September 10, 2020 at 7:19 am #47775kb101engineerParticipantSeptember 10, 2020 at 9:56 am #47776ScreamerParticipant
Cool!September 10, 2020 at 11:23 am #47777
The first time that I heard a reading for the blind service on an SCA subcarrier, I was about 13. I was amazed that such a service existed. From the description of all the different types of content carried on Gaule’s networks, including current news, I imagine that running this operation keeps him quite busy.September 10, 2020 at 12:03 pm #47778
I met Jerry Gaule about 46 years ago. He used to hang around the KKEY transmitter and was always involved in some personal radio station, usually in Battleground, as memory serves. Coincidentally, I also knew Jerry Delaunay, having met him on my transportation job. In addition, I once did a Golden Hours program, myself although I only remember doing it once.September 10, 2020 at 12:57 pm #47779lastdayParticipant
Very cool indeed.September 11, 2020 at 7:22 am #47782
(…waiting for Gerry’s reply freaking out because we’re discussing his operations in here…)
KFAE-67 and KPBX-67 used to be simulcasts of Washington Talking Book and Braille Library’s Evergreen RRS which shut down for lack of funding in IIRC 2013 or 2014. It’s good to see that somebody’s filling the void left behind by their (and Golden Hours’) departure. KFAE’s 67 kHz audio, as I used to observe it when vacationing in Pendleton, was always very tinny and distorted during the Evergreen simulcast years, like it was being fed from Seattle over a telephone line (it probably was) with shitty EQ. Hopefully this has been fixed and they’re picking up CGR directly from the stream.
Hopefully KUOW (Evergreen’s origination point) will also pick it up. Would be nice if KQAC or KBOO grab it. Doubt that Only Portland Broadcasting would touch it knowing what they did to Golden Hours. But this begs a question. How viable is a broadcast radio reading service these days, considering how vastly improved assisted information systems are in the late 2010s compared to, say, a decade ago? Outside of its core demographic (54-90 Boomers/Silents/late Greatests, a lot of whom probably don’t even have computers or don’t want to learn to use DAISY systems) I don’t see it surviving through the end of the ’30s as they die off and are replaced by the generations who were brought up using the current technologies. But who knows.
KFAE also broadcast the CGR 1 Radio Reading Service to blind and handicapped listeners on its 67kHz subcarrier. However, this requires a special FM radio capable of receiving such broadcasts; it cannot be received on a standard FM radio.
Boy, that Wikipedia text sounds familiar. I wonder who wrote that? Art imitates life. :wink wink:September 11, 2020 at 11:19 am #47783
I once had access to an SCA unit and the crosstalk was completely unacceptable! Hopefully, they’ve improved, in the last 45 years. The whole concept was pretty much replaced by SAP on television sets.September 11, 2020 at 11:38 am #47784
I played a little bit with SCA years ago, and my greatest curiosity was how to manage the crosstalk. I once heard a mass-produced radio badged “Vietnamese Public Radio” that sounded pretty good.
In my experiments, I tried two different approaches to demodulating the subcarrier: using an LM565 with the applications circuit that appeared in the Radio Shack Semiconductor Reference Handbook and using a narrowband FM demodulator IC salvaged from an old 49 MHz cordless telephone. My impression of the LM565 is that its voltage controlled oscillator tried to follow the incoming SCA signal but could never match it exactly; there were faint heterodynes that changed with the modulation. The telephone IC came with a companion 455 kHz ceramic filter and quadrature coil. I used the IC’s built-in mixer to upconvert the SCA signals to 455 kHz. This gave a slightly better result, but the cross-talk grunge was still there. It is possible that real SCA receivers use wider IF filters than what I used in my experiments.September 11, 2020 at 5:03 pm #47789Andy BrownParticipant
“tried to follow the incoming SCA signal but could never match it exactly; there were faint heterodynes that changed with the modulation.”
Re: Heterodynes> The very reason that the DSSC stereo difference channel is demodulated by using the transmitted 19 kHz pilot used to modulate in the exciter and then filtered out which is doubled in the receiver and re-inserted back into the envelope for demod using the exact same oscillator frequency you start with.
Re: Noise >Having said that, and if I recall accurately, the minimum separation required for measuring sub to main and main to sub was only -37 dB back when you had to do FM transmitter annual proof of performance measurements. I had an SCA when I was Chief at 106.7 (we used it as a backup to send telemetry from the transmitter to the studio and used a sub carrier on the STL microwave as backup command signals path from studio to transmitter) but I forget what the separation requirement measurement was or if I even did one since it wasn’t on most of the time.September 11, 2020 at 8:21 pm #47794
I once had access to an SCA unit and the crosstalk was completely unacceptable! Hopefully, they’ve improved, in the last 45 years. The whole concept was pretty much replaced by SAP on television sets.
