Is it possible to measure a 433MHz transmitter using a counter?  - Page 1
Forum section: electronics / rf-microwave

author: rodpp
author_rank: Frequent Contributor
timestamp: June 13, 2019, 02:46:07 am
content: Hello,I'm a complete noob in RF stuff, so my doubt probably is very elementary.I have some wireless temperature sensors (Oregon Scientific brand) that transmits at 433MHz. Some time ago I used a cheap wireless receiver in a Raspberry Pi to log temperatures from that sensors with success.Now a bought a cheap USB RF Tranceiver (https://www.ebay.com/itm/NEW-433Mhz-CC1101-USB-Wireless-RF-Transceiver-Module-10mW-USB-UART-RS232-MAX232/182447525829) to use in a PC running Linux logging the temperatures.I already managed how to configure the USB Transceiver, but it has 256 configurable channels, with almost zero documentation. So I could not relate the channel with the frequency, and had no success configuring it to receive the temperature data.I have a universal counter (Agilent 53132A with the 3GHz channel) and want to know if is possible to measure the frequency that the USB device is transmitting using that counter.Is it possible to connect an aerial directly at the counter input, or do I need some circuitry between the aerial and the counter?Or is it not possible at all to measure the transmission frequency using an universal counter?Thanks in advance!Regards,Rodrigo.

author: xrunner
author_rank: Super Contributor
timestamp: June 13, 2019, 02:51:50 am
content: Quote from: rodpp on June 13, 2019, 02:46:07 amYes it is very possible. If you don't have an aerial, just stick a short wire in the BNC connector and place the transmitter close by (but don't connect directly to the transmitter), it has a good chance of counting the frequency.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: June 13, 2019, 06:02:58 am
content: bare in mind an eventual duty cycle; according to regulations upto 1mW ERP there's no duty cycle limition, but for 10mW EPR it's 10% - might be a problem for the counter.since those sensors are likely battery operated, it's very likely that they don't emit a steady rf signal but it bursts.fyi:www.ti.com/lit/an/swra048/swra048.pdf

author: ogden
author_rank: Super Contributor
timestamp: June 13, 2019, 07:36:47 am
content: Quote from: HB9EVI on June 13, 2019, 06:02:58 amRight. Bursts usually are too short to be properly registered by frequency counter. Unless your transmitter have continuous, unmodulated carrier transmission mode, you can't use counter. There's other way:RTL-SDRdongle + SDR software such as SDRsharp. You "calibrate" frequency offset of your SDR from local well-known source like nearby cell tower frequency, then use it as spectrum analyzer to monitor 433 MHz transmissions:https://youtu.be/rwhxUkI-rHI?t=1

author: CJay
author_rank: Super Contributor
timestamp: June 13, 2019, 08:35:15 am
content: The RTL SDR is a good idea, but you don't need to 'calibrate' it against anything (I'm not sure you could calibrate it agains a cell tower, surely they're multi channel and quiote 'wide'? Might be easier to use an FM broadcast?).Just transmit on a known channel number with the USB device, jot down the frequency indicated by the SDR, then change channel by 1 step, transmit again, jot down the number, work out the difference and you've got your channel spacing.Capture a transmission from the Oregon devices and jot down the frequency.Work out which channel the USB device needs to be on to receive it.

author: ogden
author_rank: Super Contributor
timestamp: June 13, 2019, 08:57:09 am
content: Quote from: CJay on June 13, 2019, 08:35:15 amOP asked about measurement of frequency using Agilent 53132A, 5ppm frequency accuracy instrument, 0.2ppm with basic oven option. Most RTL-SDR dongles have cheap 50 or even 100ppm crystals, users often report even worse frequency errors. FYI 100ppm for 433MHz frequency is 43300 Hz. In short: if you are serious about frequency readings of low cost SDR dongles, you indeed shall calibrate them, adjust frequency offset:SDR calibration via GSM FCCH using Kalibrate and LTE-Cell-Scanner on RTL-SDR and HackRF

