Antennae orientation?

[SIMON CRAGG]

I have always placed the two antennae wires (Futaba), in opposite directions in the Fuz, One vertical and one horizontal, in supporting tubes. Does anybody know how critical this is?. Has anybody tried flying a model with the wires "just bundled2 into the fuz?.  One of our chaps managed to "buy the farm" yesterday, and the only fault we could find was the RX wires not secured, and just doing their own thing at the bottom of the fuz!!

[andyh]

if an antenna is pointing directly at the RF source, or at 90 degrees to a linearly polarized signal as our Tx's use, it will pick up virtually no signal.  the idea of having the two antennas in different orientations is to guard against this happening no matter what the attitude of the aircraft.  so yes, it's possible this might have caused the Rx to failsafe.

 

mind you, I see so many people flying with their Tx antennas pointing straight up out of the Tx, so that it generally points directly at the model in flight & so the model is in the weakest area of the torus-shaped RF field that I'm not surprised there are so many "mysterious" brownouts.  ?

[Peter Jenkins]

The other factor that affects range, assuming you have the 2.4 GHz aerials set at right angles to each other, is that they should be dead straight for maximum range.  I use a snake outer to slide them into or else double sided sticky tape to make sure they are correctly positioned and dead straight.

 

As andyh says, do not point your aerial at the model.  Best either to have it horizontal and aligned with the aircraft's path or pointing downwards to show as much of the aerial length to the model when it's flying.

[SIMON CRAGG]

Thanks.

 

The reason I ask is because this is the first time I have come across this potential issue. Generally, we all adhere to the tried and tested method of installing the RX, but this one had slipped through the net. At the inevitable post mortem, all the usual plethora of checks were completed ok, less the tangled RX wires which we deemed to be the culprit.

[Cuban8]

Try a range check with the RX aerials and TX aerials arranged as worst case and according to the test I've done out of curiosity, I still get full range with no problem. I've deliberately pointed the aerial (DX7 with single aerial) at a model throughout a flight (not too far away though) with no control issues. I'm not saying be cavalier with installations, naturally follow best practise, but you really can over-think this and drive yourself crazy. Sometimes theory and practise don't always run together in real world conditions, and TBH, there are so many other pitfalls that we can fall into that might cause a crash, yet don't seem to  attract the same degree of attention or concern.

Edited October 18, 2021 by Cuban8

[MattyB]

2 hours ago, SIMON CRAGG said:

I have always placed the two antennae wires (Futaba), in opposite directions in the Fuz, One vertical and one horizontal, in supporting tubes. Does anybody know how critical this is?. Has anybody tried flying a model with the wires "just bundled2 into the fuz?.  One of our chaps managed to "buy the farm" yesterday, and the only fault we could find was the RX wires not secured, and just doing their own thing at the bottom of the fuz!!

 

Rule of thumb... The transmitter antenna should be parallel and not collinear with one of the receiver's antenna(s).

 

For aerobatic models that are regularly in all sorts of orientations having one antenna vertical and the other horizontal is fine, but a trainer model that flys straight and level most of the time should have the RX aerials in the same plane as the TX aerial i.e. if you fly with your TX aerial horizontal pointing out to one side, put your RX aerials in that plane too (at 90 degrees to each other along the horizontal plane within the fuselage) to get the most consistent signal.

 

https://www.rcgroups.com/forums/showthread.php?1877474-Antenna-Orientation-for-2-4-GHz-Receiver

Edited October 18, 2021 by MattyB

[Dad_flyer]

For 2.4GHz most (all probably) transmitters have two aerials as well. One pointing out of the top, the other crosswise.

This overcomes the problem of pointing the aerial at the model. The horizontal one must end up doing most of the good work.

[andyh]

32 minutes ago, Dad_flyer said:

For 2.4GHz most (all probably) transmitters have two aerials as well. One pointing out of the top, the other crosswise.

 

definitely not all (RadioMaster TX16S):

 

 

(I had this picture already - I didn't take my Tx apart for this thread  ? )

[Jonathan M]

Andy H is correct.  I was helping a young guy trim his model recently and his Radiomaster kept blaring "RS signal low" (via telemetry) while the model was in the air, even when fairly close by.  I then noticed that his aerial was pointing vertically up, but as soon as he dropped it over to the horizontal position the warnings stopped completely.

 

My Taranis X9D+ has the same design, i.e. just a single moveable aerial.

[Dad_flyer]

I am surprised there, they are decent quality radios.

