APRS and GM300

[fchrist16]

Alright guys, perhaps someone can help me figure this out...

I have a GM300 VHF set for 1 channel (144.390) and a Opentracker 2 (OT2m by Argent Data) along with one of the serial to Mini USB B connectors from Argent Data. From the radio to the OT2m I have a cable from RPC-Electronics made for this application.

My OT2m won't TX to the GM300 to send out a beacon. Any ideas on if there's something in the GM300 programming I need to change to get it to work?

Regards,

-Frank C.

[PETNRDX]

I will take a stab at it...
Might be that the Opentracker provides a "low" on PTT and your radio PTT pin might be set for a "high".
And might be the cable you have is wanting to use one of the programmable pins on the GM 300 that is not set for the configuration you have.
Check the documentation on the Opentracker, if it provides a low on PTT, then check the wiring to make sure the PTT lead goes to the right pin on the radio.
Then last, verify in the programming that the settings are correct for that pin. Its under something like Accessory Plug settings or similar (don't remember of the top of my head)
And if the Opentracker has a lead that "checks" the RX for "busy" make sure that the settings for that pin are correct.
I have used MANY of the TinyTracks (which are similar )and if you have things set wrong in the initial set up, then that RX busy will keep you from transmitting because it thinks its waiting for other radio traffic to stop.

[fchrist16]

Thanks Steve! Got it figured out. I'm not exactly sure what did it but now it transmits...Now I just have to bring the power on the GM300 down to a reasonable level so it doesn't bleed over onto my most used repeater every time. The input for the repeater is 144.730!

Regards,

-Frank C.

[Bill_G]

A 340khz separation is just wide enough in 2M for pass-reject cavities on both to help quite a bit. Take into consideration your existing duplexer when adding a cavity to the rptr rcvr input.

[PETNRDX]

Not sure what you mean by bleed over to the repeater input.
Is this APRS system in your mobile, or is it a digi at a repeater site?
In any case, turning the power down is not very likely to make a difference.
In a vehicle, ya' end up just having to suffer the interference.
Unless you have the room for large cavities or other filters.
If this is at a repeater site, you will likely have to filter each system from the other.
If you turn the power down to even 25 percent, that is only going to be 6 dB.
Not likely enuf.

[Bill_G]

He's experiencing desense at his repeater by the new aprs station. If his rptr is another GM300 setup with the standard reject duplexer, then the front end is as wide as a barn door. He gets to learn about cavities and tuned cable lengths. Woohoo!

[fchrist16]

Actually it is my mobile rig. A 110w Spectra and a 45w GM300. I have an 03 Chrylser Town & Country. The APRS radio is under the front pax seat. I did have the Spectra under the 2nd row driver side seat but now its under the 3rd row driver seat and there is ZERO desense into the Spectra from the GM300.

Regards,

-Frank C.

[Bill_G]

You didn't move antennas. You didn't turn down the xmit power on the GM300. You just changed the physical location in a vehicle, and now rcvr interference is gone? Okay. Doesn't make sense, but you can't argue with success. At least a T&C has room for cavities if you need them. The better half won't be pleased, but it's all in the interest of science and the betterment of mankind.

[fchrist16]

You didn't move antennas. You didn't turn down the xmit power on the GM300. You just changed the physical location in a vehicle, and now rcvr interference is gone? Okay. Doesn't make sense, but you can't argue with success. At least a T&C has room for cavities if you need them. The better half won't be pleased, but it's all in the interest of science and the betterment of mankind.

Actually I did turn down the GM300's power a little bit with a friends help. He had the right test equipment...I did try moving antennas around but where I'm located if I moved the Spectra's antenna too far forward on the car I couldn't get out to any repeater except the one straight up the hillside from me. All Larsen's Magmounts (yes I know bad but the family won't let a hole into that van!).

The better half (being my brother/mother/father) wouldn't even let me think of cavities!

Regards,

-Frank C.

[Bill_G]

But how will you get into MIT if you can't install cavities and properly mount the antennas? Egads! There must be a Camry out there with your name on it. However, by the sounds of it you need a van, or a hatchback, or an Xterra. (ding!)

No, but really, we've seen radios interact in cars before. Usually they throw off birdies that couple through the antennas that no amount of separation can cure because the roof real estate doesn't exist. It can be a challenge fer sure. Sounds like you have it under control.

[fchrist16]

Well Bill I spoke too soon. Not sure what it is but the squelch breaker is back. My APRS rig keeps drowning others out. Time to get back with my friend and his monitor to lower the power, etc.

Regards,

-Frank C.

[vhacmowilmob]

How much power are you using on your APRS rig? We have ours set at 10 watts, and don't usually have problems with a digi hearing us anywwhere around, and we don't usually have desense problems (I notice some desense on the scanner, but that's to be expected)

Brad
W0VHA

[Bill_G]

So, your 2m Spectra squelch keeps spitting while the GM300 aprs radio is turned on, or only when it is xmitting?

[fchrist16]

Only when the APRS station is xmitting.

Regards,

-Frank C.

[Bill_G]

How often is your polling cycle?

[fchrist16]

When stopped or moving?

I know when I'm stopped it is every 2 minutes but when moving I do believe it's quite a bit quicker. I'm actually about to head out to the vehicle to do some tweaking to the APRS and I'll post the specifics when I get there.

Regards,

-Frank C.

[Bill_G]

Considering avg urban speeds rarely exceed 25mph, or approximately one mile every three minutes, avl poll cycles don't need to be faster than 180 sec. We set ours to 300 sec but allow for exceptions such as outbound messages.

[fchrist16]

Bill,

Check your PM inbox here.

Regards,

-Frank C.

[KE4NYVJR]

Frank,

Did you ever determine if there was any problem with the cable? I don't drop by this forum much, but I started reading this thread and noticed I made the cable, so I wanted to make sure everything was ok on that end!

Thanks!

[fchrist16]

Jason,

All is well with your wonderfully built cable! Turns out it was the smart-beaconing rate...

Regards,

-Frank C.