> "I had the impression that the rise of the Ham-band-only transceiver in > the > 1950's and 60's was based on simple economics. It was cheaper to drop > general coverage receive..."
Just the opposite, I think. Some of the poorest performing -- and least expensive receivers provided general coverage. The most expensive receivers of their respective eras were the Collins 75A, Collins 75S, Drake R-4, and National HRO, all of which were at the top-end of the purchasing ladder in their day. I have several Hallicrafters receivers between the SX-9 and SX-100 and others in between. The cheap and dirty way of providing GC was to find the calibrating Main tuning cap points, activate the xtal calibrate marker, then tune the bandspread cap to the nearest dial marker. The problem is that mechanical variations in the GC main tuning greatly affect bandspread tuning. For example, on my SX-100, the entire tuning mechanism functions on the use of a highly tensioned steel piano string. The slightest vibration on the table transfers from the chassis, into the gears, the dial string, and ultimately, the tuning caps. Because of tuning instability, the SX-100 is one of the worst receivers I've owned and unfortunately, it was my first receiver as a novice in '72. OTOH, Collins and Drake receivers from the '50s and '60 suffer no such problems. The PTOs are temperature compensated and highly linear from end-to-end. It is possible to use a PTO and a crystal heterodyne scheme at the first LO, but was very expensive. The Drake SPR-4 was such a GC SWBC receiver that had a PTO and up to 23 pre-mixer crystals - and it still didn't offer contiguous coverage to 30 MHz. Going back even further in time, look at the National SW-3, FB-7, and HRO frequency-determining topology. The SW-3 regen and HRO could certainly accommodate GC, but the real performance attained in the 1930s was realized when the bandspread clips were engaged, severely limiting tuning range to only the ham bands. For a non-PTO tuning method, National's HRO gearbox, coil boxes with taps, and elliptical tuning dial were a flash of genius. So, I see the early "ham bands only" receivers as the more superior, and expensive product. Apart from the mentioned Hallicrafters SX receivers, I don't collect and restore any other type of GC receiver. And, how anyone can elevate the SX-88 to "Delivered from God" status is well beyond my comprehension! Paul, W9AC ----- Original Message ----- From: "Ron D'Eau Claire" <[email protected]> To: <[email protected]> Sent: Sunday, October 23, 2011 3:12 PM Subject: Re: [Elecraft] KX3 vs FT817 - how do the "insidedimensions" compare? It was cheaper to drop > general coverage receive. It was also true that they were typically better > performing than most general coverage receivers, mostly due to improved > input filtering that protected the mixer from large off-frequency signals. > > As you may recall, most general coverage receivers up to that time used > simple L/C tunable input filters that required multiple knob-twiddling or > a > big "ganged" multi-section tuning cap with the stages carefully adjusted > so > they "tracked" the across the tuning range. > > A well-designed fixed tuned input filter was better, especially important > consdering the relatively easy-to-overload mixers in common use back then. > That gave the ad writers a good explanation for the limited tuning ranges. > > Ron AC7AC > > -----Original Message----- > After almost 50 years of being a ham, I see that the conventional wisdom > of NOT including general coverage in a receiver has been refuted. It was > thought to be at the expense of performance on the ham bands. > > How have modern design techniques overcome this limitation? > > 73 de Jim - AD6CW > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
