Difference between revisions of "RF-Amp"

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[[File:RF-Amp_Front.png]]
+
[[File:RF-Amp_P1943-720px.jpg]]
  
 
== RF Amplifier Features ==
 
== RF Amplifier Features ==
  
−
* From [https://zl2ctm.blogspot.com/2020/11/go-qrp-portable-ssb-rig.html Charlie Morris' (ZL2CTM) Go QRP Portable SSB Rig]
+
* Class A (Common Emitter) Amplifier
−
** Solid State Design for the Radio Amateur?
+
** Emitter resistor bypassed with capacitor for higher AC gain
−
* +22 dB gain
+
** Transformer coupled input/output for impedance matching to 50Ω
−
* Input connectors: SMA or BNC
+
** 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
 
* 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 ==
  
−
=== Schematics ===
+
=== Schematic ===
  
 
[[file:RF_Amp_Schematic-4.PNG]]
 
[[file:RF_Amp_Schematic-4.PNG]]
  
−
=== DC operating point ===
+
== 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
 +
** +28.4 dB at 9 MHz
 +
 
 +
[[File: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
 +
 
 +
[[File:RF-AMP-Rev2_LTSPICE.PNG]]
 +
 
 +
== Charlie Morris Design Calculations ==
 +
 
 +
* 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
  
−
* Ice = 10 mA
+
=== Beta DC ===
−
* Ve = 0.1 * Vcc = 1.2V
 
  
−
=== Input/Output Transformer ===
+
* Geometric mean min/max beta at operating current
 +
** =sqrt(100*300) = 173
  
−
==== [http://toroids.info/FT37-43.php FT37-43] Toroid ====
+
=== Beta AC ===
  
−
* Wideband Transformers 5 - 400 MHz
+
* Gain bandwidth product divided by operating frequency
−
* Power Transformers 0.5 - 30 MHz
+
** Assume operating frequency of 9 MHz (IF frequency)
 +
** = 300/9 = 33.3
  
−
[[file:FT37-43_10_Turns.PNG]]
+
=== 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 Transformer ====
+
=== Input/Output Transformers ===
  
−
** Input Transformer (T1 on Charlie's - T2 on this board)
+
* Using [http://toroids.info/FT37-43.php FT37-43 Toroid]
−
***  50:75.8 Ohms = 1 : 1.23 turns ratio
 
−
**** 9 turns primary, 11 turns on secondary
 
  
−
==== Output Transformer ====
+
[[file:FT37-43_10_Turns.PNG]]
  
−
** Output transformer (T2 on Charlie's - T1 on this board)
+
==== Tracks ====
−
*** 200:50 Ohms = 2:1 turns ratio
 
−
*** 10 turns primary (on transistor collector), 5 turns secondary (towards output)
 
  
−
== LT Spice Simulation ==
+
[[file:RF-Amp-tracks.PNG]]
  
−
=== Transformer 1.5 uH ===
+
==== Input Transformer ====
  
−
[[File:RF-AMP-LTSPICE.PNG]]
+
* 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 [http://toroids.info/FT37-43.php 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
  
−
=== Transformer 35 uH ===
+
[[file:RF-Amp-T2.PNG]]
  
−
[[File:RF-AMP-LTSPICE_35uH.PNG]]
+
==== Output Transformer ====
  
−
== Charlie Morris Schematics ==
+
* 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
  
−
* From [https://zl2ctm.blogspot.com/2020/11/go-qrp-portable-ssb-rig.html Charlie Morris' (ZL2CTM) Go QRP Portable SSB Rig]
+
[[file:RF-Amp-T1.PNG]]
  
−
=== IF AMP ===
+
=== Charlie's Notes ===
  
 
[[FILE:IF Amp_0046A.jpg]]
 
[[FILE:IF Amp_0046A.jpg]]
Line 69: Line 207:
  
 
[[FILE:IF Amp_0047C.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 Ω 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 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]]
 +
 +
[[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 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 [[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]]
 +
 +
== 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]]
 +
 +
[[FILE: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 ===
 +
 +
* Electret Condenser Microphone
 +
** 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)
 +
 +
[[file:KY-037.jpg]]
 +
 +
* Install Electret Condenser Microphone on small perf board
 +
* 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]]
 +
 +
=== 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
 +
 +
[[FILE: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
 +
 +
[[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

  • 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

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