Re: 1957

[Rob Landry <umar@nerodia.wcrb.com>]

On Sun, 20 Jun 1999, Dan Strassberg wrote:

> Although it makes sense that a station radiating the equivalent of 20 kW at
> 500' from Needham (or maybe by '57 it was the equivalent of 50 kW) would
> interfere with a little Class A in Cambridge only 400 kHz away, I think the
> allocation was completely in accordance with the rules, or at least it was
> in accordance with the rules that existed at the time. The explanation that
> I read at the time had nothing to do with WBZ-FM. Rather, the move was
> explained by the fact that 107.1 was almost at the 10th harmonic of FM
> receivers' 10.7-MHz IF. Now, I've never heard anyone say that 96.3, which is
> exactly at the ninth harmonic, is an undesirable frequency. Moreover, I
> would think that the local oscillator was more likely to be rich in odd
> harmonics than even ones. Still, that is the explanation that I heard. Can
> you shed any light?

When I was at WHRB we were told the move had been made because of WBZ-FM.
However, that was some 20 years after the event, and even the station's
official historian doesn't remember it, he having arrived as a freshman in
1960.

Assuming an IF extending from 10.625 to 10.775, allowing for plus and
minus 75 kHz deviation, the tenth harmonic of the 10.78 MHz IF actually
extends from 106.25 to 107.75 MHz. One would think WBZ-FM would have
applied for a channel elsewhere on the dial if this were a problem.

The only tenth harmonic problem I've heard of involved the old WJIB(FM),
which had a two-hop STL, the second hop being 945.0 MHz. Upon moving to
the Chestnut Street transmitter site, their STL receiver began to receive
interference from the tenth harmonic of what is now WJMN. I don't remember
how WJIB solved the problem.

Rob Landry
umar@nerodia.wcrb.com

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