Rigol DSA-815TG - Page 1
Forum section: electronics / testgear

author: w3amd
author_rank: Regular Contributor
timestamp: December 17, 2015, 06:23:16 pm
content: Hi All,This equipment is coming but I have some questions for anyone that may have this because it's not clear from the specs.1) What is the highest impedance setting the input can be set for? The manual says it's adjustable but doesn't give the range.2) Does the tracking generator have a dBmV output option? The manual says it's 50 ohms output impedance but in order to place this in op-amp input circuits with high impedance this should cause some high voltages to develop with even the -20 dbm output.CheersJohn

author: Howardlong
author_rank: Super Contributor
timestamp: December 17, 2015, 07:18:15 pm
content: The input and output impedances are both 50 ohms.If you use an adapter (I assume it's a minimum loss pad) the software can re-scale the reference appropriately with a loss of some dynamic range.If you want to use the TG output with a high impedance, use an inline terminator at the DUT end of the coax.

author: TurboTom
author_rank: Super Contributor
timestamp: December 17, 2015, 07:59:28 pm
content: The input impedance can be configured to be 50 or 75 Ohms.The units can be changed only globally to be dBm, dBmv, dBµV, V or W. The tracking generator output level is referenced into a 50 Ohms load and is displayed in the selected units. You can always chose a different unit when you enter a level with the digital keypad but this is automatically translated into the "global" preset unit.Please be aware that the DSAs currently shipped only permit a 20 dBm adjustment range for the TG output level which equals a 1:10 voltage range. The attenuator in the device (probably an IDT F1912 or a Peregrine PE4312) should permit a 31.5dBm range but Rigol probably needs some "headroom" above and below the available 20dBm range in order to calibrate the output level.Btw, I hunted down a few of the active components in the input branch of the DSA (those with the identification etched away) and it appears that most of them allow a pretty good margin for a higher frequency range. At least the 3.2GHz appear not to be unreasonable with the standard 815 setup. And as it seems, the bare PCB is the same for all the 800 models...Cheers,Thomas

author: Howardlong
author_rank: Super Contributor
timestamp: December 17, 2015, 08:46:01 pm
content: Quote from: TurboTom on December 17, 2015, 07:59:28 pm... but you'll need an adapter, I assume it is simply a minimum loss pad. The input termination on the SA does not change. It is simply a software re-scale taking into account the 5dB or so loss of the 75/50 ohm minimum loss pad "adapter".Sorry, I should've been far clearer in my explanation, I was writing my original reply while in the process of waiting for something else that pays money!

author: Pinkus
author_rank: Frequent Contributor
timestamp: December 17, 2015, 10:54:46 pm
content: Quote from: TurboTom on December 17, 2015, 07:59:28 pmMmmmmmhhhhh - are you sure the DSA832 uses the same PCB as the DSA815 ... and the DSA875? I haven't seen a teardown of the 832 yet. Did you take it apart? Can you post pictures of the PCB?

author: Howardlong
author_rank: Super Contributor
timestamp: December 17, 2015, 11:18:22 pm
content: Regarding the TG and dBmV, you can key in a value in dBm, mV and uV but not dBmV. It only ever displays as dBm on the TG.

author: TurboTom
author_rank: Super Contributor
timestamp: December 18, 2015, 09:58:43 am
content: Yes you are right about the input impedance - changing to 75 ohms only shifts the displayed signal. Also figured this out now...But it's definitely possible to enter TG level in dBmV if you beforehand set the global units (in the amplitude menu) to dBmV.Regarding my former statement that the hardware may be suitable for higher frequencies, I may be in error for the most relevant part - the first stage mixer. Rigol uses (most probably) a Hittite HMC213A connected "in reverse", i.e. supplying the RF signal to the "IF" terminal and outputting the IF at the "RF IN" connection. Since the mixer is a passive component, this is possible without any drawbacks (if the frequencies match the baluns in the mixer). This component is specified for an IF range of DC to 1.5GHz and RF frequencies from 1.5 to 4.5GHz.I haven't any in-detail construction information on the 832 but there's a short teardown of the 875 available here:It's obvious that this unit is a different animal with a lot more complexity in the RF section - particularly a completely separate VFO module. I wonder if Rigol intended to have all the models from the DSA800 series based on the same PCB (hence the silkscreen label "DSA800_V01.0x") and only later found out that they wouldn't meet the required specs with that approach. Considering the big leap in price between the 815 and the 832, the 832 probably is more similar to the 875 (which is not that much more expensive) than to the 815. Sorry if I may have induced some "hope for a hack" with my former statement.Cheers,Thomas

author: Howardlong
author_rank: Super Contributor
timestamp: December 18, 2015, 04:47:14 pm
content: Quote from: TurboTom on December 18, 2015, 09:58:43 amI'll take a look at that, I didn't see anything immediately obvious to change units when I looked, but it was only a cursory search and a bit of random button pushing.