New K3 SN#207 built but question on AM Filter
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Hi All
just built my K3 up to the 10 watt level (still to fit the 100w pa) have been giving it a quick test and have a question, i have fitted the AM filter in FL2 (The FM will go in FL1) and the stock filter in FL3 (2.7KHz), i have set the filters for all modes and set FL2 (6KHz) for AM mode and also selectable in SSB Modes. now when i select SSB and tune to a AM signal i can alter the bandwidth to anything up to 6KHz, when i switch to AM i can only adjust the bandwidth up to 3KHz , the audio sounds like it is a 3KHz filter too, what am i doing wrong since i cant set the 6KHz bandwidth in AM. any ideas??? regards Paul M0BMN K3 S/N 207 __________________________________________________________ Sent from Yahoo! Mail - a smarter inbox http://uk.mail.yahoo.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: New K3 SN#207 built but question on AM Filter
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Paul,
Lyle answered that earlier today. You are not doing anything wrong, that is just the result of the bandwidth required by different modulation techniques. The bandwidth displayed is the *audio* bandwidth. An AM signal requires *twice* the audio bandwidth in the IF, so your 6 kHz IF filter is limiting the audio bandwidth to 3 kHz. SSB reception on the other hand allows the audio bandwidth to be equal to the IF bandwidth, so until you can fit the 15 kHz IF filter, you are limited to using the K3 in SSB mode for AM stations that you wish to hear in Hi-Fidelity. The 6 kHz filter is great for receiving amateur AM signals - which should properly be restricted in bandwidth. 73, Don W3FPR Paul Webb wrote: > Hi All > just built my K3 up to the 10 watt level (still to fit the 100w pa) have been giving it a quick test and have a question, i have fitted the AM filter in FL2 (The FM will go in FL1) and the stock filter in FL3 (2.7KHz), i have set the filters for all modes and set FL2 (6KHz) for AM mode and also selectable in SSB Modes. > now when i select SSB and tune to a AM signal i can alter the bandwidth to anything up to 6KHz, when i switch to AM i can only adjust the bandwidth up to 3KHz , the audio sounds like it is a 3KHz filter too, what am i doing wrong since i cant set the 6KHz bandwidth in AM. > any ideas??? > regards > Paul M0BMN > K3 S/N 207 > > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by m0bmn
In a message dated 1/12/2008 3:40:37 P.M. Pacific Standard Time,
[hidden email] writes: Hi All just built my K3 up to the 10 watt level (still to fit the 100w pa) have been giving it a quick test and have a question, i have fitted the AM filter in FL2 (The FM will go in FL1) and the stock filter in FL3 (2.7KHz), i have set the filters for all modes and set FL2 (6KHz) for AM mode and also selectable in SSB Modes. now when i select SSB and tune to a AM signal i can alter the bandwidth to anything up to 6KHz, when i switch to AM i can only adjust the bandwidth up to 3KHz , the audio sounds like it is a 3KHz filter too, what am i doing wrong since i cant set the 6KHz bandwidth in AM. any ideas??? regards Paul M0BMN K3 S/N 207 ++++++++++++++++++++ It's working OK. AM bandwidth includes both sidebands. Also, if you tune in an AM station using AM mode and then switch to a SSB mode, you will note a change in the fidelity (audio band response). There was much discussion on the list a while ago on the subject. I'm looking toward the release of the fm filter that should be in excess of 12 Khz, thus improving the fidelity. The advantage of the 6 KHz filter in AM is primarily for transmitting, to maintain a legal bandwidth, and to eliminate the heterodynes to some degree. Al WA6VNN **************Start the year off right. Easy ways to stay in shape. http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: New K3 SN#207 built but question on AM Filter
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In reply to this post by m0bmn
Paul Webb wrote:
> now when i select SSB and tune to a AM signal i can alter the ] bandwidth to anything up to 6KHz, when i switch to AM i can only adjust ] the bandwidth up to 3KHz , the audio sounds like it is a 3KHz filter ] too, what am i doing wrong since i cant set the 6KHz bandwidth in AM. > any ideas??? The basic reason has already been explained, however, there are very few cases were exceeding 3kHz audio bandwidth is useful. HF broadcast stations use 5kHz channelling, which would only allow them 2.5kHz with brick wall filtering at both transmit and receive ends, although they probably do expect to suffer significant adjacent channel interference. MF broadcast stations use 9kHz channelling in Europe and 10kHz in the USA, but I suspect that adjacent channel interference is less acceptable. As they were designed to be received with LC IF filters, with poor shape factors, I suspect they don't even make use of the full channel, and if they did, they would probably be required to have filters which put the adjacent channel into the filter stop band. [ Note: excessively long lines re-wrapped. See RFC 1855. (Probably using yahoo.) ] -- David Woolley Emails are not formal business letters, whatever businesses may want. RFC1855 says there should be an address here, but, in a world of spam, that is no longer good advice, as archive address hiding may not work. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: New K3 SN#207 built but question on AM Filter
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I've seen a number of old U.S. broadcast receivers with a 10 KHz notch
