Does anyone know if it's true that when using atmega128, the crystal gives off a "signature" that someone can detect from outside the residence?
I have been told this, but can't find anything in any of the forums that confirm or deny the fact.

Please let me know what you think.

Dave

heres something that I found hope it helps

EMI (electro magnetic interference) emissions
To discuss some of the facts that have been found out and concerns of the radiation of noise from test equipment. What first needs explained is the frequency of concern to most is the 121.5 mhz frequency.

Some questions that comes to mind is where does it come from? And why is this a concern? and why is it not with Direct TV’s receivers?

Where does this come from? This might be a shock to some, but it comes from the receiver! Dish and Bev both use receivers that have a communication link with its smart cards that are not standard. So the frequency is the 4.5 mhz off the iso card to synchronize the communications with the card. All of them are that way with the exception of the 6000. Its at 4.156 mhz (which is why the 6000 requires a different flash than every other receiver). Which translates to 140.650 k and 128k baud which is not like 115.2k that Direct TV runs at. So now we have the source of the noise. The 27th harmonic off the 4.5 mhz noise. So if you take a hand held scanner and tune into 121.5 mhz with nothing in the receiver. Plug it in guess what? You will get a noise that is generated from the receiver that you can pick up! Now with a card in the receiver with most of the tests I tried. Once I leave the room with the hand held scanner I will start to get static. The farther you walk away the more the static. So the dirty little secret is that it comes from the receiver. So I used that as a baseline. Cause there isn’t much you can do with what they have designed other than reducing it.

Now, why is this a concern. The 121.5 mhz runs where emergency vehicles and such communicate. If you get enough of this noise it can interfere with the communications on radios. It’s the same thing that cable companies deal with keeping their leaks on their systems down. So enough of this leaking can cause problems.

Direct TV’s harmonics just don’t fall in line with this communication. So that’s why you don’t hear about it.

So now we know what it is where it comes from. What’s the big deal? Well if we stick something in the receiver that allows the signal to travel out of the receiver it can radiate louder than the original design. Such as an avr or emulator can allow it to travel and radiate outside the shielded case. So what do we do. I did some comparisons of the devices and different atmels. What I found was the 8515 radiates allot more than the 2313. I could lock onto that 121.5 outside my house without any static outside. Where as a standard receiver, the next room I’d start to get static.

So what can be done? Well not is all lost. I found if you put the bulk of the emulator inside the receiver. The noise is close to the original. But is their anything that we can do to keep the noise near the same and also not interfere with the video signal? Well the good new is YES.

Ferrite beads and resisters placed in the circuit, especially put on the 4.5 mhz coming off the receiver to knock down the signal. I’ve put a 100 ohm resister and I’ve heard from some a 1k ohm resister has worked even better. Ferrite beads on the lines reduce the signal. I’ve had suggested to me that why don’t you put a cap on the circuit to shunt the signal to ground? Well that’s fine for taking signals out of circuit where you don’t want them. But it just puts it to the Ground! The noise is still there. You just moved it. You didn’t eliminate it, or reduce it. So in the circuits with reducing the signal and the use of the 2313 made it from my tests about the same as the receiver with a card. That was the goal. So in the circuits with those devices installed such as resisters and ferrite beads. You can reduce the noise to levels of a standard receiver. Avrs with the device sticking out is really susceptible to having the noise radiate loud. Then the 8515 on that can make it loud. So with a compact setup emulator like Dishtoys or with allot of ferrite beads on it like Danacos and Zenontech’s it can keep the noise down. If you build your own and the resister of 100 to 1k ohms helps tremendously. I did put a resister in line with the 8515’s to see how they did. It did reduce the noise but not as low as I got with the 2313’s.

I’ve also seen shield cable out to the receiver and foil added will help too around leaving the receiver to reduce the noise.

So I hope this helps you understand what is going on what can be done.

M24C

Thanks a lot. That does help quite a bit.
The board that I have is compact and fits into my 3100 so that you can close the card door.

I'm not going to worry too much about it.

Thanks again.

Dave

Does anyone know if it's true that when using atmega128, the crystal gives off a "signature" that someone can detect from outside the residence?
I have been told this, but can't find anything in any of the forums that confirm or deny the fact.

Please let me know what you think.

Dave


I think you got it mixed up with AVR board. The AVR will transmitted the signal that caused interference with malitary aircraft signal.