Collins. But the Collins patent and improvement was not the filter but
compensating so they were mil spec. It was the first that opened the door.
> In a message dated 8/13/06 7:56:46 AM Eastern Daylight Time,
>
[hidden email] 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
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