[App_rpt-users] Portable micro-node?

[Bryan D. Boyle]

On 6/18/12 12:09 PM, Alan Adamson wrote:
> My problem with all of this is the issues with Motorola (and other
> commercial radios as well) hookup.

Depends on the radio.  Maxtracs (16 pin), GTXs, Spectras are so simple 
to interface that it's almost a non-issue.  All the signals are on the 
back...discriminator audio out, audio in, ptt, and ground.  And, unlike 
most if not all ham-grade equipment, are can handle the rigors of 
constant duty cycle rather than the ICAS rated ham equipment.

>
> The speaker isn't a speaker and ground it's a floating set of two wires and
> they bias it with voltage, and the PTT and Mic interconnection aren't that
> obvious either, as you may need to put resistors and caps in line to filter
> and cause the radio to see the correct voltage so that the PTT enables.

Audio floats above ground in a balanced system so as to minimize common 
mode interference.  On the radios I've worked on, especially Batwings, 
I've noticed no bias voltages on speaker leads.  Besides, you really 
should not be using speaker audio to drive a URI anyway.  Find the 
discriminator output, and use that.  Friends don't let friends use VOX 
on asterisk; it makes it simple to interface, because, in the end, you 
only need 3 leads plus a ground to get the thing to work if you use the 
DSP processing to derive your COS and PL decode.

You may, and I say may, depending on how you send audio back in (flat vs 
mic), have to use a 47 puff in the mic line IF there is bias voltage on 
it for a condensor mic.  Otherwise, put a pull up on to the PTT pin, and 
ground it for PTT.  The URI can handle push to 5v or pull to ground as 
the signal for PTT; it's looking for the voltage transition to determine 
(as best I can tell) whether or not it's a valid state change and act 
accordingly.  Heck, I even have some dry contacts on a broadcast studio 
audio console muting relay that can properly signal a URI to turn on the 
cluster transmitters.

It's not hard, nor complicated, if you're using the right equipment.

>
> On the GP300's, I don't think you need that adapter as they have a 2 jack
> location already provided.
>
> I think what I'm going to try, just because I have one and all the parts is
> my TH-F6A, you can put it in 9600 baud packet mode and get to the
> discriminator and mod input directly, and it has COR (but alas, it's just
> connected to the meter, not really to a valid COR on CTCSS). but I also have
> a TS-32 laying around so I may make something really small.  The radio is
> way over kill, but hey I have it and it's straight forward to connect up.
>

If you have a discriminator output, you don't need to have a hardware 
COS.  That's what the DSP is for, as well as CTCSS decoding.  A lot 
easier to interface.


-- 
Bryan
In this world, you must be oh so smart or oh so pleasant.
Well, for years I was smart. I recommend pleasant.
You may quote me.

Sent from my MacBook Pro.

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