I do wish you would use a 433 MHz or 315 Mhz rubber ducky antenna. I'll make it easy. Put a pizza platter on Jim's roof and ceiling. Add a 5/8 wave antenna with a suitable matching transformer, and I'll call it about 5 dBi gain. At 10 meters from the garage, that will probably work. At 200 meters, no way.
Sure. Like I said. Add some gain at any of the antennas to make up for the 39 dB difference in path loss between the direct versus the passive repeater, and it will work just fine. However 2.5dB gain per antenna is not going to make up for 39 dB of loss. Granted, you can run the signal levels down to the minimum detectable signal level, and possibly make it work. However, don't use my figures for doing that. I picked 0dB losses and 0dB gain antennas simply to illustrate the large difference in path loss between the two schemes. If you want a more accurate calculation, I can grind out the numbers. I'll need some details from Jim Thomson, such as the height of the garage, the height of the garage door opener, and the size of the garage.
I think differently. Using my numbers, the only way to compensate for the difference in losses is with antenna gain. Well, maybe increase the transmit power or put an RF amp in front of the receiver.
True. However, that doesn't make much difference if the antenna is outside the shielded garage. I consider that a necessity, whether using a passive repeater or a direct shot.
No, it's not. The situations that work is where there is absolutely no signal via the direct path. The basement of an emergency center is one. Another is 4 floors down in an underground garage. Jim's shielded garage may be very lossy, but is still leaky enough that cancellation (nulls) between the incident and passive repeated signals will be a problem.
Only if you're lucky. The problems with such calculations as mine is that they define the best possible conditions, where everything behaves exactly as predicted. Reality tends to suggest that this is most often not the case. Losses are never better than predicted. Power output and rx sensitivity are never up to spec. Path losses always have some extra obstructions that raise the losses. And, I haven't even thrown in Fresnel zone diffraction. There are no optimists in the RF business and antenna problems tend to be very strange:
Believe me, I have loved passive repeaters since I discovered one hiking in the hills above Big Bear Lake in southern Calif. When we finally reached the top of the mountain, there was a huge billboard on top. No advertising or embellishments. Just a billboard. I discovered later that it was a passive reflector for the microwave links used by AT&T to cross the country. I thought it was cool. Somewhat later, I blundered into periscope antennas, where a 45 degree reflector in the shape of an ellipse was perched on top of a tower, with a dish antenna pointing straight up at the reflector. Again I thought it was cool.
Then, I discovered that ecology and fiber optics had conspired to remove the billboards from the mountain tops. The FCC also took a dim view of the signal splatter produced by periscope antennas and effectively banned them. So much for my first love in antennas.
At various times in my checkered career, I've toyed with various forms of passive repeaters, and found little in the way of success. The math shows why, but I was more than willing to ignore the calculations in the hope that they might be wrong. When Wi-Fi took hold, I immediately resurrected the idea in a 200ft fir tree, pointing one dish at the WISP (wireless ISP) and the other down to my house. As long as I didn't mind climbing the tree to realign the antenna every few weeks, it worked fairly well.
I never make the same mistake twice. 5 or 10 times is more my style.