[BC] Audio "proofs"

[RichardBJohnson at comcast.net]

No. He didn't need them. He just used a good signal generator made by General Radio, of course.

In the "good old days," we needed a convenient NBS (now NIST) traceable way of measuring WATR-TV's UHF transmitter frequency to keep the frequency monitor in calibration. There was some problem-receiving channel 53 in Cambridge, so I could not use Cambridge Crystals.

I found that NBC network color used 3.579545MHz color burst that was traceable to NBS. I bought a cheap frequency counter that used a "color-TV" crystal and I built a Heathkit prescaller. The counter had a 3.579545MHz output BNC connector which I connected to a "modulator."

The modulator consisted on a length of 300-ohm transmission line taped to the 300-ohm line going to a rebroadcast receiver used to receive another NBC signal on VHF. At the end of the line, I connected two back-to-back 1N60 diodes.

This "modulator" would generate an interference pattern on the receiver. I would adjust the trimmer on the counter until the color interference was zero-beat to the color pattern on the screen (slowly changing RGB). At that time, I would measure WATR-TV's frequency and adjust the monitor accordingly.

This was a FCC approved method for making the monthly frequency measurements. Nathan Hallenstein, another NE Broadcast veteran from the FCC office approved it once he watched me do it.

Cheers,
Richard B. Johnson
Book: http://www.AbominableFirebug.com/

----- Original Message -----
From: "Dana Puopolo" <dpuopolo at usa.net>

Clarence used General Radio equipment-and actually had crystals for each
frequency. He would zero beat to your tone.

-D