RunRyder - My experience with the DX7 spread spectrum radio

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Radio - JR & Spektrum DSM > My experience with the DX7 spread spectrum radio

bob00
Veteran
Location: Toronto, ON

d_wheel: slots for futaba plugs
- I took the case apart and made the slots with a mini file. Took about 15min.

Pyrock: flight mode switch changes the following...
- flight mode (pitch and throttle curves)
- gyro rate (2 rates available, can be assigned to any flight mode)
- GV-1 RPM (RPM plugged into AUX2)

- R

12-15-2006 Over year old.

HOMEPAGE

sharam
Elite Veteran
Location: Northern California

I have also followed the XPS threads - I agree with JKos. I am not sure how the combo of the XPS module with the 9C will result in low latency. Perhaps I don't understand it. The analogy that Jim Drew gave (two cars, one faster off the blocks, one faster top end, etc.), makes sense, but I don't see how it applies to this.

My statements above are inquisitive, and not meant as a slant against XPS.

12-15-2006 Over year old.

Augusto
rrAdvertiser
Location: San Diego, CA

Quote
How did you make the slots (small saw blade; exacto blade; dremel)? Did you remove the case while cutting?

I simply took an X-Acto blade and cut them at the field. I swapped the whole thing at the field and took me about a half hour to program. The plastic is not brittle. It flexes a bit so it's pretty easy to cut with a blade. If I did it a home I would have probably opened the case like bob did.

Augusto.

Avant Aurora Ultimate

12-15-2006 Over year old.

d_wheel
Veteran
Location: Deep in the heart of Texas.

Quote
bob00 d_wheel: slots for futaba plugs - I took the case apart and made the slots with a mini file. Took about 15min. Augusto simply took an X-Acto blade and cut them at the field.

Thanks Bob and Augusto. One more question. After a quick try this morning before coming to work, I can not figure out how the case comes apart. I see the latches but don't know exactly where are what to press on them to get the case apart.

Later;

D.W.

12-15-2006 Over year old.

Paul Beard
Senior Heliman
Location: San Jose CA

Quote
I'd sure like to get a clarification about this from Mr. Beard or someone at Spektrum. Adams told me via PM that Mode 3 is not possible on this tx.

Only Mode 1 and Mode 2 is supported with DX7.

There is no mode 3 or 4 selections in the service menu.

Paul

12-16-2006 Over year old.

HOMEPAGE

GimbalFan
Elite Veteran
Location: Copter County, Nv

Quote
Only Mode 1 and Mode 2 is supported with DX7.

Thanks for clarifying that, Paul. I must admit that's a bit disappointing though.

Looks like -- short of a warranty-voiding hardware hack -- heli pilots who fly left cyclic are out of luck for now. Please consider including a Stick Mode 3 capability in the next version.

op-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-t

12-16-2006 Over year old.

MattUK
Senior Heliman
Location: Lancaster, UK

stupid question..

With this system, can 2 different DX7 transmitters use the same frequency/channel number at the same and still work ok

Matt.

----
Light travels faster than sound. That's why some people appear bright until they speak.

12-16-2006 Over year old.

RCHeliJim
Elite Veteran
Location: Orem, UT USA

There are no frequency numbers persay - the system chooses the best parts of the frequency range available upon startup - up to 40 Spektrum radios may be used at the same time in the same area.

You never choose or asign a channel in Spektrum, it does it all itself.

Go Fly, Have Fun!!
-Team Quick UK
-Team RCHeliMag

12-16-2006 Over year old.

HOMEPAGE

Micro-Maniac
Elite Veteran
Location: Pasco,Washington Formerly: Captain Chaos

My guess at an answer would probably be yes if they could attain the same channels they could probably still work given their GUID - They would listen to the commands from their bound source and ignore the others -

But as RCHeliJim stated it's not very likely two could end up using the same channels as they won't complete a link and operate until they have found and secured two clear channels each.

12-16-2006 Over year old.

MattUK
Senior Heliman
Location: Lancaster, UK

so as an example, if a situation arises (all 2.4Ghz freq/channel being used), can you have 2 seperate DX7 radio systems transmitting on the same freq/channel number at the same time? and this is possible because each dx7 transmitter has it's own unique GUID?

Matt.

----
Light travels faster than sound. That's why some people appear bright until they speak.

12-16-2006 Over year old.

Micro-Maniac
Elite Veteran
Location: Pasco,Washington Formerly: Captain Chaos

Theoretically speaking - But if all channels are already occupied then a system won't even arm or operate until two channels become available - It will scan indefinitely looking for unoccupied channels and will not arm or operate until it has secured two clear channels for itself -

When you bind a RX to a TX the RX is given a specific GUID code to look for - If you power both a TX and RX while all channels are occupied then the TX will scan looking for two clear channels to secure and the RX will standby scanning for that specific GUID to lock on to.

So if you're flying with more than 40 other systems powered up then don't cycle your TX power in flight or you'll lose your channels to another system?

12-16-2006 Over year old.

