What will the replacement for adf 4351 give?
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As of 2022 there are many badly performing clones on the market. V2/3GHz NanoVNA uses parts like ADF4350 and AD8342 which are costly and clones have been cutting costs by using salvaged or reject parts.
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ADF4351 allows 32 or 64 frequency division to obtain a lower output frequency, but the lower frequency of SAA2 uses Si5351 to output a lower frequency. adf4350 is 1 dollar cheaper than adf4351, SAA2 requires two adf4350, so using adf4350 can reduce the manufacturing cost of 2 dollars.
The ADF4351 has lower phase noise, but I guess that the ADF4350 phase
noise is not the limiting factor at the moment. ADC performance and
sequential sampling instead of simultaneous sampling most likely are the
Op 12-6-2020 om 08:43 schreef Hugen:
> ADF4351 allows 32 or 64 frequency division to obtain a lower output frequency, but the lower frequency of SAA2 uses Si5351 to output a lower frequency. adf4350 is 1 dollar cheaper than adf4351, SAA2 requires two adf4350, so using adf4350 can reduce the manufacturing cost of 2 dollars.
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The frequency tuning time of 4351 is higher - will this not make the device faster?
Not really, Now the measurement speed is 100 points/second, so 10 ms per
frequency. Frequency switch time improvement of the ADF4351 is in the
order of 60 us, so insignificant.
Sorter sampling, less averaging or a higher IF could speed up the sweep
rate. But less samples comes at a cost of increased noise level. Higher
IF would help and it would actually decrease noise levels as the noise
density is higher near the carrier. But I'm not sure if the hardware can
handle a higher sample rate and maybe there is a low pass filter in
front of the ADC inputs that sets the maximum IF frequency.
Op 12-6-2020 om 09:06 schreef firstname.lastname@example.org:
> The frequency tuning time of 4351 is higher - will this not make the device faster?
For filter tuning any speed up of the sweep is significant. Maybe decrease the time depending on the requested display data (in case that only S11 is measured the S21 is not needed to be measured) could be applied.
Maybe another hint for improvement - the matching of the port 2 when going higher above 2GHz is less than -20dB, this is not enough for filter termination and due to that it distorts the measured data even on S11, so an additional isolator or quality attenuator is needed.
I plan to publish some observations here or on FB group later when I have all data together.
At the moment the firmware sends S11 and S21 simultaneously so it would need to be changed to only send S11.
I bought two units so I could modify the second one for better performance. I'd love to see a page about hand-tuning stuff to improve results (like getting resistors to .1% or replacing an oscillator or...).
I have measured the output from the V2 on the spectrum analyzer, to see the timing. I use measurement from the V2 runing alone and with Qt. I selected center 1200MHz and span 100MHz, 3 steps. On the spectrum (see the attached picture) there is amplitude output versus time. It seems that the V2 on every frequency step makes the ECAL test, than measures S11, again ECAL, than S21. I think it is a very time consuming and the check of the ECAL could be done in a greater period.
The same concerns the CW, it switches to ECAL too. As far as it is a question of software, it will be great to apply CW generator mode for a beacon or test purposes as well. I estimate that one measurement takes about 20ms.
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