VLF MD with digital signal processing : Bee-Buzz 1

[moodz]

Does not matter how low your input noise is ..the insertion noise of the amplifier raises the noise floor above the input noise floor of any competent ADC ....and ruins the noise response of the system. The target signals are not buried in low levels ... They are actually the difference in a signal composite of transmitter and wanted / unwanted signals ..the task is to separate the wanted signals from unwanted/ transmit signals nothing to do with low noise inputs. We are not trying to receive a signal reflected off the moon ...that requires a low noise amp ...our targets are less than a meter away it's just sampling and mathematics.

[Aziz]

Hi,

I really enjoyed reading all the 6 pages. It is well done and a good source regarding amplifier noise. Go back to his home page and you will find more interesting things.

http://www.dicks-website.eu/index.html

http://www.dicks-website.eu/low_noise_amp_part1/part1.html

You can bet, that some transistors will be placed on my purchase list.

0.2 nV/sqrt(Hz) input voltage noise is easily possible.
Aziz

[Detectorist#1]

Hi Aziz,
Thank you for the answer.

[Aziz]

And how this old information for low noise amplifiers with input power transistor and ultra low source impedance is connected to real metal detector's schematic?

Hi,

I do connect the RX-coil directly to the input of the preamp (note, the preamp is AC coupled). RX coil resistor will be in range of 1 - 2 Ohm to keep the noise very very low.
But the coil will pick up a lot more EMI noise.

You can't use the preamp on a PI. Only VLF/LF detector type.
Aziz

[Carl-NC]

OK, I didn't see that there were more pages.

[Detectorist#1]

And how this old information for low noise amplifiers with input power transistor and ultra low source impedance is connected to real metal detector's schematic?

[Aziz]

? I see 0.2uv rms

See page 3. The ZTX 851, 853 and 857 comes very close to the level. With gain of 60 dB (1000 x).
Paralleling two or three of them and you are save below 0.2 nV/sqrt(Hz).
The amplifier on page 3 is the same topology I use in my preamp.
He takes 10 mA collector current. And 1 Ohm gain defining resistor. I didn't go as much (2 mA I think and 4.7 Ohm).
So we have some nice low noise transistor choises.

[Carl-NC]

The 0.2 nV/sqrt(Hz) voltage noise density is near.

? I see 0.2uv rms

[Aziz]

Look, what I have found!

http://www.dicks-website.eu/low_noise_amp_part1/part1.html

6 parts
Someone has tested more transistors for us.
The 0.2 nV/sqrt(Hz) voltage noise density is near.

An interesting reading.

[Aziz]

Hi all,

haven't been able to work on the project yet due to lack of time. I'm still coding the c-modules so you can make use of the simple & correct demodulators. With example coding of course.

The memory management for internal buffers (sin/cos-tables) will be left to the caller (except fft). Two implementation types: block-processing and sample-by-sample processing for Goertzel and Lock-in Amplifier.

The interface API forces you to use demodulation frequencies multiple of bin frequency width so you don't have any leakage effect and don't need any windowing of the samples.

And I have found some new candidates for testing USB sound cards.

Aziz

[Aziz]

Btw guys,

the Goertzel and Lock-in Amplifier decoding can even be realised in the interrupt service routine (ISR) sample-by-sample. So you don't need DMA for block processing for embedded projects. Lock-in is optimal for the MAC operation (multiply and accumulate). You need two MAC's for each sample. After getting all the samples, the result must be calculated (scaling, sqrt, atan2). Sqrt and atan2 can be realised via pre-calculated tables of course, if you don't have much horse power in the embedded project.

I will provide you with C sample source code soon so you can see how it really works. Including FFT code to make some comparisons.

Cheers
Aziz

[Aziz]

Buy a 24 bit eval board ...or make ur own. Soundblaster have not made a good card for years.

But the former models performed really very well (10 - 15 years ago however). I have boughts several models the last 20 years.

But the G3 is no good. It is band limitted to 22 kHz. SNR is bad too. Anyway, there are some other USB sound cards to test yet.
Did I say Creative go to the hell? I have to write a bad rewiew on Amazon yet.

G6 can be used for high frequency dual VLF/LF detector. And it has huge power to the TX coil.

[moodz]

Buy a 24 bit eval board ...or make ur own. Soundblaster have not made a good card for years.

[Aziz]

Sound Blaster G3
It isn't the money worth!
Payed 35 bucks (+5 shipping), it is only 10 bucks worth!
The best part: USB-C to USB-A converter.

Creative, go to the hell!

[Aziz]

This is an example of a comparision in the complex frequency spectrum:
Note, that it shows the DC-Value (k=0), positive and negative frequency spectrum of the sample data.

=== FFT/Goertzel/Lockin-Test ===

Number of Samples N = 32
Samplerate = 48000 Hz
Bin-Resolution =  1500.000 Hz
k = 1
Frequency =  1500.000 Hz
Amplitude =     1.000
Phase = -12.345679
DC =  0.250

