Difference between pages "RF-Amp" and "File:RF-Amp U2 W2AEW S21 1-30MHz.png"

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[[File:RF-Amp_P1943-720px.jpg]]
 
  
== RF Amplifier Features ==
 
 
* Useful as an IF or Antenna Amplifier
 
* From [https://zl2ctm.blogspot.com/2020/11/go-qrp-portable-ssb-rig.html Charlie Morris' (ZL2CTM) Go QRP Portable SSB Rig]
 
** Charlie references Solid State Design for the Radio Amateur (pp 19-20)
 
* Single 2N3904 NPN transistor
 
** Ft = 300 MHz (Gain Bandwidth Product)
 
*** Theoretical gain
 
**** +20 dB at 30 MHz
 
**** +29.5 dB at 10 MHz
 
**** Reality is lower due to capacitance, etc.
 
* Measured +22 dB gain @12V, +25dB gain @14V
 
* Input connectors: SMA or BNC
 
* +12V nominal power
 
* 49x49mm card
 
* 4x 4-40 mounting holes
 
 
== RF Amplifier Design ==
 
 
=== Schematic ===
 
 
[[file:RF_Amp_Schematic-4.PNG]]
 
 
== LT Spice Simulation ==
 
 
* [https://github.com/land-boards/lb-boards/blob/master/HamRadio/RF-Amp/LTSpice/2n3904%20amp.asc LTspice Simulation] - GitHub source file
 
** +28.4 dB at 9 MHz
 
 
[[File:RF-AMP-LTSPICE_XFMRS.PNG]]
 
 
== Charlie Morris Design ==
 
 
* From Charlie's notes with mods for my use
 
** [https://zl2ctm.blogspot.com/2020/11/go-qrp-portable-ssb-rig.html Charlie Morris' (ZL2CTM) Go QRP Portable SSB Rig]
 
** Charlie describes the design in detail in his video [https://www.youtube.com/watch?v=CHdtoupH2Vg Simple SSB Rig: Part 6 - IF Amplifiers] (Feb 2021)
 
** Based on the Class A RF Amplifier in [https://www.amazon.com/Solid-State-Design-Radio-Amateur/dp/0872590402 Solid State Design for the Radio Amateur] pp 19-20
 
* [https://www.mouser.com/datasheet/2/308/1/2N3903_D-2310199.pdf 2N3904 data sheet]
 
* [https://www.electronics-tutorials.ws/amplifier/emitter-resistance.html Emitter Resistance] - helpful paper
 
 
=== Beta DC ===
 
 
* Geometric mean min/max beta at operating current
 
** =sqrt(100*300) = 173
 
 
=== Beta AC ===
 
 
* Gain bandwidth product divided by operating frequency
 
** Assume operating frequency of 9 MHz (IF frequency)
 
** = 300/9 = 33.3
 
 
=== DC Operating Point ===
 
 
* Max HFE RF gain at CE current of 10 mA
 
** If Vce = 6V, this is 60 mW power dissipation
 
* Assume Ve (voltage across emitter resistor) = 1/10 Vcc = 12V/10 = 1.2V
 
** R3 is Re (emitter resistor) = 1.2V/0.01A = 120 ohms
 
* VCE = 0.7V (typical from data sheet)
 
* V(emitter) at 10% of Vcc rule of thumb = 1.2V
 
* V(base) = V(emitter) + VCE = 1.9V
 
* Base current is collector current divided by Beta DC
 
** Biasing resistors = 10x current needed by base current
 
** 10 mA in C-E, beta DC less = 10 mA/173 = 58 uA
 
** 10x the current in the biasing resistors = 580 uA (calculated)
 
* R2 is 1.9V at 580 uA = 3.29K use 3.3K
 
* R1 sources current to R2 and transistor base
 
** Voltage = Vcc (12V) - 1.9V = 10.1V
 
** Current = 577 uA + 58 uA = 635 uA
 
** R1 = 10.1 / .635 mA = 15.9K, use 15K
 
 
==== Measured DC operating point ====
 
 
* Measured with no input
 
* Vcc = 11.96V
 
* Current draw = 12 mA
 
** Quick test for wiring and more or less correct parts
 
** Expected 11 mA - close enough
 
* +BUFF = 11.84V
 
** 0.12V which is 12 mA through R4 10 ohms - expected
 
* V emitter = 1.41V
 
** 1.41V/12 Ohms = 11.75 mA close to 12 mA total measured current
 
* V on input divider = 2.06V
 
** Vbase + 0.7V - close
 
** Measured Vbe = 2.06-1.41 = 0.65 - close
 
 
=== Input resistance ===
 
 
* Xc for 0.1uF cap from emitter to ground
 
** C=0.1uF
 
** F=10MHz
 
** 1/2*pi*F*C = 0.16 ohms
 
* Parallel resistors R1, R2 paralleled with transistor input impedance
 
** R1=15K, R2=3.3K
 
** Transistor resistance = Beta AC (33.3) times re
 
*** re = 26 / Ie (10 mA in mA) = 26/10 = 2.6
 
*** SSDRA uses 25 as constant - close enough
 
**** 26 comes from Ebers-Moll approximation
 
*** Beta AC * re = 33.3*2.6 = 83.3 ohms - predominates
 
** All in parallel are 80.8 ohms
 
 
=== Gain calculation ===
 
 
* Approximation
 
* Ic = 0.01A
 
* Rc = 200
 
* Vrc = 2V
 
* Gain = Vrc / vt
 
** vt = 26 mV at room temperature
 
** Gain = 2V / .026V = 79.2 V/V
 
** Gain = +37 dB
 
 
=== Input/Output Transformers ===
 
 
* Using [http://toroids.info/FT37-43.php FT37-43 Toroid]
 
