Ham or spam?

In continuing with my tradition of irregular posts about unrelated topics, finally had a bit of time to revisit what I do to currently push to my Blog. The past me wrote a “deploy.sh” script that for reasons unknown uses a git submodule to track changes to the site - i.e. the generated files in public. I then hosted the public submodule in a separate github repo (this one). The way it worked was, I cloned the blog source code repository - made updates, and updated the git submodule. Annoying and error-prone.

Turns out this is entirely unnecessary as GitHub can easily build the site using workflows. I’ve fixed that now, which also gives me the ability to edit posts in the GitHub online editor which is very nifty. No need for a separate blog-source repository.

With the yak-shaving out of the way, I wanted to write down some notes on basic radio stuff that I was experimenting with using the kids toy walkie-talkies.

Things I have:

• A cheap Baofeng UV-5RH transceiver.
• A pair of “Nestling” kids radios that I borrowed from a friend for the kids to yell into.

My understanding of radio transmissions and reception is rudimentary. Here’s how I thought they work: walkie talkies are set to some frequency, say 466.3MHz. You shout and receive on the same frequency, as long as the radios are within range and are transmitting with enough power to get through obstacles. Turns out, it’s slightly more involved than that.

In the UK, where I live, there are a bunch of frequencies that are allowed for low power radio transmissions called PMR446. These don’t require a radio license and you’re allowed to use low power (0.5W) transmissions. The theory still holds that you send and transmit on a frequency that’s set on the radio, but there are a few subtleties.

The radio adds a “privacy code” which is a tone that is below the range of human hearing to the transmission. There are two kinds of “in-band signaling” to implement privacy codes that are popular:

• Continuous Tone-Coded Squelch System (CTCSS): The tone can either be set to Off (i.e. nothing is sent) or a tone between 67.0Hz to 250.3Hz. When the radio transmits this tone is included in the preamble. The receiving radio will receive the message but only “play” the audio if it hears the CTCSS tone it’s configured for. This gives you privacy in the sense the if other radio pairs are using the same the frequency, your radio will not play the audio received out and treat it like noise. You’re still hosed if someone else is transmitting on the same frequency, but you don’t hear their noise. You can bypass this using the “monitor” switch on the radio or disabling squelch. (sidenote: Squelch is a funny sounding word that means to suppress output until the signal strength breaches some threshold, i.e. someone’s talking on the radio and its not just static).
• Digital-Coded Squelch (DCS): Pretty much the same as above, but instead of an analogue signal - the tone is digitally encoded (bit stream). This gives you a bunch of nice features that digital transmissions give you, like error correction codes that you can’t get with analogue signals.

The Baofeng radio has a nifty feature that lets you figure out what frequency and what squelch system another radio uses. Before that I was able to hear transmissions by scanning the spectrum, but I wasn’t able to transmit at all. After using the “frequency copy” feature (it’s one green button on the right), I was able to figure out that the kids radio uses 446.04175 with a DCS code of D261N.

Now I can yell back at the kids, fun times!