John,
One reason why I don't use an external controller with any of the MTR2000
repeaters I deployed is because the audio quality within the unit is
excellent. All audio processing is done in the digital domain within the
MTR2000, so the use of an external controller calls for conversion to
analog and then back to digital, inevitably resulting in some loss of
audio quality. I also would hate to lose the excellent Motorola
reverse-burst squelch-tail elimination feature.
If remote-control of the PL tones is what you want, perhaps you can use
the external channel steering feature of the MTR2000 and remotely select
any one of 16 channels- each of which would have a different PL or DPL
setup, but the same receive and transmit frequencies.
73, Eric Lemmon WB6FLY
n0tyz wrote:
> All,
> I'm looking for some help here and I'll try and be brief with the
> description.
>
> I have basically two options to interface a PacificResearch
> controller's output (RI-300e) to a Motorola MTR2000. ( I will post
> this on the RI-300 group as well).
>
> I have found and reviewed a couple of different interfaces for the
> MTR2000 and a few other radio/controller combinations and have found
> nothing that addresses any impedance matching issues.
>
> The two options are:
> 1) Use the Aux Tx Audio input. This appears to be an unbalanced high
> impedance input.
> 2) Use the Wireline interface. This is the typical wireline
> (balanced) interface, which uses a 600-1000 input impedance.
>
> Using option 1, the audio from the controller is fed directly to the
> the radio input with a AC coupling cap per the Motorola manual. The
> advantage of this method of interfacing is that we can utilize the
> CTCSS encoding in the controller. The MTR audio path will pass the
> CTCSS signal through. (The MTR's PL encode and decode are turned off
> in favor of being able to adjust them remotely within the controller).
>
> Using option 2, the audio is fed into the Wireline Interface Board Tx
> Input. The radio's software/configuration is setup to accept the
> input audio from this source. This really produces what I'll call an
> asymmetrical audio path, with the Rx audio coming in from the Disc
> audio out of the radio, and then back into the WIB.
>
> The advantage of option 2 is that the audio "sounds" better and that
> there is a better impedance match, which I think is the reason the
> audio sounds better. However, using this option we lose the ability
> to set/change the encoded PL remotely. I have setup the MTR to
> encode the PL when using the WIB for Tx audio, and this works just
> fine.
>
> What I would perfer to use, though is the PacRes audio output into
> the Tx Aux input of the radio. But I'm not sure how to interface
> these two, as the audio does not "sound" right.
>
> The output of the controller is from a the output of an op-amp that
> goes through a 4.7uF cap before going to the output pin. Then, going
> to the radio, the input goes input the inverting input of an op-amp,
> with a 10K input resistor and a 10K feedback loop.
>
> I'm not sure if there is a need for any kind of buffering or
> impedance matching between these two if I'm going to try and use this
> interface.
>
> I can draw up the schematic in more detail and attach it to an email
> if that would help.
>
> If anyone can help out with this interfacing problem, I would
> appreciaet it!
> '73
> john
>
>
> Yahoo! Groups Links
>
>
>
>
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