Monday, December 11, 2006

Fun: Gunnplexer Radar Components

So, what's available for radar components on the open market? Most radar guns (aka cheap hardware) is either in the 10GHz band or the 24GHz band. These high frequencies are also used by ham radio operators, so they sometimes try to use these as high bandwidth line of sight radio links.

So, where to get them?

IF you want new, expect to pay $500 to $1000 per node. Advanced Reciever is one that lets you know without requesting a quote.

How about used?

Well, depending on availability, you can assemble much of the parts you need from SHF Micro.

So, my friend Creuzer was wondering about interesting feedback effects versus police radar, so let's go over what you'd have to do. Police radar works purely on doppler effect. Gunnplexers use a pair of tuned diodes to produce a beat frequency from a continuous wave source, so speed is a simple conversion of output frequency to speed. Now, how do you play games with one?

If the police radar is "dumb" (common), the radar electronics will lock onto the most powerful signal. Because your return is FAR more powerful than his reflection, you should win this fight. Now, the tricky part. You'd have to take in his signal, determine the initial doppler shift from knowing your own speed, and then fire off the right frequency to add or subtract whatever you want to to that radar signal.

A "smart" radar system (does it even exist?) that looks for a specific strength return requires more time and investment. You'd have to apply something (like, say SHF's Eccosorb AN-73) that will reduce your radar profile. Of course, you also have to protect the usually expensive components, which would require a good dielectric (radar transparent) coating of plastic over the top. You might also need to apply a fine metal mesh to your windows to keep the RF from bouncing off your head and back to the gun (and then you can control the radiant direction more). Anyway,
you'd have to take a power measurement and try to radiate back a certain percent of that. This would also help with the "dumb" radar but it's far more expense than it's worth.

Sounds simple? Well, it might be, but there's an issue. Radar gunnplexers tend to "float" their tuning all over the place within a 3GHz band, and you usually only have 100MHz or so of available bandwidth. So, know your police radar bands and hope they have it tuned! Mind you, the old hardware worked at either X band (10.5 to 10.55GHz) or K Band (24.05 to 24.24GHz). Relatively more modern hardware runs somewhere between 34.2 and 35.2GHz. I've only found one reference to these, and it was from Japan and cost about $3000 per unit if my translation is right. 35GHz is becoming more common, though, I've seen a lot of miniature radar units (for UAVs) being built around hardware at this frequency.

And that is why I don't mind spilling this little tidbit. Unless your local police is using hardware from the 80's (they might be though!), you'll probably never be able to mess with their readings.

1 comment:

Anonymous said...

Hi, I saw your gunnplexer comments. I did lots of experiements with the 10.5 GHz units back in the late 80s. BTW, the low power doppler units dont beat the freq. of 2 oscillators. They rather beat 1 local osc. against the reflection of the same osc. and provide the mixed signal from a mixer diode thats usually located in the same assembly.
Anyway, you might enjoy using a horn antenna on your gunnplexer and adding an audio amp to it. Try aiming it at your acoustic guitar with steel strings. If a guitar amp is tied to the gunnplexer you have a wireless electric guitar. Now, aim the gunnplexer through the wall at a small, thin taught foil diaphram in the next room to listen to folks talking while using a high gain audio amp and headphones. Now, try listening to the filament inside of an incandescent lightbulb. To think of it... you can hear sound from an object that is under a vacuum. That isnt possible is it? Now, aim the gunnplexer through your roof and listen to the flapping of birds wings as they fly overhead. Sheesh guy! Why would you want to waste your time pondering ways to thwart police radar when there are so many other far more interesting things to do with low cost K band or X band gunnplexers?
Imagine this. Tie a 40KHz osc. to an ultrasound emitter and aim it at a person. Now, aim another similar device that includes a frequency modulated 40KHz osc. that has a microphone tied to it. To think.. If you get both ultrasound signals into the persons ear, the audio will be reconstructed inside their ear for them to hear clearly. The sound will actually be coming from inside their own head. Tie that to a stored audio recording scolding the person for being an intruder and trigger this with your gunnplexer motion sensor from the other side of a wall. They will think God is talking to them because no apparatus can be seen anywhere.