I was really surprised to see my receiver reception quickly diminish to 15% while doing a shoot out over lake Washington the other day. I was maybe a75 feet up and a couple hundred feet out. I am currently using a Graupner MX-20 and am thinking about replacing with something with a longer wavelength. I do like the Graupner, especially the telemetry but the fear of loosing my asset is causing some serious frayed nerves. I know this subject gets a lot of traffic in other forums so I apologize to have to beat this horse here. What have you done to help extend the range of your 2.4 or did you move to something else like UHF or 1.3?
Thats odd... Ive been almost 1/2 mile with my MX-20 and wasn't having any reception issues... Let me look at my signal strength from my last flight. I was about 300-400 yards out. Josh
A half mile would be more than adequate. It has happened many times. So much so that I pretty much only listen to receiver strength for the first 7 minutes of flight. Has anyone tried the dragon stuff... http://www.rcgroups.com/forums/showthread.php?t=1518533 http://www.readymaderc.com/store/index.php?main_page=product_info&cPath=64&products_id=994
I took a photo and attached here. I used the same location that Andy did in his Cinestar Build video. The difference is that I ran my motor wires outside the boom and they run right next to the receiver. Hmmmmm
I've bought 2 MX20 3 months ago and both radios lost signal after 400-500m. I've been in contact with an engineer in Graupner.de and we made some tests. He said that the position of the antennas is critical in this system, they must be 90ยบ from each other (one vertical and other horizontal for example). I did that and didn't got any improvement. I'll be returning the radios for a replacement because there are 2 possibilities left. 1 - I have a serious problem of interference in the 2.4Ghz range in my location or 2 - I'm so unlucky that I got 2 bad radios . For comparation, I'm using a DX8 (hacked with the Sexpander mod, 12ch) for almost 2 years. I've been flying over lakes, beaches, ocean, even crossed the Iguassu Falls, in the middle of the Carvanal between and with a live down link on board, more than 500m high and 650m away (no FPV, I almost lost the CS in the wind ) and never had a radio glitch. I do use 2 satellites, in booms 4 and 6, with the Diversity Controller. I do believe the MX20 is better than the DX8 but until now my good and old DX8 is the winner. Good luck and please keep us posted about the Long Range Radio if you buy one.
Hello Morgan, It is very important that the two antennae are separated as Arthur mentioned. I have been following Arthur's dealings with Graupner.de and am also very curious as to their prognosis. Arthur is a very accomplished operator and performed his due diligence in completely testing all potential variables prior to returning the transmitters. @Arthur--please let me know when you have more info. Greetings, Adam
I use the MX-20 as well and flew my Cinestar out of range at only about 300-400 yards. Luckily the CH on signal loss feature works! The antennas are 90 degrees from each other on two axis (one horizontal and one vertical) and do not touch each other. On previous flights before this happened I noticed the telemetry telling me I was only at 15% at maybe 150 yards. So I hiked my cinestar over a mile away from my rx to test the actual range and I didn't lose signal. I also read in the mx-20 manual that the signal strength the telemetry outputs is the strength of the return channel and that the output channel is much stronger. I also checked the GPX data and it said I had really good signal strength. So I decided to ignore the telemetry percentage and its warning beep and keep flying away from me and sure enough it lost signal. Afterwards I came across this in the MK wiki when reading up about GPX data and signal quality "Quality of the PPM-Signal (not the signal strength in case on 2,4GHz receiver!)" Now when I hear the warning beep, I give it full stick back to me.
