DMR Etiquette

I have recently had a number of conversations with new DMR users wondering how to use the network without being impolite to other users, even inadvertently.  I thought it would be useful to write this all down for everyone’s future reference.  If you have anything to add or disagree with anything, please leave a comment! I will try to keep this updated.

Also, please note – these are just my opinions.

How to be Polite on DMR

  1. Listen before you talk.
    1. When you first turn your radio on, listen for a minute or two and make sure the channel is clear before keying up.
  2. Set the admit criteria in every channel to color code.
    1. This will prevent you from keying up on top of someone.
  3. Don’t use the calling talk groups (Worldwide, North America, etc) for QSOs. Think of them as the 52.525 or 146.52 of DMR.
    1. Not only is this obnoxious, but you will unnecessarily key up thousands of repeaters for no good reason.

Kenwood TM-D710/TH-D72 APRS Queries

One feature of many APRS-capable applications and radios is that they support specially-formatted APRS messages called queries or QRU. When the radio receives this message, the text “Q? ” will flash on the top of the screen.  Here are the message you can send.

?APRSM – Re-queues any pending messages.

?APRSP – Triggers immediate position beacon – this appears to work even if beaconing is disabled.

?APRSS – Triggers a status packet (with whatever status text you have set – TH-D72: Menu 39, TM-D710: Menu 608)

?APRST – Returns the path over which the packet was heard.

Another observation: If you have multiple radios with multiple SSIDs (say KD8TWG-1 and KD8TWG-2), *both* radios will respond to a message sent to one or the other.  I’m not sure if this is standard or if it’s a Kenwood thing.

Do you know of any other queries these radios respond to?  If so, please leave a comment below!

For reference, here is where I found these commands: http://df8ls.de/documents/APRS-Queries.pdf

OpenTracker USB and Motorola Mobiles

The Argent Data OpenTracker USB is a fully-featured KISS TNC – and it’s one of the least expensive, clocking in at $45 at the time this article was written.  If you’re going to build an APRS digipeater or igate, or just use it on your home station in KISS mode, it’s a great solution.  Motorola radios make excellent APRS radios, especially the CDM series – which has a VHF range of 136-174MHz, placing the APRS frequency of 144.39MHz squarely inside its bandsplit.  My home APRS station currently uses a CDM750 4-channel model.

The problem is that the OpenTracker USB’s audio level is just too low for the Motorola.  Some users were reporting as little as 1.5Kc of deviation even with the audio levels turned all the way up.

The solution? Simple.  Short resistor R6.  I simply placed a gob of solder over top of it.  It was a quick mod and I did not measure the deviation like I should have, but it seems to be working well.

Debian Jessie: Run aprx as a service

If you’d like to run aprx as a service on Debian Jessie, use this systemd script (in /lib/systemd/system/aprx.service):

 

 

Raspberry Pi: Enabling Watchdog on Raspbian Jessie

If you use a Raspberry Pi, one feature you may not be aware of is that it has a hardware watchdog.  When enabled and properly configured, if the system freezes up, the hardware watchdog will reset the system.  That’s pretty convenient if you’re putting a Raspberry Pi somewhere remote, like a tower site.  Here are instructions for enabling the watchdog on a Raspberry Pi 2 running Raspbian Jessie.

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Raspberry Pi: Adding a Real-Time Clock on Raspbian Jessie

The Raspberry Pi is a great computing device at a great price – but to keep costs down, sacrifices had to be made.  One of those sacrifices was a so-called “real-time clock” or RTC.  Without one, the device forgets the time as soon as it’s powered down or rebooted.  Fortunately, Internet connectivity is available in most cases and NTP can be used to synchronize the clock.  In cases where Internet connectivity will be spotty or nonexistent, it may be a good idea to install a real-time clock.

There are many guides to configuring this in Raspbian Wheezy, but I was not able to find much for Jessie.  Jessie is different from Wheezy in that it runs systemd, which is a completely new way to manage the system and services. I’d also like to note that this was all done on a Raspberry Pi model 2.

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A quick and unscientific spectral analysis of two Baofeng radios.

The November 2015 issue of QST contains an article by Larry D. Wolfgang, WR1B, entitled “ARRL Laboratory Handheld Transceiver Testing,” which contains information about some of the Chinese radio manufacturers and whether their products actually comply with Part 97 rules.  I own two of these radios, so I became curious – are my Baofengs  legal to use on the ham bands? So, with the help (and equipment) of a friend, I did a quick and unscientific test using a spectrum analyzer.

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