Spektrum Receivers.

[David Barker 2]

Hi all, as I started a heated debate regarding battery's to use for receiver and plane control surfaces. I'm about to fit a spectrum 6210 satellite receiver to my new Ugly Stik 60. Is there any advantage in having aerials sticking out of fuselage at right angles from each aerial. The plane is made of ply & balsa. Thanks Dave B.

[MattyB]

Balsa, ply and covering does not have any effect on 2.4GHz RF, but anything containing a significant amount of metal (engines, batteries, servos etc) will do. This means you should keep your aerials away from these components and keep the aerials at 90 to each other in accordance with the recommendations in the manual.

[Dave Hopkin]

a) Balsa/ply wont impede signal reception at all so they dont need to be outside the fuselage

b) only the last 12mm ish of the "aerial" is actually an aerial the rest (slightly thicker) is co-ax wire

c) Make sure the aerials are all (both the RX and the Sat) in opposition to each other or as close as you can to maximise received signal

[FlyinBrian]

Also HH recommend keeping satellite rx more than 3" apart.

[Phil Green]

Posted by Dave Hopkin on 23/06/2016 17:03:41:

a) Balsa/ply wont impede signal reception at all so they dont need to be outside the fuselage

True

Posted by Dave Hopkin on 23/06/2016 17:03:41:

c) Make sure the aerials are all (both the RX and the Sat) in opposition to each other or as close as you can to maximise received signal

What Dave means is "as close to opposition as your can" ie near 90 degrees, not that they should be close together - they should be as far part as possible.

Posted by Dave Hopkin on 23/06/2016 17:03:41:

b) only the last 12mm ish of the "aerial" is actually an aerial the rest (slightly thicker) is co-ax wire

Sorry Dave but not necessarily the case. I know you didnt mean 12mm, but thats not my point.
This is a common misconception. The 30mm-ish whisker bit is not the only functional part of the aerial - any quarter-wave aerial needs a counterpoise to work against in order to radiate or receive efficiently.The 'exposed 1/4 wave at the end of a length of coax' type aerials consist of a 1/4 wave element, but the coax shield is also the counterpoise and a quarter-wave of the shielded part of the coax should be RF visible as well as the last 30mm 'whisker'. This is far from ideal as the coax is badly mismatched and the signal distribution will be unpredictable at best. Again its a huge compromise.

One answer is the a type of aerial most of us are currently using in transmitter aerials, thats a coaxially-fed dipole. These aerials are a genuine dipole with two opposed 30mm elements. One is the coax inner (the whisker) and the other is a brass tube through which the feeder is routed, making it a centre-fed, coaxially-routed dipole. The tube is only connected to the shield at the feed point, so its a true 1/4 wave counterpoise.

This is a very good impedance match and hence a huge improvement in VSWR and the effectiveness of the overall radiation pattern in transmission, and improved transfer in a receiver.

But back to whiskers, ultimately, if a dipole isnt fed through a balanced line (which ours arent) or is fed via coax without a balun at the feed point, then the last quarter-wave of the feeder shield becomes the counterpoise, radiating in the case of a transmitter and sensing in the case of a receiver.

The popular-but-not-quite-right opinion that only the whisker matters is fine most of the time but if you really want the optimum results the whisker is not the only part of the aerial that should be exposed or at least visible to RF, optimally 30mm of the feeder coax should be visible too.

Cheers
Phil

[Johan]

Hi Phil,

Can you please assist as you seem to be into RF knowledge. I have a SPEKTRUM DX6 (g2),no antenna diversity transmitter and would like to know if can I connect a second antenna with 90 degree orientation to the original one at the same point on the RF board without burning out the amplifier on the board.

Only DX6 G3 has now since two months ago introduced antenna diversity on this transmitter but with a redesign of the circuit boards - no upgrade kit thus available for G2 (audio introduced).

SORRY FOR USING THIS RECEIVER forum for TRANSMITTER ISSUES

Kind Regards,

Johan.

[Masher]

Hi Johan

Sorry, I'm not Phil but can't help jumping in! No you can't just add another antenna to the Tx. It's not as simple as that - they have updated the RF board to ensure the diversity is correctly implemented. This usually involves RF switching circuitry and RF impedance matching has to be taken care of.

Sorry

[Andy48]

Posted by Dave Hopkin on 23/06/2016 17:03:41:

a) Balsa/ply wont impede signal reception at all so they dont need to be outside the fuselage

Being pedantic, surely there must be some impedance to the signal through balsa, though obviously not seriously detrimentally so.

Therefore putting the aerial outside a balsa model will be slightly better when the aerial is facing the transmitter, and worse when the aerial is at the other side as the signal has to pass through two thicknesses of the fuselage.

It would seen then that keeping the aerial inside the fuselage is best for all round reception.