Difference between revisions of "RF-Amp"

From Land Boards Wiki
Jump to navigation Jump to search
 
(47 intermediate revisions by the same user not shown)
Line 5: Line 5:
 
* Class A (Common Emitter) Amplifier
 
* Class A (Common Emitter) Amplifier
 
** Emitter resistor bypassed with capacitor for higher AC gain
 
** Emitter resistor bypassed with capacitor for higher AC gain
** Transformer coupled input/output for impedance matching
+
** Transformer coupled input/output for impedance matching to 50Ω
 
** Capacitively coupled input
 
** Capacitively coupled input
 
* Single 2N3904 NPN transistor
 
* Single 2N3904 NPN transistor
* Applications
+
* Useful as an gain block in various applications
** IF Amplifier
+
** Radio Transmitter/Receiver IF Amplifier
** Antenna Amplifier
+
** Radio Transmitter/Receiver Antenna Amplifier
** Microphone amplifier (with minor modifications)
+
** Radio Transmitter Microphone amplifier (with minor modifications)
 
* As RF Amplifier
 
* As RF Amplifier
 
** Measured Gain Bandwidth (GBW) of 150
 
** Measured Gain Bandwidth (GBW) of 150
Line 17: Line 17:
 
** Measured Gain @9 MHz, +24.7 dB at 12V
 
** Measured Gain @9 MHz, +24.7 dB at 12V
 
** Measured Gain @30 MHz, +13.8 dB at 12V
 
** Measured Gain @30 MHz, +13.8 dB at 12V
* Input connectors: SMA, BNC, or direct solder coax
+
* As a microphone amplifier
 +
** Approximately 20 dB at 1 KHz
 +
* Input connectors: SMA, BNC, or direct solder coax to SMA etches
 
* +12V nominal power
 
* +12V nominal power
 
** 12-14 VDC
 
** 12-14 VDC
Line 24: Line 26:
 
* 4x 4-40 mounting holes
 
* 4x 4-40 mounting holes
  
=== Source ===
+
=== Source Materials ===
  
 
* From [https://zl2ctm.blogspot.com/2020/11/go-qrp-portable-ssb-rig.html Charlie Morris' (ZL2CTM) Go QRP Portable SSB Rig]
 
* From [https://zl2ctm.blogspot.com/2020/11/go-qrp-portable-ssb-rig.html Charlie Morris' (ZL2CTM) Go QRP Portable SSB Rig]
 
** Charlie references [https://www.amazon.com/Solid-State-Design-Radio-Amateur/dp/0872590402 Solid State Design for the Radio Amateur] (pp 19-20)
 
** Charlie references [https://www.amazon.com/Solid-State-Design-Radio-Amateur/dp/0872590402 Solid State Design for the Radio Amateur] (pp 19-20)
 +
 +
=== HFE at 10 mA ===
 +
 +
[[file:HFE_10mA.PNG]]
  
 
== RF Amplifier Design ==
 
== RF Amplifier Design ==
Line 46: Line 52:
 
=== Additional Resistor ===
 
=== Additional Resistor ===
  
* Insert 4.7 ohm resistor to emitter bypass capacitor
+
* Insert 4.7 Ω resistor to emitter bypass capacitor
 
** Reduces maximum gain
 
** Reduces maximum gain
 
** Increases gain over 1-30 MHz bandwidth
 
** Increases gain over 1-30 MHz bandwidth
Line 79: Line 85:
 
** If Vce = 6V, this is 60 mW power dissipation
 
** If Vce = 6V, this is 60 mW power dissipation
 
* Assume Ve (voltage across emitter resistor) = 1/10 Vcc = 12V/10 = 1.2V
 
* Assume Ve (voltage across emitter resistor) = 1/10 Vcc = 12V/10 = 1.2V
** R3 is Re (emitter resistor) = 1.2V/0.01A = 120 ohms
+
** R3 is Re (emitter resistor) = 1.2V/0.01A = 120 Ω
 
* VCE = 0.7V (typical from data sheet)
 
* VCE = 0.7V (typical from data sheet)
 
* V(emitter) at 10% of Vcc rule of thumb = 1.2V
 
* V(emitter) at 10% of Vcc rule of thumb = 1.2V
Line 87: Line 93:
 
