Receiver antenna placement?

[Jolly Roger]

I’ve flown many decades on 35MHz and am only JUST switching to 2.4GHz! I know, Early Adopter eh?  So here come some embarrassingly noobie questions…

 

My new Frsky gear is fab but I can’t find much guidance on the location and orientation of receiver aerials?

All I've heard is that the last 3cm of the two 2.4 aerials is the key section, and they should be at right angles to each other and kept away from carbon fibre or other metal wires. But should they ideally be on a horizontal or vertical plane? And does the rest of the wire need to lead straight away from the receiver, before the 90deg sections? And do people tend to put the aerials inside or outside the plane?

 

Also my Frsky Tandem receivers have an additional 900MHz “T”-shaped aerial. What angle should that be placed at and should it be kept away from the 2.4 aerials?

Any advice welcome.  I’m probably overthinking this.  I usually do 😐

[Shaun Walsh]

One horizontal one vertical ideally outside the fuselage but not essential,  just keep them away from carbon fibre parts. 

[Jolly Roger]

Thanks Shaun.

And any advice on the 900MHz T aerial?

[Denis Watkins]

T on its side for range

 

[Martin Harris - Moderator]

Shame that my models don’t maintain the same orientation throughout a flight!  

Perhaps the next gimmick will be a gyro/accelerometer/GPS controlled aerial mounting to maintain optimal orientation? (All rights reserved!)

[Shaun Walsh]

8 minutes ago, Martin Harris - Moderator said:

Shame that my models don’t maintain the same orientation throughout a flight!  

Perhaps the next gimmick will be a gyro/accelerometer/GPS controlled aerial mounting to maintain optimal orientation? (All rights reserved!)

Easier to have a receiver and two satellites, 6 aerials covering all axes in opposing directions.

[Andy Stephenson]

Or you could just use a brand that doesn't need satellite receivers.

[Martin Harris - Moderator]

Or just use a random nominal 90 degree orientation which has served me well over thousands of flights since starting to use 2.4 GHz in 2009. 

Having used and checked telemetry over 15 years of regular flying on 2.4 GHz, I can say with confidence that whatever orientation has been presented, the receiver has always received an adequate signal. 
 

I believe the most important factor is to avoid potential blanking of both aerials by any large metallic object such as an engine or motor, or metal/carbon fibre in the structure. 

[GrumpyGnome]

Mirrors my experience 100%......

[Andy Stephenson]

Also don't run the antenna wire in close parallel to other wires.

[Jolly Roger]

Thanks folks. All really useful and sensible advice which I’ll follow 😇

[FlyinFlynn]

18 hours ago, Martin Harris - Moderator said:

Shame that my models don’t maintain the same orientation throughout a flight!  

 

Or your Tx for that matter.

[Martin Harris - Moderator]

Yes - another factor.  I’m lucky in that my transmitter has two integral transmitter modules each with two aerials at 90 degree to each other but with single transmitter aerials, it may pay to think about using an optimal orientation if it’s positionable. 
 

Having said that, with my previous external transmitter conversion module, I deliberately pointed the single aerial at a sport sized model flying at the limit of comfortable vision with no massive loss of signal - certainly still more than sufficient to maintain control. 

[FlyinFlynn]

...plus to that, if you do point the end of your tx antenna to your model if you should suffer a range problem simply jerking your tx upwards will present a better aspect to your model and 'should' recover control...

[Andy Stephenson]

It's likely that even if you point the antenna directly at a distant model, the Tx signal will be reflected off any metallic object in the vicinity which will reach the receiver by a different route. Also, the radiation pattern from a single Tx antenna isn't textbook perfect and there will be odd lobes of radiation coming off in different directions. Another thing to consider is that 2.4GHz receivers are far more sensitive than the old MHz ones. All this adds up to make the link as solid as it can be or should be, barring any other technical shortcomings.

[FlyinFlynn]

On 23/07/2024 at 12:39, Andy Stephenson said:

It's likely that even if you point the antenna directly at a distant model, the Tx signal will be reflected off any metallic object in the vicinity which will reach the receiver by a different route. Also, the radiation pattern from a single Tx antenna isn't textbook perfect and there will be odd lobes of radiation coming off in different directions. Another thing to consider is that 2.4GHz receivers are far more sensitive than the old MHz ones. All this adds up to make the link as solid as it can be or should be, barring any other technical shortcomings.

 

For a nominal dipole antenna, which is what a typical R/C Tx antenna aspires to be, the -3dB radiated power level appears around 78 degrees from the horizontal.(that is half power at the blue lines in the elevation plane diagram)

 

In other words, if you point your tx antenna directly at your model you will get  an order of magnitude  reduced RF energy arriving at the Rx, (-30dB in this case as shown at the 90 degree point in the elevation plane polar diagram.)

 

Having two Rx antennas doesn't increase the level of power gathered from the air except when one antenna may be shielded by something metallic in the model, then the other antenna receives the energy and the model doesn't lose the signal. That is why you separate the antennas and place them in different orientations well away from anything metallic.