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| Decent modern Signal/waveform Generator here in early 2024 |
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| nctnico:
--- Quote from: 2N3055 on January 14, 2024, 07:26:09 pm --- --- Quote from: nctnico on January 14, 2024, 06:40:54 pm --- --- Quote from: DaneLaw on January 13, 2024, 05:48:17 pm ---How accurate are these 10Mhz reference in/out sources on entry test-gear, like modern DDS-based signal generators. Got a reading that looks like +40Hz by taking the 10Mhz in/out up the Rigol unit's own counter., is that more or less what to expect on entry units in the sub 300 price cat or more the counters limitasions' --- End quote --- It could be the counter, it could be the generator. A quick test for generators with two or more channels is to have it output 2 frequencies at exact multiples but far apart. Like 1Hz and 10MHz. Then trigger an oscilloscope on the lower frequency. Most of the sub 1000 euro generators I tested show a drift on the higher frequency indicating there is a frequency offset between them. Also locking to a 10MHz source properly is something you shouldn't expect to work flawlessly (as in no frequency offset). It doesn't mean low cost function generators are bad but you have to be aware of their limitations where it comes to frequency accuracy (which -again- is typically not specified on sub 1000 euro generators). --- End quote --- Synthesized frequency resolution is usually specified on most of them to the point of being better than frequency stability of timebase (initial accuracy, drift, tempco) which will be largest contributor to frequency accuracy.. But, he is connecting AWG internal 10MHz ref out to AWG internal counter, that is running from the same reference I presume... It should count exactly 10.000000 or maybe one last count up down... It is self referenced. --- End quote --- That is the point I'm trying to get across here: On many sub 1000 euro (ballpark figure) generators you won't get exactly 10MHz. Or exactly 1Hz even when referenced from an external source. And once again, resolution is not accuracy! You may be able to set a frequency in 1uHz units but the generator doesn't have the internal divider/multiplier resolution to achieve such an accurate setting. The test I outlined by setting two frequencies is easy to do without needing external references. |
| rhb:
FWIW I got burned by an early FY6600 and bought a used 33622A from Keysight's ebay store. It is awesome, but came at a very steep price. However, no regrets despite the $3500 price. At $9k new it's a bit much. At .03% THD (measured at 0.028% by my 339A) and < 1 ps jitter (verified against a GPSDO) it's my benchmark signal source for HF. Despite swearing I'd never buy another F***Tech product I broke down and bought an FY6900. In head to head testing the most serious deficit is the FY6900 reference XO. With 1 ppb OXCOs for <$25, that's easy to fix. On instruments with external 10 MHz inputs, you just need the OXCO in a suitable enclosure. Ironically, my most expensive HPAK purchase is the only one without an OXCO. The waveform distortion outside the 0.5001-5.0000 V range may be more difficult to fix. I think an op amp swap cures that, but I may not bother as most of the time I want an AWG it's in that voltage range. I have plenty of step attenuators to go lower. And no use case for higher. Though if I did a 33 dBm 1-930 MHz Chinese amplifier ought to do under 100 MHz. The two I bought are flat to <1 dB according to my 8560A. Both the 33622A and FY6900 UIs annoy me, but in different ways. The motivation for the F***Elec is putting together the lowest cost full RF bench for HF ham bands simply to see what's possible. Not being an EE, my access to suitable test kit was non-existent until a few years ago. Now it's a mid '90s >$700k list suite. But well over 30x what I think one can do today with reasonable effort. The nanoVNA & $20 LCR/transistor tester and progeny have had major impacts. I think nctnico is spot on that it's more complicated, i.e. more factors to consider, than the datasheets indicate. Have Fun! Reg |
| 2N3055:
--- Quote from: nctnico on January 14, 2024, 07:32:33 pm --- --- Quote from: 2N3055 on January 14, 2024, 07:26:09 pm --- --- Quote from: nctnico on January 14, 2024, 06:40:54 pm --- --- Quote from: DaneLaw on January 13, 2024, 05:48:17 pm ---How accurate are these 10Mhz reference in/out sources on entry test-gear, like modern DDS-based signal generators. Got a reading that looks like +40Hz by taking the 10Mhz in/out up the Rigol unit's own counter., is that more or less what to expect on entry units in the sub 300 price cat or more the counters limitasions' --- End quote --- It could be the counter, it could be the generator. A quick test for generators with two or more channels is to have it output 2 frequencies at exact multiples but far apart. Like 1Hz and 10MHz. Then trigger an oscilloscope on the lower frequency. Most of the sub 1000 euro generators I tested show a drift on the higher frequency indicating there is a frequency offset between them. Also locking to a 10MHz source properly is something you shouldn't expect to work flawlessly (as in no frequency offset). It doesn't mean low cost function generators are bad but you have to be aware of their limitations where it comes to frequency accuracy (which -again- is typically not specified on sub 1000 euro generators). --- End quote --- Synthesized frequency resolution is usually specified on most of them to the point of being better than frequency stability of timebase (initial accuracy, drift, tempco) which will be largest contributor to frequency accuracy.. But, he is connecting AWG internal 10MHz ref out to AWG internal counter, that is running from the same reference I presume... It should count exactly 10.000000 or maybe one last count up down... It is self referenced. --- End quote --- That is the point I'm trying to get across here: On many sub 1000 euro (ballpark figure) generators you won't get exactly 10MHz. Or exactly 1Hz even when referenced from an external source. And once again, resolution is not accuracy! You may be able to set a frequency in 1uHz units but the generator doesn't have the internal divider/multiplier resolution to achieve such an accurate setting. The test I outlined by setting two frequencies is easy to do without needing external references. --- End quote --- My Rigol DG1000Z is not here at the moment. But I know that SDG6000X creates exactly 133.3333334 MHz when I set to it, for instance. I took counter, set its reference to external and slaved it to 10MHz out from AWG. That takes AWG and counter timebase out of equation, so we are measuring how accurate is AWG frequency synthesis accuracy and resolution. Best counter I have is 10 digits and it was showing set frequency on AWG accurate to 10 digits. 10 digits accurate synthesis is 1ppb (0.001ppm) accuracy and resolution. How many digits you expect to be there? 12, 15 ? parts per trillion? parts per quadrillion? It is an general purpose AWG. It is not rubidium frequency standard... |
| Detlev:
I set 10,000,001Hz here on the SDG6022 and that's what I get at the output (see photo). Both devices are synchronized to a Leo GPSDO The frequency counter has a gate time of 1s and average 100 measurements. The statistics are also interesting here. |
| Detlev:
--- Quote from: 2N3055 on January 14, 2024, 08:13:41 pm --- My Rigol DG1000Z is not here at the moment. But I know that SDG6000X creates exactly 133.3333334 MHz when I set to it, for instance. I took counter, set its reference to external and slaved it to 10MHz out from AWG. That takes AWG and counter timebase out of equation, so we are measuring how accurate is AWG frequency synthesis accuracy and resolution. Best counter I have is 10 digits and it was showing set frequency on AWG accurate to 10 digits. 10 digits accurate synthesis is 1ppb (0.001ppm) accuracy and resolution. How many digits you expect to be there? 12, 15 ? parts per trillion? parts per quadrillion? It is an general purpose AWG. It is not rubidium frequency standard... --- End quote --- Yes 😎 |
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