[GreenKeys] [External] HF radio relating to DSP TU Update

[Jeffrey Golas]

Harold, came across this today, not sure if it helps. 

http://code.beefchicken.com/keelan/gortty

Jeff KC3GJX

> On Jul 6, 2022, at 11:33 PM, Harold Hallikainen via GreenKeys <greenkeys at mailman.qth.net> wrote:
> 
> 
> 
>> On Wed, July 6, 2022 8:03 pm, Jones, Douglas W wrote:
>> From: Jim Haynes [jhhaynes at earthlink.net] -- Wednesday, July 6, 2022 8:46
>> PM
>> 
>>> I think the most successful attack on the multipath problem was a system
>>> developed at MIT called RAKE, which put the signal through a delay line
>>> and then tried to take signals from several taps on the line and combine
>>> them constructively.
>> 
>> See:  Clarence W. Hansell, "Method and Means for Reducing Multiple
>> Signals," U.S. Patent 2,310,692, granted Feb. 9, 1943, applied for in
>> 1939.  Yep, patent does exactly what you describe, using short hunks of
>> coax as delay lines.  The problem they were working on at RCA at the time
>> was multipath interference in TV signals, a common source of ghost images.
>> 
>> I found that patent when I was working on the analog delay line Wikipedia
>> page:
>> -- https://en.wikipedia.org/wiki/Analog_delay_line
>> 
>> That page is still over 50% my work, despite the passage of time.
>> 
>>         Doug Jones
>>         jones at cs.uiowa.edu
> 
> That's great! The combining signals from several taps on a line reminds me
> of a DSP Finite Impulse Response filter which, has memory for a series of
> samples, starting from the latest, then one earlier, then one earlier,
> etc., then multiplying the contents of each of those samples by a
> coefficient and adding the results. So, if you know the transfer function
> of the path (with reflections), you can do the inverse of it in the FIR
> filter. With HF, it seems tricky since the path is always changing. But I
> guess now and then you could transmit a known "sync" signal to determine
> the transfer function of the path at that time and adjust the filter as
> appropriate.
> 
> More fun stuff I don't remember from school!
> 
> Harold
> https://w6iwi.org
> 
> 
> 
> 
> -- 
> https://w6iwi.org
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