022
Location: Peterborough, Cambridgeshire, UK.
Posts: 418
Default 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.
Cathovisor is offline  
Old 23rd Feb 2023, 2:08 am   #35
m0cemdave
Octode
 
Join Date: Feb 2009
Location: Bletchley, Buckinghamshire, UK.
Posts: 1,205
Default Re: AM broadcast bandwidth?

Quote:
Originally Posted by Cathovisor View Post
*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.
Isn't that bandwidth spec missing a couple of - signs?
m0cemdave is online now  
Old 23rd Feb 2023, 11:00 am   #36
Cathovisor
Banned
 
Join Date: Dec 2022
Location: Peterborough, Cambridgeshire, UK.
Posts: 418
Default Re: AM broadcast bandwidth?

Quote:
Originally Posted by m0cemdave View Post
Quote:
Originally Posted by Cathovisor View Post
*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.
Isn't that bandwidth spec missing a couple of - signs?

No? I'm not looking at your computer though.
Cathovisor is offline  
Old 8th Mar 2023, 8:45 pm   #37
Sheppertonian
Diode
 
Join Date: Mar 2022
Location: Shepperton, Surrey, UK.
Posts: 2
Default 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).
Sheppertonian is offline  
Old 9th Mar 2023, 12:23 am   #38
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,799
Default 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
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 2:22 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.