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Camera & Transmitter Modifications

Analog Video Transmitter Modification

   Here a LawMate 1.2 GHz Transmitter is modified to improve heat dissapation or limit  thermal runaway which can destroy the transmitter. Also, we will cover some modifications to the transmitter and camera to make it perform  better and weigh less. In electronics, usually heat cycles destroy circuits and components over time.

   The 1000 mW transmitter connects from the camera for transmission through 4 wires (-) BLACK (9.0VDC to 12VDC), WHITE (Audio), RED (+) (9.0 vdc - 12 vdc), and YELLOW (video from camera).  Transmitter board is accessible once you remove metal cover. 

   Usual precautions against static electricity should be taken prior and  during all work on these circuit boards; such as: a grounded wrist strap.  

   Transmitter does not use 0.1 header hole spacing, so any pins diameter  meeting the circuit board may have to be ground down to a round shape prior to inserting header pins into board. A dremel high speed cone shape stone bit will do pin grinding quickly.  A desoldering tool or station can be used to remove the solder from these 4 input wires on the transmitter.

     As the transmitter will fail for voltage over 12 vdc, a means of protecting this is to put a voltage regulator in place. This is a  simple lightweight circuit between power and cameras & transmitter.

Telemetry data over Audio

       One channel of audio is available per Lawmate 1W 1.2 GHz flight transmitter.  This low bandwidth channel  may be used to transmit real time streaming data or aircraft flight performance information, known as telemetry. Thus a voice data to  speech circuit would provide real time backup info.
     Note: telemetry from IMU is bidirectional but camera transmitter is not two way communication. 

This example of a desoldering tool requires 220V @ 100 watts. Typically,  its prudent to provide, say 200 watts of power so as to operate efficiently with power supplies and you can maintain a higher duty cycle.

   Replaced wires soldered to board with 0.1 header pins bent right angle. Removing existing wiring saved weight as the RCA AV (audio & video)  metal connectors are no longer necessary. On the flip side aluminum cooling fins were cut from an old CPU to provide improved thermal dissapation.

Electronic Noise Isolation

   Aircraft To RFI (radio frequency interference) isolate the camera, fpv (first person  view), transmitter and power supply from noise while taking steps to  prevent this transmitter from interfering with other radio and  instrumentation & control electronics is essential to a quality  flight experience. Another option is to place the video and transmitter on a separate LiPo battery (11.1 V or 3S) but a voltage regulator  should be between the LiPo and the camera & transmitter electronics  .
     So also to electrically isolate noise, high pass  & low pass filters, ferrite core power noise isolators along with measuring interference and signal loss on the ground should be implemented where necessary. 
     Home or Base   Further range means noise and signal importance increase.   As  directional energy is focused by the antenna at remote aircraft, the S:N ratio goes up. Hence, a Patch or Parabolic Dish antenna is used.  Maintain antenna direction within its beam-width or the signal may fail.

RF Transmitter Power Output

     550 Line resolution, 30mm square,  analog color camera sensitive to 0.01 lux (about a quarter moon light at nite) shown above. RCA AV jacks were removed to save weight.

Video Display & Resolution

     In general, the higher quality video display, the better clarity and picture without any change in camera or transmitter.
     To get the most versatility from the output display you should expect  to obtain an Analog-Digital television monitor with the most interfaces  and the highest resolution, say 1920 horizontal lines by about 1020 lines vertical resolution.

    Video transmitter in its modified form with aluminum cooling fins attached and before solid 0.1 bent pins attached

RF Flight Receiver Problems

    While having a 1.2 GHz video transmitter and a 2.4 GHz rc receiver should not interfere, ground testing is essential prior to flight testing. A simple lightweight high pass filter of the receiver may be required to block out other on-board flight transmitters if the antenna is in close proximity to receiver or transceiver antenna.

  Power as radio waves,  either is sent out the antenna or is reflected back and appears in the  form of heat, a waste of battery power  which results in signal loss.   Within limits, lower voltage to the transmitter results in less power output but longer time of signal transmission. 
   Power output, the difference between power put into the antenna and the radiated power of the antenna, is typically measured with a SWR (Standing Wave Ratio) bridge meter can also be measured remotely using a multimeter or  volt meter by providing a distance between the transmitter and receiver  while taking small cuts in antenna length and measuring the receiving  signal.  SWR measures, to some extent, the power which is reflected back into the transmitter or wasted electricity and higher operating temperature.
    Received signal - using a cheap multi-meter  and binoculars, you can see signal performance change at the receiver while tweaking the video transmitter antenna length.  No SWR meter is  necessary to do this. Result: better performance.
     As supply voltage is lowered, the power output of the transmitter is also diminished.  At 12 vdc, the 1 watt transmitter is at maximum output while at 9 vdc, the 1 watt transmitter puts out about 70 percent (approximately 730 mW ) of that power. 
     Calculating that power output should be performed to determine the maximum range the sum of the components and  systems will support.
     Note: SWR meters have specific frequency ranges of operation.

