SPEKTRUM DX7 SHOT DOWN!

I had a lot of faith and confidence in the SPEKTRUM DX7, so I decided to go ahead with the integration of the hobby wireless 500mW 2.4GHz AV TX into my UAV. I plugged everything in, conducted a range test and proceeded to take-off. Video Feed was great and I was in CONTROL......so I thought. after about 45 seconds and a partial loop around my airfield I lost control of the aircraft. Luckily my failsafe settings kicked in and the aircraft began its gentle right hand glide.....10 maybe 15 seconds went by then I regained control of the aircraft and attempted to circle in for approach...lost control again. This went on for about 2 minutes until there was no longer enough air between the aircraft and the ground to be considered "flying". Yes it all ended in a crash. Luckily a pine tree had softened the impact with the ground and the only damage was to the wing which is very easily replaced. after this whole situation I conducted a little investigation and came up with something that I should have checked prior to my flight. 1) frequencies. the DX7 operates in the 2.400GHz - 2.4835GHz range and the hobby wireless 2.4GHz 500mW AV TX operates from 2.410GHz(CH 1)- 2.510GHz(CH8) 2) Although SPEKTRUM claims BULLETPROOF link in all conditions...everything has its weakness. (I STILL HAVE FAITH IN MY SPEKTRUM RADIO!) I conducted a taxi range test with just my fuselage and with the same set up as yesterday when I crashed but I changed the Freq. on the AV TX to CH 8 - 2.510GHz.....just out of the SPEKTRUM's freq. and the system worked without interference out to and beyond the approx distance of the incident yesterday....so far so good. Once I get a replacement wing I will do some more testing prior to flying again, but I am fairly confident that the freq. change made a world of difference. Anyone out there have anything like this happen? If so, feel free to add to this discussion!

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  • Spektrum 2.4ghz doesn't fully take advantage of the freq. hopping - when you turn on the system, it locks on to 2 open channels and hop between them.

    So you can imaging that eventually your 2.4ghz video Tx. will step on your 2 Spektrum channels.

    Futaba FASST system actually continously hop between all the channels in the spectrum.

    I use Futaba FASST with 2.4ghz video Tx without any issue full stop!

    I think it's still best to use a different freq. for video especially if it's high power Tx. because can still degrade the signal quality of your 2.4ghz RC gears.

    Please don't start the Spektrum vs. Futaba war - I just want to let you know what works.
  • I just came across this old thread when doing some research on the web as to the best video TX frequencies to use with DSM2 rc gear.
    One of the other things that came up was this article:
    http://www.rcmodelreviews.com/dsm2flaw.shtml

    This suggests that I may work without problems sometimes (when DSM2 picks two well-seperated frequencies) but can fail at other times when the frequencies are too close together.
    Exposed: A vulnerability in JR/Spektrum's DSM2
    A vulnerabilty in DSM2
  • Hi, you will have problems again if the AV TX and the RC RX operates in the same band (2,4 GHz). The WIDEBAND 0,5W TX in the plane overdrives the input of your RC RX. You were lucky to get any signal at all on the RC RX side if you ask me. Only way to solve it is with a cavity filter or a notch filter and that would be too heavy or inconvenient or at least too difficult to make without sofisticated RF measuring equipment (sweep generator and spectrum analyzer or a microwave network analyzer). I recommend switching to a regular 35 MHz (or the frequency band you use in your country) radio because then the frequency separation is so large that it will likely not be a problem to have a TX and RX in the same plane separated by only cm's.

    UFO-MAN
  • Hi,

    I fly RC Helicopters at a club every weekend and we all pretty much use 2.4GHz radios (predominantly Spektrum DX7's) and have never had a problem with frequency interference. There can be up to six people all flying at the same time and no one has any problems even with camera gear strapped in.
    There are a couple of things that the Spektrum hates however. These are low batteries and bad binding. It is best to buy a regulator and use a 15V 2000maH LiPo that is regulated down to 5V/6V depending on your servos/gyro if you are using one.
    With Binding all the lights on the receiver etc.. must be solid! If they are not then it means that something is wrong or the radio has not been bound properly (bind plugs don't forget them). Once the radio is bound correctly the receiver will only accept signals from that transmitter, this is the magic of digital radios. So if all that was done correctly then there should be no problem with anything even if it is on the same frequency.
    There is one guy at the club who is building a camera carrier and is sending down HD footage with a 2.4GHz transmitter and no interference.
  • How to say this nicely - uhm - "it's the proximity, stupid?"

    Having a transmitter on board the airplane with the same freq, is not at all like having the same freq on the flight line.

    The receiver can easily be overwhelmed by a transmitter that close.

    The effect is a square of distance effect, so just a few inches will make a huge difference.
    You can probably find ways to move the transmitter away from the receiver - especially if your frequencies will remain close. You can also have interference by frequencies which are harmonically related. So separating them on the plane is never a bad idea.
  • I guess I knew it would happen but now I found this article I am glad I use 5.8 GHz. It was inevitable that one would increase the noise floor on the other. And more likely the strong pal signal increasing the noise floor on the safety-of-flight critical system (transmitter link). The only way for them not to interfere by increasing noise on the other is if the used the same modulation technique and transmitted orthogonally. I guess the antennas would also have to be out of each others near field for this to work. This is only mork semi-educated opinion, I would love comment on this theory.
  • Hello,

    I just got a DX7. And i will get a range video too. Is there no way the 2.4ghz transmitter live peacefully with the ar7100 receiver? i understand how it could be a problem, but there are no DSS 1.3ghz or 900mhz transmitters for video.

    What would be the best choice. I have the dx7 but I have not bought the video yet, so any recomendations greatly appreciated.

    Best
  • There are several fine 900mhz systems out there. No matter what channel you use, the fact that a high output transmitter is sitting next to your ARxxxx receiver is going to be problematic. Any input section for that matter could be affected. Stick with off frequency transmitters, and making ample distance between the two (also servos!) is a good idea.
  • I could easily reproduce this issue powering the receiver with a freshly charged 2400MAh NiMH 4 pack (4.8V) instead of regular LiPos.

    Receiver: AR7000 DSM2 7Ch Spektrum RX
    TX: DX7.

    I don't know if the AR7000 should be powered with more than that, but when moving 2 or 3 servos simultaneously, the extra load powered down the receiver and lost control (Rx lights off). A couple of seconds after (10 secs or so) it powered itself again, contol again... waited and everything worked until i moved the servos to produce enough load to power it down right away.

    IMHO, I would say you had battery problems. Of course, I can't be sure. Hope this helps.
  • Having a 2.4Ghz Tx right next to a 2.4Ghz Rx is a bad idea. Regardless if it is Spektrum, Futaba, or Xtreme Power Systems. Once you get a certain distance, the video TX will swamp (overload) your Rx. Imagine looking into a bright spotlight and trying to see a candle in the distance. Even if the candle is changing colors (changing frequencies, ie spread spectrum) it is just a matter of time and distance before you can no longer see the candle. Check out ezonemag.com there are many many threads on this under the UAV forum and FPV forum on this. That is the reason why people with 2.4Ghz RC systems are moving to 900Mhz video or keeping 2.4Ghz video and using plain old 50Mhz or 72Mhz RC Transmitters.
    -dave
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