Cheapest RSSI Logger - Page 1
Forum section: electronics / rf-microwave

author: gigavolt
author_rank: Contributor
timestamp: November 10, 2019, 03:49:05 am
content: Does anyone know of an IC that will do RSSI measurement in the US ham VHF/UHF bands including handling the tuning for me?I'm working on a project where I want to monitor the signal strength of several amateur radio repeaters over the course of a day. The tough part is I need to monitor it in like 20 different places at the same time and so the name of the game is making the hardware that will do it as cheap as possible.I'm not sure if it's possible, but my hunch is that you could do something for ~$10. After all, you can get a cheapo Baofeng for that price, and I don't even need to transmit or demodulate the signal, just get a strength. The trouble is that I'm just not familiar with what parts are out there to handle this. Ideally, I would be able to have a microcontroller tune back and forth between the repeaters every few seconds and then record the signal level I see to flash memory.Any suggestions would be helpful.

author: gigavolt
author_rank: Contributor
timestamp: November 10, 2019, 03:56:08 am
content: Doing some more looking, it seem like a Raspberry Pi zero and an RTL-SDR is ~$15 with some batteries. Any ideas on beating this?

author: OwO
author_rank: Super Contributor
timestamp: November 10, 2019, 04:20:35 am
content: What kinds of modulation do you expect to see and what bandwidth? If it is narrowband you can probably do it with a AX5043 and a STM32. The AX5043 doesn't need to demodulate the signal; just set it to the right channel and monitor background RSSI. Do beware that it's impossible to actually get the Raspberry Pee in any volume at the label price and you should budget at least $15 for the Pee alone. If off the shelf single chip transceiver chips won't do I would still look at a STM32 + downconverter solution (for example simply using the R820T tuner IC that is used in the RTL-SDR and using the STM32 built in ADC to digitize the baseband signal).

author: gigavolt
author_rank: Contributor
timestamp: November 10, 2019, 04:25:49 am
content: It's all going to be wide band FM at 25 kHz bandwidth. I wonder if I could get away with a narrow band receiver, though, if it's cheaper. Should get me at least the right order of magnitude for signal strength.

author: OwO
author_rank: Super Contributor
timestamp: November 10, 2019, 06:17:24 am
content: AX5043 maximum rx bandwidth is around 150kHz. I can provide info about registers programming. R820T can be obtained at about $1 so could be potentially a cheaper solution, but you have to work out either sub-sampling with the STM32 ADC or using a diode detector and calibrating it...

author: gigavolt
author_rank: Contributor
timestamp: November 11, 2019, 01:38:28 am
content: Thanks! I'm gonna check out the AX5043. Do you know where to find the R820T nowadays or if there's a new substitute? It looks like it's discontinued.

author: fmkit
author_rank: Contributor
timestamp: November 21, 2019, 10:37:28 am
content: if you modify si4432 input filter very wideband receiver is possible, I use one for remote monitoring just as you described, same chip used for ch.scan and telemetry to base monitor

author: radiolistener
author_rank: Super Contributor
timestamp: November 21, 2019, 01:15:59 pm
content: just buy some cheap RTLSDR dongle, use HDSDR, set manual gain control and disable RTL auto gain. Calibrate power level, HDSDR already has option for power level calibration. After that you can use HDSDR power meter to measure power for any desired bandwidth fro 1 Hz to 192 kHzIf you change gain setting, you will needs to recalibrate power level.With standard RTLSDR you can do it for any frequency from 24 MHz up to about 1 - 1.5 GHz.With RTLSDRv3 you can do it also for short wave from 1 MHz and above.