UK Spektrum DX-7 ground range - field test

[simon_t]

Being a bit of an anorak about gadgets, I did a ground range test on a brand new Spektrum DX-7/AR7000 last weekend. I am sure that some of the European flyers have been concerned by speculation about significant range reduction when compared to the US spec DX-7s. The good news is that I don't think any heli pilots should be concerned. Our flying site is on a very large area of marshland, allowing me to walk away from the Rx in a straight line, and able to maintain line of sight as I walked away. With the AR7000 at 1m above the ground, and the transmitter at a similar height, the Rx started to occasionally enter hold at a range of 1.2Km, about 3/4 of a mile. At that range I could not see the the guys watching the Rx end, and even the cars at the site were very small! I have attached a Google Earth screen shot to illustrate the ground range. The in air range would be better, may be up to 1.5 times greater - that test will have to wait for another day.

Our flying field is the wedge shape field at the lower end of the yellow line. Most helis don't fly outside of this field, so range is not an issue even with the lower power UK spec Tx.

Futaba, via the Robbe (Futaba European Distributor) website are claiming a ground range of 2000m and an air range of 3000m for their 2.4GHz FASST system. If borne out in practise that will be pretty impressive.

Simon

[G-DAVE]

??

Been using a DX7 since December Last year --- never thought there was a problem --- it's never given any cause for concern.
Dave

[Ade_Law]

i would be interested if you did the same test with 10 tx's on at the same time.

Ade

[Ashley Davis]

why would that effect the range, the sets broadcast on a broad spektrum using pattern matching, so 10 tx or 40 it wouldn't make any difference.

[pchristy]

i would be interested if you did the same test with 10 tx's on at the same time.
Ade

It shouldn't make any difference, unless one of the "interfering" transmitters was substantially closer to the Rx than the wanted one. In that case it is a bit like trying to hold a conversation whilst standing next to a pneumatic drill!

*ALL* our RC systems are limited to 100mW ERP (Effective Radiated Power). The difference is that at 35 MHz, a telescopic aerial is quite lossy, and you need to put the best part of 1 watt in to get 100mW out! At 2.4 GHz, the aerials actually have about 2dB or so of *gain*. Also the receiver aerials are similarly more efficient, so I would expect the air range to be substantially greater at 2.4 GHz.

At 2.4 GHz, a wavelength is just over 12 cm. Once the equipment is greater than this height above the ground, it is effectively in free space, and the ground should have little impact on range.

However, 2.4 GHz does get absorbed by wet foliage (trees, grass, etc) which will reduce the range if they get between (or close to between) the Tx and Rx.

Cheers,

--
Pete

[Smoothound]

i would be interested if you did the same test with 10 tx's on at the same time.

Ade

Yeah I'm interested as well after what you said when i saw you yesterday

[Ade_Law]

i was talking to somebody the other day whos in the IT industry. i dont know the theory behind it but she was quite concerned about how the range and latency would be affected with a larger number of sets running within range of each other.

i will see if i can get some more info and update.

Ade

[Sesame]

would also be interested in seeing what effect mixing Spektrum and Futaba sets would be seeing as there are differences in how each work

[Ashley Davis]

This was all covered in the talk by Paul Beard at 3D Masters this year. The short version is that multiple spektrum sets makes bugger all difference to anything as they transmit on different frequencies and that FAAST has absolutely no effect on spektrum or vice versa. It's all a bunch of rumour mongering by people who think they know what they are talking about but unfortunately don't really.......I'm kind of fed up hearing about it really as it just sets off all the 35mhz 'heroes'....you know the ones, they always say anything new will never work.

[zagifly]

Been using Spectrum since Dec last year in planks and helis, our site near Eastbourne has areas of maintained interference where you can repeatedly fly through it and get a glitch every time. Cant get the Spectrum to be anything but rock steady and the model match has saved me a few times, we have had 5 2.4Gig sets up together with no problems. Only problem now is excuses when I crash a heli, hoping not to do it too much and with Align it's seldom component failure.
Dave Howe

[Ade_Law]

i have emailed my friend awaiting a reply with more detail. She knows her stuff on the RF side of things.

as everybody accuses me of being biased im gonna accuse paul of being biased too. as the designer of the system dont you think it is possible that he might accidentally forget to tell us about possible issues?

Ade

[Ashley Davis]

Wouldn't that be classed as negligence?

Two things:

1. Do we really think Spektrum 'forgot' to test several sets working together at once
2. 2.4ghz is not RF

[simon_t]

G-DAVE: I was never worried about range with a heli or even the planks I fly, but F3J/F3B/F3F gliders at the limits of sight are more of a worry to me!

ADE: I know its not quite the same as your comment, but we were using mobile 'phones at both ends with no effect on the range

Pete: I agree that once the 2.4GHz system is several wavelengths above ground it is effectively in free space. I have yet to see a definitive test that shows the actual increase in range for a model in the air, and whether that substantiates Futaba's (or at least Robbe's) 1.5 factor claim.

Simon

[pchristy]

Simon,

I think the 1.5 times is a very conservative estimate, but I can't prove it!

I've actually got a 1.8M thermal soarer (electric launched) and I've put one of the 6100 park flyer receivers in it. I've had it to the limits of my eyesight (admittedly not brilliant!) without problems.

--
Pete

[Smoothound]

Simon,

I think the 1.5 times is a very conservative estimate, but I can't prove it!

I've actually got a 1.8M thermal soarer (electric launched) and I've put one of the 6100 park flyer receivers in it. I've had it to the limits of my eyesight (admittedly not brilliant!) without problems.

--
Pete

This is something I've been looking into recently.

Biggest problem with the official full range Spektrum Rx's is the limited space in some of the smaller gliders, my Mini Blade for example. I was going to chance a 6100 but there is a small amount of CF in the fuse which put me off.