Homebrew Spectrum Analyzer

[Duo]

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.





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.

[DigitalJunkie]

Count me as extremely interested!

[SY]

Ditto!

[AR2]

Cool,
I am one more in the line.

[jacquesl]

You’ve got some nice equipment there man

[gbyleveldt]

Heehee, Jacques, ek is mal oor jou Avatar. Dit moet suig om in Kaapstad te bly

Sorry guys for being off topic...

[jacquesl]

Thanks man, nah, I’m 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, didn’t you typed that in Eng a couple of seconds ago?

[gbyleveldt]

Didn't want to distract the thread too much... But now I have

[Duo]

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.

[infinia]

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?