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School spectrum analyzer project.

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BlownUpCapacitor:
Hi, I am wondering if anyone knows any good sources for making spectrum analyzers. I looked at my local library and all I could find were some basic electronics 101 books.

I don't necessarily need sources that explain how a spectrum analyzer works, but rather maybe you can point me towards sources that explain the design of the things used in such devices such as voltage controlled oscillators, IF filters, mixers, and so on.

This is for a school project. In freshman year in my HS, we do something called a personal project that lasts about 8 months until sophomore year. We research, think about, and do our project. This could be baking, making a guillotine (yes someone made that in a previous year), or making a robot to help victims of forest fires get to safety. I chose to make an analog swept front end spectrum analyzer. I plan to make this work in a Tektronix 5110 mainframe.

Anyway, I'm just a bit under educated on how certain things work. I am quite familiar with electronics, It's just that I can't find any good sources that explain in great understandable detail on how certain things work. All I know about a VCO is that a varidiode will change it's capacitance based on the voltage applied to it, and we can use that to make a VCO. I'm also a bit confused on how the hell a logarithmic amplifier works.

My goal is to make a spectrum analyzer work with a bandwidth of 0-10MHz.

My basic understanding of a swept front end spectrum analyzer is that it is just a superhederodyne AM receiver with wider bandwidth and can tune across a number of frequencies really fast.

CaptDon:
There is a VCO in the CMOS 40XX series that is good for a swept VCO. Very linear. Sadly, I forget the number. You'll need a good balanced mixer. making the front end track the local oscillator + or - your I.F. frequency is a bit of a trick. Going 0 to 10MHz may be far more challenging than going from perhaps 5MHz to 10MHz where you are only going one octave and not several decades. Coming off your balanced mixer you may want a crystal filter to keep some of the junk out of your I.F. strip. Log amplifiers have been around since the radars of the WWII. They usually involve the log function of a small signal diode. We used the non-linear characteristics in the S.T.C. Sensitivity Time Control because the strength of the echo diminishes as the square of the distance so the gain starts out low for close in echos and advances to max gain over time through a non-linear function. Remember in your analyzer that High-Q narrow bandwidth circuits take time to 'ring up' like trying to accelerate a heavy weight on a pendulum and then have the nasty habit of continuing to ring which is the quality factor of the Q, sharp peak, low loss. Point being 'if you sweep to fast across a band of frequencies the I.F. won't have time to properly respond. That is why the old tube type analyzers swept slow and used the same sort of long persistence phosphors like the radar scopes to get a usable readable trace at 1 to 5 sweeps per second. Of course, now it is all digital storage and LCD screens.

MasterT:
Very time consuming and very complicated.  Better alternative is arduino + some RF IC, like si4732-a10 or similar.

BlownUpCapacitor:

--- Quote from: CaptDon on March 22, 2024, 06:52:26 pm ---There is a VCO in the CMOS 40XX series that is good for a swept VCO.

--- End quote ---

Thanks, I'll look into that.


--- Quote from: CaptDon on March 22, 2024, 06:52:26 pm ---Coming off your balanced mixer you may want a crystal filter to keep some of the junk out of your I.F. strip.

--- End quote ---

Yes, I'm planning to use 3 stages of standard 455kHz IF transformers and a crystal filter to improve selectivity.


--- Quote from: CaptDon on March 22, 2024, 06:52:26 pm ---Point being 'if you sweep to fast across a band of frequencies the I.F. won't have time to properly respond. That is why the old tube type analyzers swept slow and used the same sort of long persistence phosphors like the radar scopes to get a usable readable trace at 1 to 5 sweeps per second. Of course, now it is all digital storage and LCD screens.

--- End quote ---

Slow sweep speeds won't be an issue for me. I can use a storage CRT scope such as the Tek 7613 or Tek 314.


--- Quote from: MasterT on March 22, 2024, 09:34:28 pm ---Very time consuming and very complicated.  Better alternative is arduino + some RF IC, like si4732-a10 or similar.

--- End quote ---

I don't want to do something as simple as that. I already know like 4 people who are doing an arduino project where they use specialized pre-built devices, almost like a kit. I like to keep things as discrete and jellybean as possible.

Plus I have 8 months to do this, so plenty of time.

