White space devices

I live in the middle of nowhere (northern Minnesota). There are many TV channels that are unused. From the few searches I have done, it seems it is now ok for an experimenter to utilize these frequencies on an unlicensed basis. It looks like 10w for fixed stations and 100mW for mobile stations.

I have a cat that likes to wonder off, and this is wolf/lion/eagle territory. I have been playing around with very low power OOK transmitters with extremely short duty cycles, they just transmit a little chirp every second or so and can operate for months on a watch battery. Originally, I wanted to use one of those little 433MHz saw oscillators for arduinos commonly sold on amazon for a few bucks, but then I found out that is an illegal band in ITU region 2. And I really don’t want to add current draw and size by making it identify with my ham call either. So I thought I was putting the tracker project aside until I came across this. If I understand this new white space thing correctly, I don’t think I would be breaking the law by placing a (maybe) 1mW pulsed transmitter of extremely low duty cycle on my cat set to a white space frequency so I can track him via direction finding. Or would I? Unless he climbs a tree, it would be like the transmitter is laying on the ground, so I don’t imagine this would interfere with anyone.


Nevermind, I saw the part where it needs to access a database of available channels once a day. That’s a ridiculous requirement for a 40-100mW max device out where I live. I don’t expect a new TV station to appear out here any time soon. If anything, we will lose one or two.

It’s cool you’re exploring using those unused TV channels for your project. About your cat tracker idea, using low-power transmitters on white space frequencies might be okay, but it’s good to double-check the rules 'cause it’s still new. As long as it’s really low power and doesn’t mess with others, it might work for tracking your cat. But, you might wanna be sure it’s all good before trying it out!

Thanks for the reply. I have been putting a lot of thought into what frequency to use for that. I know in this region, 915MHz might be an option, but I was hoping to avoid such a high frequency worried that the trees and buildings might interfere or cause reflections and prevent me from direction-finding it. 70cm was about the highest I wanted to go. I don’t want the frequency low enough to skip off the ionosphere or make an antenna physically impractical either, so I need to stay above 50MHz. To my knowledge, that leaves MURS, TV white space or adding a micro to identify on a ham band. If I went with the microcontroller, I may as well use a GPS module and transmit that data once a minute instead of a OOK pulse once a second. But now I am contending with the weight and power consumption replacing batteries every day instead of twice a year. Identifying/GPS is not really an option if I want to keep the transmitter the size of a CR2032. Of course being outside, stability is another concern, so its saw filter resonator or crystal oscillator, LC tanks are not an option. My first attempt was on FM broadcast band, but it was all over the place and had to shut it down. This project turned out more difficult than I thought it would be!

Here in the UK, unused broadcast chunks get what we called PMSE allocations = programme making and special events. So if the BBC or other broadcaster needs channels, they have a very simplified procedure to get things up and running. Other people get access apart from broadcasters on a non-interference basis. Here, apart from our version of the US GMRS, everything else is controlled and not remotely up for grabs.