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HELP! Spektrum DX7 radio failure?

Old 08-07-2007, 07:36 PM
  #126  
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Originally Posted by Lip84 View Post
I was nervous about the channel hopping ....
Channel hopping is no problem, it's just a lot simpler way to implement a Spread Spectrum system. What bothers you about the concept? What I like about the DX7 is that it's from a company with wider offerings in the system and more experience - it's a second gen system.

I heard the "9c" type Futaba is soon to be out with faast inside.
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Old 08-07-2007, 07:53 PM
  #127  
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I suppose that as long as the tx and rx follow a specific predetermined algorithm then its not as much of a problem. I guess its the paranoid idea that they will decide to hop to different channels or one will hop and the other wont.

As far as the "2nd Gen" goes....it sure seems like even though its a second generation system there are still a lot of problems. I understand that this is a horror story thread but horror stories are not the only bad stories out there and they can happen to anyone.

The biggest problem I have is seeing how terrible the tech support and the service is. I work in a service type roll to some extent and understand how vital a good face and good rep is in the service world. Spektrum has earned a mondo black mark in my book and thats hard to erase. If the service is trash the product might as well be as far as I am concerned. If you believe in your product and that it is high quality, the service should be there to back it up.

Then again...that is one humble opinion amongst many.

I am very curious to see what the new 9 channel futaba faast unit will be like and how competitive price wise it is. It almost feels like its too early to jump to 2.4 ghz with so much uncertainty in the world. Perhaps going with an older futaba 9 or 12c 72mhz radio would be best and upgrading to the XPS system in a few years.

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Old 08-07-2007, 08:22 PM
  #128  
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Originally Posted by Lieutenant Loughead View Post


I told him I didn't think the receivers were the problem, since I had failures on three different receivers -- it had to be the transmitter...:
You believe the only common item in your DX7 failures is the transmitter. Let me offer another possibility - your flying site. You didn't mention if all of your problems happened when flying at the same location, and if that is the case, I would suggest the location might be a contributing factor.

I have a friend who experienced a total loss of control with his DX7, AR7000
system when flying over water. He had a conversation with a buddy of his who is a JR technician who told him the 2,4gHz systems can experience problems due to signal reflection - particularly when flying over water.

Now I don't know if water could be involved in your situation, but I would take into consideration other objects or terrain at your flying site which could reflect the signal.
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Old 08-07-2007, 09:14 PM
  #129  
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That's a good point - I had zero issues until I started flying near an Intel R&D facility, in that area I had 2 occurrences of the infamous AR6100 lockup bug. It's entirely possible they are doing R&D on 2.4 GHz systems in that building or in some other way producing a lot (possibly technically an illegal level) of RF interference.


Or maybe it's just luck.


But I had my 6100s flashed to 1.2 and I moved to the "other" vacant lot that's several hundred yards from that facility. No issues since.


Originally Posted by Lip84 View Post
As far as the "2nd Gen" goes....it sure seems like even though its a second generation system there are still a lot of problems. ....

I am very curious to see what the new 9 channel futaba faast unit will be like and how competitive price wise it is.
The Spektrum systems are by far the most popular ones out there, the reported issues are a function of this greater population IMO. It is gonna be interesting to see how futaba attacks being second fiddle in 2.4 GHz land - might be interesting times a comin'.
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Old 08-07-2007, 09:48 PM
  #130  
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Originally Posted by simibill View Post
You believe the only common item in your DX7 failures is the transmitter. Let me offer another possibility - your flying site. You didn't mention if all of your problems happened when flying at the same location, and if that is the case, I would suggest the location might be a contributing factor.

I have a friend who experienced a total loss of control with his DX7, AR7000
system when flying over water. He had a conversation with a buddy of his who is a JR technician who told him the 2,4gHz systems can experience problems due to signal reflection - particularly when flying over water.


Now I don't know if water could be involved in your situation, but I would take into consideration other objects or terrain at your flying site which could reflect the signal.
Can you elaborate on that. That would be a BIG deal if these radios don't work over water.
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Old 08-07-2007, 09:51 PM
  #131  
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Originally Posted by Lieutenant Loughead View Post
He says he found a crease in the coax cable which leads from the circuit board to the antenna. He said it could cause a problem -- "anything can cause a problem with 2.4 gigahertz."
Originally Posted by Prof100 View Post
A crease in the coax is the root cause? Do you believe him?