author: radiolistener
author_rank: Super Contributor
timestamp: June 13, 2019, 09:08:08 am
content: you can measure 433 MHz with a counter, but you will need a frequency scaler (high speed divider) in order to divide frequency to fit your counter frequency range.But I'm afraid you will not be able to measure frequency of your transmitter, because it has modulated and short period transmitting signal.The best way for your case is to use spectrum analyzer. You can replace it with RTLSDR dongle.I recommend this one:https://www.aliexpress.com/item/RTL-SDR-Blog-RTL-SDR-V3-R820T2-RTL2832U-1PPM-TCXO-SMA-RTLSDR-Software-Defined-Radio-Dongle/32939551915.htmlIt has nice dynamic range for it's price and allows to receive signals below 24 MHz (with integrated Q-branch direct sampling circuit).These RTLSDRv3 has TCXO with 0.5 ppm, so it has very small frequency error. For 433 MHz it will be theoretically not higher than ±216 Hz.In reality my RTLSDRv3 has frequency mistake 6 Hz at 9996 kHz (tested with frequency standard radiostation 9996 kHz), it means it will has mistake about 260 Hz at 433 MHz. It's about 0.6 ppm.You can check your RTLSDR frequency with AM stations, they almost all has stable frequency with max 1-2 Hz error (with rare exceptions).Unfortunately you will not be able to calibrate RTLSDR for better precision than RTLSDRv3 (0.5 ppm) already has with no calibration. Because integrated calibration formula doesn't support so high precision. But you can measure it's mistake and apply correction manually. In such way, with help of RTLSDRv3, you can measure your transmitter frequency with up to about 0.1 ppm.Just find your transmitter spike on the waterfall and you will know it's frequency.

author: CJay
author_rank: Super Contributor
timestamp: June 13, 2019, 10:38:53 am
content: Quote from: ogden on June 13, 2019, 08:57:09 amOP doesn't actually need to know the frequency, he just needs a way to net them onto the same frequency, my method does exactly that, he actually asked if he could use the frequency counter to do it and the answer is no.My method will work.Yours will too but is an excessively complex solution for the actual problem.

author: ogden
author_rank: Super Contributor
timestamp: June 13, 2019, 10:48:55 am
content: Quote from: CJay on June 13, 2019, 10:38:53 amYes you are right, your method will work well. OP did mention frequency measurement and I missed "actual problem" - USB transceiver tuning

author: Lord of nothing
author_rank: Super Contributor
timestamp: June 13, 2019, 02:09:11 pm
content: Well on 433 are not "Channels". Its a freq Band from - to Mhz.

author: ogden
author_rank: Super Contributor
timestamp: June 13, 2019, 04:07:16 pm
content: Quote from: Lord of nothing on June 13, 2019, 02:09:11 pmYes you are right. OP talks about USB dongle he uses and that thing have channels indeed:QuoteWait... That dongle can be paired only with RM1100-232, uses undisclosed configuration of CC1101 chip. No way it "out of the box" will receive wireless temperature sensor (Oregon Scientific brand) transmissions.

author: radiolistener
author_rank: Super Contributor
timestamp: June 13, 2019, 04:43:38 pm
content: but RTLSDRv3 can receive it, you're just needs to write demodulator and decoder for the signal

author: nfmax
author_rank: Super Contributor
timestamp: June 13, 2019, 04:48:01 pm
content: Quote from: radiolistener on June 13, 2019, 04:43:38 pmOr purchase an RFXCOM RFXtrx433XLhttp://www.rfxcom.com/epages/78165469.sf/en_GB/?ObjectPath=/Shops/78165469/Products/18103which can receive & decode Oregon sensors and many, many more...

author: rodpp
author_rank: Frequent Contributor
timestamp: June 13, 2019, 09:43:08 pm
content: Thanks for all contributions, I appreciate that. It's very nice to have that prompt support.So it seems that my counter will not measure the frequency, and maybe my USB RF Transceiver is useless for my application.At this moment I only want to log temperature from my Oregon sensors, but probably I can find other uses to the RFXCOM RFXtrx433XL in my little home lab...The final price including tax of the RFXCOM RFXtrx433XL is about 5 times the price of the RTLSDRv3. Is it worth that difference?Can they both receive the Oregon sensors data or only determine the transmitters frequencies?Thanks!

