SpeKtrum DX8's range and output?

[barney]

Thinking about a Dx8 but there currently appears to be a few issues with poor Range check distances and excessive frame dropping. The rest I can live with.

When first introduced SpeKtrum bragged they seldom EVER dropped a frame during testing albeit with a US spec system

In the UK we run the DX7 at lower output and I have witnessed large differences from TX to TX in range checks even when bound to the same Rx on the same day.

With JR moving to Frequency Hopping is there an undelying problem here or issue with current or future compliance?

Have Spektrum been forced to comply to ever more stringent testing. There is some doubt about the actual power level they do have. I believe US is 400mw and Europe possibly 100mw but there are quite a few threads indicating it could be as low as 100mw US and 10ms EU.

So whats the real deal.

I have an early DX7 althought its now a Sim radio and it has a long range check although its UK purchased and compliant, go figure! So is the DX8 just as fussy to connect as the Dx7 can be etc.

I have flown a Futaba 12FGH without one issue in 3 yrs connecting 100% of the time. I'm due a Radio change but would like to have onboard Flight pack voltage telemetry.

So those of you with a Dx8 what range check distances are you achieving. I have read a few struggle to reach the recommended 25? paces, and returned there radios for checking, what was the outcome of this?

If your are using the telemetry are you seeing rames being dropped regularly?

Thanks Brian

[Disc]

For me theres no contest

Futaba is the way to stay

JR doing 7 channel sets I believe is because spektrum has gone up Tranny spec wise and the deal with spektrum probably means they cannot use the same system so they have opted for a channel hoping system. I don't believe JR will drop support for any of there current systems.

Having seen and held a DX8 the DX7 is better and its not a even close to quality to any Futaba set.

I don't get why people suddenly need telemetry on battery packs in the models.. its called pre-flight for a start. Although theres an interesting thread on naff ryder where the vibe system causes the pitch to goto 0 degress no matter what when the timer goes off! could be fixed now and didn't effect every set as well.

for me wait and see the new JR set if you must swap tranny

But it'd be a cold day in hell before I swapped my 12FG for a DX8 or 7 for that matter!

[barney]

Hi Mark, Ive fingured the DX8 in the flesh and whilst I agree the difference in quality is there, I look at a TX more as means to an end. The Gimbals seem fine and programming adequate for my needs. The adaptability to charge easily is there too.

The reason for the telemetry is for Flightpacks as I'm continually underflying them sometimes well in excess of 2mins depending on the flying I'm doing. I can run anything from 4.45 -7.5 mins.
The vibrating Alarm feature is a boon as I often miss the Alarm on the 12Fg as my hearing is not brilliant.

The deciding factor for me at this point is going to be good consistant range and 100% relability with no compliance issues.

Thanks Brian

[Disc]

I'd recommend you check out runryder and you'll get a feel for how the DX8 is....

if it was me I'd be waiting for the 7 channel JR set with telemetry, and wait for the comments to start coming in before i'd go to a DX8

Also consider setting up 2 alarms on the 12FG in the mean time so one goes off say just after the 1st one ?

[sacko]

The reason for the telemetry is for Flightpacks as I'm continually underflying them sometimes well in excess of 2mins depending on the flying I'm doing. I can run anything from 4.45 -7.5 mins.
The vibrating Alarm feature is a boon as I often miss the Alarm on the 12Fg as my hearing is not brilliant.

This is what I am interested in, and the only reason id downgrade from a DX7 to the 8

Has anyone actually tested this feature? As I can only imagine that as the voltage fluctuates in flight, it would regularly drop beneath the voltage cutofff?

[millerman]

i managed 60 paces when i tested mine and it was fine but i was using an ar7100r reciever with 2 remotes i dont remember what the frame losses etc were but will test again this weekend for anybody who is interested will also do a test with an ar8000 and r7000 if i get a chance to do so must say touching wood i have not had any problems with mine but like i have said b4 im one of the luck ones

[scallybert]

Wild Guess

I'm guessing here...

Bear in mind that the 2.4GHz wavelengths are in the centimetre range. Hence proximity to conductors where the lengths & distances are in this kind of (cm) range can have an effect. eg carbon frames, shafts, maybe the ground.

So what..?

DSM2 picks 2 channels (broadband carrier frequencies) each time the Tx is powered up.

My wild guess is that interference effects due to carbon frames, etc, might vary with which channels are chosen.

Ie you might get a range check variation with the same gear, depending which channels are picked. ie random, or dependant on what else is transmitting at the time.

So range check variations might not be down to defects.

A system hopping between channels won't see this (theoretical) effect - but might see another issue.

[Gaza07]

Ive had no range check problems with mine but I have only just fitted the telemetry and not re-checked it, Also range checked with a AR7000 with no probs

[pchristy]

Barney,

From my experience, there are some things its best not to know! And to me, frame dropping is one of them!

Regarding the power output, ALL UK RC channels are limited to 100mW erp (effective radiated power). Bear in mind that at 2.4 GHz, the aerials are MUCH more efficient, and there is far less "background" noise. This means that if 100mW was adequate for 35 MHz, it will be MORE than adequate for 2.4 GHz.

To put this into perspective, the difference betwen EU and US specs means a difference of 3dB, out of path budget of 130dB. Putting that into "linear" numbers, this represents a simple doubling of the signal compared to a factor of 10 with 13 noughts after it! Totally insignificant!

One thing that many people forget is that a 2.4 GHz signal is much more easily obstructed by chunks of metal or carbon fibre. This almost certainly accounts for any variations in ground range between different set-ups than anything else. For example, I generally get much more "test mode" ground range (using the same Tx) on my Agusta 109 than I do on my (much bigger) Bell 47 - yet so far, I haven't noticed any issues in the air. It is almost certainly caused by the vast bulk of the gasser engine blocking / reflecting more of the RF signal than the Agusta does.