Far be it for me to get to technical here but...the coax leading to the antenna acts as an LC network. The center conductor is the inductive component, the shield is held at ground and the space between the center conductor and shield (across the dielectric) acts as capacitive. Most times this means nothing but as frequency increases this starts to have an effect on the signal being passed through. You have to look at the size of your coax as only being able to pass a "band" of frequencies (or a band pass filter). At 2.4ghz the change in capacitance (due to the crease) could cause a frequency block attenuating part of the spectrum. Back in the days of tube televisions the circuit boards would have actual wire coils for inductors and we would bend these a little here and there to "tune" the oscillators.

The only way to tell if this crease was a problem would be to put an FDR (Frequency Domain Reflectometer) on it and look to see where the "hole" is in the spectrum.

In short is it possible that this could have caused your problem? Yes it could have.

Use your foamy's and do a good range check. I hope it works better for you.

Last edited by rea59; 08-07-2007 at 10:14 PM.
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Old 08-07-2007, 09:57 PM
  #132  
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Failure #1 --> Site #1. Pond of water was about 100 feet from the aircraft (the aircraft was BETWEEN the water and transmitter).

Failure #2 --> Site #2. Pond of water was about 10 feet from the aircraft (aircraft and water were side by side, when seen from transmitter).

Failure #3 --> Same as failure #2. Failure #3 and Failure #2 started in almost exactly the same spot.

Failure #4 --> Site #2. Pond of water was 100 yards from transmitter. Aircraft was 100 yards from transmitter. Transmitter was between aircraft and water.

I'm really sorry I sold my Optic 6 last month... I still have my Laser 4, and plan to pay Hitec to change the Tx crystal to work on the five remaining 72 MHz receivers I have.

My original plan was to sell the five remaining 72 MHz receivers, and replace them with Spektrum receivers. I will not allow that to happen now!

I will test the electronics when I receive the Tx and Rx units. Time will tell, but at this point, I do not trust Spektrum radios!
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Old 08-07-2007, 10:00 PM
  #133  
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Originally Posted by rea59 View Post
The only way to tell if this crease was a problem would be to put an FDR (Frequency Domain Reflectometer) on it and look to see where the "hole" is in the spectrum.

In short is it possible that this could have caused your problem? Yes it could have.

Use your foamy's and do a good range check. I hope it works better for you.
I failed to mention that the tech said he was going to send the coax back with the radio, for my review. When I receive it, I will post a picture of it here.

Would such a "hole" in the spektrum cause an intermitent failure?
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Old 08-07-2007, 10:03 PM
  #134  
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Originally Posted by Lieutenant Loughead View Post
I failed to mention that the tech said he was going to send the coax back with the radio, for my review. When I receive it, I will post a picture of it here.

Would such a "hole" in the spektrum cause an intermitent failure?
I could see it if the signal were marginal - who knows. Shoulda affected your range tests though I'd think.
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Old 08-07-2007, 10:11 PM
  #135  
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Originally Posted by Lieutenant Loughead View Post
I failed to mention that the tech said he was going to send the coax back with the radio, for my review. When I receive it, I will post a picture of it here.

Would such a "hole" in the spektrum cause an intermitent failure?
Originally Posted by UncleBob View Post
I could see it if the signal were marginal - who knows. Shoulda affected your range tests though I'd think.

I agree that it should have affected you range tests but without knowing the specifics of the transmitted spectrum (IE; data packets with the carrier signal) it would be very hard to say how the symptoms would show up.
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Old 08-07-2007, 10:24 PM
  #136  
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Let me expand just a little on my previous answer. The Spektrum radio uses many channels within the 2.4ghz spectrum. The crease could have affected only a few of these. The nature of the way Spektrum selects which channel to use could have made this problem appear intermittent. Also a point to consider is the background 2.4ghz radiation in your flying area may have forced you into one of these "affected" channels. Every time you turn your radio on it selects the channel based on what it "sees" out there. That would explain why one flight would be good and the next could have used a weak channel.
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Old 08-07-2007, 10:36 PM
  #137  
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Originally Posted by Lieutenant Loughead View Post
Failure #1 --> Site #1. Pond of water was about 100 feet from the aircraft (the aircraft was BETWEEN the water and transmitter).

