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Variable selectivity?
Further information most welcome, thank-you
In the 1948 Radio handbook which I mentioned previously, there are adverts from a company by the name of Millen, and I assumed it was the same guy after he had left National. Your comment about a phenolic intersperser is no doubt some means of isolating an earthy contact? It would be interesting to know from the Lamb patent whether he proposed therein the technique of Single Signal Reception by the use of the phasing control to null out the audio image, or whether this was something that came about through experience? "Richard Knoppow" wrote in message m... "gareth" wrote in message ... WOW! A very full response, thank-you. After I posted this I realized that I forgot a part. In the Super-Pro there is a phenolic lever between the rotating cam and the rods from the movable coils. I am not sure why the rods are not moved directly by the cams. I think Hammarlund had a patent on the IF variation system but I don't have the number. The Hammarlund crystal filter is described in _QST_ Dec 1938, p.33 D.K. Oram "Full Range Selectivity with the 455 khc Crystal Filter" Oram's patent is USP 2222043 You can get patents by number from the U.S. Patent and Trade Mark Office or from Google Patents. The Google site has the advantage that patents are searchable by text for _all_ dates and are available in PDF form. I also have the Lamb patents but it will take some searching since my file is organized by patent number and not title. However, they are easily found by doing a Google search for James Lamb. You will also find his patent for the famous Lamb Noise Blanker. Lamb had more than one patent on crystal filters and wrote extensively about them in the early thirties editions of QST. AFAIK, the first application of the Lamb filter was in the HRO. The first Hammarlund filter was in the HQ-120-X and it was later applied to the Super-Pro. Some Series 100 Super-Pros have crystal filters as an add-on but these are not the later version. BTW, the Lamb patent was licensed to James Millen. At the time he was one of the principles of the National Radio company and is supposed to have been responsible for the mechanical design of the HRO. -- -- Richard Knoppow Los Angeles WB6KBL |
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