Definition for transversal equalizers

"Max Hauser" <maxREMOVE@THIStdl.com> wrote in message 
news:111oecet5h9b407@corp.supernews.com...
> "Allan Herriman"
>>
>
> Neglecting novelty items like recursive FIR implementations, there are 
> other famous nonrecursive structures that also realize Finite Impulse 
> Responses but lack the transversal (tapped-delay) structure.  A parallel 
> set of delay lines of different lengths or delays, each weighted at their 
> input or output, and finally summed, is such a structure.  (It has been 
> useful in some delay-line technologies that had constraints, for example 
> certain CCD technologies circa the 1970s.)
>
> -- Max Hauser

In the olden days when delay lines of any appreciable length were expensive 
we used a relatively wideband torsional wire acoustic delay line over the 
range 100kHz to 1MHz.  The line wasn't tapped.  We wanted to delay signals 
up to 100kHz or so and create a FIR filter sort of response.  So, we used 
frequency domain multiplexing on the line and used the line multiple times:

output at baseband at t
first pass at 150kHz downtranslate a tap out at t+T
uptranslate for:
second pass at 300kHz, downtranslate a tap out at t+2T
upstranslate for:
third pass at 450kHz, downtranslate a tap out at t+3T

End result, one delay element of length T for a FIR filter of length 4.
So, in a way, these were different length delay lines in parallel even 
though the physical line was the same one.
Note that this isn't recursive because all the signal paths are independent 
/ not added - well they are added in the delay line but separated in 
frequency so the end result is not recursive.

Fred 

"Fred Marshall" <fmarshallx@remove_the_x.acm.org> wrote in message 
news:0fednQVKW-v_DoPfRVn-og@centurytel.net...
>
> "Max Hauser" <maxREMOVE@THIStdl.com> wrote in message 
> news:111oecet5h9b407@corp.supernews.com...
>> "Allan Herriman"
>>>
>>
>> Neglecting novelty items like recursive FIR implementations, there are 
>> other famous nonrecursive structures that also realize Finite Impulse 
>> Responses but lack the transversal (tapped-delay) structure.  A parallel 
>> set of delay lines of different lengths or delays, each weighted at their 
>> input or output, and finally summed, is such a structure.  (It has been 
>> useful in some delay-line technologies that had constraints, for example 
>> certain CCD technologies circa the 1970s.)
>>
>> -- Max Hauser
>
> In the olden days when delay lines of any appreciable length were 
> expensive we used a relatively wideband torsional wire acoustic delay line 
> over the range 100kHz to 1MHz.  The line wasn't tapped.  We wanted to 
> delay signals up to 100kHz or so and create a FIR filter sort of response. 
> So, we used frequency domain multiplexing on the line and used the line 
> multiple times:
>
> output at baseband at t
> first pass at 150kHz downtranslate a tap out at t+T
> uptranslate for:
> second pass at 300kHz, downtranslate a tap out at t+2T
> upstranslate for:
> third pass at 450kHz, downtranslate a tap out at t+3T
>
> End result, one delay element of length T for a FIR filter of length 4.
> So, in a way, these were different length delay lines in parallel even 
> though the physical line was the same one.
> Note that this isn't recursive because all the signal paths are 
> independent / not added - well they are added in the delay line but 
> separated in frequency so the end result is not recursive.
>
> Fred

Well, on second thought, it seems that this implementation was more serial 
than parallel.

Fred