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G8MNY > TECH 21.08.06 23:29l 42 Lines 1772 Bytes #999 (0) @ WW
BID : 43042_GB7CIP
Read: DL1LCA DL1RX DL8FBH GUEST OE7FMI
Subj: PTT line for DRAKE L-4B PA
Path: DB0FHN<DB0FOR<DB0MRW<DK0WUE<DB0RES<ON0AR<GB7CIP
Sent: 060820/2311Z @:GB7CIP.#32.GBR.EU #:43042 [Caterham] $:43042_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 18 V.
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 reley 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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