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RF Transmitter/Receiver Distance

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ibwev

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I finally have my ProMicro communicating with the Raspberry Pi via 433 MHz RF Transmitter/Receivers https://media.digikey.com/pdf/Data Sheets/Seeed Technology/113990010_Web.pdf. The only problem is that the RF Transmitter/Receiver have to be right next to each other for the Raspberry Pi to interpret the message correctly. I am powering the transmitter with 9 volts. The datasheet says it should be able to broadcast 40 meters indoors. What can I do to improve the broadcast range?

AduinoRPiTroubleshootSchematicPic.gif
 

MikeMl

Well-Known Member
Most Helpful Member
What does the signalling on the MISO pin look like? Read this...
 

ibwev

Member
How long is the antenna
I am using a female to female jumper wire as an antenna and it is slightly longer than the recommended 173 mm length. Should I expect weaker reception if the antenna is longer than the recommended length?

This article was very helpful. I reduced the baud to 900, I pause between sending transmissions for 150 ms, and I only send one ASCII character. As a result, I am fairly reliably receiving the transmission with the RF Transmitter/Receiver about 20 feet apart through 2 sheet rock walls. Thank you for the help.
 

dr pepper

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Simple calculation for a dipole.
(speedof light/frequency)/4, so (299792458/433mhz)/4 = 173mm, so if you put a 173mm length piece of wire on the antenna connection, and another 173mm long piece of wire on the ground connection, then route them so they point away from each other you have a dipole, range should be reasonable.
This assumes the frequency is spot on 433 mhz, which it probably isnt, but still it will improve performance.
 

MikeMl

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Dr. Pepper is describing a half-wave dipole, which consists of two colinear quarter-wave elements, fed at the center, where one element connects to the transistor's output, and the other to ground. Practically speaking, the 1/2λ dipole should be about 95% of the calculated amount to account for end-effect of the dipole wires. The receiving end needs a similiar dipole to get max range.
 

dr pepper

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Yes.
I have some of those ultra cheap 433mhz modules, with a lump of random wire I get to the next room, with the dipole it goes 3 rooms across the yard and into the garage.
As instructions always say results will vary.
Another thing that increases range, and it depends on the receiver topology is the way data is sent, if the receiver is of good quality and has agc then sending a preamble before the actual data improves range and baud rate.
 

ibwev

Member
With help from contributors on this forum, I have assembled the following moisture circuit:

moisturePCBnoAntennaSCH.jpg

I am attempting to design a PCB for that circuit. So far, it looks like this:

moisturePCBnoAntenna.jpg

I was planning on using the half-wave dipole for the antenna mentioned in post 6,7, and 8. However, I neglected to mention that I am putting this device on or near a hot water tank. After reading page 11 of http://wireless.murata.com/media/products/apnotes/antenna.pdf, I realized that the half-wave dipole may not be the best solution for this circuit due to close proximity to a "large metal area".

1) Is the half-wave dipole still the best solution for this situation?

2) If so, how far does it need to be from large metal areas?

3) If not, what is another type of antenna to consider? Ideally, I would like the antenna to be small and able to broadcast through multiple walls up to 50 feet.
 

ibwev

Member
I am going to give the half-wave dipole a try. I have designed the following PCB to the best of my understanding of how to use a half-wave dipole with a 433 MHz transmitter. Will the ground plane negatively affect the coverage of the half-wave dipole?

MoisturePCBwithAntenna.jpg
 

JimB

Super Moderator
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By folding the dipole elements like that there will be some effect on the resonant frequency, it will probably be lower.

If there is a ground plane on the other side of the board from the antenna elements, it will kill the antenna stone dead, it will barely radiate any signal.

JimB
 

ibwev

Member
If there is a ground plane on the other side of the board from the antenna elements, it will kill the antenna stone dead, it will barely radiate any signal.

JimB
Should I connect my components to the antenna and get rid of the ground plane?
 

JimB

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Maybe I don't understand your board layout.
What represents "the ground plane" ?

JimB
 

JimB

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OK, I misunderstood.
When you said ground plane, I assumed that this was something which covered the whole area of the board, a common thing in the RF world.

Running the antenna under the ProMicro is a poor idea, similarly the lines from the transmitter to the ProMicro, which are run directly under the antenna will have a lot of RF coupled into them. Whether this will be a problem I do not know, but is best avoided.

JimB
 

dr pepper

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Most Helpful Member
A folded dipole might be better in your situation, I dont entirely agree with Nigels point that antenna design is an art, however in certain situations it certainly appears that way.
The only other thing I can think of would be a directional variant like a yagi, but that would be as big as a tv aerial, in fact the latter would probably work if it was one of the lower groups.
 

Nigel Goodwin

Super Moderator
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As you have a metal tank, which you can mount the unit on - simply make a 1/4 wave whip, using the tank as the ground plane - this will greatly improve performance over any PCB aerials.
 
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