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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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    USA
  • Interests
    R/C, FPV, Embedded Programming, Electronic Design.

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  1. Analog HD FPV Video. Why Not?

    The test system's AHD vTx and camera are mounted on a 3D printed chassis. It is inconveniently bulky (3.5 x 4 inches, 4.3 ounces). The ground station is also mounted in a 3D printed chassis; It consists of the AHD vRx, AHD-HDMI video converter, and HDMI recorder. Here's what it all looks like: The vTx's large form factor is not ideal but fortunately not a major issue at this point. Plus my randomly chosen parts have performance issues too (prolonged black screen drop outs, some color shifting, etc.) Non of this matters yet because for now I'm only evaluating the video resolution versus traditional analog FPV. So I don't mind that my test system is a quirky Frankenstein monster. Basic ground tests gave me a preview of what to expect. The recorded FPV downlink video shows that image resolution is better than a standard FPV system. It's also in a native 14:9 screen format instead of the typical 4:3 format. So far so good! The video also has examples of the black screen dropouts caused by the AHD-HDMI adapter. There's also random color shifting caused by an out-of-spec colorburst amplitude. But these things can be fixed by the future developers that understand the potential of AHD FPV and build us an our dream system. What's next? With the ground test out of the way I'm now ready for a quick test flight. Should be ready to fly with it next week if the weather cooperates.
  2. 50mhz TX antenna mod

    There shouldn't be any issue with installing a BNC or UHF connector on the R/C Tx. For best matching/efficiency don't use a single wire to the connector; You need both signal and shield. After mounting the connector on the case, a short piece of 50 ohm coax would be used inside the Tx wired as follows: Shield soldered directly to the PCB's ground plane (near the RF signal pad). The coax's center conductor soldered to the RF signal pad. Google for plans on how to build a vertical polarized 6-meter antenna your outdoor installation. For example: http://fedler.com/radio/6m_vertical.htm Note: I haven't built the antenna example, it's just a random project found with google.
  3. The meter is targeted for FPV hobby applications so it certainly supports the 23cm (1.2/1.3GHz) and 70cm (433mHz). But it omits the HF band (<30MHz) since FPV'ers don't use it. There's a chance you can cheat and use the 433MHz mode for HF power measurements. But I have no idea how accurate it would be since the cal data for 70cm/433MHz would be different compared to the HF band cal data. Maybe results would be good enough for you, or maybe not. The AD8318 sensor covers 1MHz to 8GHz. Adding a new frequency range not currently supported by the firmware would require Arduino coding. Hardware would remain the same.
  4. The existing code supports 60dB attenuators. For rough VSWR estimates the 433MHz setting should work OK (despite the extreme RF difference). But if you should ever need to make accurate absolute RF power measurements then you'll need to dig-in and modify the code for the HF band's dramatically lower frequencies.
  5. Thanks for doing it. Maybe you'll find someone to trade a PCB for a printed case.
  6. If you look at the photo of my blank Perfboard you can determine the size. Each drilled hole is 0.1". So I estimate the irregularly shaped board is approx 1.4 x 1.5 inches.
  7. Does it fit inside the 3D printed case I published? If not, how does it mount on the HeadPlays? Pictures would be great.
  8. You can't detect a video level compatibility issue (a common problem) by simply viewing your camera's image on a monitor. You need a o-scope or this tool to do it. Even if you cannot repair the problem yourself, you will have identified a purchase that is not 100% compatible (which is valuable knowledge).
  9. You are welcome. I hope they can help you. If you are serious about finding the best matching vTx / vRx pair then I recommend you build this tool to test your purchases: https://www.rc-cam.com/forum/index.php?/topic/4126-diy-fpv-video-calibration-tool-low-cost/
  10. As I have mentioned in my various discussions in the past, there's several RF & Video related specifications that must be maintained in order to ensure a reliable FPV system. Video emphasis is just one of many important characteristics. For example, your exact problem might not be video pre-emphasis related. It could be incorrect video level, RF carrier error, or something else. And even if all the important specifications are understood by the original designer, the end product sometimes works poorly. Performance issues can be due to economy priced components (tolerance issues) and inadequate quality control. But I agree, a well thought out FPV video system standard that is observed by everyone would be great. Unfortunately, this holy grail idea is not likely to happen in China because of their manufacturing culture. And as many experienced engineers say with a smirk: The thing about standards is that there are so many of them to choose from.
  11. From the video and your comments it seems that two main things contribute to your problem: (1) Your vTx behaves badly in your indoor flying environment as compared to your other vTx's. This suggests that it is a marginal design that acts poorly unless the RF signal is perfect. This symptom is commonly caused by an incorrect video level or a video emphasis filter design mistake (or both things together). (2) You're flying indoors. Plus you might be using a linear polarized antenna on your micro quad. So the multipathing interference will often be a nuisance under these conditions. A marginal vTx design will show more problems when it interacts with multipathing and signal fading situations. The manufacturer may not have tested their design under these conditions. There's no way for you to know why it is happening; You need full schematics and expensive test equipment. It's up the the design engineer to identify the exact problem and fix it. Could be as simple as a resistor change to increase the video amplitude or something more complex involving several component values in the video pre-emphasis filter. Or maybe something else. To provide a reliable (correctly implemented) fix, the manufacturer will need a few samples of the vRx's that do not work correctly with their vTx. They should check the video waveform for proper sync shape and confirm proper amplitudes of the H-Syncs, V-Syncs, colorburst, and full white luminance. Also, they should confirm that the RF carrier's center frequency is accurate to ensure their channel control software was written correctly. Keep in mind that if the manufacturer already makes a matching vRx for this vTx then it will no longer work correctly if it is used with the fixed vTx. In that case they will need to redesign their vRx too so that its video characteristics are matched to the fixed vTx.
  12. Halloween 2016: Talking Skull Project

