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Comment by rachelbythebay | Hacker News Reader

I got tired of missing things which were going on around me, and my scanner was more annoying than helpful at times, so I threw a bunch of software (and a bit of hardware) at the problem. Questions welcome!

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Very cool. I'd put the demo on the front page, actually, so people don't even have to hit the 'Demo' button to see the list construct itself.

Is this a Smartnet system? Are you running a wideband front end with a dedicated DDC for each physical channel?

(I did something like this for the Seattle-area trunked radio system a few years ago -- http://www.ke5fx.com/equinox/equinox.html -- but users have to download a dedicated Win32 client, and it only allows a single user to control the hardware at any given time.)

Good idea on the demo thing there. I dropped the "possum" call into the top page after watching a few hits come in and it got way more interesting in terms of people checking stuff out. I'll find a way to make the whole thing work without that extra click -- thanks!

The city is using a Smartnet system as far as I can tell, and I'm using a software-defined radio system to pull in the whole band and then split off the chunks I care about. I'm also decoding the control channel so we know which talkgroup is responsible for a call, which frequency they're on, and all of this.

Your approach sounds interesting, and I bet you could get a web frontend onto it which would bring about more attention and cross-platform compatibility, too! It's worth a thought if nothing else.

Ooh, neat. What kind of hardware are you using? (And are you using gnuradio? Does the gr-smartnet module on CGRAN actually work?)

gnuradio + gr-smartnet does actually work, and it will decode a control channel. I got it to give me usable data for both the city of Santa Clara system and Alameda County.

There are a lot of little bits and pieces you have to smash together to wind up with something like this, though. I wound up playing with a lot of programs in this field before deciding to build this. Discriminator taps are fun!

Yeah, I've wanted to do a web-based UI for it for a long time, but it really doesn't make sense with a single physical channel. My implementation is a historical relic compared to this one! Right now it hands off control privileges every 15 minutes if there are multiple users logged on.

I do have a dedicated receiver for the control channel, at least.

Do you plan to make any hardware/HDL details available?

I do intend to write a series of posts about the building of this system and all of the things I encountered and either fixed or hacked around later on. It's still a bit early to do a "retrospective", I think. They'll go up at my "writings" page when I do -- the URL is in my profile.

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