** 10 mA in C-E, beta DC less = 10 mA/173 = 58 uA
 
** 10 mA in C-E, beta DC less = 10 mA/173 = 58 uA
 
** 10x the current in the biasing resistors = 580 uA (calculated)
 
** 10x the current in the biasing resistors = 580 uA (calculated)
* R2 is 1.9V at 580 uA = 3.29K use 3.3K
+
* R2 is 1.9V at 580 uA = 3.29KΩ use 3.3KΩ
 
* R1 sources current to R2 and transistor base
 
* R1 sources current to R2 and transistor base
 
** Voltage = Vcc (12V) - 1.9V = 10.1V
 
** Voltage = Vcc (12V) - 1.9V = 10.1V
 
** Current = 577 uA + 58 uA = 635 uA
 
** Current = 577 uA + 58 uA = 635 uA
** R1 = 10.1 / .635 mA = 15.9K, use 15K
+
** R1 = 10.1 / .635 mA = 15.9KΩ, use 15KΩ
  
 
==== Measured DC operating point ====
 
==== Measured DC operating point ====
Line 101: Line 107:
 
** Expected 11 mA - close enough
 
** Expected 11 mA - close enough
 
* +BUFF = 11.84V
 
* +BUFF = 11.84V
** 0.12V which is 12 mA through R4 10 ohms - expected
+
** 0.12V which is 12 mA through R4 at 10 Ω - expected
 
* V emitter = 1.41V
 
* V emitter = 1.41V
** 1.41V/12 Ohms = 11.75 mA close to 12 mA total measured current
+
** 1.41V/12Ω = 11.75 mA close to 12 mA total measured current
 
* V on input divider = 2.06V
 
* V on input divider = 2.06V
 
** Vbase + 0.7V - close
 
** Vbase + 0.7V - close
Line 113: Line 119:
 
** C=0.1uF
 
** C=0.1uF
 
** F=10MHz
 
** F=10MHz
** 1/2*pi*F*C = 0.16 ohms
+
** 1/2*pi*F*C = 0.16Ω
 
* Parallel resistors R1, R2 paralleled with transistor input impedance
 
* Parallel resistors R1, R2 paralleled with transistor input impedance
** R1=15K, R2=3.3K
+
** R1=15KΩ, R2=3.3KΩ
 
** Transistor resistance = Beta AC (33.3) times re
 
** Transistor resistance = Beta AC (33.3) times re
 
*** re = 26 / Ie (10 mA in mA) = 26/10 = 2.6
 
*** re = 26 / Ie (10 mA in mA) = 26/10 = 2.6
 
*** SSDRA uses 25 as constant - close enough
 
*** SSDRA uses 25 as constant - close enough
 
**** 26 comes from Ebers-Moll approximation
 
**** 26 comes from Ebers-Moll approximation
*** Beta AC * re = 33.3*2.6 = 83.3 ohms - predominates
+
*** Beta AC * re = 33.3*2.6 = 83.- predominates
** All in parallel are 80.8 ohms
+
** All in parallel are 80.
  
 
=== Gain calculation ===
 
=== Gain calculation ===
Line 148: Line 154:
 
* Input Transformer (T1 on Charlie's - T2 on this board)
 
* Input Transformer (T1 on Charlie's - T2 on this board)
 
* Need to calculate turns ratio
 
* Need to calculate turns ratio
* 50:80.8 Ohms
+
* 50:80.8 Ω
 
* n = sqrt(Zout/Zin)sqrt(80.8/50) = 1.27 turns ratio
 
* n = sqrt(Zout/Zin)sqrt(80.8/50) = 1.27 turns ratio
 
* Turns choices
 
* Turns choices
 
* Minimum number of turns
 
* Minimum number of turns
 
* Rule of thumb - want Xl (coil impedance smallest value) to be least 4-5X the load
 
* Rule of thumb - want Xl (coil impedance smallest value) to be least 4-5X the load
** Load = 80.8 ohms
+
** Load = 80.8 Ω
** 5 * 80.8 ohms = 404.2 ohms minimum
+
** 5 * 80.8 Ω = 404.2 Ω minimum
 
