Cross-band with TRBO...

[wavetar]

Is currently a huge pain in the @ss. I've detailed the issues with trying to get an active low COR in the TRBO sticky thread. I can deal with that, but it turns out that little issue is in analog only. In digital, there's no COR whatsoever. Sure enough, if you read the descriptions in the CPS on the bottom right of the screen about the pin functions, it does state it's only available in analog. Isn't the whole point of switching users to these things to go digital? Anyway, I spent the better part of today looking for a decent COR source in the XPR4550 mobile while in digital mode. Not easy. My old standby, the switch from zero to approx 5Vdc which is present on most Moto external speaker leads when the speaker unmutes, isn't present in the TRBO mobile. It sits at a constant 6.3 volts or so, no matter what. The most promising I've found so far is on one of the audio PA leads. It switches from 4.5Vdc to 9Vdc when the speaker unmutes. I've taken this & run it through some various diode/resistor/transistor switching circuitry to try & utilize it. I'm close, as I can get it to work reliably most of the time. It seems if I get it to the point where it works all the time from TRBO to 800MHz, going the other way causes my 800MHz link radio to alternate between receiving & transmitting. Back off some resistor values a little bit, and the 800MHz to TRBO then works fine, but TRBO to 800MHz becomes flakey.

Anyone out there mess with this yet? Or, anyone know of a controller which can work with a voltage swing from 4.5 to 9 volts as a COR?

I thought of trying to use some controllers with VOX...unfortunately the ones I have here (and any others I recall working with) require raw unfiltered discriminator audio to work, as they basically monitor the high frequency noise components (up to around 6KHz) and supply a COR when the receiver quiets upon carrier receive. Not exactly VOX per se, but it works. Guess what the damn TRBO radio doesn't provide on "RX audio pin 11"? You guessed it, no raw unfiltered audio. Oh, the CPS says it can do it, and you can program it that way, but nothing changes! It remains filtered & squelched.

I want to throw these radios in the closet & not bring them out until Motorola releases their 15th firmware update in about 3 years which addresses all these issues.

[ve3nsv]

I did analog to digital using an IP-223 and C-Soft and it work well using vox both ways. Kind of an expensive controller though.

[Astro Spectra]

Wavetar,

Sounds to me like you are there with the 4.5 to 9V transition but you need a more reliable method of sensing that?

Here what you could do to get a reliable COR output.

You need any old 8 pin op amp, something like the TL082 or similar. Performance not an issue as we’re only going to use it as a comparator.

If you only have a 5V rail to work with run it of ground and +5V. Next build a half rail reference out of two 10K resistors, in series from the 5V rail to ground and connect the non-inverting (+) input of the op amp to the common point between the two. You should see 2.5V here with a DVM.

Next we build another divider but this time it connects to the voltage you’ve found. Our job is to scale it so that mid way between 4.5 and 9V we get a voltage equal to 2.5V. This means another series string of two resistors, the ‘top’ resistor of 18K goes to the voltage you’ve found and the ‘bottom’ resistor of 10K goes to ground. Now connect the inverting (-) input of the op amp to the mid point of these two resistors.

With this arrangement, when the ‘Trbo voltage goes thru 6.75V your opamp output is going to swing from 5V to ground.

If you have a 12V rail to work with the job actually easier.

This time we run the op amp of 12V and build the half rail divider out of two 10K resistors as above which gives us a 6V reference, which is good enough to compare with. Now take a single 10k resistor and connect it from the ‘Trbo to the inverting input and you’re good to go.

Either way if you want the logic output to be the other polarity just swap the op amp inputs.

Hey, I hope I’m not telling you to how to suck eggs!

John

[wavetar]

John, that's a promising design concept & one I plan on following up on. Thank you very much!

Todd