[sdiy] Can you call the low pass filter in a frequency shifter an antialiasing filter?

[cheater cheater]

Thanks!
So is there an easy explanation of what a quadrature mixer is? I'm
happy for heavy maths, but heavy electronics scare me a bit ...
I'm afraid the only things I can find arr involved radio-world descriptions.

Cheers,
D.

On Tue, Oct 5, 2010 at 00:10, Eric Brombaugh <ebrombaugh1 at cox.net> wrote:
> Sorry - Local Oscillator. It's an RF systems term that refers to the shift
> frequency that's applied to a mixer in a heterodyne system. For what it's
> worth, a Bode Frequency Shifter is basically an audio implementation of a
> quadrature mixer - something that's used throughout wireless communications,
> albeit at higher frequencies.
>
> Eric
>
> On 10/04/2010 01:53 PM, cheater cheater wrote:
>>
>> Hi Eric,
>> sorry, what's an LO?
>>
>> Thanks,
>> D.
>>
>> On Mon, Oct 4, 2010 at 18:38, Eric Brombaugh<ebrombaugh1 at cox.net>  wrote:
>>>
>>> On 10/04/2010 02:12 AM, cheater cheater wrote:
>>>>
>>>> Hi,
>>>> I have come across this question today and I don't know what the
>>>> filter is called exactly, or if it can be specifically identified with
>>>> a special name for it. Any ideas?
>>>
>>> There are a number of ways to implement a frequency shifter, but I'll
>>> assume
>>> you're referring to the analog Bode-style shifter such as is described in
>>> this Moog patent:
>>>
>>> http://www.pat2pdf.org/pat2pdf/foo.pl?number=3,800,088
>>>
>>> There are two types of LPF in this architecture, both used in the
>>> generation
>>> of the local oscillator. At block 17 is a 20kHz LPF that is used
>>> primarily
>>> to clean up the 20kHz osc and ensure that there are no higher harmonics.
>>> As
>>> Tim noted, the filters at blocks 23 and 24 are image filters which are
>>> used
>>> to remove unwanted mixing products. The +/-5kHz LO is created by mixing a
>>> 15-25kHz oscillator with a 20kHz oscillator. This will produce products
>>> simultaneously at +/-5kHz and 35-45kHz - the image filters remove the
>>> unwanted tone a 35-45kHz, leaving the desired +/-5kHz tone.
>>>
>>> There are alternative ways to implement the Bode shifter that don't
>>> require
>>> this however. Some modern shifters generate the LO directly using digital
>>> techniques while still using the analog dome filter&  mixer approach.
>>> Other
>>> shifters operate entirely in the digital domain, digitizing the input
>>> signal
>>> and doing all the phase shifting and mixing numerically before outputting
>>> thru a DAC. Neither of these approaches requires the image filter, but
>>> they
>>> will require post-DAC reconstruction filters.
>>>
>>> Eric
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>>>
>>
>
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