Difference between revisions of "RF Noise Generator"
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[[file:NoiseGen-P783-720px.jpg]] | [[file:NoiseGen-P783-720px.jpg]] | ||
− | == | + | == Usage == |
* Useful as a filter test signal source | * Useful as a filter test signal source | ||
** Pass filters | ** Pass filters | ||
** Crystal filters | ** Crystal filters | ||
+ | * Would like to use as noise source for [[tinySA]] | ||
+ | ** [[tinySA]] has lower noise floor than [[NanoVNA]] | ||
+ | |||
+ | === Others === | ||
+ | |||
+ | * [https://www.youtube.com/watch?v=732ESoul088 7MHz calibration signal generator] | ||
+ | ** 0dBm and -60dBm outputs | ||
+ | |||
+ | == Design #1 == | ||
+ | |||
* From Experimental Methods in RF Design | * From Experimental Methods in RF Design | ||
** Fig 7.72 | ** Fig 7.72 | ||
Line 14: | Line 24: | ||
* Noise figure -50 dBm @ 10 MHz | * Noise figure -50 dBm @ 10 MHz | ||
− | == Schematic == | + | === Schematic === |
[[file:ng-sch-prototype.PNG]] | [[file:ng-sch-prototype.PNG]] | ||
− | == Prototype == | + | === First Prototype === |
+ | |||
+ | ==== Build / Enclosure (Original board design) ==== | ||
+ | |||
+ | * Used very old, but high quality chassis mount BNC connector | ||
+ | ** Silver connector has a nice patina | ||
+ | * Built onto Single Side PCB material | ||
+ | ** Acts as ground plane | ||
+ | ** Pads cut from PCB material and superglued down onto the Base PCB | ||
+ | * Hot glued down into plastic enclosure | ||
+ | * Ferrite toroids at top are not used | ||
+ | |||
+ | [[file:NoiseGen-P783-720px.jpg]] | ||
+ | |||
+ | [[file:NoiseGen-P790-720px.jpg]] | ||
+ | |||
+ | [[file:NoiseGen-P787-720px.jpg]] | ||
* Unique nodes in red | * Unique nodes in red | ||
Line 26: | Line 52: | ||
[[file:NG-layout.PNG]] | [[file:NG-layout.PNG]] | ||
− | === | + | * OSHPark PCB |
+ | |||
+ | [[file:NoiseGen_P1855-720px.jpg]] | ||
+ | |||
+ | === LTSpice Simulation === | ||
+ | |||
+ | * Amplifier looks flat but the result wasn't | ||
+ | |||
+ | [[file:NoiseGen_Design1.PNG]] | ||
+ | |||
+ | === Measurements === | ||
* 12V, 43mA current draw | * 12V, 43mA current draw | ||
Line 32: | Line 68: | ||
==== tinySA Measurements ==== | ==== tinySA Measurements ==== | ||
− | * 1-30 MHz | + | * Measure from 1-30 MHz |
* Power Off | * Power Off | ||
+ | * -90 dB noise floor | ||
[[file:NoiseGenOnTinySA_Off.PNG]] | [[file:NoiseGenOnTinySA_Off.PNG]] | ||
* Power On | * Power On | ||
+ | * Measure from 1-30 MHz | ||
[[file:NoiseGenOnTinySA_On.PNG]] | [[file:NoiseGenOnTinySA_On.PNG]] | ||
Line 49: | Line 87: | ||
* Lot more energy at ~400 KHz | * Lot more energy at ~400 KHz | ||
* -30 dB | * -30 dB | ||
+ | * Not too useable for filter testing | ||
+ | * Might be OK for receiver noise source | ||
[[file:NoiseGenOnTinySA_On_100KHz-1MHz.PNG]] | [[file:NoiseGenOnTinySA_On_100KHz-1MHz.PNG]] | ||
Line 54: | Line 94: | ||
==== Rigol DS1054Z Measurements ==== | ==== Rigol DS1054Z Measurements ==== | ||
− | + | * 50 MHz scope with mods | |
− | + | * UltraScope settings | |
− | + | ** SCAL 1.00 V | |
− | + | ** H 200nS | |
− | + | * FFT settings | |
− | + | ** CF = 16 MHz | |
− | + | ** 2 MHz start, 50 MHz stop | |
* RBW 416.6 KHz | * RBW 416.6 KHz | ||
* Background noise | * Background noise | ||
* Generator off | * Generator off | ||
− | * Average ~ -64 dB | + | * Average ~ -64 dB noise floor too high |
[[file:NG_OFF.PNG]] | [[file:NG_OFF.PNG]] | ||
Line 75: | Line 115: | ||
* Measured performance per EMiRFD (predicted - 50 dB) | * Measured performance per EMiRFD (predicted - 50 dB) | ||
