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G8MNY > TECH 25.03.20 11:42l 55 Lines 2322 Bytes #999 (0) @ WW
BID : 49902_GB7CIP
Read: GUEST
Subj: DC/RF Sensing PA Switching
Path: IW8PGT<IZ3LSV<I3XTY<I0OJJ<I0OJJ<GB7CIP
Sent: 200325/0934Z @:GB7CIP.#32.GBR.EURO #:49902 [Caterham Surrey GBR]
>From g8mny%gb7cip.#32.gbr.euro@i0ojj.ampr.org Wed Mar 25 10:40:42 2020
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>From: g8mny@gb7cip.#32.gbr.euro
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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, but 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 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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