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THE AM BULLETIN BOARD => Technical Forum => Topic started by: AJ1G on January 14, 2020, 01:28:07 PM

Title: Mystery National Velvet Vernier Dial
Post by: AJ1G on January 14, 2020, 01:28:07 PM
Anyone have any idea what, if any, radio or piece of test equipment (GDO, wavemeter?) the dial shown in the attached image is associated with?  Calibrated over 8 bands over a very wide frequency range from about 75 kc to 25 Mc.  My first thought is that it was from a National SW-3 receiver but as far as I have been able to tell, all of those only had      single logging scales that were used with calibration scale conversion charts.  The markings are printed and extremely small, wouldn’t be surprised if a small magnifying glass on a small post was swung over the dial to make it easier to read!  I have a couple of early GenRad frequency meters and signal generators that have such magnifiers.

I have seen information on National plug in coil sets that cover similar frequency ranges as depicted on the dial, but no noted association with this specific multi band dial.

Title: Re: Mystery National Velvet Vernier Dial
Post by: WU2D on January 18, 2020, 08:34:06 AM
Hi Chris!

My guess is that this is the dial for either a Wavemeter or a Station Monitor / Heterodyne Frequency Meter. The wavemeter was used from WW1 through 1930 as the standard instrument. By 1920 the first article on a heterodyne frequency meter comes out in Radio Experimenter. Clapp describes the device in detail in 1926. And by 1931, the ARRL Handbook shows the Station Monitor Frequency Meter as a standard adjunct for the shack.

73's WU2D
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