Extensive real world tests and results of the 2.4Ghz stuff

[Tim Mackey]

LINK.

[andy watson]

The most interesting thing in there is the system ranges- 1.3 miles for a park fly!!

[Doug Ireland]

Yes it was a bit long winded but interesting nonetheless. I wonder if the results would be similar for our 100mW sets?

[Myron Beaumont]

Doug

Could you tell me the output power they are allowed to  use in the USA .? I presume it's more than our 100 mW.& what the relationship is regarding power versus range . Bet it's not linear ! What an interesting / comforting article -They seem to have thought of just about everything .A few bob's worth involved for those tests Eh?

[Tim Mackey]

Yes the range tests were impressive huh!

US power outputs are 200mW ( peak not RMS I believe ) - the affect on range is certainly not linear - and our maximum 100mW is absoulutely fine for purpose.

[John Cole]

The range is limited by the signal picked up by the Rx aerial.  This is primarily reduced by distance according to the inverse-square law.  That would be 100% true in a vacuum.  In air, there is also a slight absorbtion effect, but radio frequencies are chosen so this effect is extremely slight.  So a 100 mW Tx would have about 70% of the range of a 200 mW Tx.

[Myron Beaumont]

John & Timbo

No problem then .If the range was severely diminished I'd have to go to Specsavers

[Myron Beaumont]

PS 

Got that wrong .I forgot to say "anyway"

[Delta Whiskey]

Interesting to see out of the lab based response times, the old 1976 AM was the fastest !

 

TRANSMITTER TESTED RESPONSE TIME (ms)
Kraft KP7C (made in 1976) analog AM 05-15
Futaba T6EX 2.4 GHz system 18-35

R 8103 72 MHz w/PPM FM receiver 20-40

JR 12X 2.4 GHz system w/12-ch Rx 25-40

Spektrum DX7 2.4 GHz system 25-40

 

and I won't mention the Futaba v Spekie result!

(I don't mean to start a war - honest) ......I sound like Mr Bush !

[David Ashby - Moderator]

Too late DW, now you've gone and done it

[andy watson]

Shhhhhhhhh

 

Don't mention the war, I think I did once but I got away with it!

 

[Brian Parker]

Have just printed and read the article, quite interesting and not unexpected with regard to the performance of the more expensive receivers.
 The test confirms that as far as Spread Spectrum is concerned it is better to pick a spot and stay there rather than to hop around all over the place.

 Two-penn'orth worth.

Regarding the response times, the AM system was the fastest because the integrity of the signal is not checked. Does this mean that with 2.4Ghz the slower the time the better (reference the budget T6EX and the 7C)?

The servo will certainly slow things down.

 The lower power rating for the UK is not necessarily a disadvantage.

 The ‘free space’ inverse square law is a reference measurement only and disregards environmental conditions.

 Consider an indoor site or even a compact flying site with industrial buildings causing multi-reflected signal paths and the effect of very strong reflected out-of-phase signals acting on a receiver with poor antenna orientation.

With our reduced power, the increased path of the reflected signal is less likely to null the wanted receive signal but at the same time provide more than enough power for limit of sight activity.

 More important is that the transmitter antenna sees a receiver antenna the same way up.

A similar test on the performance of the latest budget systems would be interesting.

[Doug Ireland]

Wow, thank you Mr Data I think I understood about a third of that! So the bottom line is this: is 2.4 better than 35meg?

[G]

Yes, the tests showed 2.4GHz was far better than 35mhz.  But let's face it, 35MHz is good enough 99% of the time.

 

I wonder if the author was sponsored by Spektrum - a lot of the tests seemed to find that Spektrum worked better than Futaba (the Futaba was good, but the Spektrum was better).  I'm sure it was unbiased, but nevertheless, as soon as I read results like that I get interested in where the author's allegiences might lie and what financial drivers might exist.

 

[John Privett]

And unless I missed it somewhere,  he only tested the Airtronics (Sanwa) and a couple of JRs for interference with a mixture on Futaba and Spektrum txs running.  He seems to have not bothered testing Futaba with the same background mixture of transmitters.

 

 Do I recall reading somewhere that whilst 200mW is permitted in the US, only Spektrum/JR use that, the other manufacturers stick to the "global" limit of 100mW - maybe for ease of manufacture?

[John Cole]

Brian: both the direct and reflected signals are attenuated strictly in accordance with the inverse square law, so my 70% figure remains approximately correct.  I did not add in my previous post that of course any attenuation due to absorbtion will tend to reduce the "advantage" of the higher-powered transmission.

[Brian Parker]

Absolutely John, we are singing from the same Hymn sheet. I took it for granted regarding the longer path of the reflected signal and inverse square law hence my reference to out-of-phase signals.
If anyone else is interested in a basic explanation of Inverse Square Law and Propagation....
 Double the distance and energy is spread over four times the area, so only a quarter of the initial energy is now within reach (the aperture or capture area). An efficient antenna will be able to capture most of the energy within reach in the aperture. Actual energy available is a function of inverse square law and the environmental affect.

Probably way off thread, sorry.

[Peter 'Ivanna Crashalot' Savage]

This is getting really confusing, on the DX6i, that i use, it says EU - 10mw (are we classed as EU? cause i know for a fact we are allowed to use 100mw)

 

Then it says US - 100mw :s

 

Also, they did not check the refresh rate of the new DX7sp designed for 3D heli pilots for really quick refresh rates.

 

One of my club mates actually said that for spektrum transmitters you have to have the aerial horizontally opposed, i never really pay much a ttention to my aerial, i normally just leave it how it came out the bag!

[John Privett]

Peter,  for any radio - 35MHz or 2.4GHz - the weakest signal is always in the direction the aerial is pointing.  So it's better not to fly with the aerial pointing directly at the model.  With 2.4GHz it's very easy to angle the aerial to one side so that it's sideways-on to the model.

 

Not sure why the DX6i would have a setting of 10mW for EU.  My understanding is that most countries permit 100mW and the USA I believe permits 200mW.  Until a change in the law 2 or 3 years ago here in the UK we were only allowed 10mW and in France it's rather more complicated - they're allowed 100mW indoors,  and 10mW outdoors across part of the 2.4GHz band, but 100mW across the rest!

[Doug Ireland]

Peter, last time I looked, we in the UK, are part of the European Union!

[Peter 'Ivanna Crashalot' Savage]

Anyway, i have my DX6i on the US mode anyway it is after all legal, unless it also changes something else. Cool thing is though, if I ever go and meet my uncle in france, I just need to change the setting

 

I knew we were 'in the EU' but was wondering if spektrum had a different way of saying it, maybe they didn't have enough memory to have UK seperately so they got lazy and couldn't be bothered to increase the memory for that reason It would be interesting to know how they managed to limit the power output via software.

[Tim Mackey]

I dont think you should be operating your DX6i on the US setting Peter. Regulations in the UK only permit a maximum of 100mW for our applications, and the US output is reputably double that...despite what it might say on your Tx screen.

Transmitting at double the allowed power is therefore not legal .

Take a look at this thread here.

Incidentally mac man is a technician employed by macgregor / JR systems, and a jolly good guy