Receiver Antenna's

[bgfireguy92]

OK So heres my question. Im looking for longer radio "whips" on receivers since most of them all are really short. I have a few lemon receivers and looking at them it looks like it "SHOULD" be easy to de solder them and put longer ones on. So heres the questions:

#1 Is this possible without affecting the board ie fry them?
#2 what wire is used/needs to be used to make the longer antennas?
#3 possible on other receivers besides the aforementioned lemon rx?

Any info would be great. Thanks.

 

[PHugger]

Antenna design is complicated - bigger does not necessarily mean better.
The length is usually related to the wavelength of the signal - usually a nice fraction or even multiple.
I'm sure one of our resident engineers (I'm looking at you Dan) can give you the straight scoop......


Best regards,
PCH

 

[Tritium]

You will not "FRY" a receiver by changing the antenna. Receivers that send telemetry are a possible exception to this fact.

Changing the antenna will do one of three things. Longer range, Same range, Shorter range. Experimentation is your best friend here.

The "Antenna Cable" is usually 50 ohm coax.

FRSky offers changeable plug in antennas for some of it's Taranis receivers.

Thurmond

 

[bgfireguy92]

well good to know that I wont fry it but since i'm not using taranis, all DSMX/DSM2 protocol, hows that going to be? I just wannna extend them like some of the orange Rx have long duals.

 

[Tritium]

I suggest going to Aloft Hobbies:

http://www.alofthobbies.com/radio-gear/frsky-accessories-1/frsky-antennas.html

Buy whichever one of these suits you and either clip off the connector and directly solder to your receiver or better yet buy some connectors (the first item on the page linked) and convert your receivers to "clip on" antennas.

Thurmond

 

[Stradawhovious]

Somewhere on RC groups is a thread where one of the CS reps from Lemon RX discussed antenna length. Long story short, unless you find that thread and follow the math I wouldn't mess with the antennae. You risk decreasing the range.

All of my Lemon RX have had plenty of range enough to fly beyond visual capabilities. If you need more range than that, I would HIGHLY consider a quality full range RX with a satellite.

 

[Mostly Harmless]

Keep in mind that the typical receiver antenna is not a whip, but a simple antenna system that consists of the feedline (typically a high-quality 50 ohm coax designed for microwave frequencies) and an antenna (typically, a coaxial dipole antenna).

On the receivers, you have the feedline exiting the case, extending to the tubular item in heat-shrink covering. This is the beginning of the coaxial dipole antenna (see a simple description here -- about 3/4 of the way down the page: http://www.gonzales.com.au/joe/projects/videolink2/video_link_2.htm ).

The length of the feedline usually has no effect on antenna performance unless the lengths get very long (then signal loss in the feedline becomes a factor).

The actual antenna is another matter. As has been pointed out, the optimum length for the antenna elements is dictated by frequency and desired "directionality." Standard receiver antennas are designed to have a fairly uniform receive gain (how well the antenna receives) in all directions (there are exceptions, but let's stay with this, for now). You CAN increase the gain of the antenna, but ONLY at the expense of directionality. You can double the receive gain in some directions, but this makes the antenna ineffective in other directions (you can't get something for nothing). Certainly, this is not a desirable feature in an aircraft that can change its direction relative to the transmitter at any time.

Multi-rotors and other FPV platforms might use antennas that are optimized to increase gain in the downward direction (sacrificing gain in the upward direction), since there is no need to receive/transmit signals from/to the upward direction.

Think of it this way... Broadcast TV antennas for the home were highly directional -- they achieved greater gain in horizontal directions, but wouldn't do well at receiving signals from directly above. And you could make them even more directional to receive better in certain directions, but then they had to be more accurately pointed towards the transmitter.

To summarize, unless you know your aircraft will maintain a fairly fixed orientation to the transmitter, it's best to leave the receive antenna as omni-directional as possible.

(Of course, there is more complexity to this, especially if using multiple antennas, but that's another discussion).

 

[mesolost]

Since antennas are "tuned" to the frequency they're designed for your gonna need to use a length that's an even fraction of the wavelength. You could probably get away with replacing them with a wire that's EXACTLY double the length but if your having signal loss I'd highly recommend getting a receiver with a satellite port and put the satellite receivers antenna's at a 90 degree angle to the primary receiver's antenna. (i.e. horizontally mount the primary receiver and vertically mount the satellite)

Sorry it's blurry but if you seen my camera you'd understand LOL

 

[Mostly Harmless]

This receiver uses a standard dipole antenna where each "leg" is 1/4 of a wavelength (adjusted for the what's called the wire's velocity factor -- how fast the signal moves in the wire). You can, as had been suggested, double the length, but this has 2 impacts. First, you'll change the ellectrical impedance of the antenna, which will reduce the receiver's effectiveness. Second, you change the antenna's receive pattern. You will get better range perpendicular to the antenna, but reduced range off the ends.

As I said, earlier.... you can't get something for nothing.