Author Topic: Spectrum analyzer  (Read 4657 times)

bkenobi

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Spectrum analyzer
« on: December 09, 2013, 02:45:31 PM »
Has anyone considered building an Arduino based spectrum analyzer to see what's actually going on with their RF signal before?  I thought about buying one a while back but the cost is way too high for a purpose built unit.  However, I've seen a few Arduino based units that seem to cost well under $100USD including the Arduino, the RF transceiver, etc.  Any thoughts on how useful something like this might be?

http://forum.arduino.cc/index.php?PHPSESSID=0effnuo7pjkfsvifj9su4b5687&topic=93777.0

bkenobi

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Re: Spectrum analyzer
« Reply #1 on: December 10, 2013, 07:45:55 AM »
This may be a better way to go.  This is a $20 setup that requires a PC but is dead simple from the looks of it.  The video that is linked shows it being used at 150MHz or so, and the documentation indicates it works up to 2.4GHz.  That's plenty good for anything that I would need for X10 or WiFi type stuff.  If I can find a dongle, I'll probably get one just to play with it since it's cheap!

http://www.rc-cam.com/forum/index.php?/topic/3891-20-spectrum-analyzer-for-testing-fpv-systems/

Tuicemen

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Re: Spectrum analyzer
« Reply #2 on: December 10, 2013, 11:58:53 AM »
I'm not sure about using for X10 or Wi-Fi I read it won't work for 2.4 or 5GHz
I use a simple app on my Android phone for checking for dead spots and signal strength.
http://jvde.us/forum/index.php?topic=89.0
True inSSider doesn't work for X10 RF but if a Wi-Fi Signal Is week and your X10 transmitter is in the same location there is a good bet it will be weak too. ;)
X10 turned me into a Software programmer.
A warning label should have been added ;)

bkenobi

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Re: Spectrum analyzer
« Reply #3 on: December 10, 2013, 02:24:26 PM »
inSSider looks like a good tool for picking the right WiFi channel based on other routers/devices in the area.  I'm not really worried about that since my nearest neighbor is outside of the range of my router or devices.  I am primarily interested in understanding the performance of my X10 RF but also extended to other frequencies if possible.  As for the X10 range, I was envisioning setting up a spectrum analyzer so that I could transmit from my MS16A's and see how strong the signal was.  Ideally, I'd use the actual antenna that I'm currently using and see how moving both it and the MS16A affects signal strength.  I'd also like to see if there's anything else causing interference.  Also, it's geeky to see what's going on at different frequencies.

I ordered one of those TV receivers since I found one shipped for <$15.  If it works, I'll probably find a way to connect it to a coax such that it can hook up to the antenna.

Tuicemen

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Re: Spectrum analyzer
« Reply #4 on: December 10, 2013, 02:58:16 PM »
Inssider will not only show which channel to use but if you walk around your house you'll see the signal increase or decrease depending on noise or obstructions like large metal devices.
It will also help find the best location for your router so signals get by some obstructions.
I recently showed it to a friend who was having connection issues. The refrigerator was directly in line with his router and Wi-Fi camera this decrease the signal so much that other noise cause disconnects.
Also it showed him placing the router at the back of the house (even though high) was a poor location ;)
X10 turned me into a Software programmer.
A warning label should have been added ;)

bkenobi

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Re: Spectrum analyzer
« Reply #5 on: February 16, 2014, 08:52:39 AM »
The slow boat from China was REALLY slow!  Actually, the module was lost in transit the first time.  Anyway, it finally arrived and I have been playing with it a bit.  Using the RTLSDR software, it is possible to tune the module to receive anything from 60MHz to 2GHz+ (depending on hardware).  Not only can it tune a single band, it can actually visualize a large band to show what frequencies are being used.

I tested by tuning in a couple radio stations.  While it works ok with the cheapo included antena for a couple stronger stations, it isn't good sound.  I purchased a PAL to F-connector and used an 18" whip (stripped coax) and could get a stronger signal, so obviously antennas matter.

Here's where I need help.  I tuned to 310MHz and clicked some buttons on my HR12 palm pad.  I could see spikes on the graph, but they were at 310.2 and a weaker one at around 309.8.  How critical is the 310MHz to the CM15A?  I'm planning on testing with my actual antenna run to see how things look to the CM15A, but if someone with more knowledge could chime in, that would be great!

bkenobi

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Re: Spectrum analyzer
« Reply #6 on: February 16, 2014, 11:27:26 AM »
I spent a bit more time with the SDR this morning.  After hooking up to my X10 antenna, I can say I have GREAT reception...of radio stations.  My setup uses a radio shack antenna mounted upside down in the attic with a 100+ foot run of RG6 coax and a powered inline filter mounted a few feet from the antenna.

What I am seeing is distinct FM stations in the standard FM band locations (88-108MHz) that show up as clear bumps in the FFT plot in SDR.  I can tune them and they play back very clear.  So, I know the setup works in that range.  I then tuned to 310MHz and tried a few controllers: 2x HR12A, 1x KR22A, 1x KR19A.  I do see variation in the broadcast frequency of several hundred kHz, but that's not the most interesting part.  I found radio broadcasts in that range!  What would be transmitting programming there?  And, is it possible that would cause problems for the X10 signals?

EDIT:
I listened to the static for a while until they broadcast a station identifier.  I was tuned to 309.9MHz and am picking up 101.5MHz.  Not sure why that would be but very strange.
« Last Edit: February 16, 2014, 11:35:39 AM by bkenobi »

Brian H

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Re: Spectrum analyzer
« Reply #7 on: February 16, 2014, 03:47:38 PM »
If the FM station in question was close to you. It may have been overloading the analyzers receiver or could be a weak harmonic of the 101.5 MHz signal.

I am not surprised that the X10 RF devices where a few hundred KHz off. Most are an RC Tuned oscillator what as few parts as they had to use and be sort of stable.
I am not sure how close the ones that used a SAW device for frequency determination are to the 310MHz.

« Last Edit: February 16, 2014, 03:49:26 PM by Brian H »

bkenobi

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Re: Spectrum analyzer
« Reply #8 on: February 18, 2014, 04:07:50 PM »
I don't know how close "close" needs to be, but the stations antenna has to be at least 20 miles away.  When I use my diy 18" whip, I don't get any duplication.  I wonder if the amplifier/filter setup I'm using is causing this.  I suppose one way to test would be to pull the amp off the Radio Shack antenna and try it on my whip to see if the results are the same (or put the whip in place of the RS would probably be easier).

Incidentally, I did stumble across a radio station the WADOT was using and found that there was some debris on the highway 50-75 miles away.   8)