    The talking skull was revised for this year's halloween (Oct-2017). I added a cheap MP3 player and retired the wireless microphone. Here's a video from the haunted house on Halloween night (talking skull begins at 1:20). https://www.youtube.com/watch?v=z_4qLQd8lug
  13. Analog HD FPV Video. Why Not?

    The Airwave AHD performance issues did not kill this AHD investigation. I also have some 5.8GHz AHD demo boards from Globaltw Tech. Nothing to build, they are ready to use. The modules on them are the Go-Link Technology MA58R0011H (vRx) and MA58T2011H (vRx). The vTx board includes a 1Watt RF PA driver too. Here's what the demo boards look like: The vTx board is about 4.5" square. Not a convenient size and so I haven't decided how I will "flight" test it yet. But the Globaltw boards do not have the bandwidth issues that were observed with the Airwave modules. So they allowed me to do some useful bench evaluation. Here is what I found: 1. The AHD to HDMI convertor I purchased has very bad behavior when it encounters a poor signal. The HDMI output takes about 3 secs to restore video after a RF signal drop-out. It's like black screen of death on steroids. So a different AHD-HDMI convertor will be needed to fly FPV; For now LOS flight would be safer/wiser. 2. AHD's wide RF bandwidth seems to have increased multipathing interference breakups. I expect that a diversity vRx configuration would help. 3. Speaking of diversity, the vRx module does not have a RSSI signal pin. Hopefully it is an unadvertised feature on a hidden pad somewhere on the module. 4. The Go-Link modules have CVBS / AHD video auto detection. This is a nice feature for security system applications. But not so nice for FPV because it falls-back to its CVBS video mode on signal drop-outs; It takes a couple hundred milliseconds for the vRx module to re-detect the AHD video signal and reconfigure to it. There may be a solution to prevent this, but I could not find any external pins that would disable the feature. So this would probably need to be done by the factory. 5. The demo boards are setup for 16 channels, with some using frequencies that are not permitted in most countries. But these AHD modules support an alternate four channel mode that is confined to frequencies that are legal for ham use in the USA, which is nice. 6. I also found that there is an unadvertised channel setting feature that involves a serial bit pattern on a single pin (instead of DIP switches). I can't find any details on the data format, but it's good to know it exists. 7. I measured about 650mW of RF on the upper frequencies and 1W on the lower frequencies. I also noticed a microstrip directional coupler and associated circuitry on the vTx's PCB board. Its intended purpose is a mystery but I suspect it's used to detect/protect antenna problems. 8. The video quality I see on the bench is surprisingly good. Despite the cheap camera there's a noticeable improvement in image resolution. So I'm excited about what it will look like while airborne. What's next? I purchased a HDMI recorder so I can record some outdoor video examples. But I've run out of free time, plus there's a week long storm due to arrive today. So it's on hold for now.
  14. Analog HD FPV Video. Why Not?

    I've made some progress on testing AHD performance. But I've mostly encountered hair pulling frustrations; It seems that the AHD gods are testing my perseverance. I built a bare-bones FPV system using the Airwave AHD AWM6W3V vTx and AWM6W2V vRx RF modules. Fortunately I found some PC boards (from previous FPV projects) that had the same Airwave module pin-out used by the new AHD RF modules. So the boards were sacrificed and re-purposed for AHD testing. Here's the details: Basic AHD vTx schematic: vTx board: Basic AHD vRx schematic vRx board: I also disabled the vRx module's antenna pre-amp pass-thru power feature. Although not documented on the datasheet, it is a simple resistor removal, as shown below: The completed vTx PCB is small enough for use on my 330 size Quad and I was expecting to do some flight testing with it. And its RF power was perfect for small field testing (measured to be 150mW). Things were looking good up to this point. However, bench testing revealed that the Airwave system's video performance is unacceptable. Although sync amplitude is good, the overall video level is about 35% too low and has about 85mV of unwanted SAG. But more importantly, the video bandwidth is too limited and this causes severe colorburst attenuation (it reduces the 11.5MHz colorburst signal by more than 50%). These problems are horribly detrimental to our application and there's no easy way to fix them. But on the positive side, standard NTSC/PAL CVBS video looks great. The AHD modules' wide video bandwidth is just the ticket for 960H cameras. Yes, 960H is better looking than standard video, but it's not as good as 720P video. So long story short, I have abandoned testing the Airwave AHD modules. I may come back to them, but for now they appear to be a dead end.
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