An Urban Legend Disproved

Discussion in 'Ham Radio Discussions' started by N2EY, Jan 1, 2015.

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  1. N2EY

    N2EY XML Subscriber QRZ Page

    In the old days it was pretty vague. Nowadays we have definite limits. -43 dB IIRC.

    K9STH has written extensively on the Collins audio-injection-SSB-to-make-CW problem.

    From what I have learned from him, it came down to this:

    The Collins rigs which used that system (KWM-2, 32S-1) could be carefully aligned to produce a single clean CW signal. But they wouldn't stay in alignment long! Within a relatively short time (weeks?) the rig would be making at least three, and often more, CW signals where there should only be one. And the spurs weren't that far down!

    It's important to consider the spirit and intent of the regs, not just the letter. The FCC did not, and does not, expect that every amateur signal will be absolutely perfect, but they DO expect signal quality consistent with good engineering practice.

    The Collins 32S-1 and KWM-2 were mid-to-late-1950s technology. In those days, CW transmitters with good signal quality were all over the place; there was NO EXCUSE for the Collins problems. Not when transmitters costing less than 1/10th what the Collins did could and did produce clean signals. Collins eventually fixed the issue in the 32S-3, by the simple method of using a separate CW crystal for transmitting.
     
  2. K9STH

    K9STH Ham Member QRZ Page

    EY:

    Not weeks, but just a few days if one was lucky!

    I know that with my 32S-1, the late Joe Johnson, W5QBM, who lived well under a mile from me, straight across the golf course, could not detect a spurious signal when the transmitter was first aligned. But, within a day, or 2, the unwanted signals would start increasing in strength until they definitely were very strong.

    Of course, since I have a 32S-3, I never really used the 32S-1 for CW. It was just the fact that I wanted to see if it was actually possible to get the unwanted CW signals down to an acceptable level. Considering the effort that it takes to achieve this, and the fact that the circuits just won't hold that close of an alignment, it is not worth it!

    Glen, K9STH
     
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