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Mr.RC-Cam

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About Mr.RC-Cam

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    RC-Cam Mentor

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    http://www.rc-cam.com
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  • Location
    USA
  • Interests
    R/C, FPV, Embedded Programming, Electronic Design.

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  1. Larry was a 1980's rock musician with a passion for R/C model airplanes. Last month (Feb 13 2020) he posted a YouTube video that shows his FPV activity that started in 1986. It's a fascinating documentary. Another recent FPV history video was posted by YouTuber CurryKitten. This video was produced after Larry posted his documentary, so it also mentions his FPV flights.
  2. The Comtech BSS-479 is no longer made and has sold out. RMRC was also selling them, so maybe they can help?
  3. Sorry, but those wonderful vRx's are no longer available. It was a sad day when Racewood closed their factory. That's an option. But you mentioned that you have a Chinese vRx that has bad UHF interference. Maybe there is a solution? What have you done so far to solve it? Thanks for your kind words. I appreciate the feedback.
  4. The BSS-479 Comtech tuner module is a better design than the lower cost Chinese made "clone" tuner modules. Plus the overall design of the FPV receiver is important too. The upgraded SAW filter's effectiveness depends on many circumstances. I normally recommend the SAW filter upgrade as a way to increase vRx sensitivity rather than promote it as cure for bad UHF noise. But if the original SAW filter is a poorly manufactured component then replacing it could help out a lot. If you are having success with the RMRC vRx then I highly recommend you choose another one if you are expanding your ground station. A bird in the hand is worth two in the bush. EMI/RFI noise is cruel. Sometimes the cure is as simple as rerouting a cable or moving the offending RF source further away. Or maybe adding a capacitor at some strategic place on the circuit board will help. Or improving the RF grounding on the metal case. Or adding EMI/RFI filtering to all the external A/V signal & Power entries. The list goes on. And sometimes a practical cure is impossible, other than replacing the inadequately designed RF device. I'm not a RMRC receiver user, so I have no idea what they may have done to improve the receiver's resistance to UHF interference. But if it has a Comtech tuner in it then that is certainly a big advantage.
  5. I looked inside my old Racewood "900MHz A/V Receiver, Deluxe Model with Comtech Tuner" and it uses a Microchip Technology PIC16C55A microcontroller. The chip is a 28 Pin DIP package. I also looked inside my Racewood "Standard Receiver" (small tan colored metal box model). It has a SOIC-18 SMD packaged PIC16C54C microcontroller. But I also recall they used a Chinese clone of that part in some production lots (it was a direct replacement IC). These microcontrollers were programmed with Racewood's firmware, which is proprietary. So I don't have the source code.
  6. It has the stock 27MHz SAW filter. You could de-solder it and replace with a ECS-D480A (17MHz SAW). The microcontroller is OTP (one time programmable). It's a Chinese clone of an old Microchip Technology part. I don't recall the part number.
  7. Possible? Yes. Practical? Not really. The Racewood 900MHz and 1280MH VRx have the same hardware. The Comtech tuner's operating frequency is handled by a microcontroller on the baseband PCB. So the firmware is different. Unfortunately the microcontroller is soldered in place and is not re-programmable. It's possible to disconnect the two wire I2C bus from the Comtech tuner and use an Arduino microcontroller (and your custom software) to control the frequency. I don't have any project links on doing this, but maybe Google will help you find some useful information.
  8. I found an interesting article that describes microscopic hair growth (tin whisker) failures in old germanium transistors. http://www.vintage-radio.com/repair-restore-information/transistor_transistor-faults.html Maybe the transistor problems in my Sampey receiver were affected by this phenomenon.
  9. Those are on the future feature wish list. Not sure when I'll have the free time to add them. However, any developer is welcome to roll up their sleeves and tackle it. This is an open source project so contributions are welcome. Some special Arc control actions (scratch-start, lift-start) are being added in hogthrob's TIG software. His code might be useful for adding the new stick functions too. https://github.com/thomastech/Sparky/pull/6 - Thomas