author: ogden
author_rank: Super Contributor
timestamp: June 13, 2019, 10:00:21 pm
content: Quote from: rodpp on June 13, 2019, 09:43:08 pmYes. RFXCOM receiver seems to be worth it - very capable transceiver supporting many RF sensors, including those from Oregon.Quote"Receiving frequencies" like plotting spectrum waterfall does not mean that you get actual data out of it. It is indeed possible to receive/decode Oregon transmissions using RTL dongle, but you needGNUradiosoftwareSDK and loads of learning:http://www.rtlsdr.com/2012/04/decoding-oregon-scientific-wireless-sensor-data-with-rtl-sdr-and-gnu-radio/https://www.rtl-sdr.com/decoding-oregon-scientific-weatherstation-messages-using-gnuradio/

author: james_s
author_rank: Super Contributor
timestamp: June 14, 2019, 02:03:42 am
content: The cheap RTL dongles have quite a lot of drift as they warm up but I find that once warm they can be calibrated to a known source and are quite stable. I use mine to receive all sorts of wireless weather gadgets around my neighborhood.

author: radiolistener
author_rank: Super Contributor
timestamp: June 14, 2019, 07:48:49 am
content: Quote from: james_s on June 14, 2019, 02:03:42 amThat's not the case forRTLSDRv3, because it uses TCXO

author: nfmax
author_rank: Super Contributor
timestamp: June 14, 2019, 07:54:36 am
content: Quote from: rodpp on June 13, 2019, 09:43:08 pmThe price difference is mostly accounted for by the effort that went into procuring the hundreds of supported devices & reverse-engineering their protocols. The firmware is updated frequently (freely downloadable) as new devices appear on the market. It can also transmit commands to many RF gadgets that use the 433MHz band. Generally, the transmit frequency is set automatically by the RFX, depending on the type of device addressed. You can adjust the receive frequency if necessary, from a set list, but almost all cheap RF sensors are broad band enough that it doesn't make any difference - anywhere in the 433MHz band will do.

author: CJay
author_rank: Super Contributor
timestamp: June 14, 2019, 08:01:51 am
content: This topic seems to be drifiting somewhat too.for the OP, you don't need an expensive USB 433MHz receiver because Oregon Scientific didn't use expensive 433MHz transmitters, they used cheap, commodity ones.There's a lot of links and information here:https://forum.arduino.cc/index.php?topic=203425.0https://forum.pimatic.org/topic/487/hardware-tip-433-mhz-receiver-for-pimatichttps://loune.net/2018/01/decoding-the-oregon-scientific-temperature-sensor/Which could easily be used to write your own code and locate cheap receivers/transceivers that are suitable for the job at hand.I'm sure there are lots of other places where the necessary information could be found.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: June 14, 2019, 11:38:06 am
content: When I read the origin post, it was a matter of measuring a frequency - not decoding the transmission protocol. If nothing has changed on that, go for a RTLSDRv3I have the one in a silver metal case which is quite accurate; I measured ~1.2ppm off with my 10MHz OCXO, what results in about +/-500Hz at 433MH; fairly ok for 29$ gadget

author: ogden
author_rank: Super Contributor
timestamp: June 14, 2019, 11:47:35 am
content: Quote from: HB9EVI on June 14, 2019, 11:38:06 amThen read again. Carefully. Especially about configuration of USB transceiverto receive temperature data. Initial plans and suggestions are changed, so you are advised to read other messages as well.

author: rodpp
author_rank: Frequent Contributor
timestamp: June 14, 2019, 01:47:10 pm
content: Thanks for all collaboration!To summarize:1- I already have some Oregon Scientific sensors;2- My final objective is to log temperature data from that sensors in a Linux computer;3- My idea when I openned this thread was to use an universal counter to determine wich of the USB dongle 256 channels corresponds to the Oregon sensors frequency. But now I realized that neither the universal counter is suitable to measure that frequency and neither my USB dongle can receive the Oregon sensors data;4- It was suggested two others USB dongles, one (RFXCOM RFXtrx433XL) that can receive the Oregon data out of the box; and another one (RTLSDRv3) that need some coding to decode that data. The first one 5x more expensive than the seconde one.5- As I said before, I already used a cheap 433MHz receiver in a Raspberry Pi to get that data before. And there are various codes that do that freely available, some of then posted in this thread. So the code to decode the data from the cheaper USB dongle (RTLSDRv3) seems to not be a problem.6- I'm inclined to buy the cheaper USB dongle (RTLSDRv3), connect it in my Linux computer, and code some lines to get the data, attaining my final objective.

