Australian ACMA regulations limit the maximum power output of ISM band video senders to 10mW. A typical WiFi card puts out 30mw with some cards offering up to 200mW. Your mobile phone, cellphone or handphone (if you're in Malaysia) develops several Watts.
Geek note: 2.4GHz AV senders use FM modulation for the vision carrier unlike "terrestrial" (ie not from a satellite) analog broadcast television which is AM modulated. Both systems use FM modulation for the audio.

Proof of Concept
I decided to use off-the-shelf video hardware so that I could quickly establish whether the concept of live video transmission from a model rocket was viable. At the time I didn't know a lot of radio theory and was concerned about issues such as:

• the limited range of this very low powered system (10mW output power)
• the effect that the rapid motion of the rocket might have on the signal ie doppler shift or other effects. (Update 25 March 2005). The magnitude of the doppler shift would cause at most a 2KHz drop in the received frequency. Obviously not a problem for a wideband mode like FM TV (could it be cause of problems for the narrower bandwidth AM audio-subcarrier?). This estimate of 2KHz of doppler shift is based on the antenna being situated at the launch location and the rocket travelling at 1000Km/h which is somewhat faster than the video rocket travels with its relatively heavy payload and low impulse mid-power rocket motors). For a discussion of doppler effects see Tony Langdon VK3JED's site.
• the attenuation of the signal cased by the airframe when it was between the transmitter and receiver as the rocket rolled during flight
• the impact of the changing orientation of the transmit antenna with respect to the receive antenna as the rocket arced over at apogee. (I was particularly keen to capture parachute ejection and was not disappointed once this was finally accomplished. I love watching the parachute unrolling and inflating in slow motion as the horizon drifts into view behind the rocket.) The deep blue of the sky suggests that the camera might have a polarising filter.

The Launch Vehicle
The mass and bulk of the components selected for the video link required the use of a larger rocket than could be safely launched with standard Estes A to D black powder motors.

Fortunately at around the same time a friend imported several Aerotech ARCAS mid-powered rocket kits from an American online hobby retailer. The diameter of the ARCAS was just sufficient to house the circuit board from the transmitter once this was removed from its case (see the construction details page), and the bullet camera could be mounted outside the rocket, parallel with the body tube, pointed directly downward and protected via a streamlined nacelle carved from a block of balsa.

The Results
The original video signals obtained during early flights were of high qualty but contained extended dropouts and are not currently available on the site. The Research Goals section further down this page discusses this problem and what appears to be its solution.

Watching the inflight model rocket video clips
I suggest the launch to apogee clip in slow motion as a starting point ie serpentine5_slo (available in either QuickTime .mov or Windows Media .wmv format) as you can enjoy the flight details including the graceful parachute deployment. If you watch carefully you can also see the engine cap flying off as the motor fires.

Extended footage of the rocket under canopy after parachute deployment is available in the long versions of each clip (ie serpentine5_slo_long.wmv) but may not be worth the extra download time for those with limited bandwidth. Under canopy the upper section of the rocket is spinning almost horizontally. However enthusiasts might enjoy stepping through the footage frame-by-frame for nice glimpses of the paddocks of country Victoria.

If you have time to download more than one clip then the normal speed clips give a realistic sense of the incredible acceleration of a rocket flight and the howl as the rocket accelerates is amazing.

Scrubbing backwards and forwards through the clip reveals interesting things about the flight of the rocket that you don't notice from the ground, and stepping frame-by-frame through the footage gives one time to linger over the details on the ground. Windows Media Player doesn't seem to allow stepping or scrubbing so I recommend QuickTime as the media playback client, so download QuickTime and then grab the QuickTime (.mov) versions of the clips because if you only ever play the footage straight through you're not getting the most out of it.

An added bonus is that the slow-motion QuickTime movies are no larger than the normal versions. To create slow motion WMV's I've had to pad the movies out with duplicate frames.

