## Extend antenna range for 2.4 Ghz transmitter

Started by Magnum, January 18, 2015, 06:01:31 AM

#### Magnum

I ordered a RC helicopter. ( 2.4 GHz )

The specs says it has a 120 ft. range.

It is reported that the range can be extended by lengthening the antenna.

The antenna length is 3.25 cm long.

Would increasing it's length to 6.5 cm increase the range ?

Do I need to solder the same diameter copper wire to it ?

Thanks.

I found this.

What do you think ?
Quote
The length of the antenna on a typical 2.4GHz receiver is 28.8 to 32 mm long, most are about 28.8 mm. The antenna is that length of bare line often at the end of a longer coaxial cable to move the antenna farther out from the receiver. Yes, the length of this is somewhat critical and can greatly vary the distance that the signal can be reliably received. To long can be just as bad as to short unless you can accurately make sure it is some odd multiple of an electrical quarter wavelength; i.e. 3/4, 5/4, 7/4 etc. Note that electrical wavelength can be different than a simple measurement as it depends on the velocity factor of any coax or other line involved.
Take care,
Andy

Ubuntu-mate-18.04-desktop-amd64

http://www.goodnewsnetwork.org

#### dedndave

multiples of 1/4 wavelength isn't always the answer
we often use 5/8 wave antennas

#### Antariy

What is the reason why it's preferable to use antennas with the length non divisible modally on the wave length? If the length will be "symmetrical", then in the antenna it will be a "standing" wave? The properly "broken" in the proper place (length of the antenna) resonance circuit, part of which is the antenna, is the reason? How would you determine the optimal length for the specific frequency, Dave?

#### dedndave

that's not as simple as it sounds, Alex
because there are many different antenna designs

the common basic models, though, are 1/4 wave (typically a vertical) with a ground plane (or counterpoise)
and - the more common 1/2 wave dipole, which is the basis for most antenna designs

beyond those, there are resonant and non-resonant "long-wires"
resonant long wires are typically some multiple of 1/4 wave in length
non-resonant antennas may be any length - and circuitry (coils and capacitors) is used to tune the antenna

the 5/8 wave antenna is a bit of an odd-ball, because it doesn't fit neatly into one of the above catagories

the basic formula is L = 984 / F(MHz)
that is one wavelength in free space, in feet
it is related to the speed of light (~300,000,000 meters per second)
in the real world (atmosphere), a length of about 95% of free space length is used
(we call that K=.95, the "propagation factor")

a common formula for a 1/2 wave dipole....
L (Ft) = 468 / F(MHz)
this formula works well for end-supported wire antennas in the HF region

#### Antariy

Quote from: dedndave on January 18, 2015, 08:23:10 AM
that's not as simple as it sounds, Alex
because there are many different antenna designs

Yes, I know, Dave, that's why I'm asking you You're a person who has great experience in the radio-transmission field, especially you said that the antenna design is your favourite hobby :t Thank you for the answer!

Quote from: dedndave on January 18, 2015, 08:23:10 AM
the common basic models, though, are 1/4 wave (typically a vertical) with a ground plane (or counterpoise)
and - the more common 1/2 wave dipole, which is the basis for most antenna designs

But why such lengths used - this best suits to resonance? Is there difference in the preferable length of the transmitter and receiver antennas?

Quote from: dedndave on January 18, 2015, 08:23:10 AM
beyond those, there are resonant and non-resonant "long-wires"
resonant long wires are typically some multiple of 1/4 wave in length
non-resonant antennas may be any length - and circuitry (coils and capacitors) is used to tune the antenna

The coil-capacitor circuit is used to be tuned in the resonance with the carrier frequency, to "force" the signal in the non-optimal antenna?
What is the case of usage of non-resonant antennas? Isn't it simpler to just use suitable antenna length, than to have losses in it and the cirtuit?