Failure #2 --> Site #2. Pond of water was about 10 feet from the aircraft (aircraft and water were side by side, when seen from transmitter).

Failure #3 --> Same as failure #2. Failure #3 and Failure #2 started in almost exactly the same spot.

Failure #4 --> Site #2. Pond of water was 100 yards from transmitter. Aircraft was 100 yards from transmitter. Transmitter was between aircraft and water.

I'm really sorry I sold my Optic 6 last month... I still have my Laser 4, and plan to pay Hitec to change the Tx crystal to work on the five remaining 72 MHz receivers I have.

My original plan was to sell the five remaining 72 MHz receivers, and replace them with Spektrum receivers. I will not allow that to happen now!

I will test the electronics when I receive the Tx and Rx units. Time will tell, but at this point, I do not trust Spektrum radios!
I understand your frustration, and hope not to sound too harsh.....but....

You sent your radios to Spektrum, and they are looking into fixing any problem they can determine is involved. I'm not sure what else you think they are going to do. I understand you lost some expensive aircraft, but unfotunately, that's a risk we all take. While I understand you stated earlier you are not a troll (and I am not accusing you of being), we also have no way of proving that one way or the other.

I guess my point is, you have repeatedly said you no longer trust Spektrum, and you wish you had your 72MHz system. If that's truly the case, then why do you not just sell your Spread Spectrum equipment, and buy what you know and trust. Spewing it here repeatedly does nothing to solve your problem.

I have never seen a duplicate of the situation you described. I hope you find an acceptable solution. And, I am sorry you lost your planes.
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Old 08-07-2007, 11:04 PM
  #138  
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Originally Posted by rea59 View Post
Every time you turn your radio on it selects the channel based on what it "sees" out there. That would explain why one flight would be good and the next could have used a weak channel.
This is something that is very interesting about all the 2.4ghz systems. They either seem to lock onto 2 specific channels (spektrum) or they tend to hop around (faast and xps, although different in how they hop).

It seems to me that with the hopping systems you will have less chance of having a channel be free and having the system pick that channel only to have it hear interference after already picking channels due to someone else turning on a 2.4ghz device nearby. Which leads me to think that hopping might actually be beneficial in this sense....am I wrong?
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Old 08-07-2007, 11:13 PM
  #139  
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Originally Posted by Lip84 View Post
...??

wow....spektrum has dropped the ball...I am still very very discouraged to buy a spektrum.

I had done research on all the 2.4 ghz radio systems and I think Im going to go back and take another look at the Futaba Faast stuff. I was nervous about the channel hopping but it looked like the best alternative to spektrum other than the XPS. Only problem with XPS is that you need to have a several hundred dollar remote to buy a several hundred dollar module for...

At least we know we can trust futaba...right?

P.S. my condolences on your loss Loughead...i feel for you.
Spektrum has many more units being field tested by us than Futaba. I would expect Futaba to have birthing problems as more units are sold, just like Spektrum.

New technologies simply have problems. It is a shame that Horizion/Spektrum did not perform better in this case, but what would make us think Tower/Futaba would perform any better.

Just a thought.

By the way, my DX-6 & DX-7 have been trouble free.
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Old 08-07-2007, 11:18 PM
  #140  
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I was just thinking of Futabas general rep on in the field and on the market. For years it seems they were THE radio brand that you could aways trust and go to (i am sure people will disagree and have had bad experiences with futaba as well).

Futaba has been around longer than spektrum though and I would think that when they get around to it they will do it right. Catch my drift?
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Old 08-07-2007, 11:25 PM
  #141  
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Originally Posted by Lip84 View Post
This is something that is very interesting about all the 2.4ghz systems. They either seem to lock onto 2 specific channels (spektrum) or they tend to hop around (faast and xps, although different in how they hop).