They have. Modern SCA rigs worth spending money on tend to have rather good filtering and a narrowband front-end tuned specifically for SCA listening. I have a little no-name Chinese “subcarrierusa” portable tunable SCA/FM/AM rig (which has been on many a road trip) that I found on Sleazebay about 15 years ago which works very well. Yes there is some main channel/L-R crosstalk (which is unavoidable in any SCA radio) but it’s not viscerally repulsive like some older purpose-built or more recent modified off-the-shelf receivers are. Some of the current fixed single-channel rigs have such tight filtering they almost sound like you’re listening to a better-quality AM station without the skywave interference.
I’ve never used any of the Metrosonix rigs (almost bought a boombox from them several years ago, though) so I can’t comment on how they work, but I know SCA services with Web sites often tend to recommend them.
You must have been using an ancient McMartin Industries TR55D, which Muzak used to issue (as well Muzak’s own STR-500 which was just the McMartin with a different logo and model number on the front panel). It had a stupidly wide SCA front-end and would produce crosstalk like you wouldn’t believe even under a strong subcarrier. I once read a report from a former Muzak field tech who spoke of a customer who had called asking why they were suddenly hearing lots of screaming behind the gentle instrumental music! They had a McMartin and the area’s Muzak affiliate had just flipped from easy listening on the main channel, to a heavy metal/alternative format. I’ve heard them myself, recrystalled for the simulcast (backup STL?) of KIXI over IIRC KJR/67 about 10 years ago, and it was as bad as people stated. It was a far cry from the audio the same SCA produced on my little portable.
Now, I do like the McMartin for its build quality. They’re all discrete transistor systems (not one IC!) and are impossible to kill, even when you want to. Reading through the marketing copy for Muzak’s stringent quality-control policies on the backs of some of their 1970s Stimulus Progression albums, which was kind of the peak period when they were using them, one wonders how they even allowed such a rig into their operations for as long as they did. It must have required the PA amp’s low-bass filter be set pretty tight.September 12, 2020 at 1:09 am #47799
I borrowed the unit from someone and think it was Stan Cox but my memory is really vague.September 21, 2020 at 9:25 am #47867
Also remember that SCA and SAP are virtually the same thing, just the frequencies and bandwidths are different. I once had a mid-2000s Sony ICF36 with the Elving ELF2A SCA demodulator and used to listen to Golden Hours on channel 10 with it and it sounded excellent. With a minimum of coaxing it could also receive the 102 kHz subcarrier which channels 8 and 12 used to have.
It was a terrible SCA rig because it was so wide, but it could receive it.September 22, 2020 at 11:06 am #47876
Nosignalallnoise’s mention of “hearing lots of screaming behind the gentle instrumental music” reminds me of my last experiments with SCA, using the IR3N06 IC scavenged from a cordless phone. The radio station which was transmitting the easy listening SCA was KLBJ-FM, Austin, TX. From what I saw on the oscilloscope, it appeared that they were using very high average modulation levels on their main channel and composite clipping, so I thought that this was a pretty extreme test of SCA.
IR3N06 is a Sharp part number, but Motorola an equivalent device, the MC3357 at one time.September 26, 2020 at 4:54 pm #47949
I’ve heard what I think you’re talking about. You’re tuning around and find what sounds like a very loud and distorted SCA, but it’s the station’s sum and difference carriers are so overmodulated they spill over into the SCA bandwidth. It almost sounds like you’re tuning the sideband of a strong AM station. From my own observations it happens primarily on 67.
Of course a little bit of splatter is normal and should be expected on SCA even on a very selective receiver. Excessive crosstalk either means the receiver’s subcarrier frontend section is too wide (like an unmodded McMartin or the modded Sony) or the station’s trying a little too hard to “stand out” above its competition…. or both.
I’ve actually coaxed some of the ICOM rigs on Global Tuners to bring in SCA audio by playing with the narrowband FM filters and 1 kHz fine-tuning. It’s doable but doesn’t work very well since the ICOMs aren’t meant for it and aren’t filtered accordingly. The stations’ main channels usually obliterate any SCA audio. If you want to experiment, though, ordah yaself a pizza, bring up one of the rigs in da Noo Yawk area and try WBAI since (last I hoid) they use both 67 and 92 kHz (99.567 or 99.592 IIRC). It would help if GT had a spectrum or waterfall display.September 27, 2020 at 10:38 am #47954
In my experiments with the IR3N06 narrowband FM IC, I took the composite output of an FM receiver’s detector, and performed some rudimentary high-pass filtering and lots of attenuation. I then fed this to the built-in mixer in the IC. The idea here was to upconvert the subcarriers to 455 kHz. Thus, instead of using a crystal with the local oscillator in the IR3N06, I used an AM radio local oscillator coil and a varactor diode, so that the subcarrier detector could be tunable.
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