Sin/Cos-Table, Data (cos(x))-Table:
k=0 : sin=  0.000000000 cos=  1.000000000 Data=  1.226875426
k=1 : sin=  0.195090322 cos=  0.980785280 Data=  1.249817157
k=2 : sin=  0.382683432 cos=  0.923879533 Data=  1.234336475
k=3 : sin=  0.555570233 cos=  0.831469612 Data=  1.181028295
k=4 : sin=  0.707106781 cos=  0.707106781 Data=  1.091941220
k=5 : sin=  0.831469612 cos=  0.555570233 Data=  0.970498815
k=6 : sin=  0.923879533 cos=  0.382683432 Data=  0.821368045
k=7 : sin=  0.980785280 cos=  0.195090322 Data=  0.650279922
k=8 : sin=  1.000000000 cos=  0.000000000 Data=  0.463809265
k=9 : sin=  0.980785280 cos= -0.195090322 Data=  0.269122039
k=10: sin=  0.923879533 cos= -0.382683432 Data=  0.073699963
k=11: sin=  0.831469612 cos= -0.555570233 Data= -0.114947001
k=12: sin=  0.707106781 cos= -0.707106781 Data= -0.289569257
k=13: sin=  0.555570233 cos= -0.831469612 Data= -0.443456168
k=14: sin=  0.382683432 cos= -0.923879533 Data= -0.570693948
k=15: sin=  0.195090322 cos= -0.980785280 Data= -0.666392920
k=16: sin=  0.000000000 cos= -1.000000000 Data= -0.726875426
k=17: sin= -0.195090322 cos= -0.980785280 Data= -0.749817157
k=18: sin= -0.382683432 cos= -0.923879533 Data= -0.734336475
k=19: sin= -0.555570233 cos= -0.831469612 Data= -0.681028295
k=20: sin= -0.707106781 cos= -0.707106781 Data= -0.591941220
k=21: sin= -0.831469612 cos= -0.555570233 Data= -0.470498815
k=22: sin= -0.923879533 cos= -0.382683432 Data= -0.321368045
k=23: sin= -0.980785280 cos= -0.195090322 Data= -0.150279922
k=24: sin= -1.000000000 cos= -0.000000000 Data=  0.036190735
k=25: sin= -0.980785280 cos=  0.195090322 Data=  0.230877961
k=26: sin= -0.923879533 cos=  0.382683432 Data=  0.426300037
k=27: sin= -0.831469612 cos=  0.555570233 Data=  0.614947001
k=28: sin= -0.707106781 cos=  0.707106781 Data=  0.789569257
k=29: sin= -0.555570233 cos=  0.831469612 Data=  0.943456168
k=30: sin= -0.382683432 cos=  0.923879533 Data=  1.070693948
k=31: sin= -0.195090322 cos=  0.980785280 Data=  1.166392920

FFT:
k=0  f=    0.000 Hz Re= 0.249999999999999970000 Im= 0.000000000000000000000 Mag= 0.249999999999999970000, Phase= 0.000000
k=1  f= 1500.000 Hz Re= 0.488437713033456510000 Im=-0.106904632671585720000 Mag= 0.499999999999999890000, Phase=-12.345679
k=2  f= 3000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=3  f= 4500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=4  f= 6000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=5  f= 7500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=6  f= 9000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=7  f=10500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=8  f=12000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=9  f=13500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=10 f=15000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=11 f=16500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=12 f=18000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=13 f=19500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=14 f=21000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=15 f=22500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=16 f=24000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=17 f=25500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=18 f=27000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=19 f=28500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=20 f=30000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=21 f=31500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=22 f=33000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=23 f=34500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=24 f=36000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=25 f=37500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=26 f=39000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=27 f=40500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=28 f=42000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=29 f=43500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=30 f=45000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=31 f=46500.000 Hz Re= 0.488437713033456620000 Im= 0.106904632671585540000 Mag= 0.499999999999999940000, Phase=12.345679

Lock-in Amplifier:
k=0 : f=    0.000 Hz Re= 0.249999999999999940000 Im= 0.000000000000000000000 Mag= 0.249999999999999940000, Phase= 0.000000
k=1 : f= 1500.000 Hz Re= 0.488437713033456510000 Im=-0.106904632671585650000 Mag= 0.499999999999999830000, Phase=-12.345679
k=2 : f= 3000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=3 : f= 4500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=4 : f= 6000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=5 : f= 7500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=6 : f= 9000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=7 : f=10500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=8 : f=12000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=9 : f=13500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=10: f=15000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=11: f=16500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=12: f=18000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=13: f=19500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=14: f=21000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=15: f=22500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=16: f=24000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=17: f=25500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=18: f=27000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=19: f=28500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=20: f=30000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=21: f=31500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=22: f=33000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=23: f=34500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=24: f=36000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=25: f=37500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=26: f=39000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=27: f=40500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=28: f=42000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=29: f=43500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=30: f=45000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=31: f=46500.000 Hz Re= 0.488437713033457070000 Im= 0.106904632671585340000 Mag= 0.500000000000000330000, Phase=12.345679

Goertzel:
k=0 : f=    0.000 Hz Re= 0.250000000000003550000 Im= 0.000000000000000000000 Mag= 0.250000000000003550000, Phase= 0.000000
k=1 : f= 1500.000 Hz Re= 0.488437713033456840000 Im=-0.106904632671585060000 Mag= 0.500000000000000000000, Phase=-12.345679
k=2 : f= 3000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=3 : f= 4500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=4 : f= 6000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=5 : f= 7500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=6 : f= 9000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=7 : f=10500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=8 : f=12000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=9 : f=13500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=10: f=15000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=11: f=16500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=12: f=18000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=13: f=19500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=14: f=21000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=15: f=22500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=16: f=24000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=17: f=25500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=18: f=27000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=19: f=28500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=20: f=30000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=21: f=31500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=22: f=33000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=23: f=34500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=24: f=36000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=25: f=37500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=26: f=39000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=27: f=40500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=28: f=42000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=29: f=43500.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=30: f=45000.000 Hz Re= 0.000000000000000000000 Im= 0.000000000000000000000 Mag= 0.000000000000000000000, Phase= 0.000000
k=31: f=46500.000 Hz Re= 0.488437713033460060000 Im= 0.106904632671580390000 Mag= 0.500000000000002220000, Phase=12.345679
End.