Difference between revisions of "RF-Amp"

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== RF Amplifier Features ==
 
== RF Amplifier Features ==
  
* Useful as an IF or Antenna Amplifier
+
* Class A (Common Emitter) Amplifier
* From [https://zl2ctm.blogspot.com/2020/11/go-qrp-portable-ssb-rig.html Charlie Morris' (ZL2CTM) Go QRP Portable SSB Rig]
+
** Emitter resistor bypassed with capacitor for higher AC gain
** Charlie references Solid State Design for the Radio Amateur (pp 19-20)
+
** Transformer coupled input/output for impedance matching to 50Ω
 +
** Capacitively coupled input
 
* Single 2N3904 NPN transistor
 
* Single 2N3904 NPN transistor
** Ft = 300 MHz (Gain Bandwidth Product)
+
* Useful as an gain block in various applications
*** Theoretical gain
+
** Radio Transmitter/Receiver IF Amplifier
**** +20 dB at 30 MHz
+
** Radio Transmitter/Receiver Antenna Amplifier
**** +29.5 dB at 10 MHz
+
** Radio Transmitter Microphone amplifier (with minor modifications)
**** Reality is lower due to capacitance, etc.
+
* As RF Amplifier
* Measured +22 dB gain @12V, +25dB gain @14V
+
** Measured Gain Bandwidth (GBW) of 150
* Input connectors: SMA or BNC
+
** 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
 
* +12V nominal power
 +
** 12-14 VDC
 +
** 5 mm terminal block for power
 
* 49x49mm card
 
* 49x49mm card
 
* 4x 4-40 mounting holes
 
* 4x 4-40 mounting holes
 +
 +
=== Source Materials ===
 +
 +
* 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)
 +
 +
=== HFE at 10 mA ===
 +
 +
[[file:HFE_10mA.PNG]]
  
 
== RF Amplifier Design ==
 
== RF Amplifier Design ==
Line 25: Line 42:
  
 
== LT Spice Simulation ==
 
== LT Spice Simulation ==
 +
 +
=== As Built - Rev 1 ===
  
 
* [https://github.com/land-boards/lb-boards/blob/master/HamRadio/RF-Amp/LTSpice/2n3904%20amp.asc LTspice Simulation] - GitHub source file
 
* [https://github.com/land-boards/lb-boards/blob/master/HamRadio/RF-Amp/LTSpice/2n3904%20amp.asc LTspice Simulation] - GitHub source file
Line 31: Line 50:
 
[[File:RF-AMP-LTSPICE_XFMRS.PNG]]
 
[[File:RF-AMP-LTSPICE_XFMRS.PNG]]
  
== Charlie Morris Design ==
+
=== Additional Resistor ===
 +
 
 +
* 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
 +
 
 +
[[File:RF-AMP-Rev2_LTSPICE.PNG]]
 +
 
 +
== Charlie Morris Design Calculations ==
  
 
* From Charlie's notes with mods for my use
 
* From Charlie's notes with mods for my use
Line 56: 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 64: 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 78: 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 90: 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 125: 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 150: 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 184: 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 190: 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 216: 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 229: Line 258:
 
[[file:RF-Amp_S21_40dBAttenOutput_1-30MHz.png]]
 
[[file:RF-Amp_S21_40dBAttenOutput_1-30MHz.png]]
  
=== Measure Input Impedance ===
+
== W2AEW S11 Measurement Method ==
 +
 
 +
* 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
 +
 
 +
<video type="youtube">7TtKE39TWpI</video>
 +
 
 +
* Calibrate NanoVNA using External 30 dB Attenuator
 +
** See [https://youtu.be/7TtKE39TWpI W2AEW #337 video] above
 +
** 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]]
 +
*** [[NanoVNA#RF_Demo_Kit|NanoVNA RF Demo Kit]] has similar connectors, etc to RF Amp
 +
* 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 ===
 +
 
 +
* 9 MHz measurements
 +
** 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
 +
* 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
 +
 
 +
[[file:RF-Amp_U2_W2AEW_S21_1-30MHz.png]]
 +
 
 +
[[file:RF-Amp_U2_W2AEW_S11_1-30MHz.png]]
 +
 
 +
== Compare RF Amp vs Kits and Parts Amp ==
 +
 
 +
* RF-Amp
 +
** [https://media.digikey.com/pdf/Data%20Sheets/NXP%20PDFs/2N3904.pdf 2N3904 transistor]
 +
** Ft is is 300
 +
** Measured at 150 GBW
 +
* [[Kits_and_Parts_Universal_Wideband_Small_Signal_RF_Amplifier|Kits and Parts - Universal Wideband Small Signal RF Amplifier]]
 +
** [https://www.onsemi.com/pdf/datasheet/2sc5551a-d.pdf 2SC5551A transistor]
 +
** Much higher Ft 3.5 GHz
 +
*** Gain is much flatter over bandwidth
 +
**** 1.5 Mhz = 26.6 dB
 +
**** 30 Mhz = 24.9 dB
 +
** Good as broadband amplifier
 +
* Both would be equivalent at 9 MHz as IF Amp
 +
* Kits and Parts would be better as Antenna Amplifier
 +
* RF Amp card current draws 11 mA
 +
* Kits and Parts  card current draws 30 mA
 +
 