− | == Better Design == | + | == Better Design #2 == |
− | * C1 is connected Emitter of Q1 to GND to reduce power supply noise | + | * Replace Zener as noise source with 2N3904 B-E junction reverse biased |
+ | * C1 is connected Emitter of Q1 to GND instead of +12V to reduce power supply noise | ||
* Higher noise than EMiRFD design | * Higher noise than EMiRFD design | ||
− | |||
** Usable from 1-10 MHz | ** Usable from 1-10 MHz | ||
** -40 dBm at 1 MHz | ** -40 dBm at 1 MHz | ||
− | ** - | + | ** -80 dBm at 30 MHz |
* Nearly zero power supply current | * Nearly zero power supply current | ||
[[file:Better_Noise_Gen_schematic.png]] | [[file:Better_Noise_Gen_schematic.png]] | ||
+ | |||
+ | [[file:NoiseGen_V2-P1852-720px.jpg]] | ||
+ | |||
+ | === Better Design #2 - LTSPice Simulation === | ||
+ | |||
+ | * Falls off in a straight line (in dBm) with frequency | ||
+ | ** 10 dB at 1 MHz | ||
+ | ** 0 dB at 10 MHz | ||
+ | ** -10dB at 100 MHz | ||
+ | |||
+ | [[file:LTSpiceSim_Better2.PNG]] | ||
+ | |||
+ | === tinySA Measurements === | ||
* Off | * Off | ||
Line 91: | Line 144: | ||
[[file:V2-NoiseGenOnTinySA_OFF_1MHz-10MHz.PNG]] | [[file:V2-NoiseGenOnTinySA_OFF_1MHz-10MHz.PNG]] | ||
− | * On | + | * On, 1-30 MHz |
+ | ** Consistent with the LTSpice simulation | ||
− | [[file:V2-NoiseGenOnTinySA_On_1MHz- | + | [[file:V2-NoiseGenOnTinySA_On_1MHz-30MHz.PNG]] |
− | == | + | == Better Design #3 - Cascode Amp with output buffer == |
− | * | + | * Previous design is probably good into receiver but not as good for tinySA tracking generator |
− | ** | + | ** Want to be able to drive passive/crystal filters for testing |
− | * | + | ** Can already use [[NanoVNA]] but I'd prefer the tinySA due to lower noise floor |
− | ** | + | * Goal |
− | ** | + | ** Flat response across 1-30 MHz |
− | * | + | ** Good parts of Design #2 |
+ | ** Transistor seems to be a better noise source than a zener | ||
+ | * Idea - replace amp stage with cascode output stage followed by emitter follower for better match to 50 ohm load | ||
+ | |||
+ | === Example cascode design === | ||
+ | |||
+ | [[file:CascodeExample-720px.jpg]] | ||
+ | |||
+ | * Replace R1 with 0.1uF in parallel with 470K (from the the previous) | ||
+ | * Remove R2 | ||
+ | |||
+ | === Better Design #3 - LTSpice Simulation === | ||
+ | |||
+ | * Output stage is high gain, but limits bandwidth | ||
+ | |||
+ | [[file:Cascode2.PNG]] | ||
+ | |||
+ | == Better Design #4 == | ||
+ | |||
+ | * #3 output stage was limiting the bandwidth | ||
+ | ** Remove output stage | ||
+ | |||
+ | [[file:Cascode2_Sch.PNG]] | ||
+ | |||
+ | * PCB design | ||
+ | |||
+ | [[FILE:NoiseGen_V3_3D.png]] | ||
+ | |||
+ | [[FILE:RF_Noise_Cascode2_PCB.PNG]] | ||
+ | |||
+ | {| class="wikitable" | ||
+ | ! Qty | ||
+ | ! Value | ||
+ | ! RefDes | ||
+ | ! | ||
+ | ! Qty | ||
+ | ! Value | ||
+ | ! RefDes | ||
+ | |- | ||
+ | | 2 | ||
+ | | 100K | ||
+ | | R2,R5 | ||
+ | | | ||
+ | | 3 | ||
+ | | 0.1uF | ||
+ | | C1-C3 | ||
+ | |- | ||
+ | | 1 | ||
+ | | 150K | ||
+ | | R3 | ||
+ | | | ||
+ | | 3 | ||
+ | | 2N3904 | ||
+ | | Q1-Q3 | ||
+ | |- | ||
+ | | 1 | ||
+ | | 470K | ||
+ | | R1 | ||
+ | | | ||
+ | | 4 | ||
+ | | TestPoint | ||
+ | | TP1-TP4 | ||
+ | |- | ||
+ | | 1 | ||
+ | | 560 | ||
+ | | R4 | ||
+ | | | ||
+ | | | ||
+ | | | ||
+ | | | ||
+ | |- | ||
+ | |} | ||
+ | |||
+ | * < 3 dB down at 100 MHz | ||
+ | |||
+ | [[file:RF_Noise_Cascode2.PNG]] | ||
+ | |||
+ | === Cascode Design Videos === | ||
+ | |||
+ | <video type="youtube">18F_LL6KiUw</video> | ||
+ | |||
+ | <video type="youtube">r5Z5W_7B8Go</video> | ||