filter in the audio to get rid of the high pitched hetrodynes from the adjacent channels. But the wide IF sure brightens up the music when listening to your local honky-tonk station, and nobody gave a rip how wide their IF was if their music sounded good. That's why I was hoping for the option of going as wide as I see fit when conditions allow. But then who (other than yours truly) would be using a K3 to listen to the local BC when he could be working CW while enjoying 100 Hz selectivity? Dave W5DHM > > > The basic reason has already been explained, however, there are very few > cases were exceeding 3kHz audio bandwidth is useful. HF broadcast > stations use 5kHz channelling, which would only allow them 2.5kHz with > brick wall filtering at both transmit and receive ends, although they > probably do expect to suffer significant adjacent channel interference. > > MF broadcast stations use 9kHz channelling in Europe and 10kHz in the > USA, but I suspect that adjacent channel interference is less > acceptable. As they were designed to be received with LC IF filters, > with poor shape factors, I suspect they don't even make use of the full > channel, and if they did, they would probably be required to have > filters which put the adjacent channel into the filter stop band. > > David Woolley _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: New K3 SN#207 built but question on AM Filter
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On Sun, 13 Jan 2008, Dave Martin wrote:
> adjacent channels. But the wide IF sure brightens up the music when > listening to your local honky-tonk station, We don't have any AM honky-tonk local stations...that's why a top-knotch receiver would be great to listen to the Grand Ole Opry. > But then who (other than yours truly) would be using a K3 to > listen to the local BC when he could be working CW while enjoying 100 > Hz selectivity? Can I join you if the BC is kinda, sorta, stretching it from Baltimore to Nashville kinda local? Back in the old days, one of the first things hams did that migrated up here to work in the airplane and radio plants from their country backgrounds was to insure that their receivers could tune-in "down home" stations. 73 k3hrn Thom,EIEIO Email, Internet, Electronic Information Officer www.baltimorehon.com/ Home of the Baltimore Lexicon www.tlchost.net/hosting/ Web Hosting as low as 3.49/month _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: New K3 SN#207 built but question on AM Filter
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In reply to this post by Dave Martin-2
I would. :=) I'm not a hardcore ham operator, and
one of the big selling points for the K3 for me was getting excellent broadcast radio receive capability (say, on par with a Drake R8B or AOR7030). (I currently run a K2-100 with which I'm very satisfied.) - Paul, N6LQ --- Dave Martin <[hidden email]> wrote: > I've seen a number of old U.S. broadcast receivers > with a 10 KHz notch > filter in the audio to get rid of the high pitched > hetrodynes from the > adjacent channels. But the wide IF sure brightens > up the music when > listening to your local honky-tonk station, and > nobody gave a rip how > wide their IF was if their music sounded good. > That's why I was > hoping for the option of going as wide as I see fit > when conditions > allow. But then who (other than yours truly) would > be using a K3 to > listen to the local BC when he could be working CW > while enjoying 100 > Hz selectivity? > > Dave W5DHM > > > > > > The basic reason has already been explained, > however, there are very few > > cases were exceeding 3kHz audio bandwidth is > useful. HF broadcast > > stations use 5kHz channelling, which would only > allow them 2.5kHz with > > brick wall filtering at both transmit and receive > ends, although they > > probably do expect to suffer significant adjacent > channel interference. > > > > MF broadcast stations use 9kHz channelling in > Europe and 10kHz in the > > USA, but I suspect that adjacent channel > interference is less > > acceptable. As they were designed to be received > with LC IF filters, > > with poor shape factors, I suspect they don't even > make use of the full > > channel, and if they did, they would probably be > required to have > > filters which put the adjacent channel into the > filter stop band. > > > ... > > David Woolley > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > ____________________________________________________________________________________ Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: New K3 SN#207 built but question on AM Filter
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In reply to this post by David Woolley (E.L)
On Sun, 2008-01-13 at 02:49, David Woolley wrote:
> Paul Webb wrote: > ... > The basic reason has already been explained, however, there are very few > cases were exceeding 3kHz audio bandwidth is useful. HF broadcast > stations use 5kHz channelling, which would only allow them 2.5kHz with > brick wall filtering at both transmit and receive ends, although they > probably do expect to suffer significant adjacent channel interference. > > MF broadcast stations use 9kHz channelling in Europe and 10kHz in the > USA, but I suspect that adjacent channel interference is less > acceptable. As they were designed to be received with LC IF filters, > with poor shape factors, I suspect they don't even make use of the full > channel, and if they did, they would probably be required to have > filters which put the adjacent channel into the filter stop band. Even with the 10 kHz channel spacing used in the USA, AM broadcast stations do not have 5 kHz audio bandwidth. The FCC requires a guard band between stations. As I recall, rgulations require that the audio start to drop off at about 4 kHz so that it can be down 20 dB or so by 6 kHz (the passband edge of the adjacent station). So there's not much point in the receiver audio being wider than 4 kHz. Al N1AL _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
