Rigol DSA815-TG strange "spur" - Page 1
Forum section: electronics / testgear

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: February 07, 2025, 11:26:43 am
content: I was checking some amateur radio equipment recently and came across a spurious signal that is generated in my Rigol SA. I have checked with another 815 owner and his produces the same spurious signal.The test is to feed the spectrum analyser from a signal generator with a carrier around 144.320 MHz and look for the spur some 11 KHz lower and at a level close to -40 dBc. This spurious signal only seems to appear around 144.3 and is not present on another spectrum analyser that I checked it with.Any ideas what may be the cause and is it something that happens with other 815s?ThanksSJ

author: wn1fju
author_rank: Frequent Contributor
timestamp: February 07, 2025, 08:11:57 pm
content: Same results with mine. At 144.32 MHz, I get the spur about 10 kHz lower. At 144.33 MHz, the spur is about 15 kHz lower. And so forth, 144.34-->20 kHz, 144.35-->25 kHz.OK, how about lower than 144.32. The spur is about 5 kHz lower at 144.31. But then something mysterious happens precisely at 144.3 MHz: the entire noise floor on the spectrum analyzer jumps up about 20-30 dB. At 144.29 MHz, it is back to normal. I was using an HP 8642B signal generator, which is pretty good, and I verified the same thing using a different signal generator, so it is definitely the DSA815-TG.So whatever is causing the spur seems to be related to 144.3 MHz. Perhaps some internal clock?

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: February 07, 2025, 09:39:21 pm
content: My signal generator is an IFR 2025, which is also pretty clean.I have raised the matter with the UK Rigol distributor, who is taking it up with Rigol. It’s a really strange one.Thanks for the feedback73 SJ

author: thm_w
author_rank: Super Contributor
timestamp: February 07, 2025, 10:39:16 pm
content: There is mention of 14.3MHz in the original dsa815 thread:https://www.eevblog.com/forum/testgear/spectrum-analyzer-rigol-dsa815/?action=printpageThough I see no mention of 144MHz.

author: shabaz
author_rank: Frequent Contributor
timestamp: February 08, 2025, 12:18:54 am
content: I don't own a DSA815 so I can't try it myself, and I've not done the sums either, but there's a couple of things you could try (maybe you have already tried these, otherwise definitely worth a shot):(1) Reduce your RBW from 100 Hz down to 10 Hz and see if anything changes(2) Reduce your input signal power level down to (say) -20 dBm instead of the current -10 dBm, without changing any other setting, and again, see if anything changes (i.e. does the spurious signal level change, and if so, by how much).

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: February 08, 2025, 09:41:04 am
content: Quote from: shabaz on February 08, 2025, 12:18:54 amChanging levels and RBW makes no difference. I am not sure of other frequencies as I have only seen it when inputting a signal over a small range of frequencies around 144.32 MHz.SJ

author: Evariste
author_rank: Newbie
timestamp: March 21, 2025, 11:50:58 am
content: Hello,I confirm, I have exactly the same problem, test carried out with the DG4162 generator, and the problem appears from 144.303 Mhz

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: March 21, 2025, 11:55:49 am
content: Quote from: Evariste on March 21, 2025, 11:50:58 amSorry, I didn't reply earlier. Telonic (the UK Rigol distributor) had a response from Rigol in China, the problem does not exist on the latest boards but is there on earlier ones. Rigol don't have a solution, other than scrap your old SA and buy a new one. Well, I suppose we pay our money and take our chances with Chinese junk test equipment.SJ

author: Evariste
author_rank: Newbie
timestamp: March 22, 2025, 03:35:37 pm
content: Thanks for the info, my next one will be in SIGLENT 👍

author: enjoi4283
author_rank: Newbie
timestamp: April 29, 2025, 11:45:50 am
content: Anecdotaly I've heard that updating to the latest firmware and running the autoalignment sometimes fixes the issue. Its worth a try if you're having issues.