Posted by
Jack Smith-6 on
Aug 13, 2006; 12:55pm
URL: http://elecraft.85.s1.nabble.com/Up-conversion-tp392867p392897.html
> I think there were other changes, too. IIRC, the 390A is in some ways simpler
> than the 390.
>
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.
> The story goes like this:
>
> Back during the Cold War, No Such Agency had the idea for a secure comm
> system which eventually became known as F9C in FCC mode labeling of the time.
> They wanted to use R-390As for the system, but the phase shift through the
> mechanical filters was a problem. So they had a version of the R-390A made with
> R-390 type LC IF strips. This variant was designated R-725.
>
> To cover their tracks about the reason for the variant, a cover story about
> an electronically-steered RDF system was invented. The cover story was so
> convincing that the "other folks" apparently never became aware of, nor penetrated,
> the F9C system. Eventually the F9C system was replaced by newer technology,
> which is why we know the story now.
>
> 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. 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.
>> 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.
>> I imagine the move to crystal filters was driven by the desire to reduce
>> receiver size and to remove the need for skilled technicians to align
>> the IF stages.
>>
>
> I think the main reason was the amateur HF SSB transceiver, which began
> replacing 'separates' in the late 1950s and early 1960s. While the first ones
> (Cosmophone 35, KWM-1 & -2) used 455 kc mechanical filters, other manufacturers
> went to crystal filters in the HF range, probably to both save money and avoid
> being dependent on Collins.
>
> IMHO, the amateur HF SSB transceiver is what really made SSB popular with
> hams. By the early 1960s, a ham could buy a 100-watt-class SSB xcvr for about the
> price of a really good receiver. No critical zero beating, and the whole
> works was much smaller and lighter than the common desk-crusher AM rigs.
>
>
> In the VHF and UHF world, Motorola stuck with potted LC
>
>> IF filters at 455 KHz (the famous "Permakay") well past the 1970's,
>> although GE went to crystal filters with the Master Pro (and maybe
>> before that; I'm a bit hazy on GE's gear between the ProgLine and
>> MasterPro.)
>>
>
> 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.
>
>>> I'm not sure of the exact dates when it was first done, but by the mid
>>>
>> 1960s
>>
>>> the use of computers to do circuit simulation and calculation was
>>>
>> mainstream
>>
>>> in electronic design. Such design tools probably had an effect in that
>>>
>> many
>>
>>> "paper designs" could be tried out in a short time, particularly for
>>>
>> things like
>>
>>> filters..
>>>
>>>
>>>
>> I received my EE undergrad degree in 1968 and I recall using a
>> transmission line simulation program. Batch mode, submit your card deck
>> and get the answer back the next day. Zverev's classic book on filter
>> design was published in 1967 and its data tables are derived from
>> computer programs, but the book itself is silent on using computers to
>> design filters.
>>
>>
>
> 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.
>>> Agreed. The main filter in the K2 uses selected microprocessor crystals
>>>
>> and
>>
>>> some varicaps, yet gives very good CW performance and multiple bandwidths.
>>>
>> By
>>
>>> comparison, one can easily spend half the cost of a basic K2 (or more) on
>>>
>> a
>>
>>> couple of packaged CW filters for an HF IF. For VHF? I don't want to go the
>>>
>> re.
>>
>>>
>>>
>> I've been quite pleased with the filters as narrow as 200 Hz that I've
>> built using 8 MHz micro processor crystals.
>>
>
> My point exactly.
>
> I have to grade them for
>
>> minimum Q and frequency matching, but the resulting filters are textbook
>> matches to the Gaussian prototype designs.
>>
>>
>
> It is my understanding that the crystals in Elecraft products are graded in
> similar fashion. I think they are selected/matched for a number of different
> parameters.
>
> Sometimes I wonder how many "microprocessor crystals" in the HF range
> actually wind up working with microprocessors...
>
>
>> One of the two articles I've submitted to the ARRL for consideration
>> for QEX covers some of my crystal filter work. Have yet to hear if it's
>> accepted, however.
>>
>>
>>
>
> I hope they are accepted.
>
> 73 es tnx de Jim, N2EY
>
>
>
>
>> Jack
>>
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