Difference between pages "File:RF-Amp W2AEW S11 1-30MHz.png" and "RF-Amp"

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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 ==
 +
 +
* 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
 +
* Re-calibrate at 1.5-31.5 MHz
 +
* 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]]
 +
 +
== 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]]

Revision as of 12:16, 13 November 2021

RF-Amp P1943-720px.jpg

RF Amplifier Features

  • Useful as an IF or Antenna Amplifier
  • From 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

RF Amp Schematic-4.PNG

LT Spice Simulation

RF-AMP-LTSPICE XFMRS.PNG

Charlie Morris Design

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

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 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 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

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

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 ohms for S11 measurement
  • DC current = 12 mA

Measure S21

  • Put 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

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 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 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

Measure Input Impedance

  • Shows VSWR at 14.4 MHz = 1.56:1
  • At 9 MHz
    • VSWR = 1.7:1
    • Impedance = 81-j10

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

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

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

RF-Amp VSWR 1-30MHz 7to10Turns.png

  • With output transformer
  • Slightly better with 1 extra winding

RF-Amp VSWR 1-30MHz 7to10Turns-2.png

W2AEW Measurement Method

  • See 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
  • Scan 1-30 Mhz
    • Overdriven at 1 MHz
  • Re-calibrate at 1.5-31.5 MHz
  • 9 MHz measurement
    • 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

Video

Assembly Sheet

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