 +
== Use of Card as a Microphone Amp ==
 +
 
 +
[[file:MicAmp_P1946-720px.jpg]]
 +
 
 +
* Charlie's video
 +
 
 +
<video type="youtube">iVxN4u9EVj8</video>
 +
 
 +
=== Charlie's Schematic/Calculations ===
 +
 
 +
* [https://zl2ctm.blogspot.com/2020/02/ Charlie's page]
 +
* This was from a couple of months later than the video
 +
 
 +
[[file:Mic_Amp_1A.jpg]]
 +
 
 +
[[file:Mic_Amp_1B.jpg]]
 +
 
 +
[[file:Mic_Amp_2.jpg]]
 +
 
 +
=== Test with Electret Microphone ===
 +
 
 +
[[FILE:MicAmp_P1947-720px.jpg]]
  
* Shows VSWR at 14.4 MHz = 1.56:1
+
[[FILE:MicAmp_P1949-720px.jpg]]
* At 9 MHz
 
** VSWR = 1.7:1
 
** Impedance = 81-j10
 
  
[[file:RF-Amp_AttenOutput_VSWR_2021_1-30MHz.png]]
+
* 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
  
=== Change Input Transformer turns ratio ===
+
=== Wiring up Mic to Amp ===
  
* Above had 9:11 turns ratio
+
* Electret Condenser Microphone
* Change to 7:9 turns ratio
+
** Removed from [https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313&_nkw=KY-037&_sacat=0 KY-037 microphone] (Arduino sensor card)
* 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]]
+
[[file:KY-037.jpg]]
  
* New turns improved the input VSWR slightly
+
* Install Electret Condenser Microphone on small perf board
* Was: At 9 MHz, VSWR = 1.7:1, Impedance = 81-j10
+
* Cable using 18" RG-174 coax to input of RF Amp card
* After: At 9 MHz, VSWR = 1.6:1, Impedance = 76.7-j12
 
  
[[file:RF-Amp_vswr_40dBAttenInput_Turns7to9_1-30MHz.png]]
+
[[FILE:MicAmp_P952-720px.jpg]]
  
==== Tune input transformer====
+
=== Schematic Mods ===
  
* Isolate output by replacing output transformer with 200 resistor
+
[[FILE:RF_Amp_Schematic-MODS.png]]
* 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]]
+
=== Part Value Changes ===
  
* With output transformer
+
* No transformers
* Slightly better with 1 extra winding
+
** 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
  
[[file:RF-Amp_VSWR_1-30MHz_7to10Turns-2.png]]
+
[[FILE:RF-Amp_MICAMP.PNG]]
  
== W2AEW Measurement Method ==
+
=== Tested ===
  
* See [https://youtu.be/7TtKE39TWpI W2AEW #337 video] below
+
* In application output goes to Balanced Modulator
* Insert 20 dB attenuator and calibrate with attenuator installed
+
** Output level should be +7dBm for ADE-1 Mixers
* Open/sort/thru at the output side of the attenuator
+
* Tested into [[AudioAmp386]] - works
  
[[file:RF-Amp_W2AEW_S21_1-30MHz.png]]
+
=== Mic Amp LTspice Simulation ===
 +
 
 +
* Low frequency response can be improved by increasing the value of the emitter bypass capacitor
 +
 
 +
[[FILE:Mic_Amp_LTSpice_Sim.PNG]]
 +
 
 +
* With 100uF cap across emitter resistor
  
[[file:RF-Amp_W2AEW_S11_1-30MHz.png]]
+
[[FILE:Mic_Amp_Ce-100uF_LTSpice_Sim.PNG]]
  
 
== Video ==
 
== Video ==
 
<video type="youtube">7TtKE39TWpI</video>
 
  
 
<video type="youtube">CHdtoupH2Vg</video>
 
<video type="youtube">CHdtoupH2Vg</video>

Latest revision as of 22:30, 15 November 2021

RF-Amp P1943-720px.jpg

RF Amplifier Features

  • 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

HFE at 10 mA

HFE 10mA.PNG

RF Amplifier Design

Schematic

RF Amp Schematic-4.PNG

LT Spice Simulation

As Built - Rev 1

RF-AMP-LTSPICE XFMRS.PNG

Additional Resistor

  • 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

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 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

  • 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

  • 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

  • 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

FT37-43 10 Turns.PNG

Tracks

RF-Amp-tracks.PNG

Input Transformer

  • 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

  • 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

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

  • 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

  • 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

  • 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

  • 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

  • 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

  • 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

  • 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

Use of Card as a Microphone Amp

MicAmp P1946-720px.jpg

  • Charlie's video

Charlie's Schematic/Calculations

Mic Amp 1A.jpg

Mic Amp 1B.jpg

Mic Amp 2.jpg

Test with Electret Microphone

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

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

RF Amp Schematic-MODS.png

Part Value Changes

  • 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

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

Mic Amp LTspice Simulation

  • 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

Assembly Sheet