A DICTIONARY OF SW-40+ BY PART #...Assumes 40M band
Capacitors
- C2...47pf
- Capacitive voltage divider, in combination with C3. Reduces the RF amplitude of the VFO signal injected into U1 mixer while providing DC isolation.
- C3...10pf
- See C2 above. C2 and C3 also affect the VFO's frequency.
- C4...2700pf
- Part of Q2 Colpitts VFO oscillator.
- C5...2700pf
- Part of Q2 Colpitts VFO oscillator.
- C6...3300pf
- Couples resonant RF energy from L1 into oscillator transistor, while blocking Q2's DC base bias voltage.
- C7...68pf
- Resonant tuning trim capacitor. Tweak to get the VFO into the correct frequency range to cover subsection of 40M band.
- C8...82pf
- Bandspread capacitor. Sets the span of VFO tuning range.
- C9...10pf
- Capacitive voltage divider, in combination with C10. Reduces the RF amplitude of the VFO signal injected into U5 mixer.
- C10...270pf
- See C9 above. C9 and C10 also affect the VFO's frequency.
- C11...47pf
- Part of an L-network (with RFC1) to convert U1's 1500-ohm output impedance down to be compatible with the IF filter.
- C12...150pf
- Increases Y1's series resonant frequency to give the proper (symmetrical) I.F. filter response shape.
- C13...150pf
- Provides proper RF coupling between Y1 and Y2.
- C14...150pf
- Provides proper RF coupling between Y2 and Y3.
- C15...150pf
- Increases Y3's series resonant frequency to give the proper (symmetrical) I.F. filter response shape.
- C16...68pf
- Increases Y4's series resonant frequency above the I.F. filter's center frequency to give about a 800 Hz offset.
- C17...47pf
- Part of the internal Colpitts BFO oscillator in U3.
- C18...47pf
- Part of the internal Colpitts BFO oscillator in U3.
- C19...33nf
- Filters out RF mixing components (mostly 8MHz.), leaving audio frequencies below 1.6 Khz. unattenuated.
- C20...0.1uf
- Audio coupling capacitor - blocks DC output of U3.
- C21...0.1uf
- Audio coupling capacitor - blocks DC output of U3.
- C22...150pf
- Low-pass filter for U4 - attenuates audio above 2Khz.
- C23...150pf
- Low-pass filter for U4 - attenuates audio above 2Khz.
- C24...0.1uf
- Delays receiver audio turn-on after transmitting to avoid clicks, in combination with R8, D6.
- C25...820pf
- Part of U4b's audio bandpass filter (800 Hz).
- C26...2.2nf
- Part of U4b's bandpass filter (800 Hz).
- C27...47uf
- Couples audio to headphones, blocks U4's +8v D.C. output voltage from headphones too.
- C28...47pf
- Part of U5's internal Colpitts transmit-mixer oscillator
- C29...150pf
- Part of U5's internal Colpitts transmit-mixer oscillator
- C30...47pf
- Tunes T2 primary to 7 Mhz. resonance.
- C31...220pf
- Couples RF from T1 to T2, to give nice bandpass frequency response.
- C32...47pf
- Tunes T3 to 7 Mhz. resonance.
- C33...10nf
- Couples RF into Q4 buffer and blocks DC base bias voltage.
- C34...10nf
- Couples RF from Q4 into Q5 and blocks DC voltages.
- C35...10nf
- Couples RF into gate of Q6 and blocks gate bias voltage.
- C36...0.1uf
- Couples RF into PI-filter and blocks Q6's DC output voltage.
- C37...470pf
- Part of PI-low-pass filter.
- C38...1nf
- Part of PI-low-pass filter.
- C39...470pf
- Part of PI-low-pass filter.
- C40...47pf
- Connects receiver to antenna, resonates with RFC3 at 7 Mhz.
- C101..0.1uf
- Supply bypass capacitor keeps stray RF out of U1.
- C102..10nf
- Bypass capacitor to keep RF out of U2.
- C103..10nf
- Keeps noise and RF from modulating the VFO...only DC allowed.
- C104..10nf
- Keeps one of the two inputs of U3 at RF ground potential.
- C105..10nf
- Supply bypass capacitor keeps stray RF out of U3.
- C106..47uf
- Keeps RF and audio noise out of U5's DC supply.
