[ARC5] Novice receivers.

[Bruce Long]

I always wondered why early crystal filters where overly complicated.  ( a generalization know)  It never occurred to me the designers where precluded from using the simpler Lamb filter due to patent constraints.  Perfectly obvious but with decades of thinking of the simple half-lattice xtal filter as public domain not so obvious after all 

      From: Fernando - LU2DFM <lu2dfm at gmail.com>
 To: arc5 at mailman.qth.net 
 Sent: Monday, November 16, 2015 6:56 PM
 Subject: Re: [ARC5] Novice receivers.
   

Thank you very much.  I was with the wrong notion that the SP-200 was
elarlier than th HQ-120. 


On Mon, Nov 16, 2015 at 03:06:19PM -0800, Richard Knoppow wrote:
>    Yes, if you look at the Super-Pro data sheets you will find that before
> about 1940 a crystal filter was offered as an add on but the design was
> quite different. It was to be blunt crude, probably a work around of the
> original Lamb patent.
>    I mis-spelled the name, it is Oram.  The patent can be found at:
> 
> http://www.google.com/patents/US2222043
> 
>    The application date is 1939, issued in 1940.  The HQ-120-X was the
> first receiver to employ this circuit. It was also offered as the HQ-120 (no
> X) without the filter but I think very few were sold so the filter became
> standard.
> 
>    James J. Lamb had several patents on crystal filters, for instance:
> 
> 
> US 2156786 A
> and
> US 2054757 A  which I think was the original.
> 
>    You may also want to look at:
> 
> US 2101549 A
>    Lamb's patent on the noise blanker.
> 
> On 11/16/2015 1:32 PM, Fernando - LU2DFM wrote:
> >On Mon, Nov 16, 2015 at 01:20:25PM -0800, Richard Knoppow wrote:
> >
> >>This same filter, invented by Donald Orem, the chief engineer of Hammarlund,
> >>was introduced on the HQ-120-X and was eventually used in the Super-Pro. The
> >I always though that it was the other way around, since my understanding
> >is that the Super Pro predates the HQ-120 for some years.
> >
> >Can you expand on this?
> >
> >Many thanks.
> >
> 
> -- 
> Richard Knoppow
> 1oldlens1 at ix.netcom.com
> WB6KBL
> 
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-- 
73 de Fer, LU2DFM
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