 
[[file:FT37-43_10_Turns.PNG]]
 
 
==== Tracks ====
 
 
[[file:RF-Amp-tracks.PNG]]
 
 
==== Input Transformer ====
 
 
* Input Transformer (T1 on Charlie's - T2 on this board)
 
* Need to calculate turns ratio
 
* 50:80.8 Ohms
 
* n = sqrt(Zout/Zin)sqrt(80.8/50) = 1.27 turns ratio
 
* Turns choices
 
* Minimum number of turns
 
* Rule of thumb - want Xl (coil impedance smallest value) to be least 4-5X the load
 
** Load = 80.8 ohms
 
** 5 * 80.8 ohms = 404.2 ohms minimum
 
*** More turns = larger capacitance and drops bandwidth
 
** Toroid is FT37-43
 
** From [http://toroids.info/FT37-43.php Toroid page]
 
***  Xl = 404.4 at 9 MHz is 4.5 turns, round up to 5
 
** Try nearest integer numbers turns ratios
 
*** 5:6 = 6% error
 
*** 6:8 = -4.6%
 
*** 7:9 = -1.1% << good choice
 
*** 8:10 = +1.7%
 
*** 9:11 = +4.0%
 
*** 10:13 = -2.19%
 
* Use 7:9 turns ratio for optimal input transformer
 
 
[[file:RF-Amp-T2.PNG]]
 
 
==== Output Transformer ====
 
 
* Output transformer (T2 on Charlie's - T1 on this board)
 
* T2 - different than Charlie's design since my Crystal filters are all 50 ohms in/out
 
* SSDRA suggest presenting 200 ohm load to the collector
 
** Can't find reference in SSDRA
 
** Reflecting back 50 ohms load to 200 ohm collector...
 
* 200:50 ohms
 
* n = sqrt(200/50) = 2.0:1 turns ratio
 
* 10:5 turns
 
** 10 turns primary (on transistor collector)
 
*** 10 turns = 35 uH
 
** 5 turns secondary (towards output)
 
*** 5 turns = 8.75 uH
 
** 15 turns = 9.5 in
 
 
[[file:RF-Amp-T1.PNG]]
 
 
=== Charlie's Notes ===
 
 
[[FILE:IF Amp_0046A.jpg]]
 
 
[[FILE:IF Amp_0046B.jpg]]
 
 
[[FILE:IF Amp_0046C.jpg]]
 
 
[[FILE:IF Amp_0047A.jpg]]
 
 
[[FILE:IF Amp_0047B.jpg]]
 
 
[[FILE:IF Amp_0047C.jpg]]
 
 
== NanoVNA Measurements ==
 
 
* '''Goal''': Measure RF-Amp performance using a [[NanoVNA]] running [https://nanovna.com/?page_id=90 NanoSaver software on PC]
 
* S21 (gain) needs to be measured with a [[RF_Attenuators#40_dB_Attenuator|40 dB attenuator]] on input to RF-Amp to avoid compression on the output
 
* S11 (reflection) input impedance can't be measured with input [[RF_Attenuators#40_dB_Attenuator|40 dB attenuator]] because S11 just ends up measuring the attenuator
 
** Output should be terminated to 50 ohms for S11 measurement
 
* DC current = 12 mA
 
 
=== Measure S21 ===
 
 
* Put [[RF_Attenuators#40_dB_Attenuator|40 dB attenuator]] on RF-Amp input, measure S21 at output
 
** [[NanoVNA]] provides 50 ohm load to RF-Amp to properly terminate output
 
* Measure S21 with 9:11 input transformer
 
** S21 @ 100 KHz = -8 dB dB
 
** S21 @ 1.45 MHz = 35.4 dB (peak gain)
 
** S21 @ 9.1 MHz = 24.3 dB
 
** S21 @ 16 MHz = 20.1 dB
 
** S21 @ 30 MHz = 12.7 dB
 
* Peak gain justifies use of 40 dB attenuator to protect [[NanoVNA]]
 
 
[[file:RF-Amp_S21_40dBAttenInput_1-30MHz.png]]
 
 
==== LTspice vs NanoVNA ====
 
 
* LTspice simulation was pretty similar to [[NanoVNA]] results
 
** -10 dB at 100 KHz
 
** +32 dB at peak
 
** Lower output at higher frequencies
 
 
[[file:RF-Amp_S21_LTspice-vs-NanoVNA_1-30MHz.png]]
 
 
=== Measure Input Compression ===
 
 
* Is there compression if the [[NanoVNA]] drives the input directly?
 