RE: New K3 SN#207 built but question on AM Filter
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> Even with the 10 kHz channel spacing used in the USA, AM broadcast > stations do not have 5 kHz audio bandwidth. The FCC requires a guard > band between stations. As I recall, rgulations require that the audio > start to drop off at about 4 kHz so that it can be down 20 dB > or so by 6 kHz (the passband edge of the adjacent station). I don't think that's right ... or wasn't the last time I was around an AM station (I spent most of my career in TV). I remember the AM guys doing proof to 10 KHz. Admittedly, many of the directional stations could not maintain 10 KHz through the phasors and the high end got trashed at night but the old allocation systems generally kept first adjacent situations far enough apart that 10 KHz could be obtained on groundwave during the daytime. "In the day" most receivers would start to roll off somewhere around 6 KHz and the better ones had a 10 KHz notch for nighttime conditions. Given the DSP demodulation in the K3, it's a shame that there isn't an "offset" option to do "vestigial sideband" demodulation (offset the AM filter to the upper sideband or lower sideband) and demodulate carrier and one sideband for better fidelity. This would work quite well if the carrier were placed at the -6dB point on the composite filter passband since it would keep the proper ratio between carrier and sideband. Alternatively, the carrier could be moved to 1 KHz from the -6 dB point and the DSP could equalize out the 6 dB boost in audio below 1 KHz from the "opposite" sideband. 73, ... Joe, W4TV > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of Alan Bloom > Sent: Sunday, January 13, 2008 10:48 PM > To: David Woolley > Cc: [hidden email] > Subject: Re: [Elecraft] New K3 SN#207 built but question on AM Filter > > > On Sun, 2008-01-13 at 02:49, David Woolley wrote: > > Paul Webb wrote: > > > ... > > The basic reason has already been explained, however, there > are very few > > cases were exceeding 3kHz audio bandwidth is useful. HF broadcast > > stations use 5kHz channelling, which would only allow them > 2.5kHz with > > brick wall filtering at both transmit and receive ends, > although they > > probably do expect to suffer significant adjacent channel > interference. > > > > MF broadcast stations use 9kHz channelling in Europe and > 10kHz in the > > USA, but I suspect that adjacent channel interference is less > > acceptable. As they were designed to be received with LC > IF filters, > > with poor shape factors, I suspect they don't even make use > of the full > > channel, and if they did, they would probably be required to have > > filters which put the adjacent channel into the filter stop band. > > Even with the 10 kHz channel spacing used in the USA, AM broadcast > stations do not have 5 kHz audio bandwidth. The FCC requires a guard > band between stations. As I recall, rgulations require that the audio > start to drop off at about 4 kHz so that it can be down 20 dB > or so by 6 > kHz (the passband edge of the adjacent station). > > So there's not much point in the receiver audio being wider > than 4 kHz. > > Al N1AL > > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
RE: New K3 SN#207 built but question on AM Filter
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This is admittedly topic skew, but for non-critical occasional am listening, it would be nice to have a much lower cost option than the $120 filters. A cheap ceramic or 2-xtal filter, about 15Khz bw would have been a nice addition to the K3, maybe even as a st'd component.
73, Barry N1EU
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RE: Wide Filters (was:New K3 SN#207 built but question on AM Filter)
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> A cheap ceramic or 2-xtal filter, about 15Khz bw would have been > a nice addition to the K3, maybe even as a st'd component. I don't know if off the shelf ceramic filters are available at the right frequency. The issue with two or three crystal filters would be image rejection (the image is only 30 KHz away). Based on data for the INRAD 6-pole 7 MHz "front end" filter, the 8-pole filter (KFL3B-FM) should have sufficient rejection for transmit use. I suspect someone could build their own wide filter if/when parts are available. The key would be to make sure it could not be used for transmit! 73, ... Joe, W4TV > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of Barry N1EU > Sent: Monday, January 14, 2008 7:37 AM > To: [hidden email] > Subject: RE: [Elecraft] New K3 SN#207 built but question on AM Filter > > > > This is admittedly topic skew, but for non-critical > occasional am listening, > it would be nice to have a much lower cost option than the > $120 filters. A > cheap ceramic or 2-xtal filter, about 15Khz bw would have been a nice > addition to the K3, maybe even as a st'd component. > > 73, > Barry N1EU > > > > Joe Subich, W4TV-3 wrote: > > > > > >> Even with the 10 kHz channel spacing used in the USA, AM broadcast > >> stations do not have 5 kHz audio bandwidth. The FCC > requires a guard > >> band between stations. As I recall, rgulations require > that the audio > >> start to drop off at about 4 kHz so that it can be down 20 dB > >> or so by 6 kHz (the passband edge of the adjacent station). > > > > I don't think that's right ... or wasn't the last time