In a message dated 8/13/06 7:56:46 AM Eastern Daylight Time, [EMAIL PROTECTED] writes:
> If you don't have it, I'll send you a PDF of the "Cost Reduction Study" > report Collins did that lead to the R390A. I'd really like a copy - thanks! I think others would too. > > > The story goes like this: > > > > Back during the Cold War, No Such Agency .... > > > > It is my understanding that, long after the F9C system was in operation, > an > > electronically steered RDF system using the receivers *was* developed! > > > > All ancient history now. > > > I worked for the FCC as an engineer for several years after EE graduate > school and had an opportunity to visit a monitoring station. As I > recall, they used 51J4's for general listening and Racal 17 (US model > numbers RA117 and RA6117) for DF use with the Wullenwebber array. I don't know if the R-390/R-725 were used with the Wullenwebber system or something else. Either way, it makes sense that the phase characteristics of the mechanical filters were a problem. The > > RA17 series receiver used LC filters for wider bandwidths and a crystal > lattice filter for the narrower bandwidths. The military used the same > Wullenwebber antenna system (elephant cages) and I had heard (but never > seen one in person) that they used R390's. Or R-725s, which would look very similar. > >> Drake's first R4 used 50 KHz IF for selectivity but later receivers went > > >> to crystal filters. > > > Actually the R4, R4A, and R4B all used LC filtering at 50 kHz for > selectivity > > and passband tuning. Only the R4C used all-crystal filtering. > > My first Drake was a R4C. A family of HF ham receivers that bridged the change from low-frequency LC selectivity to HF crystal filters. R-4B and the Drake 2-B/2-C family may have been the last manufactured ham rxs to use LC IF filtering for multiple-bandwidth selectivity. > > > > Could it be that obtaining a suitable FM-bandwidth filter was easier/less > > expensive (for Motorola, anyway) with LC circuits? > > > The design problem with FM filters is both bandwidth and ensuring group > delay specs are met, as otherwise audio distortion is an issue. My > junkbox also has a wideband 70 MHz center frequency IF filter from a > Western Electric analog microwave system. It has a bandwidth of 10 or 20 > MHz and excellent group delay characteristics, which, of course, were > essential for a microwave system carrying hundreds of multiplexed analog > SSB channels. > By contrast, IIRC, RCA made some mechanical filters for receivers they provided to the military in the 1950s. From what I read, they were just different enough from Collins design that they avoided patent infringement. They were also (allegedly) quite fragile. > > Well, I graduated EE school in 1976, and by then programs like SPICE > were > > part of the curriculum. Still batch processing, though, but the whole idea > was > > neither new nor revolutionary then. > > > In my senior year (1968) the engineering department was bringing on line > a remote access time share system using IBM-selectwriters (IBM golf-ball > typewriter type terminals) but it was highly experimental and was down > more than it was up. My course in computer programming (Numerical > Methods) was oriented towards solving physics problems. Perhaps my timeline was a bit too soon. By the time I was in EE school (fall of 1972), SPICE and other circuit-simulation-by-computer stuff was common at the school I went to. Perhaps it was a lot more recent than I realized at the time. 73 de Jim, N2EY _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
