Re: AM radio receiver - design
- From: "miso@xxxxxxxxx" <miso@xxxxxxxxx>
- Date: Mon, 9 Feb 2009 14:17:03 -0800 (PST)
On Feb 9, 8:24 am, cs_post...@xxxxxxxxxxx wrote:
On Feb 6, 10:51 am, "Joe G \(Home\)" <jo...@xxxxxxxxxxxxxxx> wrote:
I am looking for a super sensitive / selective AM radio design.
Where I am I get lots of interference ....
Have you seen any good designs on the internet you can suggest.
Many have made some good suggestions on the antenna front.
For a receiver, if you really want something economical that can pick
out exactly the bandwidth of interest and reject everything else, try
looking at a quadrature sampling detector, aka Tayloe Mixer. The
basic idea is to do a very high dynamic range commutating mixer with
four phases of a digital clock, giving you a a quadrature IF either at
zero or in the kilohertz range. You use some op-amp filters to
remove strong interference, then put the result into a high quality
stereo sound card (it's still an RF signal at this point not 'audio'
but the frequency range is within the bandwidth of high end audio
converters). From then on, the remainder of the signal processing is
all digital - highly customizable IF filter bandwidths, detector
algorithms, etc.
I'm amazed that has a patent. It is very similar to designs used at
least a decade earlier.
In the early 80s, we did a modem using a similar scheme, but at that
point it could be done in DSP. The easiest way to derive IQ signals
via sampling is by decimation and alternate sample inversion.
Assume this is your sample stream
1 2 3 4 5 6 7 8 9 10
Produce two streams as such
+1 -3 +5 -7 +9
+2 -4 +6 -8 +10
This assumes sampling at 4x. You could need to do clock recovery of
the carrier with a multiplier.
.
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