*** More turns = larger capacitance and drops bandwidth
 
*** More turns = larger capacitance and drops bandwidth
 
** Toroid is FT37-43
 
** Toroid is FT37-43
 
** From [http://toroids.info/FT37-43.php Toroid page]
 
** From [http://toroids.info/FT37-43.php Toroid page]
***  Xl = 404.4 at 9 MHz is 4.5 turns, round up to 5
+
***  Xl = 404.at 9 MHz is 4.5 turns, round up to 5
 
** Try nearest integer numbers turns ratios
 
** Try nearest integer numbers turns ratios
 
*** 5:6 = 6% error
 
*** 5:6 = 6% error
Line 173: Line 179:
  
 
* Output transformer (T2 on Charlie's - T1 on this board)
 
* 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
+
* T2 - different than Charlie's design since my Crystal filters are all 50 Ω in/out
* SSDRA suggest presenting 200 ohm load to the collector
+
* SSDRA suggest presenting 200 Ω load to the collector
 
** Can't find reference in SSDRA
 
** Can't find reference in SSDRA
** Reflecting back 50 ohms load to 200 ohm collector...
+
** Reflecting back 50 Ω load to 200 Ω collector...
* 200:50 ohms
+
* 200:50 Ω
 
* n = sqrt(200/50) = 2.0:1 turns ratio
 
* n = sqrt(200/50) = 2.0:1 turns ratio
 
* 10:5 turns
 
* 10:5 turns
Line 207: Line 213:
 
* 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
 
* 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
 
* 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
+
** Output should be terminated to 50 Ω for S11 measurement
 
* DC current = 12 mA
 
* DC current = 12 mA
  
Line 213: Line 219:
  
 
* Put [[RF_Attenuators#40_dB_Attenuator|40 dB attenuator]] on RF-Amp input, measure S21 at output
 
* 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
+
** [[NanoVNA]] provides 50 Ω load to RF-Amp to properly terminate output
 
* Measure S21 with 9:11 input transformer
 
* Measure S21 with 9:11 input transformer
 
** S21 @ 100 KHz = -8 dB dB
 
** S21 @ 100 KHz = -8 dB dB
Line 239: Line 245:
 
** Measured output with scope - not clipped at 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
 
*** 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
+
*** Vpp = 12.4V with 50 Ω load resistor
 
** Starts clipping at 7 Mhz and down
 
** Starts clipping at 7 Mhz and down
 
* Therefore, can measure input impedance at 9 MHz
 
* Therefore, can measure input impedance at 9 MHz
Line 320: Line 326:
 
* Kits and Parts  card current draws 30 mA
 
* Kits and Parts  card current draws 30 mA
  
== Modified to use as Microphone Amp ==
+
== Use of Card as a Microphone Amp ==
 +
 
 +
[[file:MicAmp_P1946-720px.jpg]]
  
 
* Charlie's video
 
* Charlie's video
Line 337: Line 345:
 
[[file:Mic_Amp_2.jpg]]
 
[[file:Mic_Amp_2.jpg]]
  
=== Test electret microphone ===
+
=== Test with Electret Microphone ===
 +
 
 +
[[FILE:MicAmp_P1947-720px.jpg]]
  
[[FILE:ELECTRET_MIC.jpg]]
+
[[FILE:MicAmp_P1949-720px.jpg]]
  
* Determine Electret operating point
+
* Charlie assumes voltage/current - didn't measure
 +
* I chose to determine Electret operating point through measurement
 
* DC powered
 
* DC powered
 
* AC coupled output
 
* AC coupled output
 
* 13.8VDC (max) power
 
* 13.8VDC (max) power
* Attach decade resistor box
+
* Attach decade resistor box between power supply + side and Electret mic + side
* Adjust resistance to get 4V across mic at 13.8 VDC supply
+
** Adjust decade resistance value to measure 4V across mic with 13.8 VDC supply
* Selected value = 33K pullup to 13.8V gets 4V across mic
+
** 2V with 12V power supply
* 2.5V out with 12V supply
+
* Selected value = 33K Ω pullup to 13.8V gets 4V across mic
 +
* 2V out with 12V supply
 +
* Secure with zip ties and secure with superglue
  
