
DIY Spectrum Analyzer 0 to 1750MHz (1999) - dschuetz
http://lea.hamradio.si/~s53mv/spectana/sa.html
======
wpietri
For what it's worth, this is a 2007 web translation of a 1999 article on hand-
building a spectrum analyzer. To me it looks very analog; I can't imagine
anybody building this today except as a sort of electronics historical
reenactment project. If you're wondering how it all fits together, I think
this is the better place to start:

[http://lea.hamradio.si/~s53mv/spectana/lcd.html](http://lea.hamradio.si/~s53mv/spectana/lcd.html)

But you'll find the whole series of articles in this directory:
[http://lea.hamradio.si/~s53mv/spectana](http://lea.hamradio.si/~s53mv/spectana)

~~~
madengr
If you crack open a real spectrum analyzer (not some hacked together SDR toy)
you’ll still find plenty of distributed and analog circuitry. That’s what it
takes to get spur-free performance.

~~~
jjoonathan
SDRs are total spur-fests, yes, but at 0% the cost of a real SA (rounded) the
economics sometimes work out :-)

That said, at the high end of the SDR range, the new AD937x chips ($325 in qty
1k!) make impressive claims wrt automagic spur suppression. They still don't
beat high-IF or YIG preselected SAs, but now they claim to be in the ballpark
under non-overload conditions. Has anyone here dug deep enough to comment?

~~~
madengr
The pre-selection is a big deal. The AD936x needs good front end filtering to
reject n*LO. For instance 5x146 MHz = 730 MHz, which translates that 730 MHz
nation-wide LTE signal smack-dab into the 2m amateur band. Unless they have a
new front-end architecture in the AD937x, all the I/Q calibration won't help
them.

Of course as you said, for $325 it's not a consumer chip, so some $ will be
spent on external passives.

~~~
jjoonathan
Ah, right, I/Q calibration can't suppress anything out-of-band. Makes sense.

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setquk
I’m building a slightly crappier and less ambitious 0-200MHz one at the moment
for HF use. Basically a step attenuator, LPF, a pair of NE602 for first and
second LO+mix, an old Toko helical filter for first IF and hand built crystal
filter (12MHz) for second IF resolution filter and then an AD8307. First LO is
a VCO with varactor control driven from an opamp ramp generator. Doesn’t work
yet as the Toko filter is broken and I can’t find a suitable replacement and
can’t be bothered to make a helical filter.

The things look like rocket science but they are basically superhet receivers
with a log converter instead of speakers and a much larger tuning range.

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jhallenworld
The sheet metal work in projects like this interests me. In the 1930s the new
technology of the time was shortwave radio, so hobbyists built their own.
Short Wave Craft was a magazine that supported this hobby- it's very much like
Popular Electronics or Byte magazine. Always there were sheet metal plans
included in the project. Here is an issue of it (pages 51 and 35 have typical
chassis plans):

[https://www.americanradiohistory.com/Archive-Short-Wave-
Tele...](https://www.americanradiohistory.com/Archive-Short-Wave-
Television/30s/SW-TV-1934-12.pdf)

So did hobbyists have access to sheet metal brakes? Not really- they either
use a vice and hammer, or bought pre-made chasses from a place called "Blan
the Radio Man"\- a store in NYC's old Radio Row:

[https://en.wikipedia.org/wiki/Radio_Row](https://en.wikipedia.org/wiki/Radio_Row)

[https://i.pinimg.com/originals/d5/4f/2c/d54f2c957af5cec29831...](https://i.pinimg.com/originals/d5/4f/2c/d54f2c957af5cec2983151c613875e47.jpg)

~~~
Hasz
If you're working with thin steel sheet, or some aluminums, building your own
sheet break is pretty easy to do, even without access to a machine shop.

[https://duckduckgo.com/?q=diy+sheet+break&t=ffab&iax=videos&...](https://duckduckgo.com/?q=diy+sheet+break&t=ffab&iax=videos&ia=videos)

It's a much cleaner finish than the hammer+vice combo.

~~~
jhallenworld
Also you can get cheap brakes from Grizzly or Harbor Freight.

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userbinator
I recognised this guy from the format of his webpages (very fast loading, no
unnecessary stuff --- a look at the source suggests it's handwritten HTML); he
has also built his own GPS receiver:

[http://lea.hamradio.si/~s53mv/navsats/theory.html](http://lea.hamradio.si/~s53mv/navsats/theory.html)

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lpasselin
Are there tools to easily create xkcd style diagrams similar to these?

~~~
pjc50
I'm fairly sure that's technical pen on paper which has been scanned, run
through a quantize filter to clean it up, and shrunk.

~~~
bArray
For sure, although not completely impossible to replicate in software.

------
auslander
[https://xkcd.com/730/](https://xkcd.com/730/)

