What's on your SCA?

[tomservo]

Are a lot of stations still using SCA for anything?

In an old copy of FM Atlas I found recently it listed the various things stations had put on, but even in this 1995 edition only about half the stations utilized the service.

Does it affect reception or anything using SCA?

 

[littlejohn]

Yes it affects reception... coverage will suffer slightly (the amount being a function of the injection level, the subcarrier content, and the subcarrier frequency), because the noise floor will increase slightly. Some older receivers had severe heartburn from subcarriers; modern ones are not nearly as badly affected. Since the change in reception is purely subjective to each listener (at what point do >you< change stations because of noise on the received signal?) the effect is quite hard to measure. If you have an Audemat box and their Golden Ear software, you canb to a degree quantify the effect. Presumeably, you could then make a judgement as to whether the change is worth the money you get renting the subcarrier. My experience has been that data transmission does the least damage, and audio programming not related to the main audio does the worst. My totally subjective opinion is, a top ten station in a top 25 market is better off without it.

 

[tomservo]

Interesting.

In some mutlipath prone parts of various towns I've heard stations that often took on a very unusual sound in challenging reception areas... Almost a "tunnel" or whistling sound in high end; I've always wondered if that was terrain caused or had something to do with an SCA or other service.

The public radio station in Birmingham, AL ran RDS for a while that was audible in the audio during quiet phases. There was this chk-chk-chk-chk in the background. It went away when they shut that down.

Considering that SCA decoding radios are, um, out of the mainstream then, I'd say it doesn't make much sense to implement this service.

 

[Doctor_Technical]

Zach:

Some earlier versions of RDS encoders had a "less than perfect" output spectrum, byproducts of which would leak back into the baseband spectrum. For RDS to be audible with current equipment, something has to be installed wrong or operated egregiously out of tolerance.

Mississippi Public Broadcasting still uses 67 kHz for their radio-reading service. The service is still actively used and supported.

Zach, since you are somewhat close to the Inverness MPB transmitter I'd be glad to show you the system the next time I'm up there.

Paul E. Burt
Global Security Systems, an RDS alerting company

 

[TPO]

There are a few stations in this area using SCA. One has the local radio reading service on 67 khz and uses the 92 khz for transmitter telemetry. Another uses the 67khz for talkback to their remote site.

 

[PaulBWalkerJr]

When I worked for CCR Williston, we had KYYZ and KEYZ in the same building.. and our transmitter telemtry was sent back to the station via SCA to the Moseley.(spelling?)

 

[littlejohn]

Using the subcarrier for remote return - or subaudible on AM - is a fairly common and cost effective solution for remotely located plants. They can usually be run at very low injection which means a minimal degredation of the signal. One thing which bothers me about these installations though. Why do so many of these systems have a 'Filament On' tally on the return?

 

[EDwalker]

One thing which bothers me about these installations though. Why do so many of these systems have a 'Filament On' tally on the return?

Hehe. But thats exactly why I've preferred - if a land line isn't available - a cell phone remote connection rather than subcarrier return. When
you've got a site so remote you can't get phone service, it usually means its tough to get to or takes a long time. Its nice being able to read the
line voltage (among other things) when the transmitter is off the air....if ya know what I mean.

 

[littlejohn]

Yeh, but pretty much everything out there offers a dialup backup now anyhow. I let the jock read a box instead of beeping and booping and maybe turning something he shouldn't. I can call it and scan it if I need. Best of botrh worlds.

 

[tomservo]

Doctor_Technical, check your Messages.