It seems to me that with the hopping systems you will have less chance of having a channel be free and having the system pick that channel only to have it hear interference after already picking channels due to someone else turning on a 2.4ghz device nearby. Which leads me to think that hopping might actually be beneficial in this sense....am I wrong?
I'll preface this by saying I have never read anything "yet" on the Faast or XPS systems but on the surface of it you may be right in that the "hopping" systems may be better.

That was one of the first things I noticed about the Spektrum system. What if the channel is clear and then someone turns on a 2.4ghz device (other than another radio) that interferes with your selected channel? The same issue you had with 72mhz except other flyers could also affect you.

This just goes to show how you can't make everything 100% bullet proof, but you try to get as close as you can. I think Spektrum has a wonderful system which is a vast improvement over the older 72mhz systems and in the years ahead will have a system that is even better yet.
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Old 08-07-2007, 11:26 PM
  #142  
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Originally Posted by Lip84 View Post
This is something that is very interesting about all the 2.4ghz systems. They either seem to lock onto 2 specific channels (spektrum) or they tend to hop around (faast and xps, although different in how they hop).

It seems to me that with the hopping systems you will have less chance of having a channel be free and having the system pick that channel only to have it hear interference after already picking channels due to someone else turning on a 2.4ghz device nearby. Which leads me to think that hopping might actually be beneficial in this sense....am I wrong?
In order to "have interference" two signals have to be on (or near) the same frequency at the same time. A "channel" is actually a band of frequencies. You could have multiple things going on inside a DSM2 "channel without ill effects, and you could have devices sharing channels the channel hopping systems use without ill effect. The Spektrum systems seem to be transmitting at least one packet every 5.6 milliseconds, or about 180 packets per second, each packet containing as a payload the current commanded positions for the controls.

How many packets would have to get dropped for YOU to notice? For me ... quite a few. Add to that the fact that bad data is discarded, not used, and the control system is pretty robust.


Originally Posted by rea59 View Post
What if the channel is clear and then someone turns on a 2.4ghz device (other than another radio) that interferes with your selected channel? The same issue you had with 72mhz except other flyers could also affect you.

Even the Spektrum systems use CDMA, so in theory they could channel share but they choose not to. The frequency (within the channel) the RX-TX lock to isn't fixed, the carrier wanders about within the band in a pseudo-random manner. The RX "knows" the wander pattern and can decode the signal but outside observers see normally distributed noise.
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Old 08-07-2007, 11:37 PM
  #143  
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Originally Posted by rea59 View Post
I'll preface this by saying I have never read anything "yet" on the Faast or XPS systems but on the surface of it you may be right in that the "hopping" systems may be better.

That was one of the first things I noticed about the Spektrum system. What if the channel is clear and then someone turns on a 2.4ghz device (other than another radio) that interferes with your selected channel? The same issue you had with 72mhz except other flyers could also affect you.

This just goes to show how you can't make everything 100% bullet proof, but you try to get as close as you can. I think Spektrum has a wonderful system which is a vast improvement over the older 72mhz systems and in the years ahead will have a system that is even better yet.
The FCC requires that all 2.4ghz devices not lock on to any channel in use. This applies to any device operating on the 2.4ghz frequency. That is one of the first requirements to use the frequency.
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Old 08-07-2007, 11:41 PM
  #144  
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Originally Posted by UncleBob View Post
The Spektrum systems seem to be transmitting at least one packet every 5.6 milliseconds, or about 180 packets per second, each packet containing as a payload the current commanded positions for the controls.

How many packets would have to get dropped for YOU to notice? For me ... quite a few.