=== Mic Amp Component Values ===
+
=== Wiring up Mic to Amp ===
  
 
* Electret Condenser Microphone
 
* Electret Condenser Microphone
Line 359: Line 372:
 
* Install Electret Condenser Microphone on small perf board
 
* Install Electret Condenser Microphone on small perf board
 
* Cable using 18" RG-174 coax to input of RF Amp card
 
* Cable using 18" RG-174 coax to input of RF Amp card
 +
 +
[[FILE:MicAmp_P952-720px.jpg]]
 +
 +
=== Schematic Mods ===
  
 
[[FILE:RF_Amp_Schematic-MODS.png]]
 
[[FILE:RF_Amp_Schematic-MODS.png]]
 +
 +
=== Part Value Changes ===
  
 
* No transformers
 
* No transformers
** transformers replaced by passives/jumpers
+
** Transformers replaced by passives/jumpers
* R1 - 15K = OK
+
* R1 - 15K Ω
 
* R2 - 3K (small difference vs 3.3K on RF Amp)
 
* R2 - 3K (small difference vs 3.3K on RF Amp)
* R3 - 120 = OK
+
* R3 - 120 Ω
* R5 - 50 ohms
+
* R4 - 10 Ω
** Install R5 to simulate balanced modulator 50 Ohm load
+
* R5 - 50 Ω
 +
** Install R5 to simulate balanced modulator 50 Ω load
 
** Install R5 on long leads to easily remove
 
** Install R5 on long leads to easily remove
* T1 primary winding - 560 ohm
+
* 33K Ω pullup to bias Electret mic
 +
* T1 primary winding - 560 Ω
 
* C1 - 0.1 uF
 
* C1 - 0.1 uF
 
* C2 - 10 uF
 
* C2 - 10 uF
 
* C3 - 47 uF
 
* C3 - 47 uF
** Add capacitor from Vc point (transistor collector and 560 ohm resistor) to T1 output side
+
* Add 10 uF capacitor from Vc point (transistor collector and 560 Ω resistor) to T1 output side
 
* Install output SMA connector
 
* Install output SMA connector
** Goes to Balanced Modulator
+
* Built SMA to RCA cable
 +
** Cut in half SMA male-male
 +
** Made 2 SMA to RCA cables
 +
 
 +
[[FILE:RF-Amp_MICAMP.PNG]]
 +
 
 +
=== Tested ===
 +
 
 +
* In application output goes to Balanced Modulator
 
** Output level should be +7dBm for ADE-1 Mixers
 
** Output level should be +7dBm for ADE-1 Mixers
 
* Tested into [[AudioAmp386]] - works
 
* Tested into [[AudioAmp386]] - works
 
[[FILE:RF-Amp_MICAMP.PNG]]
 
  
 
=== Mic Amp LTspice Simulation ===
 
=== Mic Amp LTspice Simulation ===
Line 387: Line 414:
  
 
[[FILE:Mic_Amp_LTSpice_Sim.PNG]]
 
[[FILE:Mic_Amp_LTSpice_Sim.PNG]]
 +
 +
* With 100uF cap across emitter resistor
 +
 +
[[FILE:Mic_Amp_Ce-100uF_LTSpice_Sim.PNG]]
  
 
== Video ==
 
== Video ==

Latest revision as of 22:30, 15 November 2021

RF-Amp P1943-720px.jpg

RF Amplifier Features[edit]

  • Class A (Common Emitter) Amplifier
    • Emitter resistor bypassed with capacitor for higher AC gain
    • Transformer coupled input/output for impedance matching to 50Ω
    • Capacitively coupled input
  • Single 2N3904 NPN transistor
  • Useful as an gain block in various applications
    • Radio Transmitter/Receiver IF Amplifier
    • Radio Transmitter/Receiver Antenna Amplifier
    • Radio Transmitter Microphone amplifier (with minor modifications)
  • As RF Amplifier
    • Measured Gain Bandwidth (GBW) of 150
    • Measured Gain @7 MHz, +25.2 dB at 12V
    • Measured Gain @9 MHz, +24.7 dB at 12V
    • Measured Gain @30 MHz, +13.8 dB at 12V
  • As a microphone amplifier
    • Approximately 20 dB at 1 KHz
  • Input connectors: SMA, BNC, or direct solder coax to SMA etches
  • +12V nominal power
    • 12-14 VDC
    • 5 mm terminal block for power
  • 49x49mm card
  • 4x 4-40 mounting holes

