Thoughts and Links to a Few Things Discussed on Our Tech Net Tonight

PL on your receiver, or CTCSS:

We all know that you need to transmit a PL tone to unlock a repeater.  That’s how we keep repeaters from keying up unnecessarily.  In the old days, when there weren’t many around, we didn’t use PL at all.  Today, with ham repeater channel pairs all used up in all metro areas, it becomes necessary to place repeaters on the same frequency, and as far apart as geographically as possible, but then separate them further by requiring each to use a different PL tone for access.  That way we get better frequency reuse, where we can place them somewhat closer together, and users can make sure they only bring up their own system, and not the other ham group’s repeater.

On our own receivers, though, there has never been such a rule that we use PL.  The official term for PL on your receiver is CTCSS, which stands for Continuous Tone Coded Squelch System.  It basically means that, when set to this mode, you won’t hear anything from your receiver’s speaker until it hears a specific subaudible PL tone to open it up.

By the way, you would be correct to say that, while your own radio might not need to use it, when seen from the perspective of the repeater, it indeed uses CTCSS on its own receiver before your voice gets repeated.

OK, so besides not hearing other people on your repeater’s channel that might be far away, what other use does CTCSS have.  There are a number of them, but I’m only going to mention one other that you may care about.  If you are walking or driving around, and hearing occasional beeps, squawks, or blasts of white noise from your radio, using CTCSS will prevent random junk from coming out of your speaker.

As an example, in my house, my cable modem emits a digital harmonic that just happens to fall right on 147.33 MHz, the frequency of our two meter repeater.  I can’t monitor that frequency for very long without CTCSS, because the receiver is always opened by the digital noise.  With CTCSS, it’s blissfully quiet until someone keys up the repeater, which transmits a PL tone to my receiver, opening up the speaker.

As a parting note, beware that there are still quite a few ham repeaters that don’t transmit PL.  You’ll just have to check on a case-by-case basis.  To save you a little bit of time, I can assure you that all of the K7DAA, GVARC, and SBCARA repeaters do transmit PL.  On the two K7DAA repeaters, I also perform one other, very minor trick:  I turn off the PL transmit tone about 1-2 seconds before the repeater transmitter drops.  This gives your receiver time to notice that the PL tone is gone, and it again mutes the speaker before the usual squelch crash when the repeater’s transmitter drops off the air.  Nothing is perfect, though.  You’ll still hear a crash after an ID or other very short transmissions, but not during regular conversations.

 

DMR (Digital Mobile Radio):

I’ve bought two of the TYT MD-380 UHF DMR radios for $100 or so on Amazon (a click opens an Amazon search window–multiple vendors)

Hytera is a well-respected name in the DMR two-way radio industry.  They are now marketing to hams through Gigaparts

Hotspots:  Even though most of us in the South County and Hollister areas can use the W6YYY DMR repeater on Crystal Peak, it’s very nice to have your own little DMR system at home or portable in the car.  At present, the two most popular ways to do this are:

  1.  Buy the SharkRF Openspot, a relatively new all-in-one product with no DIY skills needed:  SharkRF website here
  2.  Buy the DVMega board, plug it into either a Raspberry Pi, an Arduino, or a BlueDV board (if you use Android), and add software

By the time you are done, any of the above will end up costing you about $200-300, just so you know.  The Shark has the least number of fiddly things you’ll have to do to get it running, but the ham that sells them gets backed up often, so you’ll spend a week or three in back-order status (not a big deal, though).

The BlueDV is a neat unit that you can control with your Android device, but as an Apple guy, I didn’t find that as attractive.

If you do Arduino, make sure you buy the Arduino Due (Due is Italian for Two).  Not just any Arduino will work.

If you go the route I did, with the Raspberry Pi, be sure and get the Pi 3 like I did.  It is faster than the others, and has built-in WiFi.  All of the choices in #2 use the DVMega radio board.  Note that you can buy either a single- or dual-band board.  There is about $40 difference.  I bought the cheaper UHF-only model, since almost all of the DMR activity is on UHF around here.  I also mentioned the DHAP, which is the 3D-printed case that my hotspot rides around in.  It’s perfectly OK to put a DVMega/Pi combo in one of the taller cases designed for the Rasberry Pi (and only $12 or so), but I wanted something more integrated that also included space for batteries.  That’s how I ended up with the Hardened Power Systems DHAP case.  It’s $99, but includes a dual-mode power supply, and space for four 3.7 volt Li-Ion batteries for easy portable use.  I had to wait about 3 weeks for delivery, by the way.  And yes, I got the bright yellow one!

So far, I’m the only one in the area with a DMR Hotspot, but Dan, KJ6LXX says he might go for a Shark, so feel free to ask him for opinions.  If you try to duplicate what I did, I can certainly help you with it.  Since we’re in the very early days of DMR radio, not a huge amount of “…For Dummies” guides are available yet, so don’t feel shy about asking lots of questions, or for help getting something going.

Mel, KK6MES, and Steve, W6MNL, are the two folks whose brains I’ve been able to pick regarding the DMR world, so feel free to hit them up with questions if/when you hear them on the repeater.

As was also mentioned tonight, the listing of DMR radio manufacturers roughly by cost and features as of today:

  1. Motorola–top of the line, expensive, but used gear on eBay.  Watch out for $300+ programming software you must have!
  2. Hytera–like Motorola, the only two that can do roaming across multiple ham repeaters.  Just began marketing to hams.  See Gigaparts above.
  3. Connect Systems, or CSI–very ham-friendly people, very solid gear, American company.
  4. Kenwood–surprise!  Let’s see what Kenwood brings to the market in DMR.  Note the link to VA3XPR.net, a good source of DMR news
  5. TYT or Tytera–I know, they’re Chinese, but several of us really like their MD-380 radio.  UHF-only, excellent tx and rx audio, easy to use.
  6. All the other Chinese vendors, only because I don’t know their product personally.  Wouxon and Alinco also have ham DMR stuff.

As a parting thought, before I buy or build any of the above, I usually have a look at various reviews and comments on all these items on YouTube.