2.4Ghz Rx antenna and Tx positions?

[Bill McCreadie]

I have come across various posts which refer to being careful with antenna positions but don't go into much detail. I have also seen that some Rx's have 2 antennas and some only have one.

Are there rules as to how these should be positioned within the model and also on the TX?

Bill.

[Biggles' Elder Brother - Moderator]

Bill, I can't speak generally but in the case of Futaba 2.4 rx's the two aerials (or at least the bare metal bit at the end) should be positioned within the model so that they are at right angles to each other. This can be any pair of right angles, vertical or horizontal, as long as they are at right angles.

 

Regarding Tx the general concensus, as far as I understand it and follow it, is that your aerial should be straight ahead (in the side to side direction) and inclined so as to be at right angles to the ground. This means that if you hold your Tx at an inclination of approx 45 degrees (as many people do) then the aerial will be at 45 degrees to the Tx and hence vertical relative to the ground. If on the other hand you hold your Tx horizontal, as I notice a lot of 3D as "younger fliers" tend to, then your aerial should be at 90 degrees to your Tx as your Tx is parallel to the ground.

 

As far as I understand it the most important thing is not to have the aerial so that its tip pointed at the model as this is the direction of weakest signal. The strongest signal is outward from the length of the aerial.

 

Hope this is helpful and makes some sort of sense - it quite hard to describe without a diagram!

 

BEB

[Martin Harris - Moderator]

There's quite a lot on the subject in this thread...

[Bill McCreadie]

Read you suggested thread with interest but still a little confused as everyone has a pet Tx position they swear by!

Very little mention of Rx antenna position except for the dual antenna type being at right angles to each other.

What about the Rx's which have only one short antenna with a shrink wrapped thingy on the end. How should these be positioned?

Bill.

[david field 1]

Further to the queries on receiver aerials. I use two different tx,s . 1/ a Hitec Optic 6 with a2.4 ghz module and 2/a 2.4 ghz Twister. The Hitec receiver have twin aerials on 6 chanel

rx a.nd 1much shorter aerial on the 4 channel. The Twister rx,s have only a single short aeriel. I have had the same problem with both radio,s on short aerial rx,s that is , Flying a fair distance away , about 200 yards away. on initiating a gentle turn to come back the models have continued to turn , no corrective measures work, three times i have been lucky enogh to land in trees / bushes, but once breaking an aircraft ( since repaired). Are the short aerial receivers suitable for only clse work say 100 meters or so? Can the short aerials be lengthened? now to keep the aerial straight. " different models were involved, flying speeds were medium, I have turned both models at much lower speeds. There was sufficient height to recover from tip stalls. Any one else had similar 2.4ghz probs with short aerial rx,s.

David field

[Tim Mackey]

I would say that the reason you are having issues with the smaller short aerial receivers is purely down the fact that these are classed as park fly range receivers only, whereas the twin aerial/rcvr units are full range.

No, you cant just extend the short aerials and expect better results...in fact you'll goose it up even more.

[NigelH]

There's some good Spektrum installation advice here and here

 

[Peter Beeney]

 

With regard to the previous discussion about aerial orientation, since then I’ve casually studying how various people hold the transmitter when flying; and it seems that how ever the tx and rx aerials are positioned quite often they seem be pointed directly at each other, perhaps mostly only momentarily, but it’s never caused the slightest problem as far as I can see. I use a Spectrum AR500 in a small powered glider, it’s just bundled in, the aerials are not in anyway located, they just stay where they stop, and that’s never given the slightest indication of receiving any weak signals etc. Quite often I deliberately point the tx aerial straight at it. I’m sure there are many similar installations which are also just as secure.

We did a little check on a receiver today, we did a similar exercise on this very same AR500 recently, the results of which I posted at that time, but this afternoon, with the aerial orientation in mind, it was even more severe. This is my Assan micro 6 channel, full range receiver. The single aerial is 18 millimetres. 3/4’’ long; so I reckon that puts it in the ‘very short’ bracket. It’s placed on a metal framed chair, with a 4 cell battery and two Spektrum DS821 servos connected. The rx is specifically positioned with it’s aerial straight and directly in line with the tx, but pointing away. The tx is 600 metres away, with the tx held normally at waist height; in line of sight across a shallow valley.
We had full control all the time, turning the tx aerial in every direction made no difference. I made many tries, mostly with the tx aerial pointing directly at the chair, as near as I could tell, the one exception came when I was facing away from the rx, with the aerial straight out. But as I don’t usually fly facing away from the model, especially at that range, I felt I could discount that.
Then to put more pressure on, we switched on two 2.4 tx’s under the chair and went through the sequence again. With the exception of one servo twitching slightly during a ‘rest’ period, to see what happened, the full result was exactly the same. Overall, we considered this to be a success.
When we did the AR00, we found the result was exactly the same, although here I was checking for any possible interference, so we used three under the chair.

So quite why people are experiencing this signal loss due to aerial positioning I’m at a bit of a loss to understand. I‘ve always thought that in general terms the air range is ten times the ground range, so for a model that is reasonably high that is a long way. So far we’ve not actually tried to reach the limit of ground range, that might be the next task.

I don’t think I’m going to have any fears about send the Assan rx off on a mission……

PB

[Weyfly]

After troubles with my 2.4ghz TX module, I have brought a FRsky one until its replaced. Has anyone adjusted/cut off/removed/turned it round the carrying handle to clear it away from the preferred aerial position or do you just use it 'as is'?

 

I have a JR 9X11 which means the FRSKY aerial cannot lie directly parallel with the top of the TX due to the interference of the carrying handle.

[Frank Skilbeck]

Posted by david field 1 on 28/09/2011 10:09:28:

Further to the queries on receiver aerials. I use two different tx,s . 1/ a Hitec Optic 6 with a2.4 ghz module and 2/a 2.4 ghz Twister. The Hitec receiver have twin aerials on 6 chanel

rx a.nd 1much shorter aerial on the 4 channel. The Twister rx,s have only a single short aeriel. I have had the same problem with both radio,s on short aerial rx,s that is , Flying a fair distance away , about 200 yards away. on initiating a gentle turn to come back the models have continued to turn , no corrective measures work, three times i have been lucky enogh to land in trees / bushes, but once breaking an aircraft ( since repaired). Are the short aerial receivers suitable for only clse work say 100 meters or so? Can the short aerials be lengthened? now to keep the aerial straight. " different models were involved, flying speeds were medium, I have turned both models at much lower speeds. There was sufficient height to recover from tip stalls. Any one else had similar 2.4ghz probs with short aerial rx,s.

David field

This isn't my experience with the park flyer Rx's from Spektrum AR6100 & AR6110 plus orange single aerial DSM2 Rx's and also the FrSky 4 channel single aerial, in all cases the control has been fine for as far as I am comfortable flying the plane. I always have the Tx aerial horizontal (Spektrum Dx6i) and then pointing down from Tx (FrSky hack module on Cockpit Sx)

[Daithi O Buitigh]

Regarding the length of the aerial (I'm old-fashioned - when I was an itty-bitty apprentice someone in class said something about 'antennas' and the tutor responded "Gentlemen, the plural of antenna is antennae and only insects have those - we use aerials")

 

2.4 GHz is 12.5 cM in wavelength and a quarter wave aerial would measure 3.2 cM (approximately) but in reality slightly less due to a few other factors. Trimming or lengthening it will seriously affect it's performance as it HAS to be resonant at the required frequency. Doubling or quadrupling its electrical length to half or full wave simply won't work unless you have the necessary gear to retune the receiver front end

 

Daithi/GI7OMY

Edited By Daithi O Buitigh on 25/01/2012 00:49:22

[Weyfly]

Well, if the carrying handle doesn't interfere with the Frsky TX aerial, I suppose that the next thing is to ask, "whats the size of my donut?" Could I for instance stand facing the slope edge and fly to my left or right using a horizontal aerial. I have always used Spektrum before and had the aerial angled upwards and had so many problems you wouldn't believe it.

[Tim Mackey]

Strange, as I fly with Spektrum - and always angle the aerial upward when flying and never have an issue. I fly a LOT on the slope too.

[Weyfly]

The re occurring fault turned out to be the module, HH are replacing but out of stock, so I needed a unit to keep flying hence the change to Frsky. I now have to decide whether to change everything over or wait for new stock to arrive.