Author Topic: I need some tips on PCB board and antenna design.  (Read 1451 times)

JimK

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I need some tips on PCB board and antenna design.
« on: March 16, 2016, 06:25:12 PM »
Before sending my custom boards out to OSHPark, I need some advice.

I'm designing a custom ATmega32U2 board that will accommodate a small 1" x 1" RF riser board.
The riser board will house a Hope RF 433 MHz Radio Module, either the RFM69CHW or the RFM98W(LoRa) module. The footprints are identical, so either will work (although the firmware will be completely different).

On the PCB layout of the Radio riser board I have done the following:
The board is 2 layer.
The bottom layer consists of a full ground plane.
No traces run directly beneath the RF module.
I plan on using a simple wire antenna, and the hole for the antenna is right next to the Antenna pad of the module.

Questions:

#1. In an earlier thread it was suggested that a copper pour be put directly beneath the RF module, and have rows of vias connecting this pour to the ground plane below. I guess this essentially gets a ground plane in extremely close proximity to the bottom of the RF module. Of course this pour would be covered in solder mask, and I'd also probably include a layer of Kapton Tape to insure no contact with the RF module.
Is this is something that will help in range and reliability?

#2. Does the guage of the antenna wire make any difference? I know the Moteino I bought came with 24 guage copper. I want to use a thicker 22 guage. Is there an ideal guage? Does a change in guage mean the length should change?

#3. Is there any advantage of using a U.FL connector, and pair it with the appropriate commercial antenna?
http://www.digikey.com/product-detail/en/anaren/66089-0406/1173-1021-ND/3069143
Does this type of combination give greater range than an simple wire antenna?

Any other tips would be appreciated...

john4444

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Re: I need some tips on PCB board and antenna design.
« Reply #1 on: March 17, 2016, 12:23:58 PM »
Hi JimK,
The simple answer to each of your questions is no.
I am afraid that there are a lot of details that would require a lot of explanation and specific qualifications.
Without getting into the details, here are some simplified explanations:

Quote
#1. In an earlier thread it was suggested that a copper pour be put directly beneath the RF module, and have rows of vias connecting this pour to the ground plane below. I guess this essentially gets a ground plane in extremely close proximity to the bottom of the RF module. Of course this pour would be covered in solder mask, and I'd also probably include a layer of Kapton Tape to insure no contact with the RF module.
Is this is something that will help in range and reliability?
A ground plane is needed to maintain the RF properties of the module.
If the ground-plane is either directly under the module or separated by the thickness of the PCB will make no noticeable difference in RX/TX distance.
Quote
#2. Does the guage of the antenna wire make any difference?
No.
Not until the thickness of the wire begins approaching a significant percentage of the length.
Even then, the RX/TX bandwidth increases but not the RX/TX distance.
Quote
#3a. Is there any advantage of using a U.FL connector...
No.
Every extra item between the module and the antenna reduces the RX/TX distance.
Quote
3b. and pair it with the appropriate commercial antenna?
No.
there will be no difference between the digikey antenna and a straight wire with the same connector.

Quote
Any other tips would be appreciated...
There are only a few ways to effectively increase the range:
increase the transmit power. Since these are used in pairs, increase power at both ends. However, there can be legal restrictions.
reduce the noise. This usually means reducing the transmitted and/or received bandwidth. However, the RMF modules are already very good.
directional antenna. A narrow bandwidth Yagi antenna can provide gain as well as directionality over a wire antenna.
line-of-sight. It is possible to achieve very long range at low power when there is nothing in the way. Gain altitude ie: tall towers, balloons or orbiting satellites.
slow the data-rate. Transmitting/receiving data below the noise floor is easily done at slow data rates or transmitting the data multiple times.

Good luck with your project
John AE5HQ
John AE5HQ

JimK

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Re: I need some tips on PCB board and antenna design.
« Reply #2 on: March 17, 2016, 01:10:43 PM »
Thanks John for your very detailed answer!!!!!!

Sounds like I can keep things simple...which is OK by me.

Thanks again!!!!!!!!!!!!