HF phone rig for 20-40 meter band

  
A simple project, within most of homebrewers capabilities. Very simple tuning, a single stage to align, besides VFO frequency adjusting. Easy to find, cheap components. Reduced dimensions and low power requirement, a totally portable rig. It's worth while to spend some words about the DSB modulation. It's simply a type of amplitude modulation (AM). It is common knowledge that an AM signal is composed by a carrier and two sidebands, wich take the whole information. The figure below represents an AM signal at 14.000 KHz, modulated with a 5 KHz bandwide BF signal.
HF phone rig for 20-40 meter band - schematic

The receiver is a direct conversion unit. It is composed by a double tuned preselector, equipped with a BF965 mosfet, delivering a 10 dB gain, and a product detector using a "classic" NE602 (2) (further 18 dB of gain). A variable capacitor C4 allows to adjust the sensitivity according to the connected antenna, so we may find a right compromise to limit the effects of the strong broadcastings operating at the band edges. The detected audio is amplified by a 2N2222 transistor and an LM386 (3) IC delivering a few hundreds mW into an 8 Ohm speaker. RLYA MIC +12 +12 PTT +12 +12 TX RLY VFO U2 NE602 U1 LM386 RX RX TX +12 RLYB +12 TX TX TR2 BF965 TR1 2N5320 C41 220n C33 1n DZ1 6.8V C38 100m C40 10n C37 220n R24 10K C36 10n C24 100m C23 100n C25 220m R14 10 C26 100n R17 18K C30 22n C29 10m C31 1n L5 100m R18 1K R19 82K R4 56K R5 82K R6 68 K R7 150 C16 4.7 D1 1N4001 R22 470 R10 470 C27 10m R15 470 XTAL C1 C2 L1 L2 22m C6 100n C4 60p C7 100n R1 2.2 C8 1n R2 5.6 R3 47 C9 100n L3 C13 60p C14 C15 10n +12 RX +12 RX R23 22K TR4 2N2222 C11 100m C10 100n C17 10n C18 10n C19 C20 60 C21 100m C22 100n L4 C5 100p C32 100n C34 C35 R9 10K R13 1K KEY R20 10K C3 100n R8 10 TR3 2N2222 R16 47K D2 1N4001 R21 3.3K R12 15 C28 10n R11 1K D3 1N4148 C12 10n C39 10n RLYA...



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