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G8MNY > TECH 06.02.07 10:00l 42 Lines 1771 Bytes #999 (0) @ WW
BID : 1630_GB7CIP
Read: DL8FBH GUEST DL1GMC OE7FMI
Subj: PTT line for Drake L-4B PA
Path: DB0FHN<DB0FOR<DB0MRW<DK0WUE<DB0RES<TU5EX<ON0BEL<GB7CIP
Sent: 070206/0817Z @:GB7CIP.#32.GBR.EU #:1630 [Caterham] $:1630_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Updated Aug 06)
(8 Bit ASCII Graphics use code page 437 or 850)
THE PROBLEM
If wired directly to a IC735 Tx send connector, the IC735 relay contacts weld
up with the linear relay's back emf.
L I N E A R I C 7 3 5
14V S4 _____ SEND PTT
())))Ä´>ÃÄÂÄÄÄÂÄ/oÄ´relayÃÄÂÄ´>ÃÄÄo o)ÄÄ \ Tx
===== === ³ ~~~~~ ³ PTT ³ ³ reed
100u³ 2k2 10n=== GND ³ ³ relay
ÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄo ÀÄÄÄÄÁÄÄÄ
This old large valve HF PA used an inductive 12V PTT relay that is run on 18V.
MY CURE
Not wishing to modify either pieces of kit, I chose to find a simple fool proof
solution in the inter connecting lead.
To stop the back emf & inrush current to the IC735's reed relay SEND contact,
I added a 35V 4u7 in series with a 100ê across linear's PTT 2 pin plug.
L I N E A R I C 7 3 5
14V S4 _____ P L U G SEND PTT
())))Ä´>ÃÄÂÄÄÄÂÄ/oÄ´relayÃÄÂÄ´>ÃÄÄÄo ÄÄÂÄÄÄÄÄÄÄÄÄÄ(o o)ÄÄ \ Tx
===== === ³ ~~~~~ ³ PTT 100ê ³ ³ ³ reed
³ ³ ³ ³+ ³ ³ ³ relay
100u³ 2k2 10n=== GND === 4u7 ³ ³ ³
ÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄo ÄÄÁÄÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÁÄÄÄ
L E A D
The added operate & release delay is not detectable (1mS?), & there is no
longer a spark & shocking back emf if U manually earth the phono plug etc.
Why Don't U send an interesting bul?
73 de John, G8MNY @ GB7CIP
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