How not to blow up my new Rigol RSA3015N analyser. - Page 1
Forum section: electronics / testgear

author: hrapcio
author_rank: Newbie
timestamp: November 12, 2024, 08:14:08 am
content: hi AllI am new to this forum and work mostly in the automation and plc programming field but I find electronics very interesting which due to lack of time i could not pursue earlier.So I have brand new RSA3015N analyser (it combines spectrum analyser, EMI, vector analyser) and i am interested in mostly troubleshooting EMI problems in control panels which do happen and later to do my own experiments as a hobby. In particular i would like to use high voltage probe Micsig MDP3000 and troubleshoot control panel with EMI issue.That panel has a large inverter which produces PWM signal (3khz is base carrier frequency) which interferes with the meters readings.My plan is to:1: Do spectrum analysis in place near the meters which are affected - I need to figure out exact steps - please fee free to comment2: Choose EMI filter - starting probably with common mode choke and if they dont work good enough moving to common mode/differential setupCan you please kindly advise me on how not to blow up my expensive instrument:1: i already ordered DB blocker 5328-SD3235-ND from Digikey (from 7khz upwards)2: what else do i need for PWM measurements ? attenuator or limiter etc? My high voltage probe outputs around 3 Volts but i read spectrum analyser do not like PWM signal as its too similar to DC3: i have sanwa PC7000 multimeter which is great and allows me to do reading in DBM - shall i use it always to check the signal strenght first?4: shall i always connect the signal to my old rigol oscilloscope DS1074Z?thanks in advance for any help and really glad i am hereRegards

author: Kean
author_rank: Unknown
timestamp: November 12, 2024, 08:54:39 am
content: If you are unsure, then it is always best to use a combination of DC block, attenuator, and limiter.You can get a low cost combined one from RF Explorer, and available via DK or Mouser. This is what I often use.https://j3.rf-explorer.com/rf-explorer-power-limiter.htmlhttps://www.digikey.com/en/products/detail/seeed-technology-co-ltd/109990003/54878743V RMS into 50 Ω is about 22 dBm, so under the +30 dBm limit of this protection of this device,but more than the +10 dBm max of the RSA input.Oops, RSA input max is +30 dBm.Certainly additional attenuation would be a good idea on the RSA input, e.g. 20 dB and make sure it is rated for more than 1 Watt (1 W is +30dBm).Measuring unknown signals with DMM or scope before connecting to the RSA is certainly a good idea, but you may not see much if the frequency is beyond the DMM/scope bandwidth.An RF power meter is useful to have, but the sensors in those can also be blown if you make a mistake.

author: hrapcio
author_rank: Newbie
timestamp: November 13, 2024, 09:30:31 am
content: thanks for your valuable reply @KeanI just purchased the item you suggested but i have DC block from fairview 7khz-23ghz. I also purchased additoinal 20db attenuator.Can you please help me to understand the following?:1: i assume connecting in series RF explorer unit + 20db db attenuator is no problem? Similarly connecting RF explorer + fairview dc block should not be a problem but i dont see a practical reason for that yet.2: just wonder how come RF explorer describes the unit as DC to 3GHZ while more expensive dc block only unit has band starting from 7khz (other units had muchhigher lower freq. but i am working in the lower range at the moment). Is there a quick test i could do to test RF explorer regarding bottom frequency?3: What am i actually gaining by using the limiter up to 3GHz - i understand that Rigol goes up to 1.5GHz - is the main reason to protect from the power transfered in the higher frequencies but does it matter if Rigol upper limit is 1.5 Ghz?Thanks for help

author: Kean
author_rank: Unknown
timestamp: November 14, 2024, 07:49:15 am
content: I'm no expert, but I think the attenuators/limiters will have poor return loss at higher frequencies, so if you input much power at frequencies beyond the specification it will likely get reflected. And unless you are living/working around high field strength microwave transmitters, and have fancy antennas connected, then you aren't likely to be picking up much over 3 GHz.I'd still recommend an attenuator rated for higher power just in case it has to dissipate more than the typical 1W rating. Also, I don't think you need to worry about buying expensive parts specified for over 3-6 GHz unless you plan to buy a higher frequency analyzer in future. That DC block rated to 23 GHz was likely overkill.I noticed you also mentioned in your first post about using the MDP3000 high voltage probe. That is a differential oscilloscope probe with 1 MΩ output, so it won't work on the RSA which has a 50 Ω input. You would need a high impedance buffer capable of 100 MHz or more to allow the use of that.Typically you would use a near field probe to look for localized EMI issues, and most of those will not be very efficient at picking up signals over 1 GHz. But they could pick up quite high amplitudes at the lower frequencies of your inverter, so again doing some initial checks with a power meter is a good idea.Finally, I looked quickly at the specs of the Sanwa PC7000. The dBm feature on that is for audio frequencies and only specified up to 20 kHz. You also need to set the reference impedance to 50 Ω to get appropriate readings. Audio measurements would likely be done based on something like 600 Ω.