I was around > > an AM station (I spent most of my career in TV). I remember the AM > > guys doing proof to 10 KHz. > > > > Admittedly, many of the directional stations could not > maintain 10 KHz > > through the phasors and the high end got trashed at night > but the old > > allocation systems generally kept first adjacent situations > far enough > > apart that 10 KHz could be obtained on groundwave during > the daytime. > > > > "In the day" most receivers would start to roll off > somewhere around > > 6 KHz and the better ones had a 10 KHz notch for nighttime > conditions. > > > > Given the DSP demodulation in the K3, it's a shame that there isn't > > an "offset" option to do "vestigial sideband" demodulation > (offset the > > AM filter to the upper sideband or lower sideband) and demodulate > > carrier and one sideband for better fidelity. This would > work quite > > well if the carrier were placed at the -6dB point on the composite > > filter passband since it would keep the proper ratio > between carrier > > and sideband. Alternatively, the carrier could be moved to 1 KHz > > from the -6 dB point and the DSP could equalize out the 6 dB boost > > in audio below 1 KHz from the "opposite" sideband. > > > > 73, > > > > ... Joe, W4TV > > > > > > > > > >> -----Original Message----- > >> From: [hidden email] > >> [mailto:[hidden email]] On Behalf Of Alan Bloom > >> Sent: Sunday, January 13, 2008 10:48 PM > >> To: David Woolley > >> Cc: [hidden email] > >> Subject: Re: [Elecraft] New K3 SN#207 built but question > on AM Filter > >> > >> > >> On Sun, 2008-01-13 at 02:49, David Woolley wrote: > >> > Paul Webb wrote: > >> > > >> ... > >> > The basic reason has already been explained, however, there > >> are very few > >> > cases were exceeding 3kHz audio bandwidth is useful. HF > broadcast > >> > stations use 5kHz channelling, which would only allow them > >> 2.5kHz with > >> > brick wall filtering at both transmit and receive ends, > >> although they > >> > probably do expect to suffer significant adjacent channel > >> interference. > >> > > >> > MF broadcast stations use 9kHz channelling in Europe and > >> 10kHz in the > >> > USA, but I suspect that adjacent channel interference is less > >> > acceptable. As they were designed to be received with LC > >> IF filters, > >> > with poor shape factors, I suspect they don't even make use > >> of the full > >> > channel, and if they did, they would probably be > required to have > >> > filters which put the adjacent channel into the filter stop band. > >> > >> Even with the 10 kHz channel spacing used in the USA, AM broadcast > >> stations do not have 5 kHz audio bandwidth. The FCC > requires a guard > >> band between stations. As I recall, rgulations require > that the audio > >> start to drop off at about 4 kHz so that it can be down 20 dB > >> or so by 6 > >> kHz (the passband edge of the adjacent station). > >> > >> So there's not much point in the receiver audio being wider > >> than 4 kHz. > >> > >> Al N1AL > >> > >> > >> _______________________________________________ > >> Elecraft mailing list > >> Post to: [hidden email] > >> You must be a subscriber to post to the list. > >> Subscriber Info (Addr. Change, sub, unsub etc.): > >> http://mailman.qth.net/mailman/listinfo/elecraft > >> > >> Help: http://mailman.qth.net/subscribers.htm > >> Elecraft web page: http://www.elecraft.com > >> > >> > > > > _______________________________________________ > > Elecraft mailing list > > Post to: [hidden email] > > You must be a subscriber to post to the list. > > Subscriber Info (Addr. Change, sub, unsub etc.): > > http://mailman.qth.net/mailman/listinfo/elecraft > > > > Help: http://mailman.qth.net/subscribers.htm > > Elecraft web page: http://www.elecraft.com > > > > > > -- > View this message in context: > http://www.nabble.com/New-K3-SN-207-built-but-question-on-AM-F Sent from the Elecraft mailing list archive at Nabble.com. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
RE: Wide Filters (was:New K3 SN#207 built but question on AM Filter)
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I think part of the problem is not only finding an economical AM filter,
but ALSO being able to PREVENT users from trying to TRANSMIT THROUGH IT! Tom N0SS At 09:17 01/14/2008, Joe Subich, W4TV wrote: > > A cheap ceramic or 2-xtal filter, about 15Khz bw would have been > > a nice addition to the K3, maybe even as a st'd component. > >I don't know if off the shelf ceramic filters are available at >the right frequency. The issue with two or three crystal filters >would be image rejection (the image is only 30 KHz away). Based >on data for the INRAD 6-pole 7 MHz "front end" filter, the 8-pole >filter (KFL3B-FM) should have sufficient rejection for transmit >use. > >I suspect someone could build their own wide filter if/when parts >are available. The key would be to make sure it could not be used >for transmit! > >73, > > ... Joe, W4TV > > > > > -----Original Message----- > > From: [hidden email] > > [mailto:[hidden email]] On Behalf Of Barry N1EU > > Sent: Monday, January 14, 2008 7:37 AM > > To: [hidden email] > > Subject: RE: [Elecraft] New K3 SN#207 built but question on AM Filter > > > > > > > > This is admittedly topic skew, but for non-critical > > occasional am listening, > > it would be nice to have a much lower cost option than the > > $120 filters. A > > cheap ceramic or 2-xtal filter, about 15Khz bw would have been a nice > > addition to the K3, maybe even as a st'd component. > > > > 73, > > Barry N1EU > > > > > > > > Joe Subich, W4TV-3 wrote: > > > > > > > > >> Even with the 10 kHz channel spacing used in the USA, AM broadcast > > >> stations