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

Mon, 16 Sep 2002 11:58:32 +1000

G'day Adam

From the sound of all that you and others have said about blowby with
analogue IF systems, there must be room for improvement with a lot of rigs,
ie shielding can be improved.

I must admit looking at a lot of my gear, on most there is no shielding
between the input and output pins on IF crystal filters.

I find these pages a very useful resource, thanks.

Regards

Wade VK4ACB

----- Original Message -----
From: "Adam Farson" <[email protected]>
To: <[email protected]>
Sent: Sunday, 15 September 2002 10:17
Subject: RE: [Icom] RE: Filtering at 9 MHz vs. 455 kHz

> 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
>
>
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