Quote from: dedndave on January 18, 2015, 08:23:10 AM
the 5/8 wave antenna is a bit of an odd-ball, because it doesn't fit neatly into one of the above catagories

the basic formula is L = 984 / F(MHz)
that is one wavelength in free space, in feet
it is related to the speed of light (~300,000,000 meters per second)
in the real world (atmosphere), a length of about 95% of free space length is used
(we call that K=.95, the "propagation factor")

a common formula for a 1/2 wave dipole....
L (Ft) = 468 / F(MHz)
this formula works well for end-supported wire antennas in the HF region

Yes, I know this formula, with exception that it is for a metric system I was interested in how would you decide which type (length) of antenna to use in which situation/carrier frequency? For an instance - how do you usually decide to use 5/8 wave? For what kinds of transmission/antennas? Is that more useful in some frequency range etc

#### Magnum

984/2400 = .41 feet = 5 inches

Would this be a good starting length ?
Take care,
Andy

Ubuntu-mate-18.04-desktop-amd64

http://www.goodnewsnetwork.org

#### dedndave

Andy - a 5/8 wave antenna would be ~2.95 inches
.05 inches is pretty small, so just use 3"

Alex - yes, the lengths used provide resonance
the real issue is "optimal transfer of energy"

antenna impedance, transmission line impedance, transmitter impedance, standing waves - all come into play
if you have a mis-match, a portion of the power will be reflected back into the transmitter - a bad thing
there are also other issues - antenna "gain", radiation efficiency, and so on

directivity is how gain is accomplished - we usually consider that a good thing
but, it's a bad thing if you need omni-directional capability

in the case of Andy's RC transmitter and receiver, directivity is a bad thing
you want good communications in all directions
the real solution is to boost transmitter power   :P

#### Antariy

Quote from: dedndave on January 18, 2015, 10:01:08 AM
Alex - yes, the lengths used provide resonance
the real issue is "optimal transfer of energy"

antenna impedance, transmission line impedance, transmitter impedance, standing waves - all come into play
if you have a mis-match, a portion of the power will be reflected back into the transmitter - a bad thing
there are also other issues - antenna "gain", radiation efficiency, and so on

directivity is how gain is accomplished - we usually consider that a good thing
but, it's a bad thing if you need omni-directional capability

Well, the question was: how did you choose the antenna length in some particular case? You did suggested to Andy to try 5/8 length, but how would you know that for this frequence this length is the best? If that's too boring to describe you just might to point to some article with the answer.

Quote from: dedndave on January 18, 2015, 10:01:08 AM
in the case of Andy's RC transmitter and receiver, directivity is a bad thing
you want good communications in all directions
the real solution is to boost transmitter power   :P

Directional antenna in the transmitter will probably do ok (just Andy needs to not miss the heli from the direction of the look).
As for power of transmitter - this will probably cause problems with the laws, if that would interfere with equipment around and people will find who is the reason.

#### dedndave

it's not so much a "selected length", in spite of how it may appear
it's more about selecting an appropriate antenna topology - then deciding the length from that

a 5/8 wave antenna is very similar in behavior to a 1/4 wave antenna, but with a little gain
1/4 wave and 5/8 wave antennas are naturally omni-directional
that's what makes these topologies desirable in this situation

a directional antenna might be ok on the "controller" end
the guy can just make sure he faces the model at all times - not hard to do

but, at the model end, directivity is bad
you have a good signal, turn the craft to a different heading and, BANG, no more signal   :icon_eek:

#### Antariy

Quote from: dedndave on February 06, 2015, 09:24:32 AM
it's not so much a "selected length", in spite of how it may appear
it's more about selecting an appropriate antenna topology - then deciding the length from that

a 5/8 wave antenna is very similar in behavior to a 1/4 wave antenna, but with a little gain
1/4 wave and 5/8 wave antennas are naturally omni-directional
that's what makes these topologies desirable in this situation

a directional antenna might be ok on the "controller" end
the guy can just make sure he faces the model at all times - not hard to do

but, at the model end, directivity is bad
you have a good signal, turn the craft to a different heading and, BANG, no more signal   :icon_eek:

Thank you for the answer, Dave :t

Yes, I was talking about transmitter only directional antenna, too.

#### dedndave

it has to be a beer can - soda won't work   :lol: