Spectrum Analyzer questions.

[Housedad]

I'm almost done getting my bench complete.  The bench as of now is mostly for expanding my education and after I learn enough for breadboarding, repair, etc.   I've been trying to save money where I can.   I want to learn both logic and analog circuits as I go along including radio. 

One question I have is about the spectrum analyzers on Ebay.   I see that there is the Instek GSP-810 (150KHz-1GHz) available from the ITT sale and I can get one below $400.   Is this enough analyzer for my use or should I wait till I have a lot more money for it and get something new?   Having taken advantage of the ITT stuff has worked out for me so far, but not having ever used an Spectrum analyzer before, I am not sure that it would be a good deal for my situation.  If so, I would want to get one before they are gone and prices go through the roof for something.

[danadak]

One general purpose investment is a DSO scope with FFT in it. You
can get a Rigol 100 Mhz (hacked from 50 or 70) that gives you a
basic SA capability. Also gives you a fairly good DSO, 4 channels,
and serial buss decoder function.


Regards, Dana.

[CJay]

My personal opinion (and I'm sure lots will be along shortly to tell me how wrong it is) would be that a SA with tracking gen option for $400 is a damn good buy.

You can buy much better but unless you are the kind of person who wins the lottery twice it will be much older, more expensive and harder to maintain without some specialised skills and parts.

I *think* they're modeled after a Hameg derived design which was a collection of fairly easily available parts, as such they are fairly easy to repair and don't have too much (or any)  specialised unrepairable RF voodoo inside them.

You don't get ultra high performance from it but if you want to tweak, tune and design radio stuff then it's a useful piece of kit.

It'll also hold its value reasonably well I think, can't see it selling for much less than that $400 in a year or two unless a daylight to DC SA gets released to market for $500 brand new...

[dimkasta]

You do not say much though about what are you going to use the analyzer for. Analog? Digital? Audio?

That said, I have to say that Rigol FFT is a joke. Really low point resolution.

Dave has a video comparing FFTs on scopes if you think that you can save some money combining the two devices.

But for a better decision, you need to define what your needs are. How high a res are you going to need, up to what frequencies and with what noise floor.

[Housedad]

I would want it mostly for learning and researching radio.  Most of what I learned many years ago is in the realm of digital and low power analog circuits.  One of my desires before I depart this realm is to learn how radio works and how to use it.   There has always been a desire to learn HAM.  The oscilloscopes I have now are The DS1054Z (hacked to 100Mhz) and a Instek GOS-6112 100Mhz.  I did watch Dave's video and the 1054z did not look all that usable for FFT. 

[nugglix]

For HAM usage you might want to think about it.

J3E bandwith is ~2.4kHz. (*)
Morse much smaller, down to ~500Hz.

The machine as detailed here
    http://www.gwinstek.com/en-global/products/SpectrumAnalyzers/Spectrum_Analyzers/GSP-810
shows a RBW of 3kHz.
The RBW is the "Resolution BandWidth", the smallest bandwith the machine can be used to distingiush signals.

So if you need to build/check SSB filters for example, this machine wouldn't be of much help.


And of course I can't avoid to mention W2AEW and his really helpful videos.
Look at
  http://www.qsl.net/w2aew//youtube/W2AEW_video_index.pdf
and search for spectrum analyzers.

*: https://en.wikipedia.org/wiki/Types_of_radio_emissions

[danadak]

Another highly usable instrument is the VNWA. If you are focused on
filter work and/or RF work network design, this is a very versatile
addition to lab. And it will give swept frequency plots of circuits/
filters.



You can download the SW for free and check it out.


http://sdr-kits.net/VNWA/RadCom_VNWA_Review.pdf


Regards, Dana.

[Housedad]

I see that I have a lot to learn before jumping in.   

[tecman]

If you are not in a rush, keep your eyes out for a real instrument on ebay.  Several years ago I picked up a Tek 2714 analyzer for $ 450.  It is "intended" as a cable TV analyzer, but you can switch off the cable specific stuff and it is very nice 9kHz to 1.8 gHz spectrum analyzer.  It needed a new 74XX IC in the front panel key scan/reader logic that prevented a few keys from working.  The biggest downside was it was a 75 ohm input.  After doing a little digging in the service manual I saw that the "real" working impedance was 50 ohms.  they have an input connector with an integral 25 ohm series resistor.  I purchased a new connector (no resistor) as a replacement.  It has a few db error due to the resistor change (I did not recalibrate it for amplitude) but it works fine for my needs.

Look for something like a 2711, 2712 or 2714.  It is a far better solution.

paul

[G0HZU]

In my opinion, you should try and buy something decent unless you just want to tinker. The GW Instek analyser would make a reasonable educational tool if you wanted to learn the basics of using a spectrum analyser but it is going to be of very limited practical use for real world applications. I glanced through the specs and it looks pretty grim.

[Housedad]

I have to agree.  i will wait until something more inline with my needs comes along or wait long enough to get up the money for a new Rigol.

Thanks for the info everyone.