On Oct 24, 2007, at 12:37 AM, John Barrett wrote:
> Re splitting the simplex: a circulator with the radio hooked to the
> input, the transmit chain on the standard output, and the receive
> chain feeding the load port is what I was thinking – a relay would
> do the job just as well, but would require changes to the PC based
> Packet Engine software to support flipping the relay before and
> after transmitting. I don’t think that’s a built in feature, and
> source code is not available.
Whoa whoa whoa, wait... one of your goals snuck into the last two e-
mails... you're using the isolator to split TX/RX on a rig that has a
single RF connector???
So you're just trying to figure out how to "split" a radio that
doesn't have a separate TX/RX and uses a single RF connector...?
Did I misinterpret what you're trying to do there? If all you're
looking to do is split TX/RX in the "simplex" radios, that's a lot
easier than you think -- no isolator required.
That can be done a number of ways...
1. Coaxial RF-rated relay... triggered by PTT logic signal, perhaps
with a "sequencer" made out of discreet logic or if you're into
writing some trivial ASM or BASIC code, a microcontroller -- which
receives the PTT signal and then keys the relay first, then keys the
rig slightly afterward. (All depending on timing/speed of the rig to
respond to the PTT signal and start transmitting RF.) Your packet
engine must be providing a PTT somewhere, right?
2. Use (relatively cheap but VERY good quality) older commercial
radios were TX/RX chains inside are already separate and isolated to
some extent from one-another. (GE MASTR II, Motorola Micor, etc.)
3. Surgery on the rig -- something inside is switching between the TX
and RX chain... find the right point and lift traces (or whatever)
and add coax and a connector to bring out the appropriate "side"
while leaving the other connector intact. (This is similar to #2,
but "harder" in more modern rigs, and you'll need to study the
schematic to see how that rig is doing its T/R switching. Not always
for the electronics beginner.)
Heck, I'd go find a couple of MASTR II mobiles, buy crystals, tune
'em up, and go. Not only would you get the benefit of the separated
T/R sections inside, but the front-end filtering on the M-II is heavy-
duty, and would help your other design problems... not much gets
through those helical-coil filters on the front-end of that
receiver. (Arguably, that's also a trade-off, the M-II isn't as
sensitive as a modern barn-door-wide front-end rig.)
--
Nate Duehr, WY0X
[EMAIL PROTECTED]
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