− | + | <video type="youtube">jnK0lSekFg4</video> | |
− | + | <video type="youtube">SZW0qLmUPeY</video> | |
− | + | <video type="youtube">zAoLwpkbXmE</video> | |
== Assembly Sheet == | == Assembly Sheet == | ||
[[RF Noise Generator Rev 1]] | [[RF Noise Generator Rev 1]] |
Latest revision as of 19:22, 10 October 2021
Contents
Usage
- Useful as a filter test signal source
- Pass filters
- Crystal filters
- Would like to use as noise source for tinySA
Others
- 7MHz calibration signal generator
- 0dBm and -60dBm outputs
Design #1
- From Experimental Methods in RF Design
- Fig 7.72
- Described as "not flat"
- "Junk box" parts
- (2) 2N3904 transistors
- (2) 5V (nominal) zener diodes
- Noise figure -50 dBm @ 10 MHz
Schematic
First Prototype
Build / Enclosure (Original board design)
- Used very old, but high quality chassis mount BNC connector
- Silver connector has a nice patina
- Built onto Single Side PCB material
- Acts as ground plane
- Pads cut from PCB material and superglued down onto the Base PCB
- Hot glued down into plastic enclosure
- Ferrite toroids at top are not used
- Unique nodes in red
- Prototype on single sided copper clad PCB
- KiCAD zener packages have backwards silkscreen (will need to fix on OshPark PCBs)
- OSHPark PCB
LTSpice Simulation
- Amplifier looks flat but the result wasn't
Measurements
- 12V, 43mA current draw
tinySA Measurements
- Measure from 1-30 MHz
- Power Off
- -90 dB noise floor
- Power On
- Measure from 1-30 MHz
- 100 KHz-1 MHz
- Power Off
- Power On
- Lot more energy at ~400 KHz
- -30 dB
- Not too useable for filter testing
- Might be OK for receiver noise source
Rigol DS1054Z Measurements
- 50 MHz scope with mods
- UltraScope settings
- SCAL 1.00 V
- H 200nS
- FFT settings
- CF = 16 MHz
- 2 MHz start, 50 MHz stop
- RBW 416.6 KHz
- Background noise
- Generator off
- Average ~ -64 dB noise floor too high
- Noise Generator On
- Falls off with frequency, but better than -50 dB
- Measured performance per EMiRFD (predicted - 50 dB)
Better Design #2
- Replace Zener as noise source with 2N3904 B-E junction reverse biased
- C1 is connected Emitter of Q1 to GND instead of +12V to reduce power supply noise
- Higher noise than EMiRFD design
- Usable from 1-10 MHz
- -40 dBm at 1 MHz
- -80 dBm at 30 MHz
- Nearly zero power supply current
Better Design #2 - LTSPice Simulation
- Falls off in a straight line (in dBm) with frequency
- 10 dB at 1 MHz
- 0 dB at 10 MHz
- -10dB at 100 MHz
tinySA Measurements
- Off
- On, 1-30 MHz
- Consistent with the LTSpice simulation
Better Design #3 - Cascode Amp with output buffer
- Previous design is probably good into receiver but not as good for tinySA tracking generator
- Want to be able to drive passive/crystal filters for testing
- Can already use NanoVNA but I'd prefer the tinySA due to lower noise floor
- Goal
- Flat response across 1-30 MHz
- Good parts of Design #2
- Transistor seems to be a better noise source than a zener
- Idea - replace amp stage with cascode output stage followed by emitter follower for better match to 50 ohm load
Example cascode design
- Replace R1 with 0.1uF in parallel with 470K (from the the previous)
- Remove R2
Better Design #3 - LTSpice Simulation
- Output stage is high gain, but limits bandwidth
Better Design #4
- #3 output stage was limiting the bandwidth
- Remove output stage
- PCB design
Qty | Value | RefDes | Qty | Value | RefDes | |
---|---|---|---|---|---|---|
2 | 100K | R2,R5 | 3 | 0.1uF | C1-C3 | |
1 | 150K | R3 | 3 | 2N3904 | Q1-Q3 | |
1 | 470K | R1 | 4 | TestPoint | TP1-TP4 | |
1 | 560 | R4 |
- < 3 dB down at 100 MHz
Cascode Design Videos