Signal Analyser - Low Frequency Spectrum Analyser - Page 1
Forum section: electronics / testgear

author: Rod___
author_rank: Newbie
timestamp: February 12, 2019, 12:18:03 pm
content: Hi,I hope this is the corect part of the forum, my apologies if not.I'm looking for, what I would call, a low frequency spectrum analyser. i.e. one that can plot the characteristics of filters working in the range of say, 100Hz to 100kHz. Preferably with a tracking generator.I would prefer a stand-alone unit, i.e. not requiring a PC to display the plot.Does anyone have any recomendations?Many thanksRod

author: Berni
author_rank: Super Contributor
timestamp: February 12, 2019, 12:34:25 pm
content: A possible choice is the Agilent 89410A:https://www.keysight.com/en/pd-1000002367%3Aepsg%3Apro-pn-89410A/vector-signal-analyzer-with-w-cdma-capability-dc-to-10-mhz?cc=US&lc=engIt plots magnitude and phase of a filter from DC to 10MHz with plenty of resolution and dynamic range.These can be a bit hard to find, but there are also some older units that go to 100KHz and some do have a signal generator built in.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: February 12, 2019, 03:25:14 pm
content: The other units Berni is referring to may be the Hewlett Packard 35665A Dynamic Signal Analyzer:https://www.keysight.com/en/pd-1000001333%3Aepsg%3Apro-pn-35665A/dynamic-signal-analyzer-dc-to-1024-khz?nid=-536902471.536882157.00&cc=US&lc=engThere are several threads around here that discuss it.

author: Keysight DanielBogdanoff
author_rank: Unknown
timestamp: February 12, 2019, 06:35:58 pm
content: Not trying to hijack the thread, feel free to remove this post.Since your frequency range is so low, you might be interested in a frequency response analyzer or frequency response analysis with an oscilloscope.Here's an old webcast on that topic if you're interested:Or a shorter video on it:You could get a scope with frequency response analysis capabilities for under $1k.

author: tautech
author_rank: Super Contributor
timestamp: February 12, 2019, 07:19:08 pm
content: Quote from: Rod___ on February 12, 2019, 12:18:03 pmYou can do FRA/Bode plots with a $499 100 MHz 4ch scope plus a $159 25 MHz AWG and have 3 points of band pass and phase measurements.Band pass example:https://www.eevblog.com/forum/testgear/siglent-sds1204x-e-released-for-domestic-markets-in-china/msg1435854/#msg1435854Band pass and high pass example:https://www.eevblog.com/forum/testgear/siglent-sds1204x-e-released-for-domestic-markets-in-china/msg1436912/#msg1436912

author: tomato
author_rank: Regular Contributor
timestamp: February 12, 2019, 07:30:07 pm
content: Quote from: Rod___ on February 12, 2019, 12:18:03 pmHP/Agilent/Keysight and Stanford Research make several good instruments.

author: DaJMasta
author_rank: Super Contributor
timestamp: February 12, 2019, 08:19:17 pm
content: As said, Dynamic Signal Analyzers are sort of the go-to name for the older equipment designed for this specific use. Since then, digitizers have become cheaper and having a dedicated instrument for just this hasn't really justified a dedicated instrument in that many current lineups. Modern scopes will all give you FFT analysis capability, but to get a reasonable dynamic range compared to a DSA, you'd probably want a 12 bit scope with enhanced resolution from oversampling - an 8 bit converter just doesn't compare.Otherwise, there are a number of full blown spectrum analyzers that go down to very low frequencies, some end in the kHz band, but many offer low frequency extensions to 100Hz, 20Hz, or 10Hz. This is also somewhat common on older SAs, whereas it seems to be an optional extra on more modern instruments. The TG may not go down to this frequency, but any signal generator would, so by interconnecting the trigger signals and a little on-instrument configuration, you should be able to get a bode plot pretty easily.Otherwise, the modern equivalent is probably an audio analyzer. Very high dynamic range, low noise, and usually with fast enough converters to manage 100kHz+ worth of bandwidth. Not so inexpensive of an option, but with the internal signal generator to cover the range and give you more comprehensive testing than just a TG.PC and frontend/generator/software is probably the cheapest to get really good dynamic range, a scope with more than an 8 bit converter and a signal generator is probably the simplest/cheapest option new, and an older DSA is probably not too expensive of an option for the specialized bit of gear. A soundcard and software is a great inexpensive option if you can verify that it doesn't filter out stuff above the audio band - a lot of sound cards will rolloff above 20kHz just to keep the system noise level down.

author: LapTop006
author_rank: Unknown
timestamp: February 13, 2019, 03:17:38 pm
content: There's theOmicron Bode 100that Dave did a few videos on recently (#1103 & #1104). It's on my long term test equipment list.Quote from: Keysight DanielBogdanoff on February 12, 2019, 06:35:58 pmWhat lets Keysight down somewhat here (as in a few other areas) is that the fixturing just isn't there in the ways it used to be. There's a couple of things (most recently AC power analysis) where I'd happily spend a chunk of money on a well designed test fixture vs rolling my own. HP in the old days often had those, but over time that seems to have gone away (not that it's specific to Keysight, it's also sadly true with a bunch of the older manufacturers).

author: tecman
author_rank: Frequent Contributor
timestamp: February 13, 2019, 04:41:31 pm
content: I have an analyzer that I use quite a bit at home and work. I had an older HP but wanted to upgrade. All of the HP and SRS units in descent shape were too rich for my wallet. I found and bought an Advantest R9211C which was reasonable in price and has the same performance as the other units. The only negative is that the user interface is not as intuitive as HP, but certainly not a show stopper. You can fine them on ebay (also check the A, B and E models) for around $ 1000 when the phase of the moon is correct. They are 2 channel, 10 mHz to 100 kHz, internal sig generator (sine, sweep, multisine, etc) and HPIB interface. My unit has a built in printer that will do a screen print as well. Good unit for a budget buyer.paul

author: Berni
author_rank: Super Contributor
timestamp: February 13, 2019, 04:58:24 pm
content: I managed to get my Agilent 89410A for $240 on ebay. But that was an incredibly lucky find (One of my luckiest buys ever on ebay), people want 1 to 3 grand for one these days.

author: tecman
author_rank: Frequent Contributor
timestamp: February 13, 2019, 04:59:04 pm
content: See attached

author: voltsandjolts
author_rank: Unknown
timestamp: February 13, 2019, 05:03:21 pm
content: I own a Digilent Analog Discovery just for its bode plot feature alone.https://store.digilentinc.com/analog-discovery-2-100msps-usb-oscilloscope-logic-analyzer-and-variable-power-supply/

author: Rod___
author_rank: Newbie
timestamp: February 16, 2019, 04:31:42 pm
content: Many thanks to all that replied to my post.Your replies were all instructive and useful, the Advantest R9211C looks interesting as it has its own sweep generator.I now have a much longer 'saved searches' list on ebayThanks again,Rod

author: joeqsmith
author_rank: Super Contributor
timestamp: February 16, 2019, 05:08:13 pm
content: I have an old HP3589A 10Hz to 150MHz network / spectrum analyzer. It has GPIB and it's easy enough to control it from a PC. If you did need to work at higher frequencies, it would have plenty of head room. It's very easy to setup and run from the menus. See the manual for the specs.The downside, it's fairly old, large and heavy. For some reason these now sell for $2,000+ USD on ebay.https://isurplus.com.au/manuals/HP%203589A%20User%20Manual.pdf