# Two\-Transistor FM Transmitter

## Description

Compact 9 V, through\-hole FM voice transmitter based on the approachable two\-transistor Instructables/Art Swan topology, with improved bias stability, separated audio/RF supply filtering, edge\-accessible LC tuning, and capacitively coupled antenna output on a 2\-layer PCB\.

## Project Details

- **Owner:** tratzum
- **Created:** 8/27/2026
- **Last Updated:** 8/27/2026
- **Visibility:** Public

## Key Components

### CT1 — [Generic Capacitor](https://flux.ai/jharwinbarrozo/generic-capacitor~1d.md)

- Voltage Rating: 50V
- Capacitor Type: Air/ceramic trimmer, C0G characteristic
- Package: C\_Disc\_D5\.0mm\_W2\.5mm\_P5\.00mm
- Role Details: Edge\-accessible hobby trimmer in parallel with L1; lead spacing hardware\-dependent
- Role: Tuning
- Functional Group: RF Oscillator
- Part Type: Non\-Polarized Capacitor
- Capacitance: 5\-30pF

**Pins:**
- P1 [pin 1]
- P2 [pin 2]

### J1 — [Pin Header 01x02 2\.54mm Vertical](https://flux.ai/jharwinbarrozo/generic-pin-header-01x02-2p54mm-vertical~4uy.md)

- Role: Power Connector
- Functional Group: Power Input
- License: https://creativecommons\.org/licenses/by/4\.0/
- Role Details: Pin 1 BAT9V positive, pin 2 GND
- Part Type: Connector

**Pins:**
- P1 [pin 1]
- P2 [pin 2]

### J2 — [Pin Header 01x02 2\.54mm Vertical](https://flux.ai/jharwinbarrozo/generic-pin-header-01x02-2p54mm-vertical~4uy.md)

- Role: Audio Input
- Manufacturer Name: uxcell / user\-supplied
- Connector Positions: 2
- Allow Substitutes: Adaptable 5\-6 mm cylindrical electret capsules; verify polarity and lead fit
- Connector Type: Electret microphone capsule
- Role Details: Direct\-mounted cylindrical electret capsule; adaptable 6\.4 mm body outline, 2\.54 mm nominal pin spacing with 1\.1 mm plated holes\. Pin 1 = MIC\_POS \(\+\); pin 2 = GND and metal case/negative\.
- License: https://creativecommons\.org/licenses/by/4\.0/
- Functional Group: Audio Preamplifier
- Manufacturer Part Number: Amazon ASIN B00LUUHB1K
- Mount: Through Hole
- Product Info Url: https://www\.amazon\.com/dp/B00LUUHB1K
- Part Type: Connector

**Pins:**
- P1 [pin 1]
- P2 [pin 2]

### J3 — [Pin Header 01x02 2\.54mm Vertical](https://flux.ai/jharwinbarrozo/generic-pin-header-01x02-2p54mm-vertical~4uy.md)

- Mount: Surface Mount
- Manufacturer Name: bnafes / user\-supplied
- Functional Group: RF Output
- Package or Case Code: Adaptable 1\.6 mm edge\-launch, 4 mm contact spacing
- Connector Type: SMA edge launch
- Allow Substitutes: Common 1\.57\-1\.6 mm board edge\-launch SMA; first\-article fit required
- Role Details: Adaptable 1\.6 mm PCB edge\-launch SMA female\. Pin 1 = ANT\_OUT center tongue; pin 2 = all top/bottom ground tabs\. Footprint uses 4 mm ground\-tab center spacing and flush board\-edge lands; first article must be test\-fitted\.
- License: https://creativecommons\.org/licenses/by/4\.0/
- Manufacturer Part Number: Amazon ASIN B07GXSN7VS
- Connector Positions: 1 RF \+ ground tabs
- Product Info Url: https://www\.amazon\.com/dp/B07GXSN7VS
- Connector Gender: Female
- Role: RF Output
- Part Type: Connector

**Pins:**
- P1 [pin 1]
- P2 [pin 2]

### Q1 — [2N3904TA](https://flux.ai/lcsc/2n3904ta~z5rj.md)

- Functional Group: Audio Preamplifier
- Product Info Url: https://lcsc\.com/product\-detail/Transistors\-NPN\-PNP\_ON\-Semicon\_2N3904TA\_ON\-Semicon\-ON\-2N3904TA\_C258184\.html
- LCSC Part Number: C258184
- Role Details: Divider\-biased electret microphone preamplifier
- JLCPCB Part Class: Extended Part
- Manufacturer Part Number: 2N3904TA
- Datasheet URL: https://storage\.googleapis\.com/graviton\-electric\-symbols/document\_assets/lcsc/2109100930\_onsemi\-2N3904TA\_C258184\.pdf
- Manufacturer Name: onsemi\(安森美\)
- Role: Audio Amplifier
- Part Type: Bipolar Transistors \- BJT
- Package or Case Code: TO\-92\-3\_L4\.9\-W3\.7\-P2\.54\-L

**Pins:**
- B [pin 2]
- C [pin 3]
- E [pin 1]

### Q2 — [2N3904TA](https://flux.ai/lcsc/2n3904ta~z5rj.md)

- Product Info Url: https://lcsc\.com/product\-detail/Transistors\-NPN\-PNP\_ON\-Semicon\_2N3904TA\_ON\-Semicon\-ON\-2N3904TA\_C258184\.html
- LCSC Part Number: C258184
- Role: RF Oscillator
- JLCPCB Part Class: Extended Part
- Role Details: Common\-base VHF oscillator; pins 1=E, 2=B, 3=C
- Manufacturer Part Number: 2N3904TA
- Datasheet URL: https://storage\.googleapis\.com/graviton\-electric\-symbols/document\_assets/lcsc/2109100930\_onsemi\-2N3904TA\_C258184\.pdf
- Manufacturer Name: onsemi\(安森美\)
- Part Type: Bipolar Transistors \- BJT
- Functional Group: RF Oscillator
- Package or Case Code: TO\-92\-3\_L4\.9\-W3\.7\-P2\.54\-L

**Pins:**
- B [pin 2]
- C [pin 3]
- E [pin 1]

*The full schematic, PCB layout, bill of materials, and interactive design are available at [https://flux\.ai/tratzum/two\-transistor\-fm\-transmitter\~cc](https://flux.ai/tratzum/two-transistor-fm-transmitter~cc).*

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*Generated from [https://flux\.ai/tratzum/two\-transistor\-fm\-transmitter\~cc](https://flux.ai/tratzum/two-transistor-fm-transmitter~cc)*