Re: Firmware with arbitr
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I think as I have said before some people are confusing dynamic range with directivity for S11. There is also directivity with an Open load and directivity for a Shorted load. The two are not the same. The O/S ratio is ignored in many discussions here.Sent from my Samsung Galaxy smartphone.
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-------- Original message --------From: "Dr. David Kirkby from Kirkby Microwave Ltd" <drkirkby@...> Date: 07/09/2019 03:30 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] Firmware with arbitr On Fri, 6 Sep 2019 at 20:16, <erik@...> wrote:>> There are two problems with dynamic range:> In S11 its the directivity of the bridge, which is limited but acceptable.I have never come across the term ¡°dynamic range¡± being used for S11>> In S21 the limit for the dynamic range is the leakage. Both as direct RF> leakage but also because of leakage between the two VFO's in the SI5351> which you can only solve by using two SI5351I am not saying that you are wrong, since I have never looked at thecircuit, or even block diagram. But it looks to me as if the system dynamicrange is limited by random noise, rather than any leakage.On professional VNAs, the dynamic range is never limited by internalleakage, so it¡¯s rarely necessary (or desirable) to perform an isolationstep in the calibration. But if external leakage occurs, then the isolationis useful, but it? is suggested that the* isolation measurement isperformed with at least 4 times the number of averages of the othermeasurements.* I don¡¯t know if that¡¯s done in the NanoVNA, but it maybebest if the isolation measurement is performed with at least 4 averages. Idon¡¯t know if there¡¯s any averaging taking place normally, but if data isshown after 10 averages, it maybe better if the isolation measurement wasperformed with 4*10 = 40 averages.DaveIf you look at the low-end Agilent N9912A FieldFox, it is obvious that thedynamic range at high frequencies is *not* limited by noise. There is awide band increase increase>> The signal strength is limited because of the low iIP3 of the SA612> (-14dBm) and you loose 10dB when going to harmonics mode.> So between the leakage and the maximum input level of the SA612 is your> dynamic range. Most ADC's will easily perform better then needed for this> application>>> >> --Dr. David Kirkby,Kirkby Microwave Ltd,drkirkby@...://www.kirkbymicrowave.co.uk/Telephone 01621-680100./ +44 1621 680100Registered in England & Wales.Company number 08914892.Registered office:Stokes Hall Lodge,Burnham Rd,Althorne,Chelmsford,Essex,CM3 6DT,United Kingdom
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