Yes, there is a spike, but one can control that by putting a diode across
the relays coil or a zener diode across the collector and emitter of the
transistor, just a shade higher than the operating voltage. When a spike
develops, it's clamped. A switching transisor for this could be isolated
also, in that it's emitter would only go to an insulated jack on the
transceiver. This way it would only see the relay coil. However, I like
the relay better as it should be used if a higher current rating is
needed. Evidently, that relay in question is a weakling.
Best,
Will
On Fri, 4 Feb 2005 15:52:03 -0500, Bolbach, Timothy <TBolbach@ssoe.com>
wrote:
Will,
By using a relay the switching currents and voltage spikes
encountered when completing the inductive amplifier relay circuit is
isolated from the transceiver ground plane. Also, the circuit minimizes
a path back into the transceiver for RF feedback. By using a transistor
output, the transistor would have to be referenced to the transceiver
ground. Unless, of course, it is opto isolated, well.... that's a
different story. - KD8CN = Tim
-----Original Message-----
From: Will Matney [mailto:craxd1@ezwv.com]
Sent: Friday, February 04, 2005 3:21 PM
To: Amps@contesting.com
Subject: Re: [Amps] IC-718 and AL-811: Icom manual misleading,interface
necessary according to Icom technician
I believe if it were me, and I were building transceivers, that I would
make sure it would switch everything out there, including the oldies.
That
just sounds like an awful small amount of switching power either way it
goes. Ameritron says its at 100 mA on their switching, and that actually
may be a little high as I imagine it switching a 12 Vdc DPDT 10 amp
contact relay. I know using either a 2N2222A or even a 2N3904 will
switch
those with no overloading of the transistor, they run as cool as a
cucumber. If that little relay is that small, I would have just used one
of those transistors in it's place, switching to ground. I think, if I
recall, Rich Measures has a schematic on his website for converting some
of the old amps to low voltage, low current, switching. See, to me, I
dont
think an end user ought to have to do this, it ought to be there to
begin
with in the transceiver. I'll almost bet that what they pay for that
little relay is more than the cost of the transistors!
Best,
Will
On Fri, 04 Feb 2005 12:08:02 -0800, <gdaught6@stanford.edu> wrote:
Hi Will,
I wonder if you got a reply from someone that dont know what they're
talking about by the sounds of it. Heck, a small 2N2222A will switch
the load there with room to spare.
The transistor switch is what I use: I simply installed one in my
amplifier, so it pretty much doesn't care what the source of the T/R
switch signal is.
Surely, they dont have the
switching coming straight off an IC? I dont have a schematic of it
here to look at and see what they've done, but that just dont sound
right. Also, if it has an actual internal relay, even a small reed
type at that, it sould switch that amount.
No, it's not an IC, it's a small relay. My (contesting) experience
was that the contacts would begin to stick, even when switching well
within their specified voltage & current.
When they said "either" 16
volts or 2 amps, but not both, is a bunch of hogwash. It just sounds
to me like a ploy to get around warranty work no matter what!
I don't know. I've had nothing but good experiences with Icom. But
the T/R switch output is way happier seeing my 0.6v @ 2ma load than it
was seeing my 12V relay.
73,
George T. Daughters, K6GT
__________ NOD32 1.880 (20040928) Information __________
This message was checked by NOD32 antivirus system.
http://www.nod32.com
--
Using Opera's revolutionary e-mail client: http://www.opera.com/mail/
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|