Audio upconverter to see audio spectrum with an Agilent Spectrum Analyzer

[xardomain]

Hello,
I would like to find a way to see the audio spectrum using my spectrum analyzer (HP ESA1500L) and found this on Ebay:

https://www.ebay.it/itm/Spectrum-Analyzer-Low-Frequency-Converter-BG7TBL-SA-LF-CONV-Spectrum-Analyzer-ts/183780250687?_trksid=p2485497.m4902.l9144

this should work, provided I take into account the 50Ohm impedance input.

Has Anyone has tried something similar and/or this specific product?

TIA

Giuseppe Marullo
IW2JWW - JN45RQ

[DaJMasta]

It's doable, similar approaches are used for low frequency on some SDRs, and it's basically just mixing it with a carrier and then trying to keep the images to a minimum.  That said, you'll probably get better results with a PC sound card and a spectrum display program, like the freeware Spectrum Lab.

A lot of SAs will be usable below their rated frequency, though, see if you can just set your span to start at 0Hz and maybe there will be a good bit of usable area in the audio band even if it's not specified as being totally even or leveled.  My R3477, rated to 9kHz, would give you a usable spectrum plot to about 200Hz, where the noise floor started spiking up so the dynamic range was really small.

[xardomain]

Hello DaJMasta,
I tried with my SA, but it seems it is not capable to go that low.

I am uncomfortable with using a sound card, I always get the feeling it is not a real instrument, but I will give it a go.

It happened to me that I already have a LF converter (HamItUp v1.3) that should go as low as 300Hz, so I could use it for a quick test with the SA. It is a pretty decent unit, with 125MHz TCXO and a 10MHz timebase input.

I still need to adapt the impedance, it has 50Ohm but I found some schematic on the net for that.

Giuseppe Marullo
IW2JWW - JN45RQ

[jpb]

You don't mention things like budget and performance requirements or how low the audio frequency goes (if it is below 10Hz then sound cards may start to tail off).

To make a sound card more like a real instrument you could build this front end (the pcb is available on ebay):
http://www.pmillett.com/ATEST.htm

If you have lots of cash then something like the Picoscope 4262 is very low noise and true 16 bits up to 5MHz - there is quite a lot of info on it on these forums, e.g. :
https://www.eevblog.com/forum/projects/using-a-picoscope-4262-as-a-low-frequency-recording-spectrum-analyzer/