[IRCA] 738 & SAH's from Michigan - Friday morning 9/7/2012
738 Tahiti is already in this morning @ 1030 UTC with some audio, but I'm plagued with t-storm noise right now. I'm also seeing a carrier fading in and out on 737.8 - has anyone noticed this before? It's been here the last few mornings and always disappears or fades out completely by 1100 UTC. The fading would suggest that it isn't local, but I could find no reference to anything being so far off frequency here. I see a lot of talk about SAH's (sub-audible hets I presume?). Can someone provide good audio demonstrating this phenomena? Thanks, Tim Tromp West Michigan ___ IRCA mailing list IRCA@hard-core-dx.com http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: irca@hard-core-dx.com
Re: [IRCA] 738 & SAH's from Michigan - Friday morning 9/7/2012
You have already described it yourself. The terminology dates back to the 1960's-70's when offsets were measured using trace oscilloscopes to see the visual representation of the frequency difference between two stations close in frequency. An audible heterodyne was often not present with differences of a few kHz, thus 'subaudible'. Visually, you could 'see' the offset, and sometimes the beat between the two signals which might or more likely not be audible. So you saw the SAH on the scope. You used the same equipment to determine the actual offset value. You could also manually count the beats - audibly or visually, as applicable - to determine the offset. Russ Edmunds 15 mi NNW of Philadelphia Grid FN20id FM: Yamaha T-80 & Onkyo T-450RDS w/ APS9B @15'; Grundig G8 AM: Modified Sony ICF 2010's barefoot --- On Fri, 9/7/12, Tim Tromp wrote: > From: Tim Tromp > Subject: [IRCA] 738 & SAH's from Michigan - Friday morning 9/7/2012 > To: "irca@hard-core-dx.com" > Cc: "ABDX" > Date: Friday, September 7, 2012, 6:51 AM > 738 Tahiti is already in this morning > @ 1030 UTC with some audio, but > I'm plagued with t-storm noise right now. I'm also > seeing a carrier > fading in and out on 737.8 - has anyone noticed this > before? It's been > here the last few mornings and always disappears or fades > out completely > by 1100 UTC. The fading would suggest that it isn't > local, but I could > find no reference to anything being so far off frequency > here. > > I see a lot of talk about SAH's (sub-audible hets I > presume?). Can > someone provide good audio demonstrating this phenomena? > > Thanks, > Tim Tromp > West Michigan > > ___ > IRCA mailing list > IRCA@hard-core-dx.com > http://montreal.kotalampi.com/mailman/listinfo/irca > > Opinions expressed in messages on this mailing list are > those of the original contributors and do not necessarily > reflect the opinion of the IRCA, its editors, publishing > staff, or officers > > For more information: http://www.ircaonline.org > > To Post a message: irca@hard-core-dx.com > > ___ IRCA mailing list IRCA@hard-core-dx.com http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: irca@hard-core-dx.com
Re: [IRCA] 738 & SAH's from Michigan - Friday morning 9/7/2012
It's possible that your 737.8 is a spur from something further east. Here in IL, it would've been almost as good as yesterday for DU's if not for bad storm QRN. I managed some audio on 702 and 738 during lulls but quit as it was too noisy. 738 put a reasonable het on 740 on the truck rx at times. 73 KAZ Barrington IL -Original Message- >From: Tim Tromp >Sent: Sep 7, 2012 5:51 AM >To: "irca@hard-core-dx.com" >Cc: ABDX >Subject: [IRCA] 738 & SAH's from Michigan - Friday morning 9/7/2012 > >738 Tahiti is already in this morning @ 1030 UTC with some audio, but >I'm plagued with t-storm noise right now. I'm also seeing a carrier >fading in and out on 737.8 - has anyone noticed this before? It's been >here the last few mornings and always disappears or fades out completely >by 1100 UTC. The fading would suggest that it isn't local, but I could >find no reference to anything being so far off frequency here. > >I see a lot of talk about SAH's (sub-audible hets I presume?). Can >someone provide good audio demonstrating this phenomena? > >Thanks, >Tim Tromp >West Michigan > >___ >IRCA mailing list >IRCA@hard-core-dx.com >http://montreal.kotalampi.com/mailman/listinfo/irca > >Opinions expressed in messages on this mailing list are those of the original >contributors and do not necessarily reflect the opinion of the IRCA, its >editors, publishing staff, or officers > >For more information: http://www.ircaonline.org > >To Post a message: irca@hard-core-dx.com > ___ IRCA mailing list IRCA@hard-core-dx.com http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: irca@hard-core-dx.com
Re: [IRCA] 738 & SAH's from Michigan - Friday morning 9/7/2012