LaserSteve:
No one expects you to build this, but you can Learn from the Master:

https://lea.hamradio.si/~s53mv/spectana/sa.html

This was popular:

https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1985/11/page23/index.html

The must have books for a beginner in RF:

Experimental Methods in RF Design, Bob Larkin, Rick Campbell, and Wes Hayward

Has a full Spectrum Analyzer design that is very good and inexpensive. Covers home made crystal filters well, at levels from beginner to advanced. Covers VCO design and  Preamp / IF /RF amplifiers from DC to 2 Ghz  Its a great book, but it has doubled in price recently, for an 8 month school project it's perfect.. Try to find it used or on inter-library loan. Goes into the theory and design  of every receiver circuit element without high order math from a amateurs' radio point of view.  Learn what is in that book and have a good start on a career.  I think of it as a book that you'd have to pry from my cold, dead, hands...

But NOT dumbed down like the ARRL Handbook, of which OLDER like 1980s-1990s editions are a good read...

Navy NEETS, the full set... Free from the US Navy...

Art of Electronics, Volume one, Winfield Hill..  Probably can find a PDF on-line.

You need this chart eventually:

https://www.minicircuits.com/app/DG03-111.pdf

You need this chart now...
https://www.minicircuits.com/app/AN40-012.pdf

_-------------------------------------------------------

You will eventually need the circuit in figure 6 of this:

https://interferencetechnology.com/wp-content/uploads/2015/02/WyattArticle.pdf

Also make it with a 1 Mhz TTL Crystal oscillator

-----------------------------------------------------

Print out copies and download the images on this page:

https://techlib.com/electronics/detect.htm

You'll need a rudimentary RF voltmeter, the above page is it.  Dr. Wenzel made that page  for me way back when I was building a SA, like two decades ago. Its accurate.

You'll need attenuators:

https://www.qsl.net/z33t/rf_step_attenuator_eng.html

Eventually you will want a Ebay "DDS" frequency  synthesizer for testing and measuring resolution and level.

For RF under 200 Mhz or so, Manhatten Style PC construction  is great for beginners:

https://qrpme.com/docs/K7QO%20Manhattan.pdf

Snag some Analog Devices inc  RF log Amps and Detectors...  Their web site is a treasure trove for a beginner

Like these:, https://www.ebay.com/itm/166352071945?itmmeta=01HSMAM3EZGBGHTD6ZKK80N4PH&hash=item26bb5b2d09:g:rKgAAOSwKsFlFLEN&itmprp=enc%3AAQAJAAAA0EISSxez%2BBTXxKGsQFea8desWappsYYsz%2FnSnqNuzInJ8rr5A7OGWcg3xPL%2FHpJR4dAm3Ezj8EkPOLlidRfntmKKk7I%2FWGWCvFcJ2igsyf%2B6TpSgfCKaS10YeTcw3xzvehi4yjheZn3BaIzCvwXZfz1hoCE7%2BY0F9ssrStos%2Br5CdiobDBIDMEkeyRosjBwnX%2F85%2F5kv1USYFyMoSdK%2BaaL7hUWOVaYX0PMfy6i7v4hcfuro2xEOhwjxUXHP4Ai3pDlPypm9u8Bz%2B13hzrqujMU%3D%7Ctkp%3ABk9SR9S30IrNYw

There are other varients.

Shop Class:   Interdigital filters are a key part in High End Spectrum Analyzers with High Side IFs for greater performance. This is a Java calculator that helps you make them:

https://www.changpuak.ch/electronics/interdigital_bandpass_filter_designer.php 

Can be made with hand  saw, file, taps, and drill, but have your parents permission before using power tools and have supervision.



This program, you may need later:  http://www.hp.woodshot.com/   One of my favorite tricks with Appcad is to turn hobby shop brass tubing  into  Solid Coax Cables  and RF fittings such as cased diode detectors.

https://www.broadcom.com/info/wireless/appcad  Also hosted at Broadcom...


Lastly:  www.minicircuits.com 
www.rfparts.com
 www.amplifiedparts.com  (Great Knobs)
https://www.rf-microwave.com/en/home/ (Italy, but ships to US)
www.mcmaster.com  = Hardware treasure trove.

Steve
















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