RF Receiver & S:N ratio

     Radio reception is limited by a fundamental factor, that is, Signal to Noise Ratio or S/N ratio. No matter how strong the video or audio message is, if  this information (RF voltage level) is below the noise level; then that information is reduced to garbage. 
       Hence tuning the signal and improving its reception strength is critical to audio, video or data perception and or use.   Sharp narrow tuning is refered to as Q and it is related to a fourier analysis - a wave front examination.  A sharp tuning is not without its disadvantages.
     Another related aspect of S:N ratio is the bandwidth of both the transmitter and the receiver. Up to a point, the narrower  the bandwidth, the more effective the signal power becomes and further  operational range is the result for point to point communications.

     View of camera and 2 axis mount with 2 small servos attached. Aluminum side brackets not shown; they are used to guide the camera into the  slot between the two plywood rails in the airplane above.

Calibration & Metrology

Camera mount servo default range 90 degrees (pitch) and 90 degrees (yaw) or 45 degrees left and 45 degrees right.

Note: Facing nose from inside the plane, left side is called port side and starboard is the right side. Green LEDs (shown above) are hot (electric) glued to fuselage behind  camera.  Alternately, the left side features red LEDs to compliment the Green LEDs and both flash at night.

External camera mount directs  fixed lens camera with two micro servos using remote control receiver and IMU for tracking.  Display using field station fpv equipment or recorded SD onboard memory.

External Signals Interference

 Most of the focus here is related to the aircraft electronics or the base station, however electromagnetic interference can come from many sources: the sun, railroad trains, tv or radio towers, etc. One should be aware of the  nature and scope of these problems and take steps to reduce their effect.

Other Camera Hardware

 For High Definition, a GoPro  camera, despite its somewhat awkward shape for video recording is used but not for real time first person view (fpv) use.   A GoPro video camera introduces an unacceptable delay in a video stream. (~1sec.)
    There are better analog video cameras which offer 650 lines resolution at more than double the price available for fpv use.
     Much higher resolution industrial cameras exist, small, light, extreme dynamic range, some military grade. These cameras may exceed standards in professional cinematography with optical resolution miles away to resolve details, in color, out to the infared spectra; useful in low light piercing haze with clarity.  Some cameras now use machine vision or computer image resolution of objects, behaviors, in real-time off the CCD imaging array at the focal point of the optics, matched superbly.
     SAR or synthetic aperture radar is another method of producing vivid dynamic image displays, some video, of internal buildings, structures and into the ground but it is not the same as ground penetrating radar - oil drilling company favorite. 

 Calibration is maximizing performance; it is a process of taking functionality and fitting or testing the range of what one would expect for its limitations and  operational values. Calibration validates the state of operation.
     If you can measure the  characteristics of the camera, such as, the field of view, its resolution at a distance, the optics and power usage; then you can know  what to expect under what conditions of use. Metrology is essentially quantitative dimensions or numerical aspects of interest from a  reductionism perspective. In application, metrology is a means of assurance that the technology will work within the expected use and  foreseeable environment.

Books and Other Resources

The Art of Electronics, by Paul Horowitz & Winfrield Hill, Cambridge University Press, (C) 1980, 1989
     note: online pdf versions also may be found.

The Infrared Handbook, Edited by William L. Wolf & George J. Zissis, Office of Naval  Research, Department of the Navy, (c) 1978, 2012, 1st Edition, (Note:  1st edition is inexpensive)

 ARRL Antenna book, (22nd Edition) & ARRL handbook, by
The American Radio Relay League, Inc.,arrl.org

See also theSensor pagefor more resources.

OPTICS, Microscope Tutorials:  MicroscopyU  

Modern Optical Engineering, (2nd Edition), by Warren J. Smith, McGraw-Hill, (c) 1990

Bandwidth vs. Resolution

   Video Resolution relates to the smallest detail visible to the eye. Higher or more bandwidth in a  signal means potentially sharper or more resolution possible and vice versa. Visual resolution refers to what can be seen in TV lines (TVL).
  Format Resolution details only what can be viewed by the particular format of the signal. HiDef yields 1020 horizontal lines maximum resolution.  XGA specifies  768 horizontal lines.  A standard NTSC video signal has a typical  horizontal resolution of about 330  TVL in a maximum of 4.2 MHz bandwith.  Droping NTSC video signal to 3MHz bandwidth gives only about  240 TVL. 
  Ample Bandwith means a (NTSC) circuit  must have a minimum bandwith about 6.5 times the highest frequency in the signal to maintain a signal attenuation or loss to less than 0.1 dB  (decibel).  Using minimum slew rate of 52 V/us or even better 80 V/us provides best signal within this bandwidth.
    The trade-off for increased bandwidth is a faster change in signal phase versus frequency which can produce degradation in group delay and group-delay distortion parameters. 
   Note, both NTSC and PAL TV signals are both interlaced unlike DTV, VGA, SVGA, and XGA, which are progressive scans.