do not have 5 kHz audio bandwidth. The FCC > > requires a guard > > >> band between stations. As I recall, rgulations require > > that the audio > > >> start to drop off at about 4 kHz so that it can be down 20 dB > > >> or so by 6 kHz (the passband edge of the adjacent station). > > > > > > I don't think that's right ... or wasn't the last time I was around > > > an AM station (I spent most of my career in TV). I remember the AM > > > guys doing proof to 10 KHz. > > > > > > Admittedly, many of the directional stations could not > > maintain 10 KHz > > > through the phasors and the high end got trashed at night > > but the old > > > allocation systems generally kept first adjacent situations > > far enough > > > apart that 10 KHz could be obtained on groundwave during > > the daytime. > > > > > > "In the day" most receivers would start to roll off > > somewhere around > > > 6 KHz and the better ones had a 10 KHz notch for nighttime > > conditions. > > > > > > Given the DSP demodulation in the K3, it's a shame that there isn't > > > an "offset" option to do "vestigial sideband" demodulation > > (offset the > > > AM filter to the upper sideband or lower sideband) and demodulate > > > carrier and one sideband for better fidelity. This would > > work quite > > > well if the carrier were placed at the -6dB point on the composite > > > filter passband since it would keep the proper ratio > > between carrier > > > and sideband. Alternatively, the carrier could be moved to 1 KHz > > > from the -6 dB point and the DSP could equalize out the 6 dB boost > > > in audio below 1 KHz from the "opposite" sideband. > > > > > > 73, > > > > > > ... Joe, W4TV > > > > > > > > > > > > > > >> -----Original Message----- > > >> From: [hidden email] > > >> [mailto:[hidden email]] On Behalf Of Alan Bloom > > >> Sent: Sunday, January 13, 2008 10:48 PM > > >> To: David Woolley > > >> Cc: [hidden email] > > >> Subject: Re: [Elecraft] New K3 SN#207 built but question > > on AM Filter > > >> > > >> > > >> On Sun, 2008-01-13 at 02:49, David Woolley wrote: > > >> > Paul Webb wrote: > > >> > > > >> ... > > >> > The basic reason has already been explained, however, there > > >> are very few > > >> > cases were exceeding 3kHz audio bandwidth is useful. HF > > broadcast > > >> > stations use 5kHz channelling, which would only allow them > > >> 2.5kHz with > > >> > brick wall filtering at both transmit and receive ends, > > >> although they > > >> > probably do expect to suffer significant adjacent channel > > >> interference. > > >> > > > >> > MF broadcast stations use 9kHz channelling in Europe and > > >> 10kHz in the > > >> > USA, but I suspect that adjacent channel interference is less > > >> > acceptable. As they were designed to be received with LC > > >> IF filters, > > >> > with poor shape factors, I suspect they don't even make use > > >> of the full > > >> > channel, and if they did, they would probably be > > required to have > > >> > filters which put the adjacent channel into the filter stop band. > > >> > > >> Even with the 10 kHz channel spacing used in the USA, AM broadcast > > >> stations do not have 5 kHz audio bandwidth. The FCC > > requires a guard > > >> band between stations. As I recall, rgulations require > > that the audio > > >> start to drop off at about 4 kHz so that it can be down 20 dB > > >> or so by 6 > > >> kHz (the passband edge of the adjacent station). > > >> > > >> So there's not much point in the receiver audio being wider > > >> than 4 kHz. > > >> > > >> Al N1AL > > >> > > >> > > >> _______________________________________________ > > >> Elecraft mailing list > > >> Post to: [hidden email] > > >> You must be a subscriber to post to the list. > > >> Subscriber Info (Addr. Change, sub, unsub etc.): > > >> http://mailman.qth.net/mailman/listinfo/elecraft > > >> > > >> Help: http://mailman.qth.net/subscribers.htm > > >> Elecraft web page: http://www.elecraft.com > > >> > > >> > > > > > > _______________________________________________ > > > Elecraft mailing list > > > Post to: [hidden email] > > > You must be a subscriber to post to the list. > > > Subscriber Info (Addr. Change, sub, unsub etc.): > > > http://mailman.qth.net/mailman/listinfo/elecraft > > > > > > Help: http://mailman.qth.net/subscribers.htm > > > Elecraft web page: http://www.elecraft.com > > > > > > > > > > -- > > View this message in context: > > http://www.nabble.com/New-K3-SN-207-built-but-question-on-AM-F >ilter-tp14780362p14800931.html >Sent from the Elecraft mailing list archive at Nabble.com. > >_______________________________________________ >Elecraft mailing list >Post to: [hidden email] >You must be a subscriber to post to the list. >Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > >Help: http://mailman.qth.net/subscribers.htm >Elecraft web page: http://www.elecraft.com > > >_______________________________________________ >Elecraft mailing list >Post to: [hidden email] >You must be a subscriber to post to the list. >Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > >Help: http://mailman.qth.net/subscribers.htm >Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Barry N1EU
I am hoping that Elecraft will have a different option for AM listening by the time that my K3 arrives (in April). Perhaps the roofing filter can be bypassed for AM listening. There are several radios out there that have DSP-only selectivity for AM reception: RX-320, Jupiter, etc. (Which also applies to transmitting on those radios). I purchased the 6kHz AM filter, but now I realize that the 15kHz FM filter is better suited for full-fidelity AM listening. The 6kHz filter may not see much use, even if I were to transmit on AM.
