Why is 1-2 GHz shielding important?
I keep hearing that very high frequency shielding is important. Why is that?
Is it more important than LF or around 100 MHz shielding? and why?
Im still green in this subject, so every post is recommended. Thank you.
Regards,
Steve
its important at any freq.
One reason for good shielding as you increase freq, is that smaller and smaller lengths of circuit tracks, component leads etc start becoming more efficient radiators. This will increase the problem of RF inside an enclosure.
TX output stages should ALWAYS be shielded from Local Oscillators. Feedback can cause all sorts of osc. instability, resulting in the generation of spurii. Just as you dont really want LO RF getting into the RX front end before the mixer stage.
just a few random thoughts :)
Dave
Expanding on what Dave tells you, there are particularly troublesome frequencies you might need to make special provision for. These are the frequencies that could interfere with domestic broadcasts and emergency services. Also consider what would happen if someone held a mobile phone near your equipment, would it be able to withstand the high field strength. It can be quite enlightening to hold a mobile phone near some electronic equipment and see how it behaves, many devices will simply crash. This includes some VERY expensive and supposedly secure millitary equipment - but that's another story!
Brian.
Thanks guys. I guess in general you can thats it's because the higher the frequency gets, the more important it is to shield because of the higher speed, the shorter the wavelength the more easier it is for the electrons to release from the copper and is therefore radiated more.
For LF, lets say 1 kHz, the speed is simply to slow for the electrons to let go of the copper and can therefore not radiate anything.
not quite .... electrons travel in a circuit at the same speed regardless of freq ... just a little less that the speed of light because of what is called the "velocity factor" of the cable, wire etc.
Its isnt electrons that get radiated from a wire/antenna, its photons. All electromagnetic radiation is in the form of photons. The only difference is, as they increase in frequency they have more energy. Photons of light have more energy than photons of microwave RF. Photons of X-rays have more energy than photons of Light. Photons of Gamma Rays have more energy than photons of X-Rays.
It is actually the electrons that are the source of the photons. Without getting too deep into the physics of it all....
when electrons are energised they move to a higher level around the atom. When they loose that energy they release it as photons (amongst other particles)
cheers
Dave
Than you davenn. Last post really cleared my mind up a lot! Thank you.
Ah!, LF radiation CAN be a problem with attenuators, due to the eddy currents flowing. There was once a very good Airmec 201 signal generator that went down to 50KHz, and its 120 dB attenuator got increasingly inaccurate at low level/low frequency outputs. To cure the problem they had to cut a narrow slot in the attenuator casing to stop eddy currents.
Frank
I guess the main problem is IC material. silicon may be have higher sensitivity when freq is higher. However, when freq is higher then a point, the sensitivity will be low. so , light is also electromagnetic wave ,but we do not need special shielding in most situation. ...
chj