[Elecraft] Up-conversion.

[N2EY at aol.com]

In a message dated 8/13/06 7:56:46 AM Eastern Daylight Time, 
jack.smith at cliftonlaboratories.com 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