Spectrum Analyzer Rigol TG-815

[N8AUM]

Electro,  tnx for info, good read !

So I was not amused seeing the TG bleed into the front end. Here`s what it looks like on my brand new unit.
Yellow trace TG off
Blue trace TG on and both input & output terminated
Purple trace TG on input & output left open

Tried same on my HP 8591  ZIP !

[markone]

Blue trace TG on and both input & output terminated
Purple trace TG on input & output left open

The terminated I/O result does not seem promising ...

[N8AUM]

Blue trace TG on and both input & output terminated
Purple trace TG on input & output left open

The terminated I/O result does not seem promising ...

I agree if trying to look for something at those low levels.
Still, cant beat the price !

[Andy2]

That's an interesting screenful.  I have a friend with an 815 and I'll ask him to run the same test. Just for the record, here is my Rigol 1030a-TG running the same test. Same settings (I think) and same trace colours. The 1030a is a 3GHz instrument, so I limited the sweep to 1500 MHz to make the comparison easier.    Interesting that your 815 seems to have a few dB lower noise especially at the lower end.
If I get a spare few minutes, I'll run the same procedure on my Signal Hound and see what it says. As the TG and SA are physically seperate units, the leakage should be lower.

[N8AUM]

That's an interesting screenful.  I have a friend with an 815 and I'll ask him to run the same test. Just for the record, here is my Rigol 1030a-TG running the same test. Same settings (I think) and same trace colours. The 1030a is a 3GHz instrument, so I limited the sweep to 1500 MHz to make the comparison easier.    Interesting that your 815 seems to have a few dB lower noise especially at the lower end.
If I get a spare few minutes, I'll run the same procedure on my Signal Hound and see what it says. As the TG and SA are physically seperate units, the leakage should be lower.

Pretty sure you will nothing unless both are close in proximity to each other. Cant wait to see your results.

[Andy2]

OK, I've just attempted to run the procedure on the SigHound and it's rather difficult. For a start, I cannot make a normal sweep and a TG sweep share the screen, but there is a further problem - selecting a TG sweep seems to invoke a whole new setup of the instrument and the noise levels are simply not comparable. Maybe I'm missing something, but it was more trouble than it was worth! I later set the SH to do a normal (non TG) sweep and used the TG in CW mode at spot frequencies, like a signal generator. The leakage level was so low that a 30KHz RBW would not see it. I had to get down to 10KHz or less to lower the noise floor enough to see any leakage at all (using 2dB per div). At this level (around -110 - 120dBm), the analyser's own internal spurii are showing up anyway, so I stopped there.
This test was done with the units in their normal configuration, side-by-side in an instrument case but with the SMA extension leads disconnected.  All interesting stuff for a Sunday afternoon!

[G0HZU]

My old Advantest TR4172 analyser has an internal Tgen and the analyser shows a noise trace just below -100dBm with a 30kHz RBW.

If I turn on the Tgen and set it to 0dBm and look at the leakage at 1500MHz then it doesn't show anything. i.e. the noise floor stays the same. So I can't see any leakage effects at this RBW setting. If I search around up to 1800MHz I can see places where the noise trace lifts up to about -100dBm.

I also have a HP8566 analyser with an external HP85644A TGen and I'd expect this to perform even better. But it's too much hassle to connect it all up to test it...

[N8AUM]

It only makes sense that it would be difficult to keep a strong signal source from "leaking" in due to the 815 being physically small.
Now I have to go back and re read this entire thread to see if Joe ever did come up with an answer or solution. 

[markone]

Blue trace TG on and both input & output terminated
Purple trace TG on input & output left open

The terminated I/O result does not seem promising ...

I agree if trying to look for something at those low levels.
Still, cant beat the price !

I'm trying to understand if this instrument is capable to trace a passive filter response curve with a decent dynamic range ( 80dB ?) ....

[G0HZU]

In my experience, pretty much all spectrum analyser TGens aren't really up to making critical measurements of high performance RF filters. (as in filters with low insertion loss and decent stopband performance)

I think the recent images of the 3GHz Rigol look OK for tracking gen leakage and the 815 leakage plots look reasonable up to about 1GHz.

I think the problem will get worse if the analyser ports are padded with external attenuators to improve the port VSWR of the analyser in an attempt to reduce measurement uncertainty of low insertion loss filters.

This will compromise the ability to measure stopband performance accurately and one way around this is to measure the passband loss using the external attenuators but then remove the attenuators (and renormalise/recal) for the stopband measurements.

A bit tedious but probably worth it in a lot of cases...



 

[Mr Simpleton]

Beeing late to the party... I had a simple tubular filter at hand, and ran it through Signal Hound and TG... As Andy said, one is not able to adjust RBW, so a bit hard to dig deep down, still I do have close to 100 dB range here. Not too shabby.

[G0HZU]

The Signalhound performance looks really good. However, I suspect that this is because it is housed in a separate box and the 'tracking' will presumably be software based. So this gives it an edge.

Note:
I looked up the specs for my old HP85644A external tracking gen when used with my HP8566B analyser and they claim a dynamic range (in terms of max TGen level to the analyser noise floor) of 141dB up to 1800MHz.

However, I seriously doubt that this is based on a leakage test. For the leakage test I would hope/expect it to be better than 100dB across this range but it could be a lot better (or worse!)