Some years ago when I was trying to get 459 MHz working in a helicopter, this proved to be a big problem. It works well in the (mostly wood) Lark, but I had a very difficult job getting it working in a Shuttle! I did manage it, but it wasn't straightforward. Aerial positioning was absolutely critical.

2.4 GHz, with its even shorter wavelength, is even more susceptible. BUT, the use of dual receivers, and the robust nature of Spread Spectrum transmission techniques substantially mitigates the effects. The whole point of SS transmissions is that it shouldn't matter if packets get dropped - there is enough redundancy in the signal, and it is transmitted fast enough, for the receiver to reconstitute the signal without the pilot being aware. Unless you are noticing a slowing down of the controls in flight, don't worry about it!

Regarding JRs partial move to frequency hopping, I believe this has more to do with regulatory requirements in the Far East and contractual obligations than any technical issues. On paper, DSSM systems ought to enjoy a small but measurable advantage over frequency hopping systems. In practice, the differences are insignificant!

[millerman]

Barney,

From my experience, there are some things its best not to know! And to me, frame dropping is one of them!

Regarding the power output, ALL UK RC channels are limited to 100mW erp (effective radiated power). Bear in mind that at 2.4 GHz, the aerials are MUCH more efficient, and there is far less "background" noise. This means that if 100mW was adequate for 35 MHz, it will be MORE than adequate for 2.4 GHz.

To put this into perspective, the difference betwen EU and US specs means a difference of 3dB, out of path budget of 130dB. Putting that into "linear" numbers, this represents a simple doubling of the signal compared to a factor of 10 with 13 noughts after it! Totally insignificant!

One thing that many people forget is that a 2.4 GHz signal is much more easily obstructed by chunks of metal or carbon fibre. This almost certainly accounts for any variations in ground range between different set-ups than anything else. For example, I generally get much more "test mode" ground range (using the same Tx) on my Agusta 109 than I do on my (much bigger) Bell 47 - yet so far, I haven't noticed any issues in the air. It is almost certainly caused by the vast bulk of the gasser engine blocking / reflecting more of the RF signal than the Agusta does.

Some years ago when I was trying to get 459 MHz working in a helicopter, this proved to be a big problem. It works well in the (mostly wood) Lark, but I had a very difficult job getting it working in a Shuttle! I did manage it, but it wasn't straightforward. Aerial positioning was absolutely critical.

2.4 GHz, with its even shorter wavelength, is even more susceptible. BUT, the use of dual receivers, and the robust nature of Spread Spectrum transmission techniques substantially mitigates the effects. The whole point of SS transmissions is that it shouldn't matter if packets get dropped - there is enough redundancy in the signal, and it is transmitted fast enough, for the receiver to reconstitute the signal without the pilot being aware. Unless you are noticing a slowing down of the controls in flight, don't worry about it!

Regarding JRs partial move to frequency hopping, I believe this has more to do with regulatory requirements in the Far East and contractual obligations than any technical issues. On paper, DSSM systems ought to enjoy a small but measurable advantage over frequency hopping systems. In practice, the differences are insignificant!

if even i had any clue as to how dsm2 and dssm works i would have said that too

[Gaza07]

I wonder how many dropped frames other systems suffer just because you cant see them doesnt mean they are not there or never have been,
I agree that seeing these on your tx might not be the best thing for paranoid flyers, Does anyone know how frames are transmitted per second and what is the actual percentage of dropped frames just seeing 20 doesnt realy tell you anything and might just make you worry

[millerman]

I wonder how many dropped frames other systems suffer just because you cant see them doesnt mean they are not there or never have been,
I agree that seeing these on your tx might not be the best thing for paranoid flyers, Does anyone know how frames are transmitted per second and what is the actual percentage of dropped frames just seeing 20 doesnt realy tell you anything and might just make you worry

i agree with this does the futaba system have a way of showing this information as it would seem spektrum have opened up a channel to see how your radio is performing and futaba does not afaik thus being very hard to make comparason

[scallybert]

[...]On paper, DSSM systems ought to enjoy a small but measurable advantage over frequency hopping systems.

That was DSSS over FHSS, AIUI. ( )

However, it's been suggested that while DSM2 is DSSS, FASST is not FHSS; and that FASST is a frequency hopping DSSS.

[The Wikipedia sections on these acronyms seems pretty good.
DSM2 - Spektrum
FASST - Futaba
DSSS - Direct Sequence Spread Spectrum (scatters over a wide band)
FHSS - Frequency Hopping Spread Spectrum (hops between narrow channels)]

[pchristy]

However, it's been suggested that while DSM2 is DSSS, FASST is not FHSS; and that FASST is a frequency hopping DSSS.

There's more than an element of truth in that. Like many other systems (Bell/Hiller mixing?) both systems have elements of frequency hopping and direct sequence.

However, when you look at them on a spectrum analyser, a DSM2 channel is about 1MHz wide. A FASST channel is only about 100KHz (and yes, you have to be quick to see it!)

(For comparison, a 35 MHz channel is only 10 KHz wide, including guard bands! Useable bandwidth is about 5 KHz, tops!)

But to me, counting packet loss is a bit like putting an oil pressure gauge in you car! If you engine is fragile, or your doing a lot of racing, its probably essential! If you have a robust, modern car, it will probably just worry you unnecessarily!

Packet loss is something that is expected in SS systems, and the systems are designed to cope with it. The only real test is "does it work"?

[Gaza07]

The thing is spektrum have fitted a counter and people are worrying, I think about nothing but if we knew that 20 30 or 40 packets lost in a 10 min flight was out of 1000s or 100,000s of packets people would worry a lot less, I have no technical knowledge of this but maybe some one who has could put this into perspective