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

[Adam Farson]

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:farson@shaw.ca


-----Original Message-----
From: icom-admin@mailman.qth.net [mailto:icom-admin@mailman.qth.net]On
Behalf Of Siu Johnny
Sent: Saturday, September 14, 2002 16:53
To: icom@mailman.qth.net
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