author: james_s
author_rank: Super Contributor
timestamp: June 14, 2019, 04:14:08 pm
content: You shouldn't need to do any coding to receive the data with a RTL dongle, that work has already been done for you. This is the one I use.https://github.com/merbanan/rtl_433

author: 0culus
author_rank: Super Contributor
timestamp: June 15, 2019, 03:08:59 am
content: Quote from: rodpp on June 13, 2019, 02:46:07 amAs others have indicated, a counter most likely will not work. The protocol those sensors use is indeed bursts of information transmitted about once per minute, and it's very brief. None of the counters I have can respond fast enough. I've had much better success using one of my HP spectrum analyzers in max hold mode. You'd also get similar results with an SDR.

author: radiolistener
author_rank: Super Contributor
timestamp: June 15, 2019, 10:19:01 am
content: Quote from: james_s on June 14, 2019, 04:14:08 pmgreat, so all things can be done withRTLSDRv3- measure sensor frequency, receive data from it and even listen the radio

author: rodpp
author_rank: Frequent Contributor
timestamp: June 16, 2019, 12:11:55 pm
content: How about the SDRPlay RSP1, old and discontinued version (https://www.sdrplay.com/rsp1/)?It is only receptor but seems to have better specs. There's one available around here, 2x more expensive than the RTLSDRv3.

author: radiolistener
author_rank: Super Contributor
timestamp: June 18, 2019, 03:25:55 pm
content: Quote from: rodpp on June 16, 2019, 12:11:55 pmIf you're talking about these cheap 50 usd dongles, I just got one, but it turned out that it is defective. I contacted with sdrplay and they said that these devices are result of stolen IP and they even don't want to discuss about it. So, it is not supported officially. Probably these cheap devices are all produced from factory rejected chips stolen from recycle bin. So, it will be just a lottery to buy it - you can get any kind of defect.It's better to buy original RSP1A, but it is much more expensive than RTLSDRv3. And I think you will not notice significant difference for 433 MHz reception. So, it's better and less expensive to buy RTLSDRv3. This is well known device, just buy fromthis verified sellerand all will be good.Also,open source project rtl_433(generic data receiver) is designed for RTL devices, so I think it will be not so easy task to link it with RSP1 devices.

author: rodpp
author_rank: Frequent Contributor
timestamp: June 18, 2019, 09:36:37 pm
content: The SDRPlay available here is an original used one, not new but not counterfeit.If I buy the RTLSDRv3 of your link, the final price with tax will be half the price of that used SDRPlay. And it will arrive about 2-3 months after purchase.There are new RTDSDRv3 available locally here, and the price is around 30% more than importing.I guess that the SDRPaly could have more future uses, if not I will buy the cheapest one.

author: radiolistener
author_rank: Super Contributor
timestamp: June 19, 2019, 12:53:17 am
content: If you're need for a solution to receive data from sensors, RTLSDRv3 is better, because it is open source and it already has ready to use software for such purposes. SDRPlay is based on proprietary software with no source code, and it will be hard to link it with software to receive data from sensors. The only advantage of SDRPlay is wide bandwidth, but it is doensn't needed at all for your task. In opposite, RTLSDRv3 supports very low bandwidth (250 kHz), SDRPlay is 2 MHz min. Low bandwidth allows to minimize CPU load.So, I recommend to buy RTLSDRv3 for your task.

author: rodpp
author_rank: Frequent Contributor
timestamp: June 19, 2019, 01:24:54 am
content: Thank you very much. You convinced me, I'll buy the RTLSDRv3.It's open source, has available code to this task and is cheaper.

author: rodpp
author_rank: Frequent Contributor
timestamp: July 04, 2019, 12:55:14 am
content: Hello,Just to register that the RTLSDRv3 arrived last week and today I installed it.Everything is working great, using the code posted above by @radiolistener:https://github.com/merbanan/rtl_433The following command line saves the data from sensors to a csv file:rtl_433 -R 12 -M time -F csv:oregon.csvThank you all!Regards,Rodrigo.