Quick look at AirHORN, an affordable Signal Generator

Nuts about Nets, LLC offers a rather affordable signal generator called AirHORN for different types of testing scenarios.

Nuts about Nets, LLC has a dual band signal generator available for Windows based workstations with USB support for under $300. I would consider a small part of this price the hardware and the larger part the easy to use software. You could likely mimic many of these features in Linux with some custom scripting and the mac80211 core, but I’ve found this tool to be worth the cost to run on the same laptop I utilize for Airmagnet Survey Pro and my multi-channel sniffing setups.

AirHORN has three different modes that it supports.

  1. Single Mode – Select any 2.4GHz ISM band channel or any 5GHz UNII-1, UNII-2 or UNII-2 extended band channel and achieve an almost 100% duty cycle on that channel (at the normal width of 22mhz wide 802.11 traffic).
  2. Traverse Mode – Scan through a set of channels at a specific interval.
  3. Pulse mode – Burst on a specific channel, and then off for a set interval.

When using AirHORN and monitoring with a spectrum analyzer, it does an extremely efficient job of utilizing all of the available spectrum.  When scanning channels, you see a perfect ‘staircase’ across the spectrum (in a swept spectrogram) as it cycles through channels.

AirHorn in spec analyzer
Here's a view from their own Spectrum Analyzer software (AirSleuth-Pro) of AirHORN stepping to channel 11.

You may wonder why any of this is useful to you.  It’s actually a pretty handy device to have in your bag of tools for a few different reasons.  It’s great at causing mass chaos on a specific channel, to the point where nearby devices can barely pass traffic at all. The impact to client devices varies a bit on different device driver implementations, for instance, while having AirHORN enabled on channel 1,  my Mac Book Pro (Late 2009 model) would not pass any traffic on the air and would result in 100% packet loss. Other devices would get a few packets across; it seemed to vary greatly based on the client chipset and driver.   Why would creating chaos be of any use?  It’s a great way to test your infrastructure vendor’s automatic interference mitigation. Use an AirHORN device and time the difference is takes to notice the interference, and do something about it with different vendors.

The AirHORN USB adapter itself is somewhat of a normal Wireless NIC with a custom driver on it, and the adapter is sending out 802.11b frames as fast as it can, sending about 1500 byte frames of garbage data. It also monitors its own efficiency using what Nuts about Nets calls “Indirect Measurement of Microwave Interference”, which they have a pending patent on.   The only thing I’d probably want to change on this device right now would be the ability to change the TX power of the device and add 64 bit OS support.  Nuts about Nets has another similar device, “WifiCopper 802.11b Packet Injector” that lets you send out a measured packet and size rate into the air.

This device is useful for a number of different thing, including simply testing antenna design in some fashion to see how well it measures for signal strength (Though this may be a fine driver for it, I would hope you’re measuring your antenna characteristics with more appropriate tools if you’re in the business of high end antenna design).   You can also use the device for testing RF shielding,  as it certainly beats putting cups of water in the microwave and running them for hours while you measure around your cafeteria!

Their entire product line is worth checking out, it’s all fairly affordable and their support is quick to respond. While I haven’t had the chance to use their other tools, I’d certainly give them a try, especially when they are a fraction of some of their competitions cost. AirHORN has been mentioned on Network World before, and in various other blogs, most with favorable things to say.

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