Source Materials[edit]

HFE at 10 mA[edit]

HFE 10mA.PNG

RF Amplifier Design[edit]

Schematic[edit]

RF Amp Schematic-4.PNG

LT Spice Simulation[edit]

As Built - Rev 1[edit]

RF-AMP-LTSPICE XFMRS.PNG

Additional Resistor[edit]

  • Insert 4.7 Ω resistor to emitter bypass capacitor
    • Reduces maximum gain
    • Increases gain over 1-30 MHz bandwidth
    • Possible better for Antenna Amplifier application at lower frequencies
  • +22.4 dB at 9 MHz

RF-AMP-Rev2 LTSPICE.PNG

Charlie Morris Design Calculations[edit]

Beta DC[edit]

  • Geometric mean min/max beta at operating current
    • =sqrt(100*300) = 173

Beta AC[edit]

  • Gain bandwidth product divided by operating frequency
    • Assume operating frequency of 9 MHz (IF frequency)
    • = 300/9 = 33.3

DC Operating Point[edit]

  • 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 Ω
  • 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 = 3.29KΩ use 3.3KΩ
  • 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 = 15.9KΩ, use 15KΩ

Measured DC operating point[edit]

  • 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 at 10 Ω - expected
  • V emitter = 1.41V
    • 1.41V/12Ω = 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[edit]

  • Xc for 0.1uF cap from emitter to ground
    • C=0.1uF
    • F=10MHz
    • 1/2*pi*F*C = 0.16Ω
  • Parallel resistors R1, R2 paralleled with transistor input impedance
    • R1=15KΩ, R2=3.3KΩ
    • 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 = 83.3Ω - predominates
    • All in parallel are 80.8Ω

Gain calculation[edit]

  • 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[edit]

FT37-43 10 Turns.PNG

Tracks[edit]

RF-Amp-tracks.PNG

Input Transformer[edit]

  • Input Transformer (T1 on Charlie's - T2 on this board)
  • Need to calculate turns ratio
  • 50:80.8 Ω
  • 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 Ω
    • 5 * 80.8 Ω = 404.2 Ω minimum
      • More turns = larger capacitance and drops bandwidth
    • Toroid is FT37-43
    • From Toroid page
      • Xl = 404.4Ω 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

RF-Amp-T2.PNG

Output Transformer[edit]

  • Output transformer (T2 on Charlie's - T1 on this board)
  • T2 - different than Charlie's design since my Crystal filters are all 50 Ω in/out
  • SSDRA suggest presenting 200 Ω load to the collector
    • Can't find reference in SSDRA
    • Reflecting back 50 Ω load to 200 Ω collector...
  • 200:50 Ω
  • 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

RF-Amp-T1.PNG

Charlie's Notes[edit]

IF Amp 0046A.jpg

IF Amp 0046B.jpg

IF Amp 0046C.jpg

IF Amp 0047A.jpg

IF Amp 0047B.jpg

IF Amp 0047C.jpg

NanoVNA Measurements[edit]

  • Goal: Measure RF-Amp performance using a NanoVNA running NanoSaver software on PC
  • S21 (gain) needs to be measured with a 40 dB attenuator on input to RF-Amp to avoid compression on the output
  • S11 (reflection) input impedance can't be measured with input 40 dB attenuator because S11 just ends up measuring the attenuator
    • Output should be terminated to 50 Ω for S11 measurement
  • DC current = 12 mA

Measure S21[edit]

  • Put 40 dB attenuator on RF-Amp input, measure S21 at output
    • NanoVNA provides 50 Ω 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

RF-Amp S21 40dBAttenInput 1-30MHz.png

LTspice vs NanoVNA[edit]

  • LTspice simulation was pretty similar to NanoVNA results
    • -10 dB at 100 KHz
    • +32 dB at peak
    • Lower output at higher frequencies

RF-Amp S21 LTspice-vs-NanoVNA 1-30MHz.png

Measure Input Compression[edit]

  • 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 Ω 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 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

