Help me to buy the SA needed for my repair work - Page 1
Forum section: electronics / general

author: ARMCortex
author_rank: Newbie
timestamp: May 20, 2023, 10:05:36 am
content: Hello to allI have to repair for some time some gps beacons which send their signal by radio waves (150 MHz).I can repair almost all the failures except in the radio part but now I have to evolve.So I'm going to buy a spectrum analyzer but ... I have no particular knowledge on their use except the theory on the internet.What is important for me is to capture the RF signal to analyze its power. The beacon send a short signal every 10 seconds (some models every minute).So I want to see if the signal is coming out of the FM chip -> the amp -> the RF switch -> the antenna.I will also use it to test the gps and glonass signal (1575/1602 MHz).So I have determined that:- a device that goes up to 2GHz is sufficient.- which blocks the DC input (I have 3 Volt) so that no DC filter is inserted in addition to the attenuators.- which has a TG for testing antennas.- that I can use occasionally to test other devices (like car remotes, garage ..)- not too big on my desk.- a reasonable budget $3000 (but I prefer the cheapest possible).I see the Siglent SSA3021X-plus but the question (probably a stupid one from a user who has never used an SA) is, when the short signal is going to be emitted, will I be able to record (on the device or a computer) it or keep track of it on the screen even after the signal?Thank you for help.

author: EE4all
author_rank: Regular Contributor
timestamp: May 20, 2023, 01:40:26 pm
content: I would suggest the SSA3021x plus and then software "upgrade" it to the SVA model at some point. You mention also using it for antenna analysis, and you will need a directional coupler to go with the basic SSA model to do this, whereas the SVA uses the internal one, and is far more capable for that. Don't forget possible need for external attenuators, 50 ohm load(s), and possibly an active probe depending on how accurate you need measurements. I would not normally use an analyzer to measure total power output accurately, but given your budget, you can get close enough (be sure you are using enough attenuation and a proper 50 ohm load).Yes, you can keep the signal on the screen, but you will need to use trigger functions on the analyzer if the DUT only sends the burst at long wait intervals as you descibed.

author: Bicurico
author_rank: Super Contributor
timestamp: May 20, 2023, 03:38:15 pm
content: Depending on the duration of the beacon signal, you might actually have trouble with the SSA3021-Plus.Note that this spectrum analyzer does not look at the selected frequency range in realtime, but instead will sweep from start frequency to end frequency. Depending on the RBW/VBW and frequency range, one sweep might take longer than the short bleep of your beacon signal! There is only one way to find out: fnd out how long the signal is on and how long it takes to sweep the frequency range of interest.A good example if WIFI: you will get poor results measuing it with a regular spectrum analyzer, due to the channel hopping.What you need is a realtime spectrum analyzer, than can capture a whole frequency range in one go. Of course they are a magnitude more expensive than swept spectrum analyzer.A cheap alternative - cheap enough for testing purposes and get you started, would be a SDR based spectrum analyzer, like RTL2832U dongles, HackRF, Adalm Pluto, etc. Note that those can be used to visualize the presence of the signal and demodulating the signal (when applicable and with available software based demodulators), but you won't be able to make quantitative measurements.regards,Vitor

author: strawberry
author_rank: Super Contributor
timestamp: May 20, 2023, 05:24:56 pm
content: SPAN . wider spectrum range will take more time to scan. faster update rate will rise noise floor

author: ARMCortex
author_rank: Newbie
timestamp: May 20, 2023, 07:07:32 pm
content: thank you for your answers.I have indeed looked at the real time analyzer but the usb models. The SH USB-SA44B (Signal Hound is not very present in Europe) and the Tek RSA306B (I can get one second hand).Of course, a unit with a screen would be more pleasant than connecting each time the pc but the recording function on pc is very interesting.with my lab power supply, I see +/- the peak of consumption which corresponds to the emission of the signal.I also see it on the graphical bar of my multimeter (it doesn't have time to calculate and display a value) the power amp is powered only when the beacon is transmitting. I would say that we are approaching 0.5 seconds (a little below).

author: tautech
author_rank: Super Contributor
timestamp: May 24, 2023, 10:02:24 am
content: SSA3000X Plus models provide an adjustable trigger function for irregular signals. < I have never used it.See P34.https://int.siglent.com/u_file/download/22_08_24/UserManual_UG0703P_E02D.pdfI would try with a fast span/sweep to increase the possibility it detects the chance of capturing the beacon signal however there seems to be sufficient trigger capability if you study the manual to properly capture a signal the meets te trigger settings.