  10. Weld Current Calibration Notes: The PWM controller board has a multi-turn trim Pot that affects the Welding Current. See photo: But before any attempts to change the trim Pot's factory setting it is important to understand how it interacts with the front panel's Current Adjustment. The front panel current setting changes the gain of the PWM based inverter. This is the user's control for adjusting the weld current. It has a end-to-end range of about 60 Amps. The internal trim Pot is used to apply a constant offset to the Weld Current. It can "move" the weld current up or down about 60 Amps. It's a "factory" calibration adjustment for setting the minimum weld current. And since it is an offset, that means it also affects the absolute maximum current. Although far short of the advertised 200A specification, it's possible for Sparky to achieve 125A (short current). When the trim Pot is calibrated to allow 125A maximum current the minimum current will be about 65A. If a lower minimum current is needed then the maximum current will be reduced by the same amount. Adjusting the trim Pot means that the machine's top cover must be removed. This exposes dangerously high voltages to the world. The unprotected circuitry can harm (or kill) you! Do NOT proceed with adjusting the trim Pot until you have had proper training with working on high voltage equipment. Proceed at your own risk.
  11. The physical location of Partom's pot suggests it is the video level adj. So give it a try. It's very unfortunate that the other board is missing the video adj pot. And it appears to be hand soldered and has a lot of flux residue. Disappointing to see.
  12. Thanks for the kind feedback. Sorry, but nothing to offer in that RF power category. After the product quality fiasco with Lawmate, followed by the Racewood factory closure, I evaluated several higher powered 1.3Ghz vTx's. None met my quality / performance expectations. That was several years ago and it doesn't appear anything has changed given what's available today. My workaround back then was to in-house modify an expensive 1000mW vTx from a China supplier (I forget the brand). With our modifications it was a reliable performer. But every sale was at a loss due to market pricing pressures. Did that for a couple years to support our customers. Unfortunately the mods were too time consuming and so we ended sales. Fortunately this was after the FPV market had shifted to 5.8GHz.
  13. These observations are ongoing issues that the suppliers ignore. And the reason for the video calibration tool. You are now getting acquainted with the performance issues that haunt many FPV systems. Along with what you observed, be prepared to find that some systems will alter the video level after you change antennas. And sometimes whenever you change RF channels. These undesirable quirks are due to inadequate RF designs, mostly affecting the 900MHz-1.3GHz systems. I doubt the suppliers care and most users are unaware of these problems. The video cal tool not only allows you to properly calibrate a good set of components, it also helps you identify the bad performers that need replacement. I suggest calibrating the video levels after everything is installed and the desired RF channel has been set. Do the cal with the vTx and vRx several meters apart, preferable outdoors (less multipath from workshop walls). Replace the bad parts in installations that suffer a lot of video level instability as the model is moved around (will cause poor video performance in flight). Whenever **anything** in the FPV model or ground station is altered then repeat the video calibration. You're on your way to experiencing better FPV video performance. Your video diversity system should work better too. Enjoy!
  14. It appears that the two minimOSD boards are not identical, perhaps due to sloppy components. Some ideas to try: 1. Ensure battery voltage is at least 8V when powering the boards. 2. Retest with a different video patch cable connecting the two modules. Should be short, good quality. 3. Check the two boards' video input termination. With nothing connected, use a DMM and measure the Vin input resistance of each board (DMM across Vin & Gnd). They should be identical values (within 1%) that are very close to 75 ohms. If beyond 1% mismatch, replace the resistor that has the worst deviation (so it is a match). 4. There is also a 75 ohm series resistor on the video output of the MAX7456 chip. One end of the resistor is on the boards' Vout pin, the other is at the negative (-) junction of the two 47uF tantalum caps. Check them (meter across Vout and 47uF cap junction), should match within 1%. If beyond 1% mismatch, replace the resistor that has the worst deviation. If the resistor values are good matches then the easy answer is to just use the boards as-is; When you adjust a vTx video level you'll need to set it so that the image results match exactly what you saw in the validation test. That is to say, the upper right "T" area will have a subtle darkness, as displayed in your posted image.
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