Front View Lens

10x Optical Telephoto-Wide Zoom 24 mm Objective Lens  
SONY Handycam hack

To IMAGE page - Shutter control

  Disassemble 400 line resolution CCD video handycam to salvage stepper motors and associated plastic housing. Stepper motors control the 10x Telephoto Zoom, focus, and aperture/mechanical shutter.  Replacement CMOS camera has full HD resolution.  Stepper motor controllers remain with camera body.  So, stepper motor controllers need to be added for integrated automatic operation. If servo motors are used, their electronic contol is straightforward but requires mechanical mods. Accurate alignment of replacement CMOS detector is required for crisp imaging.

  Lower right: motor driven shutter/aperture which slides into middle between left side Zoom and right side to new HD CMOS or CCD camera.  Lower left: a slider encoder to locate position of zoom lens. When not in use, the shutter slides shut to prevent CCD from light burn damage.  Camera reticule size and sensitivity should be matched ideally to optics of lens set; this optical zoom works with the 4x improvement imager.  
   It can be used as color desktop inspection macro scope or 200-400  foot AGL (above ground level) telephoto camera with near Infrared optics for (monochromatic) night viewing. Programming and adding a gimbol to it may prove to be a nice portable tracker.          
                   Weight: 2.4 ounces

     Definition: LUX Physics a basic unit of  illumination in the SI and MKS systems, equal to one lumen per square  meter (0.0929 foot-candles or one candela per square meter): abbrev. lx

Using a telescopic lens, Camera effective focal length is now the camera lens focal length times magnification.  Assume double magnification, f 2.4 becomes f 5 (approximately).   Higher magnification requires a more sensitive CMOS.  As focal length increases, field of view decreases.

   Magnification: Objective focal length divided by eyepiece focal length.

   Electronic shutter of CMOS detector: to avoid skewing of fast moving image across field of view - use a global shutter. 

SONY C mount (32 tpi) manual telephoto zoom   48 mm Objective Lens

  24 mm or .95 inch aperture lens. Using resolution limit equation, the maximum this lens can resolve is as follows:

   Aperture: f 2.4 (approximate)  Area of Lens: A=pi x radius 2 or (12x12)=144
 A = 3.14 x 144 = 452 sq. mm
   Area of detector: 64 sq. mm
Objective Lens to Detector: 452/64 = 7

  First, the Original CCD 1/3 inch to 1 lux sensitivity with 270 k pixel resolution in color.
  Next, the new CMOS 1/3 inch (8 mm) to .001 lux sensitivity with 2 M pixel resolution in color - 1,024 lines resolution (horizontal). 
One would  infer the pixel size is much smaller with a corresponding increase in resolution. 
   The new CMOS camera eye has about 8 times the pixels of the original CCD, frame rate can be approximately 5 times faster, no data on the Signal to Noise (S/N) ratio yet. Where imaging involves low contrast, angular resolution calculations are limited beyond the Dawes limit.      (Yellow Light)
       R = 5.62 -4Emm/Lens Dia. 24mm

Angular resolution in radians:
2.341 E-5 mm or 0.00002341 radians

Convet Radians to Degrees:
                                       multiply by 57.30
Angular Resolution per Rayleigh:
   a = 0.039 / aperature in mm
   a = .039 / 24 mm = .001625
   This zoom lens can optically resolve to 5 arc seconds. From here, the image sensor array further limits resolution with technical innovation pushing the boundaries while specializing results.

   As this lens aperture is much larger coupled with fast tiny CMOS pixels, human eyes can not resolve objects with this faster speed, higher accuracy, or  broader wavelength range - provided the image is in focus. 

  Glass lenses set to metal frame, solid construction, smooth, built for professional use.  Double the aperture of the 10x above zoom, it can optically resolve to 2.5 arc seconds.  Weight: 15.8 ounces. 

Note: User of this information should investigate any requirements, including legal limitations, prior to using this information.  This is your responsibility.  Any liability is specifically disclaimed under any  legal theory for your omission or inattention or intentional use of this information. Use at own risk.

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