[Icom] RE: Filtering at 9 MHz vs. 455 kHz

Sat, 14 Sep 2002 18:50:04 -0600

Hi,
Blow by? That's only in analog filtering. DSP is totally different animal.
Just we need much more powerful micro processors to make REAL good DSP
filters. In music filed it is happening too. The amp modelling digital 
amps are showing
up more and more and I had to admit, they're getting better. Soon I hope 
I don't have
to fix my boy's tube amps any more(Marshall, Fender, Ampeg, Boogie, etc.)
Our brain and ears are pretty good filters as well when it's audible.
73,
Tony, VE6CGX

George, W5YR wrote:

>It might be interesting to note that one advantage of multiple-conversion
>receiver architectures is that they allow effectively cascaded crystal
>filters to be operated at different i-f frequencies. In this way, the
>advantages of cascaded filters can be obtained without excessive steps
>being required to minimize blow-by and related effects.
>For each filter, however, at each i-f, the blow-by problem exists.
>Sometimes extraordinary design and construction measures are required to
>reduce blow-by such that 60-90 dB ultimate rejection can be realized.
>
>On balance, there are both disadvantages and advantages to multiple
>conversions. It  happens that reducing the blowby problem is one of the
>advantages.
>
>73/72, George    
>Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
>Amateur Radio W5YR -  the Yellow Rose of Texas
>In the 57th year and it just keeps getting better!
>
>
>Adam Farson wrote:
>  
>
>>Hi Johnny,
>>
>>The RF blow-by issue does not arise at all in DSP IF filtering systems, as
>>there is no case where the analogue IF signal ahead of the ADC
>>(analogue/digital converter) can re-enter the signal path on the other side
>>of the DSP. The analogue output of the DAC (digital/analogue converter)
>>after the DSP is no longer at IF; it is at baseband (audio) frequency.
>>
>>Please refer to <http://www.qsl.net/ab4oj/icom/pro_dsp.html>
>>
>>In an analogue IF system with classical crystal filters, proper shielding
>>will minimise blow-by. The filter should be mounted above a shielded
>>compartment, in such a way that the filter case straddles a shield with the
>>filter input and output terminals on opposite sides of the shield.
>>
>>Best 73,
>>Adam, VA7OJ/AB4OJ
>>North Vancouver, BC, Canada
>>http://www.qsl.net/ab4oj/
>>Note new e-mail address:
>>mailto:[email protected]
>>
>>-----Original Message-----
>>From: [email protected] [mailto:[email protected]]On
>>Behalf Of Siu Johnny
>>Sent: Saturday, September 14, 2002 16:53
>>To: [email protected]
>>Subject: Re: [Icom] RE: Filtering at 9 MHz vs. 455 kHz
>>
>>Hi Stephen,
>>
>>Based on your argument, would this mean that a DSP IF filter will not face
>>the RF radiation problems?
>>
>>Looking forward to your advice because I am not a radio profession.
>>
>>TNX & 73
>>
>>Johnny Siu VR2XMC
>>
>>----
>>Your Moderator: Dick Flanagan W6OLD, [email protected]
>>Icom FAQ: http://www.qsl.net/icom/
>>    
>>
>
>--
>----
>Your Moderator: Dick Flanagan W6OLD, [email protected]
>Icom FAQ: http://www.qsl.net/icom/
>
>  
>

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