According to the ARRL web site, 9 kHz is the ARRL's recommendation for double-sideband AM. A typical AM Broadcast signal's BW is 10kHz. Passing these signals through a 6kHz filter will result in a restricted-audio sounding signal. This is good for AM ham reception on the crowded 75m band but it is not full-fidelity sounding on AM BCB or SW. (I have heard some SW stations that must be using a wider bandwidth than 10kHz, based on how nice they sound on an old Hallicrafters radio - the kind with just the IF transformers for selectivity. Radio China International comes to mind). 73, John W2XS |
Re: New K3 SN#207 built but question on AM Filter
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In reply to this post by David Woolley (E.L)
David Woolley wrote:
> HF broadcast stations use 5kHz channelling, which would only allow them > 2.5kHz with brick wall filtering at both transmit and receive ends, although > they probably do expect to suffer significant adjacent channel interference. Absolutely, and there is a lot of it -- which is why it's so cool to listen to SWBC in SSB mode, one sideband or the other. Since in AM mode it is one station's lower sideband interfering with another station's upper sideband (or vice-versa), choosing the sideband being interfered with the least is a terrific aid to listening. Bill W5WVO SWL since 1957 (age 10) _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: New K3 SN#207 built but question on AM Filter
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In reply to this post by Barry N1EU
John W2XS wrote:
> the other). If the highest modulating frequency is 5kHz, then the BW of > each sideband will be 5kHz, and the total AM signal will have a BW of 10kHz. > At the receiver, one of the sidebands is discarded, and the other is > demodulated. So, a 6kHz filter should produce a nice sounding AM signal > since a 5kHz-wide signal is passing through it. If you do that with standard AM (envelope) detection, you will get up to about 20% (even) harmonic distortion. You will probably get better audio treating it as SSB, in spite of frequency and phase errors. To reproduce single sideband full and reduced carrier signals accurately, you need synchronous detection. (It should also be quieter for double sideband full carrier.) (For Scroggie fans, consider the phasor diagram for 100% modulation at the point where the sideband is at 90 degrees to the carrier. That gives an amplitude of sqrt(2) when you should just have the nominal carrier amplitude of 1. At 0 and 180 degrees, you get the expected amplitudes of 2 and 0.) -- David Woolley "The Elecraft list is a forum for the discussion of topics related to Elecraft products and more general topics related ham radio" List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm> _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
AM bandwidth, the rest of the story :=)
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In reply to this post by Joe Subich, W4TV-3
OK< I looked it up. According to Title 47, part 73.44 of the FCC
regulations, <http://www.fcc.gov/mb/audio/bickel/amfmrule.html#AM> the modulation of an AM broadcast station must be down 25 dB at 10.2 kHz from the carrier. Assuming a 3-pole low-pass filter (e.g. a pi-network), the filter attenuation is 18 dB per octave, which implies a cutoff frequency of no more than 3.9 kHz. The -3 dB bandwidth would be a little higher than that. That's about what I remember from my broadcasting days many, many years ago. If you think about it, a double-sideband AM signal can't have a bandwidth greater than 1/2 the channel spacing without interfering with adjacent channels. And it has to be somewhat less than that given real-world filters. So there is not much point in having a receiver with much more than 4 kHz or so audio response (8 kHz or so RF bandwidth). > I remember the AM guys doing proof to 10 KHz. Right, in order to confirm that the modulation is down 25 dB at 10.2 kHz. Al N1AL On Sun, 2008-01-13 at 20:40, Joe Subich, W4TV wrote: > > Even with the 10 kHz channel spacing used in the USA, AM broadcast > > stations do not have 5 kHz audio bandwidth. The FCC requires a guard > > band between stations. As I recall, rgulations require that the audio > > start to drop off at about 4 kHz so that it can be down 20 dB > > or so by 6 kHz (the passband edge of the adjacent station). > > I don't think that's right ... or wasn't the last time I was around > an AM station (I spent most of my career in TV). I remember the AM > guys doing proof to 10 KHz. > > Admittedly, many of the directional stations could not maintain 10 KHz > through the phasors and the high end got trashed at night but the old > allocation systems generally kept first adjacent situations far enough > apart that 10 KHz could be obtained on groundwave during the daytime. > > "In the day" most receivers would start to roll off somewhere around > 6 KHz and the better ones had a 10 KHz notch for nighttime conditions. > > Given the DSP demodulation in the K3, it's a shame that there isn't > an "offset" option to do "vestigial sideband" demodulation (offset the > AM filter to the upper sideband or lower sideband) and demodulate > carrier and one sideband for better fidelity. This would work quite > well if the carrier were placed at the -6dB point on the composite > filter passband since it would keep the proper ratio between carrier > and sideband. Alternatively, the carrier could be moved to 1 KHz > from the -6 dB point and the DSP could equalize out the 6 dB boost > in audio below 1 KHz from the "opposite" sideband. > > 73, > > ... Joe, W4TV > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: New K3 SN#207 built but question on AM Filter
