Measurement of noise figure of HF103 rc1

    

“Fairly accurate comparative measurements may be made with HDSDR.  Please remember the method used, without reference to a suitably calibrated source measurements will not be absolute. But this method might provide an experimenter with a useful way of comparing equipment. “  

Source:   Signal Measurement with HDSDR  Thanks to the HDSDR Authors and to G4ZFQ.

My RF reference is a 14 pin metallic dip crystal oscillator at 20MHz with sine wave output. It’s output is 400 mVpp sine wave on 50 Ohm resistor. I placed a  20dB attenuator at the output so that the reference on a 50 Ohm load is  40mVpp,  -24dBm.  I measured the levels with an Hantek Oscilloscope.  

The procedure to measure NF is as follow:

- Connect the reference generator to HF103 antenna input and run the HDSDR application.

- Set RFgain to 0dB attenuation.

- Select the Smeter to rms mode (click with the mouse on peak/rms indication to toggle mode). This is important as peek/rms ratio is different for sinewave or noise. We need rms to measure NF.

- Select USB demodulator. I used a 3 kHz bandwidth filter.

- Tune to generator carrier and measure the tone level with the S-meter; verify that it is the expected value. In case adjust calibration gain to read  the generator level ( mine is -24 dBm ),

- Move to a clean frequency one MHz up or disconnect the generator and terminate the antenna on 50 Ohm.

- Measure the S-meter level of the noise signal with 3kHz bandwidth.   My measure is -125 dBm

- Now we can compute the thermal noise component on 3kHz

at 20°c of a 50 Ohm

K = Boltzmann's constant = 1.381 × 10-23W/Hz/K,

T = 290 K at room temperature 

B = Bandwith

KTB for B 1Hz  =  -174 dBm at room temperature. 

KTB for B 3000Hz =  -174 + 10 log( 3000 )  = - 139 dBm

The measured noise figure is:  NFmeasured =  - 125 - (- 139) = 14 dB 
The expected measurement error should be in the range 1 - 2 dB.

The estimated NF value based on HF103 scheme is:

( I use https://www.everythingrf.com/rf-calculators/cascaded-noise-figure-gain-calculator)

Stage    NF(dB)     Gain(dB)        Note /source

1            0.1            -0,1                Insertion loss 1st filter estimated value

2            1.3            -1.3                DAT-31A-SP+ datasheet typ value

3            0.2            -0.2                Insertion loss 2nd filter estimated value

4            6.2            20                  LTC6400-20 datasheet typ value

5            30,7         Soft. value      LTC2208 see  High speed ADC: one that no one had ever told you  

( see: ADC Noise Figure—An Often Misunderstood and Misinterpreted Specification by Walt Kester  )

NF        13.63                               Preview NF based on estimated components noise figure

The estimated and the measured are within the error margin.  

Here the noise level with no antenna connected.





Comments

Post a Comment

Popular posts from this blog

A look into the RX-888 mkII

Image
  The RX-888 mkII designed by Justin Peng and Howard Su  arrived!   It is an evolution of the first RX888. The curiosity won out and I opened it. Be careful if you decide to open your device because two heat pads are used to carry the heat from the R828D and the LTC2208 to the aluminium case. I managed to slide them out without damaging them by moving the PCB very gently. A plastic wide stick may help to push out the pads and after to reassemble the radio. The PCB layout is similar to RX888 In HF the input attenuator is a  PE4312   covering a 31.5 dB attenuation range. This replaces the 0, -10 ,-20 dB attenuator of RX888.  It is followed by the low pass filter at 64 MHz.  Then two switches PE4259   select the HF input or the VHF tuner R828D produced by Rafael Micro that replaces the R820T2. The added transformer connects in a balanced way to the R828D IF outputs. An AD8370  digitally controlled variable gain amplifier (VGA) pro...
Read more

RX888

Image
Yesterday I received the RX888 designed by Justin Peng and Howard Su.  The first impression in o pening the shipping package  is that it is very small.    It is as big as the Cypress fx3 superspeed explorer kit ! Thanks to Guy Atkins'  SWLing post  I was able to resist the desire to open it right away to see the interior.   I started looking at HF. I connected it to my old I7-3770 pc and to the 10 meters wire antenna that I have on the balcony of my house.   My city is Turin and here the local transmitter in MW has frequency 999000 Hz synchronized to a high precision reference. I tuned this station and without calibration of the internal oscillator of R888 I measured an accuracy better than 1 ppm. This is not obvious after a transport of more than 10000 Km. In case there is the internal trimmer that allows you to calibrate the reference oscillator when you have a reliable reference. Frequency calibration test The ExtIO_RX888.dll v0.4 has...
Read more

HF103 rc1

Image
HF103 is a HF only prototype of BBRF103  that started at the end of 2019. Thanks to Andrew G4XZL for ideas, test reports and advice.  Here after the modifications. Hardware: - It is designed for LW-MW-HF band only: 0-30MHz. - A Low Noise Amplifies has been added to improve NF of receiver. - The Clock reference used is a low noise xtal oscillator with lower phase noise and spurs than Si5351a.     - The RF attenuator of HF103 uses  DAT-31-SP+   - The PCB has been made larger 100x100 mm to increase spatial separation between components' groups (COVID style)  Here the  scheme and PCB layout . Some pictures of hardware Case  ADC and RF layout                                                                       LNA, filter, attenuator ...
Read more