MattUK
Senior Heliman
Location: Lancaster, UK

Thank you Captain Chaos

So each DX7 system needs two freq/channels to work, so if there are 40 usable freq/channels on the 2.4Ghz that would mean only 20 users could fly at once (2 per user) or is it 40 users with 80 freq/channles available?

Matt.

----
Light travels faster than sound. That's why some people appear bright until they speak.

12-16-2006 Over year old.

Micro-Maniac
Elite Veteran
Location: Pasco,Washington Formerly: Captain Chaos

40 systems / 80 channels.

12-16-2006 Over year old.

MattUK
Senior Heliman
Location: Lancaster, UK

Quote
So if you're flying with more than 40 other systems powered up then don't cycle your TX power in flight or you'll lose your channels to another system

lol,

again thanks.

----
Light travels faster than sound. That's why some people appear bright until they speak.

12-16-2006 Over year old.

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Radio - JR & Spektrum DSM > My experience with the DX7 spread spectrum radio

Augusto
rrAdvertiser
Location: San Diego, CA

Quote
With this system, can 2 different DX7 transmitters use the same frequency/channel number at the same and still work ok Matt.

Interesting question with an even more interesting answer.

The DX7 uses spread spectrum. Being that the case it means that a certain bandwidth is assigned to each channel (in this case 1 MHz) and the transmission occurs by the signal being spread within that frequency bandwidth.

As a reference, the system used by many cellular companies in the US called IS-95 CDMA like Verizon's uses a similar system of spread spectrum via direct PN (Pseudo-random Numbers) sequence spreading and the channel banwidth assigned for it is 1.25MHz.

This cellular phone channel of 1.25 MHz bandwidth is actually used SIMULTANEOUSLY by ALL the cell phones connected to that base station in that channel. In other words, there are SEVERAL cell phones using the SAME channel yet they don't interfere with each other because they are spread using different PN sequences despite occupying the same channel.

That's the advantage of spread spectrum. The way this is accomplished is by spreading the transmission via the mixing with a spreading code called the PN code. A regular radio signal when mixed with this PN spreading code ends up looking like noise in the channel. The same happens to other signals spread with different codes in that same channel. To recover the signal the receiver uses that same unique PN code that was used by the transmitter to "de-spread" the noise and recover only that particular signal again and not the other ones simultaneously present in that channel.

Because the other "noise" from the other radios was spread using different codes their signal remains as noise and is not recovered because the PN sequence is not the one used to spread it and remains as noise leaving only the correct one recovered.

This code being different and non-colliding between several cell phones is what allows the simultaneous use of several cell phone calls in the same 1.25MHz channel.

The system used in the DX7 doesn't use this ability of simultaneous use of the same channel or channel pairs (at least not yet) and decided to assign only one radio/receiver set to a pair of 1MHz channels BUT despite not using that same pair of channels for simultaneous radios they DID assign different PN spread codes to every transmission.

Why is that so important? Because in the unlikely case that for some odd reason two radios ended up using the same two assigned channels they WOULD STILL NOT INTERFERE WITH EACH OTHER the same way several cell phones using the same channel don't interfere with each other simply because their spreading PN codes are different and non-colliding.

This is a feature that I REALLY liked when I discussed the technology with Paul.

Augusto.

Avant Aurora Ultimate

12-16-2006 Over year old.

GimbalFan
Elite Veteran
Location: Copter County, Nv

I like the entertainment value of the description in Hedy Lamarr's 1942 patent application that outlines spread spectrum as being like two identical player piano rolls (the PN code), one in the tx and one in the rx.

As long as both rolls turn the same speed and the matched sets of holes line up simultaneously (tx & rx are bound), the rx knows which piano 'note' (frequency) to next use to hear another segment of the signal.

Cool technology.

op-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-t

12-16-2006 Over year old.

ts250x
Heliman
Location: Shropshire England

Just bought myself a DX7 this morning,I use a JR 2610 at mo so the DX7 is great as they are very much the same to look at.What I would like to know is why is there less movment on the throttle stick on the DX compaired to the JR would anyone know if there are any stops in the TX that I can remove to get full movment thanks

12-17-2006 Over year old.

midwestpilot
Elite Veteran
Location: Crystal Lake, IL

throttle stick travel

It was done on purpose... to not have the stick pegged so high and then need to add rudder... to make it easier on the hands.

From what I remember the stick is calibrated to that new travel and you get 100% travel... so no worries

In life there is no spacebar!

Rich Erikson AMA 6175

12-17-2006 Over year old.

HOMEPAGE

ts250x
Heliman
Location: Shropshire England

HHmmmm thing is more travel is better for me because I fly my raptor with the v curve so with less movment on the stick will make it a wee bit to sensative I think, would you know if there are any stops and if so would it be ok to remove them?

12-17-2006 Over year old.

Micro-Maniac
Elite Veteran
Location: Pasco,Washington Formerly: Captain Chaos

You say you were using a JR radio before the DX7 so that radio also should have had a reduced throttle stick throw as all JR radios have had for some time now - Maybe you just now noticed it with the DX7?

It would require recalibration if the stops were removed.

12-17-2006 Over year old.

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Radio - JR & Spektrum DSM > My experience with the DX7 spread spectrum radio

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