** Test by driving directly from NanoVNA set to CW = 9 MHz
 
** Measured output with scope - not clipped at 9 MHz
 
*** Approx. 1Vpp input = +22.1 dBm gain which matches the S21 with the attenuator on the input
 
*** Vpp = 12.4V with 50 Ohm load resistor
 
** Starts clipping at 7 Mhz and down
 
* Therefore, can measure input impedance at 9 MHz
 
* Other evidence of compression
 
** Compare S21 gain with no input attenuator, put external [[RF Attenuators|40 dB RF Attenuators]] on output of RF-Amp to protect [[NanoVNA]] input
 
** S21 shows lower gain in lower frequencies so clipping/compression is happening
 
** Was: 35 dB at 1.4 MHz
 
** Is: 23.1 dB at 1.5 MHz
 
* Due to compression can't accurately measure lower frequencies with attenuator at output
 
* Compression below 7 MHz matches what was on scope
 
 
[[file:RF-Amp_S21_40dBAttenOutput_1-30MHz.png]]
 
 
=== Measure Input Impedance ===
 
 
* Shows VSWR at 14.4 MHz = 1.56:1
 
* At 9 MHz
 
** VSWR = 1.7:1
 
** Impedance = 81-j10
 
 
[[file:RF-Amp_AttenOutput_VSWR_2021_1-30MHz.png]]
 
 
=== Change Input Transformer turns ratio ===
 
 
* Above had 9:11 turns ratio
 
* Change to 7:9 turns ratio
 
* Slightly better gain at higher frequencies
 
* Was: S21 @ 30 MHz = 12.7 dB
 
* After:  S21 @ 30 MHz = 15.3 dB
 
*  Small additional gain at 8 MHz
 
** Was: S21 @ 9.1 MHz = 24.3 dB
 
** After: S21 @ 9.1 MHz = 24.8 dB
 
 
[[file:RF-Amp_S21_40dBAttenInput_Turns7to9_1-30MHz.png]]
 
 
* New turns improved the input VSWR slightly
 
* Was: At 9 MHz, VSWR = 1.7:1, Impedance = 81-j10
 
* After: At 9 MHz, VSWR = 1.6:1, Impedance = 76.7-j12
 
 
[[file:RF-Amp_vswr_40dBAttenInput_Turns7to9_1-30MHz.png]]
 
 
==== Tune input transformer====
 
 
* Isolate output by replacing output transformer with 200 resistor
 
* Add one more output winding to input transformer T2 (7:10)
 
* VSWR nearly 1.04:1 at 11.1 MHz
 
* -19 dB return loss at 9 MHz VSWR = 1.249:1
 
 
[[file:RF-Amp_VSWR_1-30MHz_7to10Turns.png]]
 
 
* With output transformer
 
* Slightly better with 1 extra winding
 
 
[[file:RF-Amp_VSWR_1-30MHz_7to10Turns-2.png]]
 
 
== W2AEW Measurement Method ==
 
 
* Calibrate NanoVNA using External 30 dB Attenuator
 
** See [https://youtu.be/7TtKE39TWpI W2AEW #337 video] below
 
** Insert 30 dB attenuator and calibrate with attenuator installed
 
** Open/sort/thru at the output side of the attenuator using [[NanoVNA#RF_Demo_Kit|NanoVNA RF Demo Kit]]
 
* Scan 1-30 Mhz
 
** Overdriven at 1 MHz which "swamps" the RF Amp
 
* Re-calibrate at 1.5-31.5 MHz
 
** Peak gain at 1 MHz = 32 dB
 
*** Does not overdrive the Amp or NanoVNA
 
*** Downsize is a lot of noise in the return loss
 
 
=== Unit 1 - 9 MHz measurement ===
 
 
** VSWR = 1.172
 
** S11 (Return Loss) = -22.014 dB
 
** S21 (Gain) = +23.624 dB
 
 
[[file:RF-Amp_W2AEW_S21_1-30MHz.png]]
 
 
[[file:RF-Amp_W2AEW_S11_1-30MHz.png]]
 
 
=== Unit 2 - 9 MHz measurement ===
 
 
** VSWR = 1.182
 
** S11 (Return Loss) = -21.565 dB
 
** S21 (Gain) = +24.656 dB
 
 
[[file:RF-Amp_U2_W2AEW_S21_1-30MHz.png]]
 
 
[[file:RF-Amp_U2_W2AEW_S11_1-30MHz.png]]
 
 
== Video ==
 
 
<video type="youtube">7TtKE39TWpI</video>
 
 
<video type="youtube">CHdtoupH2Vg</video>
 
 
<video type="youtube">YJTsWV2kzFY</video>
 
 
<video type="youtube">xPFzFhM0ojE</video>
 
 
== Assembly Sheet ==
 
 
* [[RF Amplifier Assembly Sheet]]
 

Latest revision as of 12:32, 13 November 2021