Hi
Im making a small wireless FM receiver based on RF solutions pair of recievers/transmitters at 433 MHz.
Until now ive just been using a 17.5 cn length of cable as an antenna with good results but for production im not sure if it is a good idea to continue with this method.
How easy/difficult is it to encorporate the antenna into the PCB tracks of the PCB. I can find maybe a square inch to play with on the board. Is there alot of calculations/fine tuning required or sould i just be able to make a track say 17.5 cm long that may double back on its self to fit on the board (the board is approx 9 cm long.
Any thoughts?
Justin
Hi
Im making a small wireless FM receiver based on RF solutions pair of recievers/transmitters at 433 MHz.
Until now ive just been using a 17.5 cn length of cable as an antenna with good results but for production im not sure if it is a good idea to continue with this method.
How easy/difficult is it to encorporate the antenna into the PCB tracks of the PCB. I can find maybe a square inch to play with on the board. Is there alot of calculations/fine tuning required or sould i just be able to make a track say 17.5 cm long that may double back on its self to fit on the board (the board is approx 9 cm long.
Any thoughts?
Justin
Mark, Which piece of the board is the antenna? The grey component at the bottom of the picture?
To get any reasonable amount of efficiency from an antenna (power radiated vs power consumed as resistive losses), the length of the antenna needs to be a half-wavelength long.
At 433MHz, λ/2=3e8/(2*433e6)=0.23m or 23cm or 9".
Such an antenna is usually configured as a center-fed dipole, placed either horizontally or vertically.
Various tricks are used to make a dipole physically smaller, like bending the sides into a V, or shortening them and then adding inductance (loading coils) to maintain resonance, or making half a half-wave dipole (¼λ monopole) operated against a conductive ground-plane (vertical ¼λ antenna)
The sad reality is that anything you do to modify the antenna so that its "aperture" becomes less than ½λ greatly compromises its efficiency..
There are lots of examples of "compromised" antennas being useful. An AM Broadcast receiver uses a tiny loop-stick, but the transmitter uses a 100m full size ¼λ vertical with hundreds of wires in the earth as a counterpoise and transmits kW of power. A mobile-mounted ham transceiver uses a loaded vertical (and only radiates ~3W out of 100W fed to the antenna), but is able to communicate hundreds of miles.
This is not quite true. Theoretically there is no problem making a small antenna with arbitrary gain, what happens however is that the Q of the antenna starts to increase astronomically. Practically this means that you can shrink the size of the antenna and initially you only sacrifice bandwidth, but once you have shrunk things by something like a factor of 10 these limits really start to bite. There are plenty of folk out there selling quite efficient 433MHz antennas that are only 12mm or so in size.
The AM situation is not directly comparable to the 433MHz one as you are not normally receiver noise limited, so lousy antenna gain is not so much of a problem, but yes simple ferite rods are not greatly efficient.
I think that there would be lots of hams out there that would take issue with you on 3% efficiency for a loaded vertical. Well matched and plated with a good conductor I would expect something over 90%.
The only way of making a "directive" antenna is by increasing its "aperture", i.e. making it physically larger. All directive arrays consist of spaced elements, where each of the elements, and the spacing between them is on the order of ¼ to ½λ; think yagis, colinear arrays, t.v. antennas, phased arrays, etc.
Get me the dimensions your 12mm shortened antenna, and I will put it in my antenna-modeling software and will compare the field patterns to a resonant dipole for the same frequency. I have done this hundreds of times, and I can predict what the results will be. I'll be happy to post them here.
A top-loaded big-wheel capacitance-hat 75m mobile antenna with silver-plated bug-catcher is like 5% efficient, i.e. it radiates 5W for 100W fed to it, the other 95W goes into heating the antenna and the earth under the car. I know, cause I have been a judge in ham radio antenna efficiency contests. A simpler base-loaded whip is like 3% efficient. btw- the guy with the 5% efficient antenna won the contest over the guy whose antenna was only 4% efficient
I have used a hiQ resonant 6' diameter loop with a bandwidth so narrow that it wouldn't pass a 3kHz wide SSB voice signal on 40m, and best I was able to measure (field strength) suggested it was about 7% efficient compared to a 66ft dipole.
There isn't any such thing as an efficient shortened antenna.
If i have been using the 17.5 cm of cable with good results, is it viable to coil or loop the wire inside the enclosure i.e. does it make a difference if the length is still 17.5 cm but the cable isnt in a straight line...?
If i have been using the 17.5 cm of cable with good results, is it viable to coil or loop the wire inside the enclosure i.e. does it make a difference if the length is still 17.5 cm but the cable isnt in a straight line...?
If i have been using the 17.5 cm of cable with good results, is it viable to coil or loop the wire inside the enclosure i.e. does it make a difference if the length is still 17.5 cm but the cable isnt in a straight line...?
Did you check the paper in my first post - it gave an example of a 433MHz helical antenna
The simplest antenna is a 1/4 wavelength whip (3.28 inches long) with a solid ground plane behind it.
https://www.electro-tech-online.com/custompdfs/2009/05/antenna-1.pdf
Might provide some good reading. If not heavy.
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