Video Clips

Flight	Videos (Right-Click and Save to Disk)
Flight Number: 7 Date: June 2002 Altitude: 1500ft Engine: G64-7W	Format / Speed	Filename / Duration / Size (long versions include more recovery)	Codecs
	Windows Media Slow Motion 25%	serpentine5_slo.wmv 46 sec 5 MB (Crowd pleaser with classic chute deployment sequence.) serpentine5_slo_long.wmv 88 sec 15 MB	Windows Media MPEG-4 Video V3 1000kbps Windows Media Audio V7 32kbps 32kHz stereo
	Windows Media Normal 100%	serpentine5_nrml.wmv 11 sec 1.9 MB serpentine5_nrml_lomg.wmv 22 sec 4 MB
	QuickTime Slow Motion 25%	serpentine5_slo.mov 45 sec 1.2 MB (Classic clip in QuickTime.) serpentine5_slo_long.mov 88 sec 2.3 MB	Sorenson Video 2 Dev Edition @ 800 Kbps 22 KHz Mono 16bit QDesign Music Codec 2
	QuickTime Normal 100%	serpentine5_nrml.mov 45 sec 1.2 MB serpentine5_nrml_long.mov 22 sec 2.3 MB
Flight Notes For the first time I have successfully captured continuous footage of an entire flight including boost, coast and 'chute deployment and some recovery - a very pleasing result accomplished by using a helical antenna to boost the signal strenth at the ground station. To cover momentary dropouts footage from a completely separate secondary ground station using a yagi antenna was intercut after the flight and interestingly, appears somewhat brighter and contains artifacts including reflections which create the opportunity for further research.
Flight Number: 9 Date: Easter 2003 Altitude: 1500ft Engine: G64-7W	Format / Speed	Filename / Duration / Size (slow motion clips show boost phase only - excellent !)	Codecs
	Windows Media Slow Motion 25%	easter2launch.wmv 61 sec 3.9 MB (Great Ignition and Boost!)	Windows Media Video V8 350Kbps Windows Media Audio V8 20Kbps 22KHz mono
	Windows Media Normal 100%	easter2full.wmv 2 min 7.5 MB (Total flight + special bonus !)
	QuickTime Slow Motion 25%	easter2launch.mov 61 sec 1.8 MB	Sorenson Video 2 Dev Edition @ 800 Kbps 22 KHz Mono 16bit QDesign Music Codec 2
	QuickTime Normal 100%	easter2full.mov 2min 8MB
Flight Notes The normal speed clips show a complete flight including recovery - I make a guest appearance as the rocket is returned to the primary downlink station. It took three attempts to ignite this old White Lighting reload and the slow motion clips are particularly cool as we see one of Troy's "special" igniters finally do the trick. The primary downlink station was running a Mini-kits EME103 20dB 2.4GHz pre-amplifier. This did not make any obvious difference to the range of the system - it has been suggested this is because I am already on the receiver's "noise floor".

Email Address (Comments welcome)

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Research Goals
Capture continuous footage by experimentation with transmit and receive antennas, ensuring there are no intermittent connections, looking at transmit amplifiers or receive preamps and investigating whether the camcorder being used to record the output from the receiver is taking longer than one might expect to recover from a momentary loss of signal.

Note June 2002: This goal has been attained through higher gain helical and yagi receive antennas.

Although the signal loss in earlier flights appeared to coincide with burnout, suggesting an intermittent electrical connection associated with negative g this does not, in fact, appear to be the case. Instead it would seem that the signal was simply lost as the pattern from the two omni-directional antennae were no longer coincident. Once the rocket had attained a certain height the vertically polarised receive antenna was effectively in a null underneath the vertically polarised transmit antenna. This may also explain why the signal was regained at apogee.

Other things to sort out

• Why the audio is still dropping out occasionally - perhaps the problem is not electrical at all but the mechanical effect of acceleration on the electret microphone.
• Why no audio at all was recorded by the second ground station - does it use a different audio subcarrier ?
• Why the transmitter stops transmitting when sitting on the launch pad and need a thump to get it working again (does it actually drop out or does the A/D converter or DV codec in the camcorder go to sleep ? (I need to build a VDA to check this or incorporate an S-meter into the receiver).

• Thanks to Darren for the loan of his helical antenna and to Jason Hecker for his helical antenna design.
• Thanks to Julian for his invaluable help including aiming the helical at the rocket during flight.
  (Darren, Jason and Julian and myself are members of Melbourne Wireless, a group who, like many others around the world, are building a community broadband wireless network using 802.11b IEEE standard WiFi equipment which shares the same unlicensed region of the spectrum as this particular low-powered video transmitter).
  
• Additional inflight footage was recorded independently by David Boyd, a fellow Tripoli Australia member and his team using a 12dBi yagi antenna and their own microwave band video receiver and camcorder. David's recordings were intercut with mine using Adobe Premiere and the resulting clips were compressed in Media Cleaner Pro 5.
  
• The Aerotech Arcas launch vehicle was supplied and constructed by Dave and Cath.
• I found Terry A. Rea's pioneering Micro Video Telemetry work very useful and inspiring.
• The Clay Brothers VideoRocketry site is excellent - with a lot clips of their experiments flying small CMOS cameras on black powder motors.
• In 1998 a trip to the U.S. was organised around the launch of Space Shuttle STS 90 - Neurolab at Kennedy Space Center Florida. Here are a couple of photos from that trip.

  Irrelevant links
  

• Some D-Link 900AP+ Access Point Power Consumption Measurements that I made to answer a question on the Melbourne Wireless mailing list.
• Talking Electronics Magazine TEC-1 Z80 Microcomputer designed by John Hardy and Ken stone. Picked up this 22 year old Z80 microprocessor trainer type computer at a swap meet. Couldn't afford one when I was at high school !
• The 2.4GHz Pacific Monolithics Pacmono Antenna.