RF-Amp S21 40dBAttenOutput 1-30MHz.png

W2AEW S11 Measurement Method[edit]

  • Can't drive the RF Amp directly from the NanoVNA
    • High output level from the NanoVNA overdrives the RF Amp
    • W2AEW provides a way of driving the RF Amp card without overdriving and still measure S11

  • Calibrate NanoVNA using External 30 dB Attenuator
  • Scan 1-30 Mhz
    • Overdriven at 1 MHz which "swamps" the RF Amp
  • Re-calibrated 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
  • Tested two units
    • Unit 1 has a 7:10 input transformer (T2) ratio
    • Unit 2 has a 7:9 input transformer (T2) ratio

Unit 1[edit]

  • 9 MHz measurements
    • VSWR = 1.172
    • S11 (Return Loss) = -22.014 dB
    • S21 (Gain) = +23.624 dB

RF-Amp W2AEW S21 1-30MHz.png

RF-Amp W2AEW S11 1-30MHz.png

Unit 2[edit]

  • 9 MHz measurement
    • VSWR = 1.182
    • S11 (Return Loss) = -21.565 dB
    • S21 (Gain) = +24.656 dB
  • 20 dB gain at 15 MHz
    • Gain Bandwidth (GBW) = ~150
    • GBW is a good predictor of gain at particular frequencies
    • Calculated Gain of 14 dB at 30 MHz - measured at +12.8 dB
    • Measured at +26 dB at 7 MHz

RF-Amp U2 W2AEW S21 1-30MHz.png

RF-Amp U2 W2AEW S11 1-30MHz.png

Compare RF Amp vs Kits and Parts Amp[edit]

Use of Card as a Microphone Amp[edit]

MicAmp P1946-720px.jpg

  • Charlie's video

Charlie's Schematic/Calculations[edit]

Mic Amp 1A.jpg

Mic Amp 1B.jpg

Mic Amp 2.jpg

Test with Electret Microphone[edit]

MicAmp P1947-720px.jpg

MicAmp P1949-720px.jpg

  • Charlie assumes voltage/current - didn't measure
  • I chose to determine Electret operating point through measurement
  • DC powered
  • AC coupled output
  • 13.8VDC (max) power
  • Attach decade resistor box between power supply + side and Electret mic + side
    • Adjust decade resistance value to measure 4V across mic with 13.8 VDC supply
    • 2V with 12V power supply
  • Selected value = 33K Ω pullup to 13.8V gets 4V across mic
  • 2V out with 12V supply
  • Secure with zip ties and secure with superglue

Wiring up Mic to Amp[edit]

KY-037.jpg

  • Install Electret Condenser Microphone on small perf board
  • Cable using 18" RG-174 coax to input of RF Amp card

MicAmp P952-720px.jpg

Schematic Mods[edit]

RF Amp Schematic-MODS.png

Part Value Changes[edit]

  • No transformers
    • Transformers replaced by passives/jumpers
  • R1 - 15K Ω
  • R2 - 3K (small difference vs 3.3K on RF Amp)
  • R3 - 120 Ω
  • R4 - 10 Ω
  • R5 - 50 Ω
    • Install R5 to simulate balanced modulator 50 Ω load
    • Install R5 on long leads to easily remove
  • 33K Ω pullup to bias Electret mic
  • T1 primary winding - 560 Ω
  • C1 - 0.1 uF
  • C2 - 10 uF
  • C3 - 47 uF
  • Add 10 uF capacitor from Vc point (transistor collector and 560 Ω resistor) to T1 output side
  • Install output SMA connector
  • Built SMA to RCA cable
    • Cut in half SMA male-male
    • Made 2 SMA to RCA cables

RF-Amp MICAMP.PNG

Tested[edit]

  • In application output goes to Balanced Modulator
    • Output level should be +7dBm for ADE-1 Mixers
  • Tested into AudioAmp386 - works

Mic Amp LTspice Simulation[edit]

  • Low frequency response can be improved by increasing the value of the emitter bypass capacitor

Mic Amp LTSpice Sim.PNG

  • With 100uF cap across emitter resistor

Mic Amp Ce-100uF LTSpice Sim.PNG

Video[edit]

Assembly Sheet[edit]