Russ wrote, > An audible heterodyne was often not present with differences of a few kHz, > thus 'subaudible'. I think you meant to say a difference of a few _Hertz_ >Visually, you could 'see' the offset, and sometimes the beat between the two >signals which might or more likely not be audible. So you saw the SAH on the >scope. You used the same equipment to determine the actual offset value. > > You could also manually count the beats - audibly or visually, as applicable > - to determine the offset. > > Russ Edmunds Another important factor is that the input to the vertical amplifier in the scope is taken from the AGC buss of the receiver, and not from the audio section. This is for the same reason, the audio response of the receiver at frequencies of 15 Hz or less is poor, just as your hearing is poor at such low frequencies. It is _recommended_ to use a DC-coupled oscilloscope. The original published work on SAH's was done (ca. 1965) by Gordon Nelson using Dumont 304 scopes with DC vert coupling and with scopes using P7 phosphor, so the horizontal sweep rate could be reduced to maybe 1 or 2 sweeps/second, if needed. This technique worked best when there were just 2 signals present, so that the difference would be clearly seen as a single "beat" wave. Also the AGC time constant could be modified for better LF response. Fourier analysis could be used to identify multiple sine waves present. If you were looking at two signals, a few Hz apart, and at similar strengths, you could hear a "whoosh-whoosh-whoosh" as the two signals beat together. Nelson had discovered that two signals, a few Hz apart, *and differing by maybe => 30 dB*, could both be detected by looking for the very small displacement in the AGC voltage, when it was too small to be detected audibly. Since Nelson spent time looking for secondary European signals fading in underneath much stronger big signals, this was useful to him. He used published data from the EBU monitoring stations that listed European carrier freq's to 1 Hz resolution as a guide to identifying signals too weak to produce audio. Note, too that freq tolerances back then were much looser than today. The existance of a weak "beat" was a precursor indicator of the possibility of hearing audio as the signal hopefully faded up to readability. Getting an audible signal was always the goal. This was a guide to where to spend your DXing effort, as a SAH display of an audible SAH beat is sort of superfluous info. There is no reason this technique couldn't be done today, except for strong artifacts from sideband splash from signals 2 to 5 kHz away, masking the weak SAH trace, being so much worse today than we had in the 1960's. Bob Foxworth k2euh ___ IRCA mailing list IRCA@hard-core-dx.com http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: irca@hard-core-dx.com
Re: [IRCA] 738 & SAH's from Michigan - Friday morning 9/7/2012
Indeed, I meant Hz. Thanks for pointing that out. I expect it might be difficult to locate a working or even repairable Dumont 304 today... Russ Edmunds 15 mi NNW of Philadelphia Grid FN20id FM: Yamaha T-80 & Onkyo T-450RDS w/ APS9B @15'; Grundig G8 AM: Modified Sony ICF 2010's barefoot --- On Fri, 9/7/12, rfoxw...@tampabay.rr.com wrote: > From: rfoxw...@tampabay.rr.com > Subject: Re: [IRCA] 738 & SAH's from Michigan - Friday morning 9/7/2012 > To: irca@hard-core-dx.com > Date: Friday, September 7, 2012, 1:57 PM > Russ wrote, > > > An audible heterodyne was often not present with > differences of a few kHz, thus 'subaudible'. > > I think you meant to say a difference of a few _Hertz_ > > >Visually, you could 'see' the offset, and sometimes the > beat between the two signals which might or more likely not > be audible. So you saw the SAH on the scope. You used the > same equipment to determine the actual offset value. > > > > You could also manually count the beats - audibly or > visually, as applicable - to determine the offset. > > > > Russ Edmunds > > > Another important factor is that the input to the vertical > amplifier in the > scope is taken from the AGC buss of the receiver, and not > from the audio > section. This is for the same reason, the audio response of > the receiver > at frequencies of 15 Hz or less is poor, just as your > hearing is poor at such > low frequencies. It is _recommended_ to use a DC-coupled > oscilloscope. The > original published work on SAH's was done (ca. 1965) by > Gordon Nelson using Dumont > 304 scopes with DC vert coupling and with scopes using P7 > phosphor, so the > horizontal sweep rate could be reduced to maybe 1 or 2 > sweeps/second, if needed. > This technique worked best when there were just 2 signals > present, so that > the difference would be clearly seen as a single "beat" > wave. Also the AGC time > constant could be modified for better LF response. Fourier > analysis could be > used to identify multiple sine waves present. > > If you were looking at two signals, a few Hz apart, and at > similar strengths, > you could hear a "whoosh-whoosh-whoosh" as the two signals > beat together. > Nelson had discovered that two signals, a few Hz apart, *and > differing by > maybe => 30 dB*, could both be detected by looking for > the very small displacement > in the AGC voltage, when it was too small to be detected > audibly. Since Nelson > spent time looking for secondary European signals fading in > underneath > much stronger big signals, this was useful to him. He used > published data > from the EBU monitoring stations that listed European > carrier freq's to 1 Hz > resolution as a guide to identifying signals too weak to > produce audio. Note, > too that freq tolerances back then were much looser than > today. > > The existance of a weak "beat" was a precursor indicator of > the possibility > of hearing audio as the signal hopefully faded up to > readability. Getting an > audible signal was always the goal. This was a guide to > where to spend your > DXing effort, as a SAH display of an audible SAH beat is > sort of superfluous info. > > There is no reason this technique couldn't be done today, > except for strong > artifacts from sideband splash from signals 2 to 5 kHz away, > masking > the weak SAH trace, being so much worse today than we had in > the 1960's. > > Bob Foxworth k2euh > > > > > ___ > IRCA mailing list > IRCA@hard-core-dx.com > http://montreal.kotalampi.com/mailman/listinfo/irca > > Opinions expressed in messages on this mailing list are > those of the original contributors and do not necessarily > reflect the opinion of the IRCA, its editors, publishing > staff, or officers > > For more information: http://www.ircaonline.org > > To Post a message: irca@hard-core-dx.com > > ___ IRCA mailing list IRCA@hard-core-dx.com http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: irca@hard-core-dx.com
Re: [IRCA] 738 & SAH's from Michigan - Friday morning 9/7/2012
Here you go Tim. http://www3.telus.net/public/shallpat/4tim/ contains two .wav files from 1333UT this morning, both in LSB, one with the receiver tuned to 828.4kHz, the other tuned to 738.4 kHz There's a faster SAH on 828; if you play back the file on a spectral display program, you'd see one het at 400.05 Hz, the other at 402.7Hz, 2.65Hz separation, so the swishing sound repeats about 2 1/2 times per second. I suspect these could be 3GI and JOBB?? (the MWoffset list says that they have about a 1.5Hz separation, but the records are from 5 and 6 years ago. Guess I should try measuring them when I know for sure which station I'm hearing!) 738 has a slightly slower SAH (the two carriers are closer together), but it also sounds a bit more complex, because there are at least five (!) different hets there: 396.5, 400.9 and 401.5 Hz, with the two strongest forming the slower SAH (compared with 828) at 398.0 and 399.4Hz The strongest are likely 2NR and R. Polynesie? Both were heard this morning. Hope this helps. Nick At 10:51 07-09-12, you wrote: I see a lot of talk about SAH's (sub-audible hets I presume?). Can someone provide good audio demonstrating this phenomena? ___ IRCA mailing list IRCA@hard-core-dx.com http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: irca@hard-core-dx.com
Re: [IRCA] 738 & SAH's from Michigan - Friday morning 9/7/2012
Great information presented here, thanks Bob. And thanks to everyone else who replied and provided sample audio clips, it's much appreciated! -Tim On Fri, 2012-09-07 at 13:57 -0400, rfoxw...@tampabay.rr.com wrote: > Russ wrote, > > > An audible heterodyne was often not present with differences of a few kHz, > > thus 'subaudible'. > > I think you meant to say a difference of a few _Hertz_ > > >Visually, you could 'see' the offset, and sometimes the beat between the two > >signals which might or more likely not be audible. So you saw the SAH on the > >scope. You used the same equipment to determine the actual offset value. > > > > You could also manually count the beats - audibly or visually, as > > applicable - to determine the offset. > > > > Russ Edmunds > > > Another important factor is that the input to the vertical amplifier in the > scope is taken from the AGC buss of the receiver, and not from the audio > section. This is for the same reason, the audio response of the receiver > at frequencies of 15 Hz or less is poor, just as your hearing is poor at such > low frequencies. It is _recommended_ to use a DC-coupled oscilloscope. The > original published work on SAH's was done (ca. 1965) by Gordon Nelson using > Dumont > 304 scopes with DC vert coupling and with scopes using P7 phosphor, so the > horizontal sweep rate could be reduced to maybe 1 or 2 sweeps/second, if > needed. > This technique worked best when there were just 2 signals present, so that > the difference would be clearly seen as a single "beat" wave. Also the AGC > time > constant could be modified for better LF response. Fourier analysis could be > used to identify multiple sine waves present. > > If you were looking at two signals, a few Hz apart, and at similar strengths, > you could hear a "whoosh-whoosh-whoosh" as the two signals beat together. > Nelson had discovered that two signals, a few Hz apart, *and differing by > maybe => 30 dB*, could both be detected by looking for the very small > displacement > in the AGC voltage, when it was too small to be detected audibly. Since Nelson > spent time looking for secondary European signals fading in underneath > much stronger big signals, this was useful to him. He used published data > from the EBU monitoring stations that listed European carrier freq's to 1 Hz > resolution as a guide to identifying signals too weak to produce audio. Note, > too that freq tolerances back then were much looser than today. > > The existance of a weak "beat" was a precursor indicator of the possibility > of hearing audio as the signal hopefully faded up to readability. Getting an > audible signal was always the goal. This was a guide to where to spend your > DXing effort, as a SAH display of an audible SAH beat is sort of superfluous > info. > > There is no reason this technique couldn't be done today, except for strong > artifacts from sideband splash from signals 2 to 5 kHz away, masking > the weak SAH trace, being so much worse today than we had in the 1960's. > > Bob Foxworth k2euh ___ IRCA mailing list IRCA@hard-core-dx.com http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: irca@hard-core-dx.com
