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Variable selectivity?
"Hank" wrote in message ... In article , Richard Knoppow wrote: James Millen was one of the founders of National but eventually was pushed out of the company. He started his own company, also in Malden Mass, and probably made many parts for National as well as his own stuff. Millen made very high quality components. Millen Mfg., at least at the time I worked there, was in direct competition with National Co. on several products, and neither company supplied the other. The National HRO was a revolutionary receiver in its day and stayed one of the favorites for both ham and commercial use for some thirty years. The mechanical design is attributed mostly to James Millen and the electronic design mostly to Herbert Hoover Jr., son of the president of the US. While the HRO was a legendary product, I'd hardly call it "revolutionary." It was a follow-on to the AGS line, with objectives to maintain AGS performance at lower cost-to-manufacture, and to normalize the coil-set interface so that the tuning coils could be built all-in-one-box and interchangeable. An examination of the schematic will show it to be essentially a copy of higher-end home entertainment circuits of the era, with a crystal filter and bfo added. Much of the actual performance came from use of better coils (house-built) in the RF and IF stages, a house-built tuning capacitor, and the house-built tuning dial was superior to almost anything else around. In short, a relatively straightforward tried-and-proven electrical design, but extremely well-executed in component quality and mechanical structure, pretty much hallmarks of Jim Millen's team. Worth noting that the NC-100, National's follow-on product, had similar performance, with the advantage of having internally-mounted and switchable tuning coils. Hank While the HRO had similar circuits to home receivers of the time I rather think there was not that much variation available. The HRO did use pentode mixers in place of hexode or pentagrid mixers resulting in low noise. The NC-100 was certainly a clever design but had only one RF so its image rejection is not as good as the HRO. I forgot to mention Dana Bacon another designer at National. I am not sure what contributions he made. -- -- Richard Knoppow Los Angeles WB6KBL |
#2
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Variable selectivity?
On Mon, 14 Oct 2013, Richard Knoppow wrote:
"Hank" wrote in message ... In article , Richard Knoppow wrote: James Millen was one of the founders of National but eventually was pushed out of the company. He started his own company, also in Malden Mass, and probably made many parts for National as well as his own stuff. Millen made very high quality components. Millen Mfg., at least at the time I worked there, was in direct competition with National Co. on several products, and neither company supplied the other. The National HRO was a revolutionary receiver in its day and stayed one of the favorites for both ham and commercial use for some thirty years. The mechanical design is attributed mostly to James Millen and the electronic design mostly to Herbert Hoover Jr., son of the president of the US. While the HRO was a legendary product, I'd hardly call it "revolutionary." It was a follow-on to the AGS line, with objectives to maintain AGS performance at lower cost-to-manufacture, and to normalize the coil-set interface so that the tuning coils could be built all-in-one-box and interchangeable. An examination of the schematic will show it to be essentially a copy of higher-end home entertainment circuits of the era, with a crystal filter and bfo added. Much of the actual performance came from use of better coils (house-built) in the RF and IF stages, a house-built tuning capacitor, and the house-built tuning dial was superior to almost anything else around. In short, a relatively straightforward tried-and-proven electrical design, but extremely well-executed in component quality and mechanical structure, pretty much hallmarks of Jim Millen's team. Worth noting that the NC-100, National's follow-on product, had similar performance, with the advantage of having internally-mounted and switchable tuning coils. Hank While the HRO had similar circuits to home receivers of the time I rather think there was not that much variation available. The HRO did use pentode mixers in place of hexode or pentagrid mixers resulting in low noise. The NC-100 was certainly a clever design but had only one RF so its image rejection is not as good as the HRO. And that the HRO had two RF stages seems to be a significant factor. Even in the seventies, when Ray Moore wrote a number of articles about receiver design in Ham Radio magazine, he pointed out that one reason the HRO stood out was the 2 rf stages, which mean much better image rejection than the average receiver. The HRO-60 (or was it the 50?) added double conversion on the higher bands, but the earlier models were still contenders in that period for good image rejection on the higher bands. And of course, the design was good, so the extra stage actually helped rather than hindered. A superhet is a superhet, it's small details like this that made some better than others. A couple of years ago, I found at a garage sale for 2.00 a Grundig/Eton pocket shortwave receiver. It's a pretty crummy receiver, but without adding cost to it, they included a frequency counter. So a receiver probably as bad and as simple as my Hallicrafters S-120A from 1971 instantly gets a giant improvement in tuning because of that frequency counter. And once they did away with the analog dial, they could break the tuning segments up into smaller ranges, helping the tuning process. What initially complicates the receiver tremendously (or would if the frequency counter wasn't a single IC that also included a clock function and cost very little and took up little space), actually simplifies it. Today, you can stick with a 455KHz IF and then fuss over image rejection, or you can move to a higher IF and simplify the front end. Or go with double conversion, getting the easier image rejection, yet selectivity down where you can do things like use LC circuits. A single conversion receiver with 455KHz and one RF stage (if that) can't be much different from a circa 1930s receiver, communication or consumer, but you can now make simple receivers with other methods that actually mean better performance. It amazes me that over the past 7 years or so I've found shortwave receivers at rummage and garage sales, all nice and cheap, that are so much better than that 1971 Hallicrafters. Or even buy a new digitally tuned portable receiver for about the price I paid in 1971 for that Hallicrafters, and get nearly infinitely better capability. Michael VE2BVW |
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