- C107..0.1uf
- Keeps RF and audio noise out of U5's DC bias point.
- C108..10nf
- Keeps one of the two inputs of U5 at RF ground potential.
- C109..10nf
- Keeps RF out of U5's DC supply.
- C110..3.3uf
- Keyclick transmit waveform shaping capacitor.
- C111..10nf
- Keeps driver's RF from coupling to 7.5v DC supply line.
- C112..220uf
- Big current reservoir on 12V DC input supply.
- C113..0.1uf
- Keeps Q6's large RF output off DC supply line.
- C114..0.1uf
- Emitter sees 10 ohms-to-ground for RF, but 61 ohms-to-ground for DC.
Diodes
- D1...MV1662
- A diode whose capacitance varies with applied D.C. voltage.Used as a small variable capacitor to tune VFO frequency.
- D2...1N4148
- The full 8v is too close to maximum acceptable for SE612 chip: D2 drops 8v to 7.4v. Also adds a little RF isolation for U1, U3.
- D3...1N4148
- During receive, clips large +ve-going noise spikes. During transmit, limits gain of U4 by clipping.
- D4...1N4148
- During receive, clips large -ve-going noise spikes. During transmit, limits gain of U4 by clipping.
- D5...1N4148
- Engages mute gate very quickly, by discharging C24. When the key goes up, C24 charges slowly through R8, not D5.
- D6...1N4148
- Negative clamp for Q6. Keeps the R.F. drive generally positive for Q6: it stays "on" for a larger part of the cycle.
- D7...1N4148
- transmit signal clamp. Keeps excessively large RF voltage out of U1 during transmit. D7 and D8 clamp +ve-going RF peaks.
- D8...1N4148
- see D7 above. Two diodes are used in series to allow very large receive signals in without generating distortion.
- D9...1N4148
- transmit signal clamp. See D7. This one's for -ve-going RF peaks.
- D10..1N4148
- see D7, D8, D9 above...this one's for -ve-going RF peaks.
- D11...1N5236
- Avalanche diode sets supply voltage to 7.5 volts DC for U5.
- D12...1N5257
- Avalanche diode clamps excessive RF peaks that might occur with strange antenna loads, protecting Q6.
- D13...1N4001
- DC supply protection diode, prevents damage should input DC supply be connected with wrong polarity.
Transistors
- Q1..MPF102
- Analog switch: OFF during transmit, ON during receive.
- Q2..2N4401
- VFO Colpitts 3MHz. oscillator. Tunes about 40 Khz via D1.
- Q3..2N3906
- PNP transistor switch: ON during transmit, OFF for receive. It pulls the transmit mixer, driver up to 12v during TX.
- Q4..2N4401
- Linear buffer, loads T2,T3 filter very little, but provides low-impedance drive for Q5. Has voltage gain of 1.
- Q5..2N4401
- RF amplifier. A linear amplifier to boost RF power to drive the final amplifier.
- Q6..2SC2078
- Final (Class C, D?) amplifier. Boosts transmit RF power up to 1.5 W. Non-sinusoid output requires filtering to ant.
Resistors
- R1...470
- I.F. filter termination resistor presents the proper load impedance to the crystal filter along with 1500 ohms of U3.
- R2...10k
- Input gain-setting resistor for U4a differential amplifier. Gain is determined by R7/R2. It is large enough to prevent loading down U3's output resistance of 1500 ohm.
- R3...10k
- Part of U4a differential amplifier: required to present a balanced load to U3, and give good common-mode rejection.
- R4...510k
- Sets the D.C. bias point for U4a. Also required to give good common-mode rejection for the differential amplifier.
- R5...
- Not designated
- R6...10
- Supply isolation resistor for U4
- R7...510k
- Sets the gain of differential amplifier, with R2 (see R2).
- R8...1MEG
- Gate bias resistor: Pulls Q1's gate up to source voltage while key is up (receive). Its time-constant, (with C24) keeps the receiver muted for a short time after TX.
- R9...4.7M
- This resistor leaks a little audio past the mute gate during transmit, to provide a sidetone.
- R10...22k
- Bandpass filter input resistor. Sets the bandpass response of U4b amplifier, in combination with C25, C26 and R13.
- R11...510k
- Keeps U4b properly biased while transmitting, otherwise U4b would thump during T/R switching.