Even the Spektrum systems use CDMA, so in theory they could channel share but they choose not to. The frequency (within the channel) the RX-TX lock to isn't fixed, the carrier wanders about within the band in a pseudo-random manner. The RX "knows" the wander pattern and can decode the signal but outside observers see normally distributed noise.
I would suspect that they chose to not "channel share" for that reason. In order to not reduce the avalible number of packets per second giving a better chance for good packets to get through a "noisy" area.
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Old 08-07-2007, 11:41 PM
  #145  
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Well, from what I remember the Spektrum lock on 2 of 80 possible "channels" for lack of a better word. If another device (phone, pager, whatever) were to use that channel, it would also require the unique GUID code to operate the RX. Without that GUID, the Spektrum RX ignores the signal.
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Old 08-07-2007, 11:45 PM
  #146  
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Originally Posted by Rabbitcreekok View Post
The FCC requires that all 2.4ghz devices not lock on to any channel in use. This applies to any device operating on the 2.4ghz frequency. That is one of the first requirements to use the frequency.

So when a Spektrum TX/RX "lock" onto each other is that a "channel lock" or just a data packet "encoding lock"?
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Old 08-07-2007, 11:46 PM
  #147  
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Originally Posted by gfdengine204 View Post
Well, from what I remember the Spektrum lock on 2 of 80 possible "channels" for lack of a better word. If another device (phone, pager, whatever) were to use that channel, it would also require the unique GUID code to operate the RX. Without that GUID, the Spektrum RX ignores the signal.

I think the GUID is at the data verification layer, well past the radio. First there is the scan and select, then the radio uses direct sequence spread spectrum to isolate the signal from outside interference. Both share knowledge of the PN sequence used. Finally there appear to be several levels of data validation.

As long as no other source is too strong or is using the same "PN" series even channel sharing should be non-fatal to the link.

Direct-sequence spread-spectrum transmissions multiply the data being transmitted by a "noise" signal. This noise signal is a pseudorandom sequence of 1 and −1 values, at a frequency much higher than that of the original signal, thereby spreading the energy of the original signal into a much wider band.

The resulting signal resembles white noise, like an audio recording of "static". However, this noise-like signal can be used to exactly reconstruct the original data at the receiving end, by multiplying it by the same pseudorandom sequence (because 1 1 = 1, and −1 −1 = 1). This process, known as "de-spreading", mathematically constitutes a correlation of the transmitted PN sequence with the receiver's assumed sequence.

....

The resulting effect of enhancing signal to noise ratio on the channel is called processing gain. This effect can be made larger by employing a longer PN sequence and more chips per bit, but physical devices used to generate the PN sequence impose practical limits on attainable processing gain.

If an undesired transmitter transmits on the same channel but with a different PN sequence (or no sequence at all), the de-spreading process results in no processing gain for that signal. This effect is the basis for the code division multiple access (CDMA) property of DSSS, which allows multiple transmitters to share the same channel within the limits of the cross-correlation properties of their PN sequences.
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Old 08-07-2007, 11:54 PM
  #148  
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Originally Posted by UncleBob View Post
I think the GUID is at the data verification layer, well past the radio. First there is the scan and select, then the radio uses direct sequence spread spectrum to isolate the signal from outside interference. Both share knowledge of the PN sequence used. Finally there appear to be several levels of data validation.

As long as no other source is too strong or is using the same "PN" series even channel sharing should be non-fatal to the link.
That would take us back to the Lieutenant's case where an attenuation of a portion of his spectrum would be the most likely cause of his failures.
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Old 08-07-2007, 11:55 PM
  #149  
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Thats the thing...the theory is all there and its awesome. If it really worked like that the world would be a better place but it obviously doesnt.

I did some more research on the Futaba systems and they are having some issues with jsut releasing and providing information on them. They seem to not have any middle of the road items either. you either get the 6ch or 7ch units with somewhat limited capabilites, when compared to DX7, or you get the $1200 12channel.

Bollucks! Why cant we have a competent market with working devices for the common man!

Excuse the frustration...I am just upset over having the system I have been dreaming about for the last couple months be less than stellar...
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Old 08-08-2007, 12:04 AM
  #150  
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Originally Posted by Lip84 View Post
Thats the thing...the theory is all there and its awesome. If it really worked like that the world would be a better place but it obviously doesnt.

LOL

I have experienced many times where "theory" and "reality" don't co-exist but in this case I believe that the equipment is processing as advertised (theory) (witness the thousands of system in the field working perfectly) and that this radio has/had a specific failure which resulted in the symptoms being seen.
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