Morgan: Are you using a Lawmate 1.2/1.3 Ghz FPV transmitter by any chance? I cannot tell from your image. If so, the harmonics from that might be causing problems for the GR-24 receiver. What I fitted to the FPV 1.2 Lawmate TX (and is not covered in the DVD set -- I didn't have the space!) was a Low Pass Antenna Filter for 1.2/1.3 Ghz transmitters -- it allows the 1.2/1.3 Ghz signal to pass, but attenuates the first and second order harmonics at, you guessed itm 2.4 and 4.8 Ghz. The URL for this LPF is http://www.dpcav.com/xcart/Low-Pass-Antenna-Filter-for-1.2GHz-1.3GHz-TX.html Also as an alternative, try placing the receiver horizontally so that the two wires dangle out over the edge of the hub -- that's the way QC build their RTFs and it might work better for you -- I did check with QC regarding the "standing up" positioning shown on the DVD set and was told that there really was no wrong position, but the evidence suggests that might not be the case. It's all about trying to get as much antenna as possible "visible" (that is, line of sight) to the TX antenna on the ground and avoiding it being occluded by carbon fibre which attenuates RF signals. If you're flying at "400 feet", then you might see more of the RX antenna from the ground if the radio's horizontal. If you're flying at 20 feet AGL, they mounting the RX vertically should produce better results. I've even wondered whether it would make sense to extend twisted servo wires (to reduce induced noise) all the way out along most of a boom (beyond the 3-Axis gimbal) so that the RX would be clear of most of the carbon fibre. But then I have these possibly crazy thought experiments and haven't had the chance to try all of them. I'm speculating, but I suspect the MK board set, BL-Ctrls etc. and motor-wires are a flying noise generator -- add to that the fact that the carbon fiber frameset is an RF absorber -- whether the noise is significant Tabb or Adam can tell us better than I can, but I can't help wondering whether the GR-24 RX is listening to the MX-20 through a sizzle of locally-generated noise. I keep meaning to build some RF noise probes for my Tek scope -- they might not be calibrated but they'd at least give me a sense of what's out there in the RF spectrum around 2.4 Ghz. The Tek "near field" probe set sells for $2,270 which is almost more than the cost of the scope. To get the two GR-24 antenna wires at 90 degrees, I've been experimenting with some plastic antenna tubing -- take a couple of inches of it, and cut about 50% of the way through in the middle, heat it with heat gun just to make it more plastic, then form a 90 degree V. Let it cool and thread the two antenna wires through it until the V is fairly close to the receiver. Right now I'm holding it in place with Sugru (www.sugru.com). I'm not convinced Sugru's the way to go (expensive!) so I might resort to just silicon adhesive for the next prototype. Also I need to figure out a better way to deal with the fact that the two antenna wires emerge from the RX about 4mm apart. Maybe I need just a blob of Sugru to hold two short independent lengths of antenna tubing at 90 degrees. Still hacking on that one.... Hope the ideas above help. Andy.
Great info Andy. I use the 1.2 video transmitter, so I'll order that low-pass filter. Both my antenna are touching carbon fiber, I'll take your suggestion and fabricate some sort of bar straw holder for the wires.
Has anyone figured out why the DragonLink is connected to the RC Transmitter PPM signal?? See http://www.dragonlinkstore.com/v2/node/9 Andy.
Interesting information about the receiver position. I have mine mounted on boom 6 with the antennas pointed straight out towards the back. The antennas are not separated either. I have never had a range issue. I just looked at the flight data from my last longer range flight (wasn't super far but about 300m) and the farthest point my R/C signal from MK says 193/209 which I believe is 92% signal strength. Heres a picture of the receiver on my copter and it's mounting position. It's on the boom to the left. You can see the antennas hanging down. Josh
Yeah.....that makes a bunch of sense, Josh. The antenna wires are well clear of any carbon fiber. I think the 90 degree thing is about getting better spatial diversity rather than anything else, but I'm speculating. Are you flying a 5D Mk III or II? If it's the Mark III how did you get it to statically balance in tilt, please? Andy.
Im flying a MKII. I FINALLY yesterday got it to be perfectly balanced on all axis! I never realized that you needed to raise the COG of the camera for the ROLL to balance correctly. Mine was always able to return to center fine but would never stay in a position if tilted left or right but now it does! Josh
Thank you Arthur and Nick. This is great info. Obviously I didn't read the manual very well. I will fashion something to get my antennas in the proper positions. I am also planning on doing befor and after field tests for competitive purposes and will post the results. Thanks again for taking the time to reply.
Aha. Thought that might be the case. Yeah. Basic law of physics, I'm afraid: If the CoG of something isn't on the axis of rotation, you cannot get it to balance at an arbitrary angle. If the CoG is above the axis of rotation, it will be unstable like a pencil "balancing" on it's point on a desk; if the CoG is below the axis of rotation, it will behave like a pendulum. I suspect that's why Tabb has made reference to producing "adjustable" tilt arms soon. With bigger, heavier cameras it takes a lot of servo power to hold them in position of their CoG is not spot on the axis of rotation. Lifting the side booms raises the camera/lens CoG level with the roll axis of rotation on the vertical rear boom. Bingo! Balance! Andy.
I always did wonder why people had the arms up a little... I just figured it was more lens clearance... I do feel like an idiot. haha but glad it's correct now! Josh P.S. why are non of you flying! Ive already done a few flights today!
No. The only video downlink is for the gimbal and that is 5.8 iftron stuff. Nice tip. I do plan on setting up FPV and will purchase the Lo-Pass filter. As usual, great information. Thanks Andy. Morgan
Hey Morgan: Given you're not yet using 1.2Ghz FPV, then I'd be tempted to move the receiver out on to Boom #6 as shown in Josh's image. You've got the motor wires outside the booms, right? I wonder whether they're radiating noise that might otherwise be attenuated by the booms? Tabb may be able to comment further on this as I've not done any noise measurements. Andy.
Does this look like good antenna placement? Josh- According to the mk-wiki the signal strength given in the gpx data is not accurate for 2.4, at least as far as I can tell.