UK Spektrum DX-7 ground range - field test

[ChrisB]

not meaning to single you out here chris its just a suitable quote to start my post :-)

im not anti 2.4 when my old 9x2 gets long in the toorth I will upgrade. Im just passing on info i have gained from people knowledgeable on 2.4 gig. sure its not spectrum its general 2.4 info this applies to wireless, cameras as well as the 2.4gig we use.

my friend works in the industry and has contacts of the manufacturers of the 2.4gig chipsets and when they were told about specktrum and fasst they had serious concerns with pactet loss which would affect range and latency when a larger number of transmitters are within range of eachother.

claiming its BS is unfounded in my opinion you dont know any more than I do and without real evidence using our equipment i doubt we will ever really know.

im hoping that this weekend we can get >5 tx's at the field and do a proper test at the limit of range on the ground and see if we can replicate the effects that i have mentioned.

Ade

Ade

Didnt see your earlier post sorry,i was just responding to Ashleys post,,i know pretty much sod all about the techie side of things,all i do know is that OFCOM have approved it and more to the point i TRUST the technology

I am gonna start a POLL to get some feedback


Keen to help out with any tests at DMHC this weekend

[ChrisB]

Ade

The best and easiest way i assume is to have the test Tx`s range test button pressed to reduce power,walk the model away to get the range and try to swamp it with several other Tx`s at normal operating power

or maybe not

[Ade_Law]

what exactly does the button do? I know it reduces range but how does it do it?

if they reduce the power output then i dont think this will be a valid test chris as the background chatter will be lower per tx because it transmits at a lower power level.

im hoping a bunch of tx's on the far side of the field (about 400metres?) all models and tx's on and the fact that the ground reduces the range might be enough. if its not to enough distance to cause lockouts with 1 tx on and it does with 10 then we defo know we have a problem.

its not a situation you would see too often at our club field but its certainly something that could easily happen on a slope soaring site.

it may be too early to see this type of problem as there just arent enough transmitters around but was 2.4 becomes more popular and its rare to get that many tx's on at the same time although im sure we cant have been far off the numbers i have mentioned at charmouth.

Ade

[Ashley Davis]

With Spread Spectrum transmissions multiple systems use the same band because the transmitter and receiver side share the same sequencing code and this makes it possible for the receiver to extract the correct signal. However, the more transmissions you have the worst the Signal to Noise ratio and thus it gets harder to reliably retrieve your own data.

A good analogy would be 20 people sitting around a table and having several conversations. Because of the way the human brain works each of them can follow whichever conversation he wants. However, as you start to get more conversations the background noise increases and it gets harder to hear the conversation you want.

This is true however the DX7 uses data GUID encoding as well as pattern matching (pseudo random sequences) to encode the signal. This allows for much better coexistence:

A spread spectrum system is less susceptible to interference than other non-spread spectrum systems. In addition, with the proper designing of pseudo-random sequences, multiple spread spectrum systems can co-exist without creating severe interference to other systems. This further increases the system capacity for spread spectrum systems or devices.

It is the combination of GUID and pattern matching which makes the DX7 not suffer from the effect that Ade is talking about.


The spektrum system uses an extremely broad pattern match technology as well as keyed data, so extracting the data from the background noise is not difficult even in a crowded band. As I said, all explained extremely well by Paul Beard at 3D masters. This system was designed to work with 40 sets simultaneously in use, we are unlikely to get beyond 10 at a field, usually much less than this. In order to even be approved for use I cannot see that if latency or range became an issue with a few sets turned on it would ever get any kind of approval. Also 2.4ghz and spread spektrum are two complimenting technologies not all 2.4ghz transmissions are also spread spektrum, FAAST being one example. FAAST gets referred to as spread spektrum but the actual system employed is frequency hoping rathen than broad banding (spreading) the signal. Although you could argue that frequency hoping is also spreading the signal, but in essence it's a narrow band signal frequency hoping.

[ChrisB]

Ade

I believe the button reduces the actual output power to 1/30th of normal power,,

We can try your test to see but if that shows no faults with as many as posible all on as normal i thought a single Tx and model with reduced power at its maximum range and then one by one switch on all the other Tx`s and leave them at full power i assume this make it harder for the model with the reduced power Tx to get its signal thru all the stronger tx signals


Either way,i am well up for having an play

[Ashley Davis]

I'm not sure it will make much difference as spread spektrum is designed to deal with exactly this type of scenario but can try it.

[ChrisB]

I just thought it would be good to throw as much into the mixing pot as possible,,will be interesting for sure


I assume it will be easier to do the test with 6100Rx`s as they should suffer sooner than the twin ones

Just thought with one Tx on reduced power it is effectively whispering over the others shouting

[Ashley Davis]

single rx only gets sent the data stream once instead of twice

[mchristyuk]

I do believe at the IRCHA jamboree in the US this year that the majority of pilots (read 600 out of 750) there were using a form of 2.4ghz (Spektrum/JR, Futaba, or XPS) and as any of you have been to the IRCHA that is quite a large flight line.. plus there are going to be guys "fiddling" in the pits with their 2.4ghz stuff as well as those flying..

I think if there was going to be a problem with the 2.4ghz stuff existing together that would have flagged it up in quite a large way..

Myself I bought a Spektrum module and receiver for my PCM10x and Vibes before the UK nats this year as 2 years ago I was almost shot down from interference from the trade stands.. This year somebody else was getting hits on their radio and I was mighty glad that I had taken the plunge and spent my hard earned on some 2.4ghz equipment..

Cheers

Mark

[ChrisB]

I would personally be very surprised if there was an issue of range loss due to the amount of Txs on,,i am the first to admit i know diddly squat about the technology really but i am sure OFCOM would have done thorough tests and the system is a couple of years old now and has been used at several big events

I think the tests will prove a total success with zero problems whatever we try

I will even get in my car and drive away with the Tx if needed and test via mobile phone from a much further distance with my model on the flightline with other powered up Tx`s right next to it

[ChrisB]

Thinking about this,i reckon the confines of the field are not enough but we can sure try that first,i reckon it will need say 2 Tx`s to go off in a car down the lane to find the limit of range with just those two on and then communicating via a phone with people on the flightline fire up more Tx`s and see if the Tx`s in the car lose some of that range,if they dont then i think its case proved

[simon_t]

It will be interesting to see your results, but I suspect you will not see any effect. In fact I think you would not see an effect with 40+ Tx's, unless you put an 'interfering' Tx next to the Rx under test, where you might get the desensitisation.

Simon

[d1ver]

i carnt admit to knowing shit about this but i do know 1 thing,in new builds i do across london and uk.the 2.4 is on the way out from an insurance point ov view.another way is from to many new products jumping on band wagon i.e car alarms,home alarms,paging systems(fire servive ,medics and so on)used in every day life.
flame me for this but i use an old futaba ff9 super.
you can use wat ever.
i check wat your using u dont.
we all fly .
good side bad side.
ffs just go fly and be happy .tell us when u have lock out or crash .
new products welcome.
bitching sod off.
o and have a nice day

[Boggy]

geez diver did you have a bad day at work?? the post is about range issuses!
when you say 2.4 is on the way out do you mean in everyday use? not r.c surely.
nobody can diss you for using what probably is still the most common system.but like you say "use whatever"
when you say "i check what your using u dont" omg are you big brother!
have a scotch and calm down before replying

[ChrisB]

If they ban 2.4 which they wont,how are they gonna police it because i wont be stopping using it for sure

Also there is a slight hitch with the tests because rules is rules and there are only 4 of the 2.4 slots on the pegboard and we must all card on for some strange reason