The eBay auctions are full of low cost wireless video cameras. Many of these have been purchased by R/C'ers for use on their models. For sure, I have been curious about what these bargain priced systems were all about. Especially since there had been some web discussions that mentioned that they were completely illegal to operate in North America.
The one I was after was advertised as "Latest Version 200mw Wireless Color Spy Cam." I specifically was interested in the "latest" 1.2Ghz version, since the earlier models reportedly did not conform to the approved USA radio frequencies. Note: The vendor's name has been withheld. Just search eBay if you need to know more about the seller.
So, I bid on one of the dozens of nearly identical wireless video eBay auctions and "won" myself a wireless camera. I spent about $39 USD to have one air mailed to me from Hong Kong. It arrived in about a week. It came with the Camera/Tx (transmitter), Rx (receiver), Rx antenna, and video patch cable. It was missing the advertised mating 9V DC power cables. No instructions were provided either. Despite the missing items I was impressed with what I bought for such a small amount of money.
The receiver (shown on the right) is 4.5" x 3" x 0.85" and takes a 9V power source. A standard 9V Alkaline battery should offer about three hours of use. The removable antenna uses a TV style "F" connector, which is not the best choice for a microwave RF signal. Unlike the better (and higher priced) units, this one has a "Tuning" knob to adjust for a stable image.
Shown on the left is
the Tx/Camera unit; it is only 0.9" x 0.9" x 1.0" and weighs under 0.8 ounces:
Testing 1, 2, 3.
For my tests I powered everything using my bench supply, followed by 9V Alkaline batteries. Once I was up and running I found that the CMOS camera is pretty typical of a low cost video device. It needs lots of light, so outdoor use is best (nearly useless indoors). But bright light easily saturated the image. And highly contrasted backgrounds caused poor images too. Colors were fine, but not very accurate.
The camera has an adjustable lens to set the focus. It can be rotated to optimize the image to suit your needs. I set mine up for well defined infinity focus.
Line-of-sight range outside my house seemed worse than I expected. The reliable range should have performed better than my 100mW 2.4Ghz system, but was about 1/2 of it. At this point I assumed that the Rx might have low sensitivity due to the low cost design or maybe the generic omni antenna was to blame.
But, overall, images
were good enough for casually toying around in a R/C model by someone starting
in the hobby. However, at this point I was considering hacking in a better
camera to upgrade the video quality since I doubt it would satisfy what I
wanted. More about that in a moment.
Houston, We Have A Problem!
As I expected, it isn't a license free device since an FCC ID number is not displayed on the Tx. I had my fingers crossed that it was a "real" 1.2Ghz system so that my amateur radio (ham) license would allow me to operate it.
But, hopes for that were soon crushed. Like other users of these cheap imported 1.2Ghz systems have reported, they do not operate on 1.2Ghz at all. Mine was running at 1.16Ghz, which is a restricted frequency used for USA aviation navigation.
I tried to hack the RF amp to get it to operate at 1.24Ghz since it is a legal ham frequency. Because the Local Oscillator appeared to be stabilized (probably a SAW filter), all I could swing was 1180Mhz. Not close enough for legal use. Dang.
While I was inside the Tx, I measured the raw RF power that is driven into the aerial. Using a RF power meter, I measured 40mW when operated at 8V. That is better than the 6mW that a forum member measured on the earlier model. But, a far cry from the advertised 200mW's. Using 12V, I got 58mW (a risky sort of thing to do).
I then realized why the vendor advertises this as a 200mW unit. I removed the CMOS camera and directly powered the RF Amp. At 8VDC, it draws about 26mA. So, 8V x .026A = 208mW. Truth in advertising is a spin doctor's delight.
One of the things I discovered was that the Tx frequency drifted with battery voltage. Drift is about 7Mhz per volt. A Tx voltage change of as little as 100mV affected the received image. A voltage drop of 250mV caused the image to become unstable and required retuning the Rx (a knob on the Rx is used). I suspect that the Tx could be nearly drift free if it was operated on a voltage regulated battery source (hint, power it using a Voltage Regulator IC).
By the way, the Tx/Cam unit draws about 55mA at 8VDC. With a 9V battery, the current is a tad higher. The Video Rx draws 125mA at 9V.
Let's Make Lemonade
At this point I decided I could not legally use it in the USA. But, some of you are located in other countries that may allow its use. So, I decided to dissect mine to see if there were hack opportunities that you might like to know about.
Inside the molded plastic area is a tiny SMT packaged LM7805 5V regulator. It is mounted on small PCB that includes the necessary decoupling caps.
Although the RF transmitter needs the full "8V", the CMOS camera can only accept 5VDC. And since the camera is low power (about 30mA), an SMT packaged IC is all that is needed.
With the Vreg in place, the wireless Tx/Cam unit's voltage range is about 7.5V to 10.0VDC. So, despite the 8V rating, there is some flexibility in your choice of power.
The photo on the left
shows what is inside the power cable. The pinouts are labeled for your hacking
The Tx/Camera unit is ripe for hacking. If you ask me, the CMOS imager needs to go. A Panasonic CX161 CCD camera module would really supercharge the video quality.
If your upgraded camera uses 5VDC, then please note that the little 5V regulator board that is provided would not be able to supply the necessary current. A TO-220 package LM7805 would be needed.
I also noticed that the Tx's antenna length is a bit odd. The stock length is 4.25 inches. But, at 1.16Ghz, I would expect it to be ~4.84 inches. If/when I have time, I will try to optimize the length for max RF power and then report my findings.
The Tx would accommodate an antenna upgrade. With care, an SMA connector could be soldered to the RF amp's output. Or, skip the connector and solder the new antenna directly to the PCB. I would suggest a ground plane antenna design. As I already mentioned, a rescaled GP Patch antenna on the Rx would help improve range.
At this point it would be great to convert the Tx to operate on a legal 1240Mhz to 1300Mhz ham frequency. If anyone comes up with solution, please post the hack! Otherwise, my cheap Hong Kong system is grounded.
Please note that what you read here is all that I can share. I do not have any practical performance experiences to report. I do NOT have any recorded video samples either. Like I said, I will not use this wireless camera due to the illegal operation. However, there are dozens of other R/C's that have used these imported systems. So, if you need more info you should try searching the internet.
The Fine Print
All information is provided as-is. I do not offer any warranty on its suitability. That means that if you use this device you will do so at your own risk. .