[BC] Secondary & Tertiary Tone

[Harold Hallikainen]

> However their audio performance left something to be desired.
> That was a real problem at a time (in Australia), when we had annual
> engineering inspections by the Govt regulator - where they did audio
> performance tests on most station gear.
> The RapidQ's could barely meet the required spec in S/N (<-50dB wrt peak
> flux)and Wow & Flutter (<0.2% unwtd RMS - remember W&F?).
> I recall the FCC's specs were less onerous than ours, which ocassionally
> caused a problem with equipment imported from the US.

At the time (1970s or so), the FCC had audio performance measurement
requirements for radio stations. These were frequency response, THD, and
noise from the microphone input to the transmitter output. There were no
requirements on any other equipment (such as tape machines). Later, the
FCC left audio performance to the marketplace, figuring that a station
that sounded bad would have a difficult time getting listeners. Still
later, they became concerned about occupied bandwidth and replaced the
annual (for AM, on equipment change for FM) audio measurements with
occupied bandwidth measurements. Stations that installed NRSC compliant
audio equipment were exempt from the annual occupied bandwidth measurement
for the first few years (or something like that) since the NRSC equipment
included a low pass filter that removed high frequency audio components
that would cause sidebands far from the carrier. Of course, nonlinearity
in the transmitter itself can also create these distant sidebands, so the
exemption eventually expired. Now, pretty much, the FCC doesn't care what
you sound like as long as you stay in your channel.

Back in the tape days (reel to reel and cartridge), I'd do weekly checks
of the frequency response, verifying equalization and head alignment (and
bias on the record side). The most critical part was the mono-sum
frequency response on stereo machines. Besides my playback alignment
cartridge, I had a reference cartridge for record. I'd do the record
alignment with that cartridge, then test all the cartridges in production
that were ready to be recorded on. Any that failed the stereo mono-sum
frequency response test were delegated to use on AM where the machines
were mono and not as critical. I discovered the need for a record
reference cartridge pretty early. If I did not use a reference, half the
carts would fail one week, then the other half the next week. With the
reference cartridge, stuff that passed one week tended to pass the next.

By the way, I stopped working in stations when everything was still tape
based. The people that owned one of the stations I worked with went on to
create one of the early satellite radio networks (Transtar). All our
programming was phonograph records, tape, and network coming in by
telephone line. The news wire service used a Teletype model 15 printer.
The production board was a Gates Yard vacuum tube board. On air was a
solid state Sparta board. Stuff has changed!

Harold

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