From: Gordon Croft <gordon.croft@telus.net>
To: linux-ham <linux-hams@vger.kernel.org>
Subject: PTT problem
Date: Sun, 07 Nov 2004 14:57:34 -0800 [thread overview]
Message-ID: <418EA85E.6050706@telus.net> (raw)
Hello list,
I'm new to packet radio and am not as good at circuit design as I should
be!!:)
I've built a circuit to interface the serial port RTS signal to the
radio PTT line.
The radio is an old ICOM IC-20 and I checked to make sure it has a
positive voltage (+12V) on the PTT line . If I ground the PTT lead, it
keys the transmitter, so I think the radio is working correctly.
The circuit I built uses an opto Isolator (NTE3040).
I tried to send the circuit lay-out but the server rejected my message...
When I check the current flow on the PTT side of the opto isolator with
the computer trying to key the transmitter, I see about 14 mA and the
transmitter on the radio does not operate. If I just connect the PTT
line to ground through the ammeter, I see about 125 mA and the
transmitter does send. Is it possible that the opto isolator is
presenting too high a resistance and there's not enough current flow to
activate the transmitter? If so, how could I correct the problem?
next reply other threads:[~2004-11-07 22:57 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-11-07 22:57 Gordon Croft [this message]
-- strict thread matches above, loose matches on Subject: below --
2004-05-27 11:10 PTT problem Vittorio Vallero
2004-04-28 9:48 Vittorio Vallero
2004-05-04 2:35 ` Rodolfo Brasnarof
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