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Understanding the numbers....

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Roger Dyke20/04/2019 19:55:37
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Hi All,

I have recently purchased my first 2.4GHz transmitter/receiver. It is a Spektrum GX6 G3 with an AR6600T receiver. I think that I am now almost up to speed with programming it's capabilities. However, the range check is a bit of a puzzle. My back garden is 30 metres long so am using this as a preliminary range check just to make sure that I am in the right ball-park before I disappear to the flying field.

When I place my model on the ground at the top of the garden, I then switch it on and walk back the 30 metres. With the tx set to Range Check I observe from the telemetry readings that antenna 'A' gets the occasional fade with no 'Frame' losses and no 'Holds'. So far so good. Now, if I press the 'trainer' button to reduce the transmit power, the 'A' antenna seems to start counting endlessly with the 'B' antenna not far behind. Also the 'Frame' starts slowly counting up too. I also get the occasional 'Hold' too. If I move the tx in different directions, the numbers count either a bit slower or a bit faster depending on tx antenna position.

I have four aircraft. One with the Spektrum AR6600T receiver in, and the other three with an Orange R620X in. I have been very careful with antenna placement in the aircraft but am a little disappointed with the telemetry results coming back with the tx on reduced power. Am I missing something here.

I welcome the thoughts of all you experience 2.4-ers out there.

Many thanks in advance.

Roger

Percy Verance20/04/2019 20:26:35
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I'd raise the model off the ground Roger, preferably by a metre or so. That might make a difference.

Don Fry20/04/2019 21:01:24
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In a 10 minute flight, you should get less than 500 fades per aerial. Typical is a hundred or so. Fades is a fact of life. It's an aerial not picking up a data package. More than 500 move the aerial.

In the same 10 meter flight you can get no more than 20 frame losses. That's all the aerials losing a data package at the same time. More than 10 try another position for the receiver or slave.

Holds are a run of lost frames. You should not get holds.

Thats full power.

Now we go to range checks. A range check is a check to see is your system is good enough to maintain control at 28 meters from memory, motor on. Note, not 30 meters, but the numbers may have altered over time. The instructions also state, model on the ground. I'm being a bit pedantic but there is a fair difference between 28 and 30, and off the ground makes the system look better. But there is no point in bodging a test, or making it more difficult. Do the test. Do you still have control. If you do it's a pass, fail, sort it out.

Now we come to telemetry. Wonderful system, we now know what the system is doing. But at the range check fail/pass distance the system is at its limit. That's why this distance is used. And it shows in the telemetry data. To be expected. But I would say don't chase a bit more signal strength, or be over worried. Remember, it's only lately we have had this information. We used to do the range test. Pass you fly, fail you (should)sort it out.

Roger Dyke20/04/2019 21:13:37
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Percy: Thanks for your reply. I'd thought about doing that, but thought that I would follow the manual which states:- "With the model restrained on the ground, stand 30 paces (approx. 90 feet/28 meters) away from the model.".

I might try raising it up just to see if it makes any difference.

Mike Blandford20/04/2019 21:46:46
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A couple of things (if you are measuring accurately). 90 feet is 27.4 metres. Going 30 metres away is 10% further.
Secondly, and more significant, the range you get is proportional to the height of the receiver aerial above the ground. Depending on where on the model the aerials are, they could be very close to the ground, e.g., on a glider with no undercarriage they could be only 3 inches off the ground, on a power model with an undercarriage, they could be 6 inches above the ground. You would get a significant increase in range with this.

I always do my range checks with the model on top of my flight box, so the aerial height above the ground is about the same for all models, probably about 12 inches.

Also, in your back garden, you may be getting signal reflections that cause the range to be reduced.

Mike

Roger Dyke20/04/2019 22:07:14
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Don: I don't know as to what the telemetry number are when flying as I haven't flown any of my aircraft yet. I have only just finished converting them to 2.4GHz. On observing the numbers when operating the tx on reduced power my immediate thoughts were that the signals should be solid (no fades, no frames, etc.). Hence the posting. But thinking about it logically, if the idea of the reduced power is to simulate the aircraft being at the edge of it's communication range then I suppose I would be expected to see lots of antenna fades, bad frames, and even the occasional hold. Perhaps the telemetry is to be observed only when flying the model at full tx power and not when doing range checks on reduced power. Maybe I am looking too deeply into this as the models do seem to have full control. I am very used to 35MHz when I used to walk 30 paces with a collapsed aerial to check whether all the surfaces were moving correctly. If they were, job done. I am very new to 2.4GHz so am still a little bit nervous of it as at the moment it is the unknown.

Roger Dyke20/04/2019 22:19:39
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Mike: I have tried the test at a little shorter distance (probably about 27-28 metres) but the results are about the same. As I mentioned to Percy (above) the manual states to place the model on the ground restrained.

Reflections could play a part. Within about 3 metres to the side of the model is a aluminium framed 12' x 8' greenhouse. Maybe I need to do this test at the flying field. The reason I wanted to do this at home is because of getting a better feeling when I turn up at the field that I will be in with a chance of flying.

Martin Harris20/04/2019 23:57:43
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Depending on your locality, you may also be operating in a fairly wifi saturated area. It would be interesting to repeat the exercise in a rural location.

Mike Blandford21/04/2019 01:27:18
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Even with the model on the ground, the height of the aerial above the ground is important. The range you get could be significantly different if the aerial(s) are at the bottom of the fuselage or at the top. You could easily by looking at 4 inches or 6 inches, which would make a 50% difference to the range!