My very budget Fkysky have two. I was about to order a Radiomaster as the Flysky has some intermittent problems in the gimbals. After replacing the gimbals the problem went away, but now there is a different one.

[Nigel R]

18 hours ago, SIMON CRAGG said:

Does anybody know how critical this is?

 

It's pretty much critical.

 

I had an occasion when the satellite RX (AR6210 - no telemetry) was not bound (user error) and the main RX was shielded (by servos, I assumed at the time, not that it matters much) - fortunately this happened when the model was going vertical upward in preparation for a stall turn. One failsafe lockout later I was down and debugging - the RX LEDs quickly showed the satellite not being bound and making no useful contribution. Point being, only one aerial in one angle was not enough.

[SIMON CRAGG]

That's what I thought, just interested in others experiences really.

[andyh]

41 minutes ago, Dad_flyer said:

I am surprised there, they are decent quality radios.

My very budget Fkysky have two. I was about to order a Radiomaster as the Flysky has some intermittent problems in the gimbals. After replacing the gimbals the problem went away, but now there is a different one.

 

I imagine that having two antennas has its own issues - are they each only able to Tx at half power so that the radio is only emitting a total of whatever the maximum legal power is?

[John T]

I've been using Hitec Optima Rx's for many years now, sometimes at extreme range in electric gliders, without any problems.  These only have a single "Boosted Omni-Directional Antenna" (whatever that means) and I've often wondered how these work. It certainly makes life easier when installing in a slim fuselage.

[PeterF]

7 hours ago, John T said:

I've been using Hitec Optima Rx's for many years now, sometimes at extreme range in electric gliders, without any problems.  These only have a single "Boosted Omni-Directional Antenna" (whatever that means) and I've often wondered how these work. It certainly makes life easier when installing in a slim fuselage.

The Hitec antenna is a dipole and increases the emission / reception along the axis of the antenna reducing the doughnut shape of the gain. I flew Hitec for many years without any problems, also 3.5m thermal gliders to the limit of vision. I only used the Optima 9 with twin antennas for larger / more valuable models even if I did not need all 9 channels.

[Frank Skilbeck]

I've got several models flying with Multiplex M-Link single aerial receivers, on most I have the receiver aerial vertical but on a couple of slim gliders it just runs down the fuselage, the largest being a 1.5m Mini Blade slope soarer, I have the LQI alarm on my Profi set at 80% and it only ever goes off if I have landed in a hollow and there is no line of sight between the Tx and Rx.

 

MPX don't class the receivers as park fly, but give examples of models sizes they are suitable for.

 

In models with twin aerial receivers though I always follow the instructions and position the aerials at 90 degrees to each other.

 

I have seen other fliers so worried about Rx reception that they have the aerials taped to the outside of balsa models!

Edited October 19, 2021 by Frank Skilbeck

[Simon Chaddock]

You should also consider what might be in the fuselage between those tiny 2.4 rx aerials the TX.

Not likely to be a problem at any altitude as the TX will 'see' the aerials from the underneath if the aerials are nestling behind a big solid LiPo or a particularly dense array of servos wires when low down it might a bit different. 

[Christopher Wolfe]

I was under the impression that most modern 2.4 GHz receivers with twin antennae use diversity switching so that the antenna with best quality signal is selected.

Both antennae are interrogated multiple times and due to the orientation of the model changing during flight, positioning the antennae at 90 degrees to each other ensures that at least one of them should be obtaining a signal .

 

More info here Antenna diversity

 

Chris

[Nigel R]

23 hours ago, andyh said:

I imagine that having two antennas has its own issues - are they each only able to Tx at half power so that the radio is only emitting a total of whatever the maximum legal power is?

 

I would think it straightforward to alternate packet transmission between the antennae.

 

I can't imagine you'd want both simultaneously transmitting, they'd interfere.

[Frank Skilbeck]

6 hours ago, Christopher Wolfe said:

I was under the impression that most modern 2.4 GHz receivers with twin antennae use diversity switching so that the antenna with best quality signal is selected.

Both antennae are interrogated multiple times and due to the orientation of the model changing during flight, positioning the antennae at 90 degrees to each other ensures that at least one of them should be obtaining a signal .

 

More info here Antenna diversity

 

Chris

Not quite, most monitor the signal strength not the quality, and rather than constantly swap between aerials they swap when the signal strength (or in some cases the data quality) drops below a preset level, i.e rather than keeping selecting the strongest signal they only change once the signal on the current aerial drops below an acceptable level.