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In reply to this post by David Woolley (E.L)
David Woolley (Elecraft) wrote:
Oops. I calculated this with one sideband equal in amplitude to the carrier, well that may well be true if you are trying squeeze the last Hz out of the receiver filter, the corrected values are: > If you do that with standard AM (envelope) detection, you will get up > to about 20% (even) harmonic distortion. You will probably get better 22% (need to double check this, but no time now.) > audio treating it as SSB, in spite of frequency and phase errors. > (For Scroggie fans, consider the phasor diagram for 100% modulation at > the point where the sideband is at 90 degrees to the carrier. That > gives an amplitude of sqrt(2) when you should just have the nominal sqrt (1.5) > carrier amplitude of 1. At 0 and 180 degrees, you get the expected Half the nominal carrier amplitude. > amplitudes of 1.5 and 0.5) > > -- David Woolley Emails are not formal business letters, whatever businesses may want. RFC1855 says there should be an address here, but, in a world of spam, that is no longer good advice, as archive address hiding may not work. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: AM bandwidth, the rest of the story :=)
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In reply to this post by Alan Bloom
Back in the 'old days' of AM broadcasting in the US, the local stations
were spread out with greater than 10 KHz spacing so they would not interfere even when received on wide bandwidth AM receivers. There were a few 'clear channel' superstations that had no competition nationwide and IIRC, they had a 20 kHz swath of spectrum. Those were mostly Westinghouse stations which ran 50,000 watts and could be heard over great distances. On normal stations, one would receive maximum fidelity with a 10 kHz IF filter (if a straight sided filter would have been available back then) because the modulation was supposed to be limited to less 5 kHz (or so rumor had it in those days). 73, Don W3FPR Alan Bloom wrote: > OK< I looked it up. According to Title 47, part 73.44 of the FCC > regulations, <http://www.fcc.gov/mb/audio/bickel/amfmrule.html#AM> the > modulation of an AM broadcast station must be down 25 dB at 10.2 kHz > from the carrier. Assuming a 3-pole low-pass filter (e.g. a > pi-network), the filter attenuation is 18 dB per octave, which implies a > cutoff frequency of no more than 3.9 kHz. The -3 dB bandwidth would be > a little higher than that. > > That's about what I remember from my broadcasting days many, many years > ago. If you think about it, a double-sideband AM signal can't have a > bandwidth greater than 1/2 the channel spacing without interfering with > adjacent channels. And it has to be somewhat less than that given > real-world filters. So there is not much point in having a receiver > with much more than 4 kHz or so audio response (8 kHz or so RF > bandwidth). > > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: AM bandwidth, the rest of the story :=)
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The FCC"s frequency assignment policy protected these Class 1A stations
from both co-channel and adjacent channel interference, if my recollection of 40 year old rules is correct. Obviously greater co-channel protection was provided than adjacent channel (+/- 10 KHz) protection. As far as frequency response, I worked my way through law school as a transmitter engineer at a 50 KW AM station in Detroit 35 years or so ago. We had an RCA 50KW ampliphase transmitter model BTA-50H, for daytime operation. This particular transmitter design did not have a modulation transformer, but rather had two independent signal paths that were combined at the output port. When the signals were in phase, you got modulation peaks; when out of phase 180 degrees, you got the modulation minimum. There's a copy of the RCA review article on these transmitters at http://www.fmamradios.com/Ampliphase.html. In any event, when we ran an audio proof on the BTA-50H, we took it up to 7.5 KHz, which I recall as being the upper limit required by the then-current FCC rules. The BTA-50H would do quite well in both distortion and in amplitude response over the full audio range, if the exciter had been recently tuned, itself a challenging task, particularly with the original vacuum tube exciter. RCA came out with a solid state replacement exciter around 1975, which helped stability quite a bit. Neither of the conventional transmitters (a 10KW RCA and a 1 kW Gates) would do as well in the audio department as the ampliphase. This was before the days of asymmetrical modulation, i.e., the limit was 100% for both positive and negative modulation. (Now 125% positive / 100% negative, as I recall.) A number of AM stations now run AM digital mode, which uses two multi-channel digital signals in the upper and lower 10 KHz adjacent channel spectrum. I have some spectrum analyzer images of these signals that I'll put up on my web site one of these days. Jack K8ZOA Don Wilhelm wrote: > Back in the 'old days' of AM broadcasting in the US, the local > stations were spread out with greater than 10 KHz spacing so they > would not interfere even when received on wide bandwidth AM > receivers. There were a few 'clear channel' superstations that had no > competition nationwide and IIRC, they had a 20 kHz swath of spectrum. > Those were mostly Westinghouse stations which ran 50,000 watts and > could be heard over great distances. On normal stations, one would > receive maximum fidelity with a 10 