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Author Topic: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module  (Read 47457 times)
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yes im running a RF22 on a R3 UNO .
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just few questions to clarify if what im seing is correct.
below is a picture of a test running currently running on the bench.


if you look at the picture with only the RF22 switched on that is working as the receiver it would appear that there is a very high signal detected in the UHF range where i stay ? or am I seing it wrong ?

also the labeling of the dBs on the left hand side would it not make more sence if it started form -120 at the top and -20 at the bottom? I arleady made the mistake at looking at the spike but in reality if i understand it correct is actually the lowest detected frequency that im looking at , can it be swapped ?

other question is , I have a 17cm antenna on my receiver this would offcourse make a differences for freq. in the 800 or 900 range . what then ? or is this meant to  be used with Rf probes only and not general area scanning ?

thanx for any advice , really keen on useing this more


* example.jpg (274.57 KB, 1366x768 - viewed 74 times.)
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Hi Z,

I'm also using 0023.

I made a clean install on netbook and copied your RF22 library (from your post above) into the clean libraries folder.
Copied the code (from above) and made a new pde called 'rf22_specan_simple' and veried it.
It compiled OK.

Ran up your RF22SpecScan.exe and it runs fine.

I'll try some more later on my main PC and Laptop as this is where I want to mostly use it.

Nigel.

* rf22_specan_simple.zip (1.29 KB - downloaded 43 times.)
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Hi Z,

I'm also using 0023.

I made a clean install on netbook and copied your RF22 library (from your post above) into the clean libraries folder.
Copied the code (from above) and made a new pde called 'rf22_specan_simple' and veried it.
It compiled OK.

Ran up your RF22SpecScan.exe and it runs fine.

I'll try some more later on my main PC and Laptop as this is where I want to mostly use it.

Nigel.

OK that's good.

if you look at the picture with only the RF22 switched on that is working as the receiver it would appear that there is a very high signal detected in the UHF range where i stay ? or am I seing it wrong ?

also the labeling of the dBs on the left hand side would it not make more sence if it started form -120 at the top and -20 at the bottom? I arleady made the mistake at looking at the spike but in reality if i understand it correct is actually the lowest detected frequency that im looking at , can it be swapped ?

That looks pretty normal.  The RF22 is not meant to be a spectrum analyzer, it will only work properly for the frequency range the module and antenna is made for. You can force it to whatever frequency you want, but results will not be accurate.

RSSI is a logarithmic scale, you are reading it wrong. See http://en.wikipedia.org/wiki/DBm

I just remembered that that I have made some small improvements to the PC program, I have attached the new version.

* RF22SpecScan V0.11.zip (193.39 KB - downloaded 87 times.)
« Last Edit: April 21, 2012, 10:42:18 am by zitron » Logged

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Okay

thanx for confirming that . so for example if the RF22 radio max output is 17-20dBs then if i transmit next the the analyzer i will see a 20 dB jump in the graph but so if it was -120 it will  be -100 or around there.

regarding the Antenna issue , all i really wanna test with these unit is if RF equipments is working or not. for example if i have a 433mhz remote i just want to Tx next to it and see a jump in the graph so Accuracy is not that big of a problem. what i think i would do is make a small Antenna relay board with antenna's made for 900mhz, 433mhz and 600mhz and when i switch between them the reply will latch to the correct antenna Automatically i know its not the best but i think it will be best this setup can do.

are you planning on upgrading the Pc app with more functions ?

like to see if you can set a start line on the average incoming signal and the app will update the max output line at the top of the graph and under the setting just show a tab that updates the dB difference between the two lines.

but thank you for all the advice and info looking forward hearing form you regarding the boards
« Last Edit: April 22, 2012, 04:12:32 am by Rustie0125 » Logged

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This is and excellent project! smiley
I really want to try it out in my FPV quads.

Does anyone has PCB's to sell?
Unfortunately I have no way to make them.
(well I could but I'd probably ended up sleeping in the balcony)

Thanks!
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This is exactly what this is - a DIY project.

It would be nearly the same cost to make a few by hand and sell to you as it would be to buy commercially.

Have you seen this?
http://flytron.com/16-openlrs

Forum support as well
http://forum.flytron.com/viewforum.php?f=7&sid=5794eb0b6f028f25cacb8b980bba52fa

HTH

Nigel.
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thanx for confirming that . so for example if the RF22 radio max output is 17-20dBs then if i transmit next the the analyzer i will see a 20 dB jump in the graph but so if it was -120 it will  be -100 or around there.

