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Author Topic: Rigol DSA 815 Tracking Generator distortion  (Read 2595 times)

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Offline KD0RC

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Rigol DSA 815 Tracking Generator distortion
« on: February 24, 2014, 07:56:11 AM »
In playing with my DSA 815, I noticed that the output of the tracking generator has some distortion (some of it pretty serious...).  Here is a link to a video that shows the issue.  I really like this spectrum analyzer for my hobby use, and I don't think the distortion causes any real issue (especially if using the TG for its intended purpose...), but if you are using the TG as a general purpose signal generator, you should be aware that the signal is distorted at some frequencies.

I would be interested to see if other spectrum analyzers have this same issue.  I would also be interested to see if there are other frequencies over 100 MHz in the 815 that show distortion.  Any thoughts on this topic?

Until I get a high bandwidth oscilliscope, I won't be able to look into this any further.  If I don't win the new Tek MDO3000 scope tomorrow, I am thinking of the Agilent DSOX 2022A, considering its new lower price.

 

Offline KD0RC

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Re: Rigol DSA 815 Tracking Generator distortion
« Reply #1 on: April 05, 2014, 02:03:14 PM »
Well I apparently did not win the Tek MDO3000, so I bought an Agilent DSOX 2022A.  I am still learning to use the FFT function, so I don't think I got the span and resolution the same on these shots, but it does show that the DSA 815 has a pretty crummy looking output from the tracking generator at lower frequencies.  As it gets higher, it seems to get much better.

Here are the results:
10 KHz 3rd harmonic = -10.6 dB       7th harmonic = -21.3 dB
100 KHz 3rd harmonic = -11.9 dB     7th harmonic = -42.5 dB
1 MHz 3rd harmonic = -10.0 dB        7th harmonic = -24.4 dB
10 MHz 3rd harmonic = -10.0 dB      7th harmonic = -23.8 dB
100 MHz 3rd harmonic = -12.5 dB    7th harmonic = -48.1 dB
200 MHz 3rd harmonic = -23.1 dB    7th harmonic = -50.6 dB

I am not sure what to expect from a 'clean' signal - guess I will have to look at my Elecraft K2 (ham radio...) VFO to see how it fares in comparison.
 

Offline Ondre

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Re: Rigol DSA 815 Tracking Generator distortion
« Reply #2 on: April 24, 2014, 06:13:41 AM »
Hmm, interesting! I'll have a look at the TG's output of the 1000 series Hameg spectrum analyzer at work tomorrow. Unfortunately I won't be able to measure the full range as well.
« Last Edit: April 25, 2014, 07:07:52 AM by Ondre »
 

Offline W7NGA

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Re: Rigol DSA 815 Tracking Generator distortion
« Reply #3 on: April 24, 2014, 06:20:44 AM »
The tracking-generator was designed for sweep applications with the analyzer.
The distortion products are outside the analyzer resolution bandwidth.
In most applications, though qualified, the distortions should not be an issue.
In zero-span mode it would be a poor and dubious substitute for a signal-generator.
Additionally, you really should be terminating at the scope in 50-ohms.

Enjoy your analyzer ...

W7NGA
« Last Edit: April 24, 2014, 06:37:19 AM by W7NGA »
 

Offline Ondre

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Re: Rigol DSA 815 Tracking Generator distortion
« Reply #4 on: April 25, 2014, 07:38:34 AM »
Ok, for curiosity's sake, I checked the tracking gen of the Hameg 1010 in zero span mode. Below 200MHz the output doesn't look sinusoidal at all. The Rigol looks much better in that respect.
Here are some "screenshots" at 100kHz, 1MHz, 10MHz, 100MHz and 200MHz.
 

Online w2aew

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Re: Rigol DSA 815 Tracking Generator distortion
« Reply #5 on: April 25, 2014, 08:18:12 AM »
I've had a look at my old Advantest U3641's tracking generator.  While the TG output is rated from 100kHz to 2.2GHz, it will operate outside that range.  I found that even at 100kHz, the bottom end of the range, the 2nd and 3rd harmonic components are 35dB or more below the fundamental.  Pretty good.  Even down at 10kHz, distortion components are still 15-20dB below the fundamental. 
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