Re: [beagleboard] Beaglebone on 144.000MHz

[Gerald Coley]

How are you powerting the board?

USB or DC?

If DC, is the power supply a switcher?

What is the processor frrequency you are running at?

If you hold the reset button down, what happens to the level?

What all is connected to the board?

How are you measuring the 144MHZ?

 

Gerald

 

 

On Mon, Sep 10, 2012 at 10:21 AM, Andreas <andk...@gmail.com> wrote:

My beaglebone is quite noisy around 144.000MHz. 

And with extra wires to the GPIO:s it does not get better ;(

Do you have a clue where the 144.000MHz interference is generation in the beaglebone?

Best,

Andreas

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Gerald

 

ger...@beagleboard.org

http://beagleboard.org/

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[Kingbäck Andreas]

Thx for your reply but I think that all interference comes from poor grounding on my breadboard and all the long cables.
I'll give it a new try when I get the components for my CoolRunner-II cape. It is S9+++ om my ham radio :p

Best,
Andreas

2012/9/10 Gerald Coley <ger...@beagleboard.org>

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[Gerald Coley]

Understood!

 

Gerald

[Gerald Coley]

So, which pins did I not connect?

Gerald

On Tue, May 21, 2013 at 1:38 AM, <ass...@gmail.com> wrote:

Hi Andreas,
Beaglebone's microprocessor generates 144MHz.  I have measured the magnetic field with H-field probe and a spectrum analyser.
It is very normal for microprocessors to behave this way.
However, the beaglebone designers have  forgotten to provide the complementary ground pins for the signals from the microprocessor.
Therefore 144MHz (and some other interferences) from the processor will make your product to radiate and be very noisy.
The 144MHz only shows up when the processor is active. It is not there when processor is slows down.
I may have a solution for you if this is still a problem.

James.

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Gerald

 

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g-co...@ti.com

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[Gerald Coley]

I did not design the board for ultra low noise environments. It is designed to be sold as a $45 board. If you are working in this type of an application, my expectation would be that this would have been obvious, but maybe not.

You could design a cape that terminates the unused pins and adds a connector with a ground pair. The use whatever connections you need. You could then also put it in a shielded case.

Gerald

On Thu, May 23, 2013 at 6:19 AM, <ass...@gmail.com> wrote:

Hi again,

You can connect any pin that you would like, they will all cause common-mode noise at 144MHz and many other frequencies.  However, I measured the 144MHz to be the strongest emission peak.

If you are trying to achieve a very low noise, or trying to design a sensitive circuit, such as a receiver which operates around 144MHz, then it's bad news!

BeagleBone should have reference (GND) pins provided for every pin that is connected to the uC on the header connectors.  Use of a high-density connector would have made this possible.  But most hobbyist people like the 100mil headers.  Therefore, no room for many GND pins!  

The only suggestion I have is to use twiste-pair wires for all your GPIOs that you are intending to use.  Every GPIO wire should be twisted around a GND wire.  This way, you would have created a transmission-line for every GPIO.

Make sure your design has a solid GND plane as close as possible to the signals.  Use a GND copper-pour around your signals and don'f forget to add stitching vias.

Also, if you are able to remove the female headers from the BeagleBone, then you will reduce the emissions as much as practically possible.  Because, inside the connector shell there are wires that act like mini mono-pole antennas.

You can remove the plastic first by using a small screwdriver jammed under it from one end and twist it to raise it up.  Once the plastic is off, you can easily remove the pins one at a time with a soldering iron and a pair of tweezers.

James.

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[mickeyf]

Isn't 144 MHz the 2 meter Ham Band? Is this likely to matter either coming or going (assuming there is no 1 KW transmitter next door)?

[Ben Loftin]

Since when is a beagle not known for its noise.   Embrace the howl frequency.  Since the design is open you can always fork it and make a beagledoodle....

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[William Rust]

Since you don't have an antenna attached, and the total power that a beagle consumes is around 1 W, it's highly unlikely you'll be able to interfere with your local ham (my chibi arduinos have a max range of about 100m and that's with matched antennas and an actual transmitter circuit). As for a 1kW transmitter near you, nobody does that on 2m. Our local repeaters are only 50W and cover the county. Typical transmitters are 5-20W. (FCC regs require use of minimum power needed to complete the transmission). If you really are concerned, put the beagle inside a faraday shield (i.e. a grounded metal box, e.g. the Altoids tin).