G8MNY > TECH 14.03.24 10:30z 47 Lines 1989 Bytes #186 (0) @ WW BID : 3256_GB7CIP Read: GUEST Subj: DC/RF Sensing PA Switching Path: ED1ZAC<ED1ZAC<GB7CIP Sent: 240314/1015Z @:GB7CIP.#32.GBR.EURO #:3256 [Caterham Surrey GBR] $:3256_GB From: G8MNY@GB7CIP.#32.GBR.EURO To : TECH@WW By G8MNY (Graphics updated Dec 03) (8 Bit ASCII graphics use code page 437 or 850, Terminal Font) For PA with RF/DC sense switching (as some rigs put out DC on Tx), that used a diode to detect any +ve signals (RF/DC) from the transceiver to operate the PA PTT system.... The time constants are OK for SSB & FM. The 22uF can be omitted for FM only. TR1 & 2 BC107 etc, TR3 a TIP type PNP, D1 RF diode 1N4148 etc. D2 1N4001. Rig o)ÄÄÂÄÄÄÄÂÄÄ´ÃÄÄÄÄ> RF to Drive Relay ³ 100K _³_ 1n ³ ³ \_/ ______+12-24V ³ ³ ³D1 ³/e ³ ³ ³ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄ´ TR3 ³ ³ 22K ³ ³ ³\ PNP ³ ³ ³ ³ Ext oÄÄ¿ 470 ³ +Tx ³ ³ ³ ³/ PTT ³ LED ³ ÃÄÄÄÄ> Drive, O/P, ³ ³ ÃÄÄÄÄ´ TR1 ÃÄÄÄÄ´<ÃÄÄÙ ³ Bias, & ³ ³ ³ ³\e ³/ ³ Fan Relays ³ ³ === ÃÄÄ47KÄÂÄÄÄÄ´ TR2 ³ ³ ³ ³10n ³+ ³ ³\e ³ ³ ³ ³ === ÃÄÄÄÄÄÄ)ÄÄÄÄ150KÄÄÄÄÄÄÄÄ´ ³ ³ ³ ³22u ³ ³ +ve _³_ ³ ³ ³ ³ 10K ³ feedback /_\ ³ ³ ³ ³ ³ ³ D2 ³ ÄÁÄÄÁÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄ HOW IT WORKS D1 detects RF & passes any rig DC to turn on TR1. TR1 turning on charges up the 22uF & makes TR3 initially conduct to give fast Tx attack. When 22uF is over 2V TR2 is turned on & passes higher base current into TR3 via a Tx LED ensuring it is well turned on. The 150K +ve feedback ensure snap action (too low & it may not switch off!) External PTT earth can be put in/out on TR2 collector. I have found it was heat sensitive, due to the sensitivity of the 1st NPN. Why Don't U send an interesting bul? 73 De John, G8MNY @ GB7CIP
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