Microwaves and Wireless Devices

Put the microwave in the oven?

emc²:

How would you increase the microwaves range but without causing ill effects to humans?

UFG

I believe what you are asking is how can one extend the range of a microwave communications link where the radio transmitter is a personal device with antenna close to the operator, without harming the operator. Anyway, that is the question answered below. If you had something different in mind, you will have to let me know.

The operator aside for the moment, here are the things you can do to extend a COMM link at a fixed frequency over a short distance:

1) Increase transmit ERP (effective radiated power).

2) Increase sensitivity of receiver.

For cell phone, Wi-Fi and Bluetooth, item (2) isn't under your control, so that won't be addressed further.

Item (1) has two components: transmit power (Watts) and antenna gain. Transmit power will have some upper limit set by either practical constraints (battery power?) or legal (FCC power limit on unlicensed transmitters). If there were no constraint, you could increase power output as needed, but at some point you run into human tissue heating safety concerns. One way you deal with that is to remove the antenna from the vicinity of the operator. With a cell phone, Bluetooth is one way to do this - you essentially replace the high power transmitter right next to your head with a low power link that allows you to place the cell phone at a safe distance from you. Or you can use a wired headset, same effect. Both these approaches help with the safety issue, but don't extend the range of the link.

In order to extend the link range, you can replace the transmit and/or receive antennas with higher gain devices. This isn't available with a cell phone, but is getting common with Wi-Fi.

Typically Wi-Fi antennas, both on router and PC or laptop have omni-directional patterns, in order to allow them to work equally well in all directions. But if you have control over a situation so that you don't need omni coverage, but only a link in a particular direction, you can use higher gain antennas that establish a "pencil beam" with all the energy concentrated instead of radiating 360 degrees. The degree to which you concentrate the beam is the same degree to which you extend the range.

Here are some ballpark numbers. A typical omni pattern has a gain around 3 dBi. Don't worry about the units if you aren't familiar; we'll work that out. You could use a Yagi-Uda array at one end or both, and the Yagi could easily have 10 dBi gain.

If the router remains omni and the receiver is outfitted with a 10 dBi antenna in lieu of a 3 dBi antenna, you increase the range by the difference, which is 7 dB (not dBi). That will just more than double your range.

If you use Yagis at both ends, you will increase the range by twice that 7 dB (7 dB at both ends of the link), so you will extend the range 14 dB, which increases the range by a factor of five. You have an added advantage from the point of view of operator safety here: the concentrated beam reduces the rf power incident upon the operator (unless you get in the way of the beam, in which case it gets worse, and you will lose your link, or lose range, anyway).

So in conclusion, if you are looking at a Wi-Fi link, higher gain antennas can increase your range while reducing your rf exposure, assuming you stay out of the beam. You used to be able to do something similar with automobile cell phone installations. The phone connected via coax to an externally mounted antenna. The externally mounted antenna had little more gain than the phone antenna, but by mounting it outside the car it was getting a stronger signal from the tower, and vice versa, plus it removed the rf transmission from your immediate vicinity. This all hinged on having low-loss coax to run between cell phone and external antenna. If you lost more in the coax than you gained from the external installation, the effort was wasted.

NO.

How do I extend the interference range of a standard household microwave oven (say up to 50 feet) without causing harmful effects to humans? Not a microwave link, not a cell phone, not a wireless connection (i.e. router). A standard microwave oven.

UFG

You want to use a microwave oven as a jammer???

Bad idea on a couple accounts:

1) Unless you have specialized test equipment to measure SAR (specific absorption rate), you won't know when you have exceeded the health concern limit. And even given that equipment, you have to know how to use it.

2) It's illegal to jam a cell phone. Don't think a microwave will do that, but if it were possible, it would be illegal. It may or may not be illegal to jam Wi-Fi or Bluetooth, but it doesn't sound like a good idea.

I can think of all kinds of ways to degrade the shielding effectiveness of a microwave oven, starting with the door, but I'm not going to go into details, for the above mentioned reasons.

I would have to agree with EMC_C... it is very dangerous to play with the that kind of radiation. I have now gotten rid of my microwave oven and wont get another one. It has saved me a lot of problems.