Re: Is it possable to use a 450/455 KC BFO with the new "DSP" radios? i.f. ?


Kevin Schanilec
 

Stephan:

Danke sehr! I heard from another person whose images indicate that the IF is around 32 khz, so I think you're right - there is something else going on besides the traditional twice-the-IF imaging going on.

I too wish for the next chip to have SSB/BFO, as well as a way to clear up the various tones/hets that are on several frequencies on all SI-473X DSP receivers I have.

Kevin

--- In ultralightdx@..., "Stephan Schaa" <schaa@...> wrote:

I think there's no common IF at all. The chip mixes the HF Signals down
direct to baseband, maybe at 8 - 10 khz or so(I/Q baseband mixer). There it
makes the analog to digital conversion.

The images of local stations are probably some mixing effects in either the
external components ( (L Tank, HF Amp, AM/SW Switching....) or mixing
effekts inside the chip which tunes by switching on/of some parallel
capactors.

Becaus of this internal strucure it's not possible to add a extra BFO to
get SSB reception. At the moment I even doubt that SI could add such a
feature. But I hope for more in their next design.

73,
Stephan


_____

Von: ultralightdx@... [mailto:ultralightdx@...] Im
Auftrag von dhsatyadhana
Gesendet: Freitag, 7. Januar 2011 02:06
An: ultralightdx@...
Betreff: [ultralightdx] Re: Is it possable to use a 450/455 KC BFO with the
new "DSP" radios? i.f. ?




Yep, the IF is 45 khz or so. I get images of strong locals 90 khz below
their nominal frequency (i.e., I hear a weak image of 880 on 790).

Kevin

--- In ultralightdx@... <mailto:ultralightdx%40yahoogroups.com>
, "jimmy" <jimmyyearwood@> wrote:

45? Wow. That's looking like a "no".

--- In ultralightdx@...
<mailto:ultralightdx%40yahoogroups.com> , "ferrite61" <dxrx@> wrote:

The Internal Frequency isn't listed in the specs, but IIRC, someone has
good evidence the AM IF is about 45kHz (1/10th the typical value).

Paul S. in CT


--- In ultralightdx@...
<mailto:ultralightdx%40yahoogroups.com> , "jimmy" <jimmyyearwood@> wrote:

Has anyone tried to use an outboard/add-on BFO circuit with any of the
DSP rigs?

Looking at the block diagram of the Si4734 I see no i.f. or oscillator
coils or mention of what the intermediate frequency is. To be honest it has
me completely stumped. I understand the basic radio circuits about as well
as anyone could I guess but this digital and literally
everything-on-one-chip stuff looks like something more out of science
fiction than reality. Even Edwin H. Armstrong would be scratching his head
over this one let alone yer average Joe with a soldering iron like myself. I
have no idea what to make of it at all. I mean it has to work on the same
basic superhet principals, right? Radio from Mars! RUN FOR YOUR LIVES!..lol.



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