Mike

Don Fry21/04/2019 07:00:33
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I think I like Mikes system of getting some consistency to the test, but it's a test Roger, do your 90 paces, stand and and face the model as though flying it, and pretend it's 35 meg. It passes or fails. If a pass you fly it.

Mostly the telemetry is a bit academic in most models. But it a good teacher of where not to place the aerials.

But don't chase the numbers, it like tuning a glow motors main needle with a tachometer. More grief than useful reward.

Roger Dyke21/04/2019 07:19:26
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Martin: yes, I will be interested to see what the figures are next time I am at the flying field.

Mike: All of my antennas are in the top of the aircraft. But they are still only about 3 to 6 inches from the ground. The results are very similar from all the aircraft tested.

Roger Dyke21/04/2019 07:23:28
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Don: I think that you are right. I am probably over-thinking this and are looking at all the numbers because I can and it's available. Perhaps the old method of 'does it work ok or not' is still the best test.

Cuban821/04/2019 07:51:32
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I bought my first telemetry rx a couple of years ago and got anxious about what it was telling me, despite a solid range check at 40 metres and never having a sign of a problem when flying. Spektrum's advice for analysing the data is pretty vague and mostly unhelpful I feel. I spoke with a club mate who had been using telemetry on his dx8 with all his recent models and he was suspicious of how valid some of the info is. He range checks carefully without reference to telemetry and pays attention to keeping frame loss to a minimum on a flight test, but the figures do vary so it's difficult to make exact sense of what's happening. The RSSI alarm setting is puzzling as advice to where to set it is again quite vague. I guessed 30% and the thing was bleeping like a maniac throughout a solidly controlled flight and went totally loopy when taxying out to take off, so a bit worrying. I have it set to 10% now and it only gives an occasional random beep. I have never noticed a hold when flying or had one recorded in the data.

Roger Dyke21/04/2019 08:05:36
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Cuban8: Like I mentioned to Don (above), I am in danger of over-thinking this and it is probably a case of too much information. Especially when we can't get a solid answer (even from the manufacturers) as to what it all means as to what is good and what is bad. Thanks for the information.

Steve J21/04/2019 08:37:27
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1619 forum posts
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Setup voice alarms for 1+ holds, 10+frame losses, loss of telemetry and go fly.

Steve

PS The 6600T isn't one of Spektrum's better offerings, do not fly without the remote and expect to see more fades on the main unit (A) than the remote (B).

Roger Dyke21/04/2019 08:49:56
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Steve: Thank you for the info.

brokenenglish21/04/2019 09:05:15
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Roger, I only use simple 2.4 GHz, no telemetry, so maybe I don't understand, but my first observation would be that you're checking telemetry readings and not actual control movements.

I perform two types of range check. Firstly, like yourself, in the garden, with the wife watching the control surfaces. If she says they're waggling OK, then the check is OK. Without the wife, I just apply sufficient throttle to move the plane slightly. Again, it's either OK or not.

For the range check at the field, I simply taxy the plane normally, out to about 50m away, then select range check mode to do a 180° turn and taxy back.

For me, the bottom line is that you don't need telemetry to do a range check. I would prefer simply to check what's actually happening at the control surfaces and throttle.

I've been operating as per the above for the last 7 years, and I've never had any range problem of any sort whatsoever (never a failed check and never a problem in flight).

Maybe it depends on the type of plane you fly but, for me, telemetry is technological overkill, particularly just to do a range check!!!

Steve J21/04/2019 09:24:37
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Posted by brokenenglish on 21/04/2019 09:05:15:

Maybe it depends on the type of plane you fly but, for me, telemetry is technological overkill, particularly just to do a range check!!!

If your model only has a single receiving circuit then what you say is true. If you have two or more circuits in a model then if you do not look at the telemetry you will not know if an antenna is badly placed. I generally have telemetry installed for the first few flights of a model in order to verify the installation.

Steve

Roger Dyke21/04/2019 09:35:47
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brokenenglish: I'm inclined to agree. We tend to get blinded by all the technology with all these wonderful statistics to look at, but the bottom line is are our sticks controlling the aircraft. The old type range check has always stood the test of time for me so maybe that's the way I will continue.

Steve: I do take your point about the telemetry being useful to check whether an antenna is best placed, which does give us the opportunity to move it if necessary.

Roger Dyke29/04/2019 13:45:32
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Update

Just for interest for those who would like to know, I managed to get up to my flying field today after a few weeks lay-off due to the HS2 archaeological survey being carried out. I took two of the four of my aircraft recently converted from 35MHz to 2.4GHz. This was the first time that I was able to do an airborne test of the telemetry numbers. They were 4 successful 5 minute flights (2 each) both with an IC engine.

Aircraft 1 - Receiver Orange R620X V2 Aircraft 2 - Receiver Spektrum AR6600T

Aircraft 1 flight 1: A - 256, B - 36, Frames - 25, Holds - 0

Aircraft 1 flight 2: A - 211, B - 9, Frames - 6, Holds - 0

Aircraft 2 flight 1: A - 93, B - 0, Frames - 93, Holds - 0

Aircraft 2 flight 2: A - 113, B - 0, Frames - 113, Holds - 0

The antennas in both aircraft have been placed at 90 degs to each other and in the best places possible given the constraints allowed.

In looking at the telemetry figures whilst doing a range check on reduced power, it was a bit of a joke with the numbers dancing all over the place including picking up a couple of holds. That ignored, the control surfaces seemed to be working fine. Anyway, a good day for me, especially as one of the aircraft was even on it's maiden flight.

Roger

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