[time-nuts] Oleg' s PN test Re: A new member & PN test set

[Magnus Danielson]

Hi Oleg,

I like the simplicity here.

Would not GNUradio be a good platform to encode the calibration stuff a 
little more gift-wrapped?

What spectrum-analyzer software do you use? (Just curious)

This simple setup would be useful for many purposes.

Depending on the oscillator, the EFC can need inversion, so I sketched 
for a similar design such that I could jumper it for either polarity. In 
that design I put the inverter after the integrating op-amp.

Cheers,
Magnus

On 03/28/2016 10:04 PM, Oleg Skydan wrote:
> Hi, everybody!
>
> OK. Let's start. Here is the schematics of the "test set"
> http://skydan.in.ua/PNTestSet/PN%20Test%20set.pdf . It consists of three
> small
> boards:
> 1. Mixer board - a simple mixer (500MHz ADE-1+) with 200kHz pi-LPF at
> the mixer output.
> 2. LNA board - a non-inverting low noise AF amplifier based on AD797
> with switchable 20/40dB gain.
> 3. PLL board - contains two TL071 OP amps. One is inverting amplifier,
> the other is PLL integrator. The R4,R8,R2,R7,C8 sets the PLL parameters
> - gain, passband and damping factor. Loop parameters are also dependent
> of signal levels and VCO tuning sensitivity. So you may need to correct
> them if your setup differs from mine - VCXO's I use have tuning
> sensitivity approx 100Hz/V and I set RF level at mixer near 0dBm with LO
> level near +7dBm. If you want to build universal test set you will need
> to use some switchs to allow setting different loop parameters (I just
> use my soldering iron and change parts if needed :) ).
>
> The power supply is a simple design based on 7812/7912 regulators.
>
> I use the E-MU 0202 USB external sound card and laptop PC as the AF
> spectrum analyzer.
>
> You will also need some cables. Different fixed attenuators or
> switchable one will be also helpful.
>
> I also have several homemade low noise VCXOs for some frequencies (7MHz,
> 10MHz, 14.318MHz, 60MHz) which I use as the reference signal sources to
> make measurements at these frequencies.
>
> Another option is to test two identical oscillators (or other signal
> sources). Assuming that both signals will have identical phase noise
> characteristics we can correct the results by 3dB (or just add 3dB
> correction during calibration).
>
> The calibration and use is simple.
> 1. Set LNA gain to 20dB.
> 2. Set the FFT parameters - flattop window, small (2048..4096) points
> number and short averaging in SA software.
> 3. Connect reference signal to LO mixer port and signal you are going to
> test to RF mixer port through the attenuator. Do not close the PLL yet.
> 4. Set the beat level a bit less then the sound card full scale using
> the attenuator. Check the beat harmonics levels - they should be at
> least 30dB lower then the beat level (add more attenuation if harmonics
> are higher).
> 5. Now set the spectrum analyzer calibration so that beat level is at
> -27dB if you measure against low noise reference VXCO, or -30dB if you
> use two identical oscillators.
> 6. Switch the LNA to 40dB gain.
> 7. Set SA software to Blackman window, 131072points/96kHz SR/necessary
> averaging, close PLL, wait for the lock, measure the phase noise.
>
> Why I am calibrating to -27/-30dB:
> 20dB because the LNA gain is 20dB less during the calibration (compared
> to measurement time)
> 1dB because of FFT parameters 96k/131072 = 0.73Hz * 1.73 (Blackman
> window) = 1.267Hz, 10 log10(1.267) = 1.03dB
> 6dB is the correction inherent to used calibration method
> additional 3dB needed in case of testing identical oscillators.
>
> Now some words about results. The noise floor of this test set depends
> of the signals levels, and with the optimal levels it is in
> -160..-170dBc/Hz range (depending of the offset from the carrier). It
> completely satisfies my needs, better results can be achieved with the
> higher level mixer and/or better LNA. I just used parts that I had :).
>
> Here http://skydan.in.ua/PNTestSet/Screen%20(420)-e.png is an example of
> the phase noise measurements results of my homemade low noise 60MHz VCXO
> (two identical units were measured). The results at the offsets greater
> then 1kHz should be corrected cause the oscillators noise is too close
> to test set noise (the real oscillator noise is a bit lower then the
> displayed one). The test set noise floor and calibration spectrum is
> also there.
>
> The boards also have other use.
>
> For example I was able to measure my home made 60MHz VCXO harmonic
> content http://skydan.in.ua/PNTestSet/Screen%20(414)-e.png using the
> mixer, LNA boards and signal generator. I have no spectrum analyzer so
> it is a big help to me :).
>
> Power supply noise can be investigated with the LNA board and sound
> card. Look at this screen
> http://skydan.in.ua/PNTestSet/Screen%20(431)-e.png to see how bad the
> LDO regulator noise can be and a great difference in noise with the
> simple transistor filter (sorry there are a lot of power line noise
> pickup - I needed just to quickly check the power supply noise, so did
> not pay a lot attention to minimize them).
>
> The low noise VCXOs with the combiner and attenuator can be used to
> measure IMD3 of the receiver. If you add the mixer, LNA and signal
> generator you can measure the IMD3 of the separate units (mixers,
> filters, amplifiers and etc.).
>
> The low noise VCXO can also be used to test reciprocal mixing DR of the
> receiver.
>
> Other useful combinations are possible.
>
> If you like I can post the photos of the boards. They a bit ugly :).
> Every time I use them I think about mounting them in personal metal
> boxes, but I always find something more important to do...
>
> Best wishes,
> Oleg
> P.S. I am not aware of the attachments rules of this list, so put the
> links in the message instead of attaching files. Is it OK? Should I
> attach files next time?
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