View source for RF-Amp

[[File: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 ===

* 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 ==

=== Schematic ===

[[file:RF_Amp_Schematic-4.PNG]]

== 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

=== 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 ===

* 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 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

[[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 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

[[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 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 type="youtube">CHdtoupH2Vg</video>

<video type="youtube">YJTsWV2kzFY</video>

<video type="youtube">xPFzFhM0ojE</video>

== Assembly Sheet ==

* [[RF Amplifier Assembly Sheet]]