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Joerg · June 30th 07, 03:00 PM posted to rec.radio.amateur.homebrew

wrote:

On Fri, 29 Jun 2007 21:53:54 -0400, "Jimmie D"
wrote:

"Joerg" wrote in message
...

Tim Wescott wrote:

Jimmie D wrote:

Revamping an old homebrew SW receiver I built about 30 years ago. Is
there an IC that will serve as an AM SSB FM detector. The existing
AM/SSB detector is on a board the size of a playing card.

You could probably twist some of the FM/IF detectors into doing that.
Many of them have RSSI outputs that go as the log of the signal strength,
I've seen literature that suggests you can block the DC from that and
feed an exponential stage to get AM detection with built-in AGC. For
SSB, if you switched out the quadrature filter for FM detection and
injected a BFO into the appropriate pin you could get SSB.

But if you're playing around with a board the size of a playing card, why
not build three optimized detectors, or get ambitious and slap down a DSP
with appropriate ADC and DAC resources?

But be careful with a DSP in a receiver. They require a clock and generate
all kinds of RF noises. Might have to be in a can.

Of course, a DSP can do all sorts of other stuff like DRM. Although I
doubt DRM will ever make it into the market.

This old dog would have to learn some new tricks to implement DSP. I thought
I remembered seeing a chip somewhere that did SSb AM and FM.

The oldest one was the National LM373. You can do it with SA602/612
but you will need several. I've used the Motorola MC3357 which is an
FM chip but if you pick off before the limiter stages you can use a
diode to get AM.

Tim's right there is enough room for three descrete detectors. I can easily
squeeze it all in if I redsign the board, Maybe a PLL circuit for FM unless
someone can suggest something more modern. Probably a special purpose chip
available that I am not familar with. I wanted to adFM so I could use the rx
with VHF/UHF converter. IF is 455Khz.

FM these days uses a quadrature detector on a chip with limiter
stages. There are a lot of choices on what to do for FM. they work at
455KHz. I'd use one of the moto MC335x chips Usually the choice is
artificially limited by what you can obtain.

SSB a favorite is the ne602/sa612 chip or my favorite a DBM.

If I would build it myself I'd go all out and try to make the best dang
detector this side of the Mississippi. Definitely DBM.

AM it's hard to beat a diode detector however if you want to try
something more exotic look up reciprocating detectors.

IF DSP can do it all but it's rare that you can do that without
putting it in a can to keep all the unwanted stuff from appearing at
the input. Also unless you are willing to buy expensive most are only
fast enough to run at an IF much lower than 455kHz (a long list of
radios with IF DSP convert 455khz down to 12-15khz then use DSP to
process it).

Some are pretty brazen. AFAIK the Winradio goes from a 1st IF of around
109MHz straight down to around 15kHz. No idea how good that works, could
not find anyone who has it.

--
Regards, Joerg

http://www.analogconsultants.com

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