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In article , Jack Smith
writes: On Thu, 13 Nov 2003 17:33:19 -0800, Roy Lewallen wrote: As I recall, Armstrong invented and patented the FM radio before WWII. If I'm correct, his patent should show a schematic of the circuit he used. It's probably still available from the patent office. Roy Lewallen, W7EL Roy- Armstrong's classic paper "A Method of Reducing Disturbances in Radio Signaling by a System of Frequency Modulation" was published in 1936 in the November Proc. IRE. (The paper was presented in a demonstration at the Nov 1935 IRE New York meeting.) His field work started 1934, at 44 MHz, with a 2KW 44 MHz transmitter on the Empire State Building shortly thereafter (the article is a bit vague on the timing of this part of his operation). (Also, the frequency was changed to 41 MHz at some point during the trials.) Armstrong also notes the problem with receiver RF amplifiers at this frequency and thanks RCA for its provision of experimental VHF receiving tubes. His detector circuit looks like a conventional discriminator to me; two detectors each coupled to a tuned circuit with the outputs summed. One detector gives + and the other a - output. One tuned circuit resonates on the high side of the IF passband the the other on the low side. Each detector fed by an independent buffer amplifier. The receiver was a double conversion, with the first IF at 6 MHz and the second IF (and detection) at 400 KHz and a passband of 150 KHz. It's not necessary to go back to just a few years after the first audion. :-) The Galvin/Motorola SCR-300/BC-1000 used 7-pin glass base "miniature" tubes, battery type filaments, and was 40 to 48 MHz. Tube types were 3A4, 1T4, 1R5 in the VHF range. It started into full production in 1942 and about 50,000 were built. FM. Dan Noble migrated to Chicago to work for Galvin in 1940...after finishing a design for the first mobile police radios...pictures show those tubes to be glass, octal-base. Noble is the chief architect of the SCR-300 walkie-talkie. Interesting little gem of a then-tiny transceiver. The argument against that might be that 1942 was "after" the entry into WW2. But...those battery-filament (directly heated) tubes were in existance in late 1939. Galvin/Motorola used them in the SCR-536/BC-611, the HF-range "handie-talkie" which was started in design in 1940. Perusing the MIT "Rad Lab" volumes ("Amplifiers" is the one I have) will show that 6AG5s were already around for radar set IF strips of 30 and 60 MHz. Another 7-pin all-glass "miniature" envelope but with an indirectly-heated cathode. See also the 6AK5. Both are the "short" version (physically short compared to the "All-American Five" types with 7-pin bases and all-glass). One of the reasons one didn't see those (then) advanced tubes was that the consumer market products still went in for the cheaper octal base kind...sockets were also cheaper, many being made out of melamine-laminate stamp-outs riveted together to hold individual tube pin grabbers (first cousin to solderless joining gadgets). Most of the consumer radio equipment of the pre-1950 era were indeed low-quality "Model T" kind of things. In pre-WW2 days, a 7-pin all-glass envelope for a tube cost more to produce than the older octal base with pins soldered to tube element leads. All metal envelope tubes cost more than glass envelope types. Once tube makers ramped up for the all-glass 7- and 9-pin little ones, they got cheaper and were used in post- war consumer radios. EVERYTHING in radio was already in continuous change from the 1930s onward...even if it didn't show up in the consumer marketplace right away. I suppose it is very interesting for antique boatanchor folks to play with those "stone-age" tubes. Ho hum, I say to self, broke into vacuum tubes using a 201A from an ancient radio. Phooey. :-) My wife often uses a little AM-FM set with ear-bud listening things, the set about the size of a cosmetic compact case. Was a Give- Away sales promotion thing in the mail. Cost nothing. Obviously no tubes in it. Fine FM, including stereo sound. Len Anderson retired (from regular hours) electronic engineer person |
#2
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![]() "Avery Fineman" wrote in message ... It's not necessary to go back to just a few years after the first audion. :-) The Galvin/Motorola SCR-300/BC-1000 used 7-pin glass base "miniature" tubes, battery type filaments, and was 40 to 48 MHz. Tube types were 3A4, 1T4, 1R5 in the VHF range. My Feb. 1942 "FM" magazine has an ad from REL selling FM mobiles for police use. I assume the ad was bought in 1941. A young engineer who worked for my father at the US Patent Office had one of the MW (AM broadcast) RCA "camera-case" radios about 1940. It was based on the tubes mentioned above. Size was about 2x4x8 inches. Most of the space was taken up by the batteries. The A (filament) batteries lasted about 3 hours. I estimate the date since this fellow went on active duty with the Navy _before_ Pearl Harbor. In fact, he phoned my father with details of the losses at Pearl the next day (Monday, Dec 8, 1941). Those details were kept VERY secret for at least 2 or 3 years. My father kept the secret, and I think complained to the Navy about the security breach. Apparently nothing happened to the fellow who spilt the beans. |
#3
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![]() "Avery Fineman" wrote in message ... It's not necessary to go back to just a few years after the first audion. :-) The Galvin/Motorola SCR-300/BC-1000 used 7-pin glass base "miniature" tubes, battery type filaments, and was 40 to 48 MHz. Tube types were 3A4, 1T4, 1R5 in the VHF range. My Feb. 1942 "FM" magazine has an ad from REL selling FM mobiles for police use. I assume the ad was bought in 1941. A young engineer who worked for my father at the US Patent Office had one of the MW (AM broadcast) RCA "camera-case" radios about 1940. It was based on the tubes mentioned above. Size was about 2x4x8 inches. Most of the space was taken up by the batteries. The A (filament) batteries lasted about 3 hours. I estimate the date since this fellow went on active duty with the Navy _before_ Pearl Harbor. In fact, he phoned my father with details of the losses at Pearl the next day (Monday, Dec 8, 1941). Those details were kept VERY secret for at least 2 or 3 years. My father kept the secret, and I think complained to the Navy about the security breach. Apparently nothing happened to the fellow who spilt the beans. |
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