1984 KHJ Kahn AM stereo air check

What you are listening to

I found this cassette when I was going through things and digitized it.  It is an approximately half-hour stereo air check of the Kahn AM stereo system on KHJ during their short-lived "car radio" format.

For those of you who have listened to the KRLA air check below it sounds cleaner but noisier than the KRLA check.  Here are some facts about the KHJ installation.

KHJ put some $$ into this installation and hired the late Ron Rackley to give the KHJ antenna system a treatment.  Basically this means modifications to improve the bandwidth.  KHJ was a two-tower non-directional day, directional night. (it has since moved and is triplexed onto a site in Echo Park). The transmitter at the time was a Collins PowerRock, the best in that power class at the time. They had Pacific Recorders cart machines which matrixed the stereo to prevent phase skewing of the audio. And, importantly, they had the redesigned STR-84 exciter which was much better than its predecessor. It allowed audio phase shifts to be placed at the input of the audio processor, solving the bad tilt problem the old exciter had.  It was first class. The late Bob Kanner, chief engineer, was one of the best.

The air check is interesting for several reasons.  First it is clean clean clean.  Aside from local noise (the curse of AM radio) it sounds much like FM. It is clear this was recorded some distance from the transmitter site at night. I did not make this tape, so I do not know the exact details of of how it was made. It is possible it was made off the air monitor at the old studio location of 5515 Melrose Ave.  The night signal was not particularly strong there. It might also have been made at someone's residence on a Sony SRF-A100 receiver which had a Kahn decoder. Those are the most likely sources.

The air check reveals how well the Kahn system handled fades. There are several throughout the recording. They aren't very deep fades but they are fades.

A comment about the C-Quam (Motorola) system. Greater Media switched KRLA to the C-Quam system, and I was involved with that transition.  The generic (I think it was a Delta clone of the Motorola exciter) had some surgery to remove the output transformer which was a tilt machine.  I also did some fine adjustments to improve the audio performance. I believe it was the best that technology could be.  We later switched to the BE AM stereo exciters which used a different digital technology and those were way superior to the original Motorola design.

But I digress.  I remember being at the Wilshire Blvd studio of KRLA, watching the behavior of the C-Quam.  We had a Potomac C-Quam receiver and we also had a vector scope in the rack which could be switched to any source including the receiver.  I watched those fades, and you would see the Lissajous pattern start to tilt one way and then it would suddenly snap back to a mono sum.  It would recover and go back into stereo and this process would repeat.  It was pretty distracting to listen to. I sadly thought about how it could have been.

Chris Hays 3-1-2025

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