- R12...1M
- Sets the DC bias point for U4b.
- R13...1M
- Sets U4b's gain, and bandpass response in combination with R10, C25, and C26. Also required for DC biasing U4b.
- R14...10
- Buffer for low-Z phones - U4b may not like to see strange reactive loads.
- R15...47k
- D.C. base biasing resistor for Q2 VFO oscillator.
- R16...22k
- D.C. base biasing resistor for Q2 VFO oscillator.
- R17...2.2k
- D.C. emitter biasing resistor for Q2 VFO oscillator.
- R18...1M
- Varactor diode biasing resistor - applies the D.C. tuning voltage to D1, with minimum R.F. loading.
- R19...1k
- D.C. dropping resistor sets D11's zener operating current to about 2.5 ma.
- R20...22k
- ensures that Q3 turns off quickly when key goes up.
- R21...10k
- T/R switch base biasing resistor. Provides base current for Q3 when the KEY connects to ground, turning it ON hard.
- R22...10k
- D.C. base biasing resistor for Q4 emitter follower.
- R23...22k
- D.C. base biasing resistor for Q4 emitter follower.
- R24...500
- Emitter biasing for Q4. It is a trimpot that varies the input RF level going into Q5 RF driver.
- R25...2.2k
- D.C. base bias resistor for Q5.
- R26...470
- D.C. base bias resistor for Q5.
- R27...10
- limits the gain of Q5, and keeps it amplifying linearly.
- R28...51
- D.C. emitter bias resistor for Q5.
- R29...100
- Base swamping resistor for Q6 final - damps transients and helps to supply T4 secondary with a somewhat linear load.
Molded Inductors
- RFC1..22uH
- A L-network to match U1's 1500-ohm output resistance to the I.F. filters lower input resistance, with C11.
- RFC2..22uH
- Lower's Y5's series resonant frequency to give 800Hz TX/RX frequency offset.
- RFC3..10uH
- Resonates with C40 to 7 Mhz, coupling antenna to receiver's input.
Toroid Inductors
- L1...T50-6
- VFO tuning inductor. Resonates with (C3+C4) (C4+C5), C6, C7, C8+varactor diode, (C9+C10), at about 3 Mhz.
- L2...FT37-43
- A choke that provides a DC path to the supply for Q6, but presents a large impedance to 7Mhz RF output.
- L3...T37-2
- Part of PI-low-pass output filter.
- L4...T37-2
- Part of PI-low-pass output filter.
Transformers
- T1...
- 7 MHz. tuned transformer provides input selectivity and matches low impedance input to U1's 1500-ohm input resistance.
- T2...
- 7 Mhz. transmit filter rejects other mixer output frequencies.
- T3...
- 7 MHz. transmit filter rejects other mixer output frequencies.
- T4...FT37-43
- Broadband transformer allows Q5 to have high gain, while providing low-impedance drive to Q6.
Integrated Circuits
- U1...SE612
- A mixer/oscillator chip used here to convert 7 MHz. receiver RF down to 4 Mhz. I.F. frequency. The oscillator is unused - the local oscillator is coupled in from Q2 (VFO).
- U2...78L08
- Three-pin low-current voltage regulator outputs +8v DC.
- U3...SE612
- A mixer/oscillator chip used here to convert 4 Mhz. I.F. signals down to audio. A 4 Mhz. crystal oscillator is included.
- U4...NE5532
- A dual op-amp. Two low-noise amplifiers are used to amplify audio linearly and to drive headphones.
- U5...SE612
- A mixer/oscillator chip used here to convert 3 Mhz. VFO RF up to 7 Mhz. for the transmit amplifier. A 4 Mhz. crystal oscillator is included.
Crystals
- Y1...4MHz.
- Used in combination with Y2, Y3 to make a narrow bandpass Cohn filter to provide signal selectivity.
- Y2...4MHz
- See Y1.
- Y3...4MHz.
- See Y1.
- Y4...4MHz.
- U3 contains a transistor(s) arranged as a Colpitts oscillator using Y4 to provide 4 MHz. RF to convert IF frequencies to audio.
- Y5...4MHz.
- U5 contains a transistor(s) arranged as a Colpitts oscillator using Y5 to provide 4 MHz. RF to up-convert the 3 MHz. VFO to the 7 MHz. band.