More on GHz shielding and GPS

aps GPS gets completely saturated by it (no other sats received anymnore).

No. You seem to have long skinny slot antennas. Try bridging them from time - self-tapping screws might be a bit brutal, but they could work.

GPS gets completely saturated by it (no other sats received anymnore).

A microwave oven is not a Faraday cage. It is an RF redirector... for some frequencies. Not nearly so much for others.

Litte test circuit in tin can soldered directly on ground plane, you can see the feedthrough (1nF) caps stick out,

shielding now sufficient :-)

Feedthrough caps are simply press-fitted (2mm diameter holes).

On a sunny day (Thu, 20 Dec 2012 01:58:48 -0800 (PST)) it happened Bill Sloman wrote in :

Yes, some sort of radiator, clearly, I now tried the double Russian dolls system boxes, and it works :-) The small tin box does most of the screening, all feed through caps, need to drill more holes now for output connector and RF feedback for the PLL, and modulation. The PLL control voltage has no problem with the 1nF feed through caps, the loop filter sees 10nF. Whats 10%. Its a cheap solution. Maybe I can make a LC low pass with 1nF for the modulation that still has enough bandwidth.

for

More specifically, the door seal is usually constructed as a quarter wave transmission line at 2.45GHz. There is no direct electrical contact between the edges of the door and the body of the oven. The open circuit at the outer edge of the seal is transformed to a short circuit at the inner edge, thereby keeping the RF in at the operating frequency.

At other frequencies, such as that used by GPS, the seal is quite leaky.

This technique has several advantages of directly contacting seals- Low cost; Unaffected by insulating deposits of food or grease; Low door closing force.

John

Absolutely. If the slot is longer than 1/4 wavelength, it will radiate like hell, even if it is only 0,1 mm high.

Look at some RF boxes to be flown into space, they usually have screws on all edges of the lid, one for each centimeter. For frequencies above 10 GHz, you my have to use more screws.

What's the diode you're using? I can't quite read all the part number from the pic...

thanks--

gaps >> GPS gets completely saturated by it (no other sats received anymnore).

Microdyne used copper tape between mating surfaces to improve shielding in their machined RF housings. Much easier to stop it at its source, than to try to try it in a larger box.

Ehh, if it's exactly n/2 wavelengths, the height doesn't matter; if it's not quite there, then height matters. Height of a slot antenna is the same as the width of a dipole's conductor, so a thin slot has a high Q and narrow bandwidth (and possibly low efficiency, due to crowding effects).

If it's an odd multiple of quarter wavelengths ((2n+1)/4), it should radiate very little indeed, just as a dipole really, really sucks at odd harmonics of its resonant frequency. Again, as with a dipole, if the opening width (conductor width) is very wide, or tapered (like a bowtie or rhombic opening), it may radiate more easily.

Tim