kHz IF filter (if a straight sided > filter would have been available back then) because the modulation was > supposed to be limited to less 5 kHz (or so rumor had it in those days). > > 73, > Don W3FPR > > Alan Bloom wrote: >> OK< I looked it up. According to Title 47, part 73.44 of the FCC >> regulations, <http://www.fcc.gov/mb/audio/bickel/amfmrule.html#AM> the >> modulation of an AM broadcast station must be down 25 dB at 10.2 kHz >> from the carrier. Assuming a 3-pole low-pass filter (e.g. a >> pi-network), the filter attenuation is 18 dB per octave, which implies a >> cutoff frequency of no more than 3.9 kHz. The -3 dB bandwidth would be >> a little higher than that. >> >> That's about what I remember from my broadcasting days many, many years >> ago. If you think about it, a double-sideband AM signal can't have a >> bandwidth greater than 1/2 the channel spacing without interfering with >> adjacent channels. And it has to be somewhat less than that given >> real-world filters. So there is not much point in having a receiver >> with much more than 4 kHz or so audio response (8 kHz or so RF >> bandwidth). >> > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
RE: AM bandwidth, the rest of the story :=)
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In reply to this post by Alan Bloom
> OK< I looked it up. According to Title 47, part 73.44 of the FCC > regulations, <http://www.fcc.gov/mb/audio/bickel/amfmrule.html#AM> > the modulation of an AM broadcast station must be down 25 dB at > 10.2 kHz from the carrier. The information at 73.44(b) only applies to out of band emissions. You will note that the section applies additional limitations at 20 KHz from carrier, 30 KHz from carrier, etc. > Assuming a 3-pole low-pass filter (e.g. a pi-network), the filter > attenuation is 18 dB per octave, which implies a cutoff frequency > of no more than 3.9 kHz. The -3 dB bandwidth would be a little > higher than that. Any AM station that used a simply pi-network filter would have real problems since they would sound "muddy" an lack punch. I think you will find that they are using filters much more complex than a simple pi-network - usually with a sharp cut-off ("brick wall") response to maintain response out to 10 KHz. For example, the audio response specification for the Harris AM transmitters is: +0.2/-0.8 dB, 20 Hz to 10 kHz. Ref. 1 kHz at 95% modulation. See www.broadcast.harris.com/radio/transmission/analog.asp and look at the various specification sheets for the Analog AM transmitters. 73, ... Joe, W4TV > -----Original Message----- > From: Alan Bloom [mailto:[hidden email]] > Sent: Tuesday, January 15, 2008 1:50 AM > To: Joe Subich, W4TV > Cc: [hidden email] > Subject: AM bandwidth, the rest of the story :=) > > > OK< I looked it up. According to Title 47, part 73.44 of the FCC > regulations, <http://www.fcc.gov/mb/audio/bickel/amfmrule.html#AM> the > modulation of an AM broadcast station must be down 25 dB at 10.2 kHz > from the carrier. Assuming a 3-pole low-pass filter (e.g. a > pi-network), the filter attenuation is 18 dB per octave, > which implies a > cutoff frequency of no more than 3.9 kHz. The -3 dB > bandwidth would be > a little higher than that. > > That's about what I remember from my broadcasting days many, > many years > ago. If you think about it, a double-sideband AM signal can't have a > bandwidth greater than 1/2 the channel spacing without > interfering with > adjacent channels. And it has to be somewhat less than that given > real-world filters. So there is not much point in having a receiver > with much more than 4 kHz or so audio response (8 kHz or so RF > bandwidth). > > > I remember the AM guys doing proof to 10 KHz. > > Right, in order to confirm that the modulation is down 25 dB at 10.2 > kHz. > > Al N1AL > > > On Sun, 2008-01-13 at 20:40, Joe Subich, W4TV wrote: > > > Even with the 10 kHz channel spacing used in the USA, AM broadcast > > > stations do not have 5 kHz audio bandwidth. The FCC > requires a guard > > > band between stations. As I recall, rgulations require > that the audio > > > start to drop off at about 4 kHz so that it can be down 20 dB > > > or so by 6 kHz (the passband edge of the adjacent station). > > > > I don't think that's right ... or wasn't the last time I was around > > an AM station (I spent most of my career in TV). I remember the AM > > guys doing proof to 10 KHz. > > > > Admittedly, many of the directional stations could not > maintain 10 KHz > > through the phasors and the high end got trashed at night > but the old > > allocation systems generally kept first adjacent situations > far enough > > apart that 10 KHz could be obtained on groundwave during > the daytime. > > > > "In the day" most receivers would start to roll off > somewhere around > > 6 KHz and the better ones had a 10 KHz notch for nighttime > conditions. > > > > Given the DSP demodulation in the K3, it's a shame that there isn't > > an "offset" option to do "vestigial sideband" demodulation > (offset the > > AM filter to the upper sideband or lower sideband) and demodulate > > carrier and one sideband for better fidelity. This would > work quite > > well if the carrier were placed at the -6dB point on the composite > > filter passband since it would keep the proper ratio > between carrier > > and sideband. Alternatively, the carrier could be moved to 1 KHz > > from the -6 dB point and the DSP could equalize out the 6 dB boost > > in audio below 1 KHz from the "opposite" sideband. > > > > 73, > > > > ... Joe, W4TV > > > > > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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