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Old 1st February 2007, 01:18 PM   #1
Duo is offline Duo  Canada
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Default Homebrew Spectrum Analyzer

My latest and greatest project is a home made spectrum analyzer.

I've built the basic prototype using a TV tuner board, a 555 sweep generator, some op-amps to achieve DC level shifting and amplification, and a simple transistor RF amp and diode detector.

The display is a general purpose oscilloscope.

Here is a picture of the analyzer displaying the output of a nearby oscillator running on a battery at about 100MHz. The analyzer is picking it up through the air.

Click the image to open in full size.
Click the image to open in full size.


More on it later, I will be doing a great deal of work on this to make a full-blown analyzer capable of operating from 0 - 500MHz or so.
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Old 1st February 2007, 01:59 PM   #2
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Count me as extremely interested!
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Old 1st February 2007, 02:01 PM   #3
SY is offline SY  United States
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Ditto!
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Old 1st February 2007, 02:29 PM   #4
AR2 is offline AR2  United States
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Cool,
I am one more in the line.
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Old 1st February 2007, 05:24 PM   #5
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Youíve got some nice equipment there man
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Old 1st February 2007, 05:45 PM   #6
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Heehee, Jacques, ek is mal oor jou Avatar. Dit moet suig om in Kaapstad te bly

Sorry guys for being off topic...
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Old 1st February 2007, 06:06 PM   #7
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Thanks man, nah, Iím not in Cape Town but near it, the only that suck is some down time from koeberg once in a while, power outage

EDIT: Huh, didnít you typed that in Eng a couple of seconds ago?
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Old 1st February 2007, 06:31 PM   #8
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Didn't want to distract the thread too much... But now I have
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Old 1st February 2007, 10:33 PM   #9
Duo is offline Duo  Canada
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Here is a hand-drawn image of my working prototype schematic.

There are no embellishments as of yet; no log amp in the video section, no filters, no bandwidth limiting, no sweep rate control, no nothing really.

It does, however, function very nicely in the bands available to the TV tuner. I've only got it set up on a 12V power supply and TV tuners usually like around 30V tuning range, so later I'll make a 30V supply and driver circuit to allow the tuner sweep to go all the way.

The extras I -did- add were spectrum width and center frequency controls. This at least allows me to move the band a bit and set my span.

I'll get back with more after I've developed the additions. I do plan to make some heterodyne circuits to allow this to tune in ranges outside of the tuner's bands; such as audio frequency, AM and HF radio bands, and perhaps something into the microwave area.

Click the image to open in full size.
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Old 1st February 2007, 10:59 PM   #10
infinia is offline infinia  United States
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Hi
Nice work so far.
You can possibly use a single chip log amp for use of your AGC/det function. Use an opamp for some baseband/DC gain after this.

Is the tuner unmodified (ie PLL still closed loop) for close to the carrier (that is for audio) performance? I forgot the last IF freq for these tuners is it a SAT/TV tuner?
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