You will only see a 20dB jump if you were perviously transmitting at 0dB! Theoretically, if you are transmitting at 0dBm (1mW), and connect the tx directly to the rx with a coax cable (do not do this!) you will see 0dBm on the receiver. However in real life and if you are using antennas, you will see the rx RSSI change from about -20 (the RF22 will not report RSSI higher than -20) to -100 as you move the rx away from the tx.

regarding the Antenna issue , all i really wanna test with these unit is if RF equipments is working or not. for example if i have a 433mhz remote i just want to Tx next to it and see a jump in the graph so Accuracy is not that big of a problem. what i think i would do is make a small Antenna relay board with antenna's made for 900mhz, 433mhz and 600mhz and when i switch between them the reply will latch to the correct antenna Automatically i know its not the best but i think it will be best this setup can do.

are you planning on upgrading the Pc app with more functions ?

like to see if you can set a start line on the average incoming signal and the app will update the max output line at the top of the graph and under the setting just show a tab that updates the dB difference between the two lines.

That will probably work ok, but you will need to write your own code. I might add more to the PC program, but it's not really a priority. You can do your own data processing by collecting the serial data and plotting them in MS Excel or MatLab or even do it on the arduino chip.


This is and excellent project! smiley
I really want to try it out in my FPV quads.

Does anyone has PCB's to sell?
Unfortunately I have no way to make them.
(well I could but I'd probably ended up sleeping in the balcony)

Thanks!

Basically what Devonian said. If you want one or two boards that work right out of the box, you are better off getting the openlrs. I only have the bare pcbs.

BTW, Nigel did you get the thing working on your main PC? If your boards are working properly I'll put together some RC PPM code this weekend for you to test. I've not really been motivated to do much this past week because of the terrible weather!
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Hi Z,

My first board works just fine as a spec analyser.
I've yet to build my other boards.

I'm a bit like you, no big motivation for UHF at the moment (I have OpenLRS for UHF R/C), plus I have a couple other projects - including weather monitoring, maybe with an RFM22B and an Arduino smiley-wink
With the British weather, you should get on it !

Nigel.
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Basically what Devonian said. If you want one or two boards that work right out of the box, you are better off getting the openlrs. I only have the bare pcbs.

My problem sorry, I wasn't that clear.
I'm more of the soldering station type, I prefer to assembly my own gear. smiley

I know about Flytron gear I actually bought some other parts from them, but yes my intention is to get bare PCB's.
I have all the remaining parts just the PCB that is missing.

I got some time ago some similar RFM boards (RFM21 I believe) to do a telemetry project but got sidetracked and ended
going for BlueTooth and developing an app for it. And the the boards are still here getting dust.

But what you share here is on a another level  (special in what concerns range) and rather interests me, so I eager to try it
 and put my hands on the code as well. smiley

PS: I got you guys on the weather (Ireland here)
« Last Edit: April 26, 2012, 05:32:03 am by Nandox7 » Logged

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Hi zitron,

Where did you get your RFM22B? The only that I can find seem to have the emitting power locked and can't do the 100mW.

Thanks
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Hi zitron,

Where did you get your RFM22B? The only that I can find seem to have the emitting power locked and can't do the 100mW.

Thanks

http://arduino.cc/forum/index.php/topic,93777.msg756875.html#msg756875

I know about Flytron gear I actually bought some other parts from them, but yes my intention is to get bare PCB's.
I have all the remaining parts just the PCB that is missing.

I got some time ago some similar RFM boards (RFM21 I believe) to do a telemetry project but got sidetracked and ended
going for BlueTooth and developing an app for it. And the the boards are still here getting dust.

But what you share here is on a another level  (special in what concerns range) and rather interests me, so I eager to try it
 and put my hands on the code as well. smiley

Oh, does that mean you can help with the code?? I have 4 boards left, Rustie0125 wants 1, so you can have the last 3. PM me your address, email and how many you want.

My first board works just fine as a spec analyser.
I've yet to build my other boards.

I'm a bit like you, no big motivation for UHF at the moment (I have OpenLRS for UHF R/C), plus I have a couple other projects - including weather monitoring, maybe with an RFM22B and an Arduino smiley-wink

Cool. I can help you with the code if your weather telemetry project is something simple, like tx/rx of serial data or something.
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Hi Z,

I'm gathering together some bits as the data is apparantly sent over 433.92MHz AM radio by OOK (On-Off-Keying) and there is some info on the 'tinterweb about the protocols used.

I may just get another weather station with serial out on the receiving consol and do it that way.

I also have a Raspberry Pi on order (for ages now), maybe a low power web server and automatic weather station??!!

Too many projects and not enough time...!

Nigel.
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Thanks zitron, I'll send you a PM.
Yes I do plan to help with the code. smiley

In regards to the RFM22B I've talked to someone that is trying to get some as well and the only ones he could find
 available were the RFM22B-868-D, will those work?
Does it need to be the 433 model or it's possible to change the frequency.
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Okay  one thing iv noticed between the different in graph that you postted and the one i posted yours seems to be a lot cleaner and not as jagged spiked like mine . but that said mine is set to max output.

once i get my board from you i would like to use it to test home made 433 radios . what would be the best set of settings for use with RF probes and not antennas? i would image i would set the Tx/Rx power right down to minimum ?
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