Re: [IRCA] 738 & SAH's from Michigan - Friday morning 9/7/2012
Nick, this is a nice description and the audio samples are great. I appreciate the explanation and response, it all makes perfect sense now. Thanks, -Tim On Fri, 2012-09-07 at 21:25 +, Nick Hall-Patch wrote: > Here you go Tim. http://www3.telus.net/public/shallpat/4tim/ > contains two .wav files from 1333UT this morning, both in LSB, one > with the receiver tuned to 828.4kHz, the other tuned to 738.4 kHz > > There's a faster SAH on 828; if you play back the file on a spectral > display program, you'd see one het at 400.05 Hz, the other at > 402.7Hz, 2.65Hz separation, so the swishing sound repeats about 2 1/2 > times per second. I suspect these could be 3GI and JOBB?? (the > MWoffset list says that they have about a 1.5Hz separation, but the > records are from 5 and 6 years ago. Guess I should try measuring > them when I know for sure which station I'm hearing!) > > 738 has a slightly slower SAH (the two carriers are closer together), > but it also sounds a bit more complex, because there are at least > five (!) different hets there: 396.5, 400.9 and 401.5 Hz, with the > two strongest forming the slower SAH (compared with 828) at 398.0 and > 399.4Hz The strongest are likely 2NR and R. Polynesie? Both were > heard this morning. > > Hope this helps. > > Nick > > At 10:51 07-09-12, you wrote: > > > >I see a lot of talk about SAH's (sub-audible hets I presume?). Can > >someone provide good audio demonstrating this phenomena? > > > > > ___ > IRCA mailing list > IRCA@hard-core-dx.com > http://montreal.kotalampi.com/mailman/listinfo/irca > > Opinions expressed in messages on this mailing list are those of the original > contributors and do not necessarily reflect the opinion of the IRCA, its > editors, publishing staff, or officers > > For more information: http://www.ircaonline.org > > To Post a message: irca@hard-core-dx.com > ___ IRCA mailing list IRCA@hard-core-dx.com http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: irca@hard-core-dx.com
Re: [IRCA] 738 & SAH's from Michigan - Friday morning 9/7/2012
Hi Bob, 7.9.2012 20:57, rfoxw...@tampabay.rr.com kirjoitti: Another important factor is that the input to the vertical amplifier in the scope is taken from the AGC buss of the receiver, and not from the audio section. This is for the same reason, the audio response of the receiver at frequencies of 15 Hz or less is poor, just as your hearing is poor at such low frequencies. It is _recommended_ to use a DC-coupled oscilloscope. The original published work on SAH's was done (ca. 1965) by Gordon Nelson using Dumont 304 scopes with DC vert coupling and with scopes using P7 phosphor, so the horizontal sweep rate could be reduced to maybe 1 or 2 sweeps/second, if needed. This technique worked best when there were just 2 signals present, so that the difference would be clearly seen as a single "beat" wave. Also the AGC time constant could be modified for better LF response. Fourier analysis could be used to identify multiple sine waves present. If you were looking at two signals, a few Hz apart, and at similar strengths, you could hear a "whoosh-whoosh-whoosh" as the two signals beat together. Nelson had discovered that two signals, a few Hz apart, *and differing by maybe => 30 dB*, could both be detected by looking for the very small displacement in the AGC voltage, when it was too small to be detected audibly. Since Nelson spent time looking for secondary European signals fading in underneath much stronger big signals, this was useful to him. He used published data from the EBU monitoring stations that listed European carrier freq's to 1 Hz resolution as a guide to identifying signals too weak to produce audio. Note, too that freq tolerances back then were much looser than today. The existance of a weak "beat" was a precursor indicator of the possibility of hearing audio as the signal hopefully faded up to readability. Getting an audible signal was always the goal. This was a guide to where to spend your DXing effort, as a SAH display of an audible SAH beat is sort of superfluous info. There is no reason this technique couldn't be done today, except for strong artifacts from sideband splash from signals 2 to 5 kHz away, masking the weak SAH trace, being so much worse today than we had in the 1960's. Yes, this is very interesting. Fortunately we have now relatively cheap software defined receivers and can see the carrier traces by ±1 Hz or even better accuracy at the same time when listening. Best regards, Mauno ___ IRCA mailing list IRCA@hard-core-dx.com http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: irca@hard-core-dx.com
