Garage Door Opener Range.

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.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann
Loading thread data ...

What is the software model you've used here?

--
Mike Perkins 
Video Solutions Ltd 
 Click to see the full signature
Reply to
Mike Perkins

4NEC2: 4NEC2 does not have an easy way to produce presentable web pages, so I screen grabbed the JPG's using Irfanview and assembled the web page with jAlbum.

I also use EZNEC:

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

Do you believe the numbers it is giving you? 5.19 dB for a 1/4 wave ground plane antenna? Also, gain is in dB, not dBm. Just a little nit.

Reply to
Tom Miller

--
Nice. :-) 

Thanks, 
 Click to see the full signature
Reply to
John Fields

It is not that far away, assuming perfect ground, which explains the lower lobe to reflected upwards, which would explain 3 dB of gain. The remaining 2.19 dB sounds much like the dipole gain over an isotropic radiator. So actually, we should talk about 5.19 dBi gain or actually _directivity_. For electrically small antennas, the efficiency can be much less than 100 %, thus the _gain_ would be less.

Reply to
upsidedown

When the physical dimensions of an antenna are reduced, the antenna effective capture area and hence the obtainable receiver power drops much slower. Of course, there must be a proper match between the (reactive) antenna and the receiver.

Reply to
upsidedown

Sorry about the dB and dBm mixup. My sloppiness. Thanks.

Yes, I believe the gain figures. However, it doesn't matter because my point was that the CHANGE in gain with reduced antenna length is minimal. I've seen that in bench and field tests, so I know that works. The catch is that the antenna has to be impedance matched, which becomes increasingly more difficult and lossy as the antenna becomes shorter.

In general, unless I hit one of the limitations of NEC2, the patterns and gains of the models are fairly accurate. For this monopole, the added gain comes from reflections off the ground plane. The situation is similar to a mobile HF antenna, where the length of the antenna is considerably shorter than 1/4 wavelength. As long as the antenna is reasonably well matched and the matching losses are included in the calculations, then a short antenna can work almost as well as a real

1/4 antenna.

However, reality is never as good as the models predict. In this case, I'm using an infinite perfect ground. I have yet to find one of those outside of an antenna range. The matching losses for the shortened antennas will add more losses. At best, the 5.19dB gain will be a best case maximum, with reality being somewhat less.

You can sorta see the effects of height above ground in: The animation was originally intended to show the effect of antenna height on the pattern, but it also shows the changes in gain. Closest to the ground, it shows 5.24 dB gain. Highest shows 7.08 dB. Both are much larger than the traditional 2.18 dB gain of a free space dipole.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

Good explanation and you're correct about the directivity. Having gain in the wrong direction isn't very useful. In the case of the shortened monopole, the peak gain is in roughly the correct direction needed to be useful, so it's not an issue. However, other antenna configurations can cause problems. For example, here's an animated GIF of a common discone antenna. Up to about 400 MHz, the major lobe (i.e. maximum gain) is roughly horizontal, making the antenna quite useable. However, between 400 and 1000 MHz, most of the RF goes straight up. There's little RF left at the horizon, where it's needed. Such an antenna might be good for listening to airplanes, but not terrestrial stations.

The radiation efficiency and internal losses are included in the gain calculation. For example, if I made the antenna from lossy material, it would show up as a loss in gain. However, for a fairly close to ideal antenna, the radiation efficiency barely changes.

wavelengths gain Efficiency Radiation (db) Efficiency 0.250 5.19 100% 99.93% 0.125 4.85 100% 99.66% 0.050 4.75 100% 99.09%

Again, the problem is matching the impedance of the shortened antenna. The losses are not in the antenna. They're in the matching circuit.

wavelengths gain(db) VSWR (50ohms) 0.250 5.19 1.74:1 0.125 4.85 158:1 0.050 4.75 5954:1

The 0.050 wavelength monopole shows a feed impedance of 1.52-j707 which is going to be verrrrrry difficult to match efficiently to 50 ohms. Got a 500:1 transformer handy?

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

Suppose I simply made a dipole half inside and half outside? Would that improve my reception? ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

No. Well, maybe. Hell, why don't you just extend the existing wire antenna to the outside and treat it like a long wire antenna.

It might work. Or it might make the receiver oscillate :).

Reply to
Tom Miller

Most of this VSWR is due to the fact that the small antenna has a high (capacitive) reactance. Tuning it out with a loading coil, you only have a smallish resistance mismatch and hence much lower VSWR.

You tune out the capacitive -j707 ohms with a loading coil +j707 ohms and you only have to worry about the resistive 1.52 ohms. To match this to a 50 ohm input, the impedance ratio would be 1.52:50 or 1:33 or less than 1:6 turns ratio.

A few cm long "rubber duck" (normal mode helix) is a reasonably efficient antenna for 433 MHz.

Reply to
upsidedown

But only for certain values of "reasonably" :).

Reply to
Tom Miller

...Jim Thompson

OK Jim, What is the model # of your opener, Let's find out what the output circuit looks like. Here's a few,

Mike

--
This email is free from viruses and malware because avast! Antivirus protection is active. 
http://www.avast.com
Reply to
amdx

Door is a sheet-metal sandwich with the insulation between the two metal panels. Walls are foil-backed exterior sheathing plus foil-backed drywall inside.

Dramatic range improvement.

[snip]

How about this... Drill hole in door, fit water-tight thru-hole BNC connector, attach rubber ducky antennas to each side. Would that be enough of a "window"? ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

Genie Model 2024

Can you simply buy a 433MHz receiver that has a relay output? ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

Well, it has half a chance of working, and half a chance of making things worse. It depends on which side of the dipole you poke through the wall. Half-baked is usually the result of half-way solutions and half-ass kludges. The reason I can only offer half a reply is that I have not seen anyone build a working antenna like that, which should be a clue as to how well it might work. If you're going to drill a hole in the wall, you might as well put the entire antenna outside. However, if you insist on doing it wrong, just make sure you put the half of the dipole that goes to the coax center conductor outside the garage, and the grounded half of the dipole inside the garage. With foil backed insulation in the wall acting as a ground plane, no RF will radiate from the grounded half of the dipole, giving you a better than half-way possibility of making this technical abomination work.

1/4 wavelength at 433 MHz is about 17.5 cm.

Incidentally, the problem with attaching a bigger/better/outside antenna is that it MIGHT detune the receiver. If it's a crude TRF (Tuned RF) receiver, where all the selectivity is one tuned circuit connected directly to the antenna, any changes in antenna configuration is going to create a problem. As Mike K suggested, you'll need to look at the schematic to see if there's any isolation between the antenna and the tuning.

Beware of engineers bearing screwdrivers (and tuning tools).

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

They're all over eBay in many different configurations.

The problem will be getting one that is compatible with your cars Homelink remote. That means you'll need to buy both the receiver and transmitter because the transmitter is needed to program the Homelink thing. However, if you're not going to use Homelink, then it's not an issue.

Also, methinks we might be wrong about the frequency. The Genie 2024 runs on 390 MHz or possibly 315 MHz frequency. Genie got into problems in areas where the military was using 390 MHz for something. I'm not sure as I couldn't find any specific references. I could lookup what it does by the FCC ID number, or you could just hang a frequency counter near the trasmitter and see what frequency the remote belches.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

Looks like about 9 wires to move the control circuit board, includes the receiver, outside.

formatting link
Looks pretty simple to remove, pull it out and inspect, maybe draw a schematic.

I got that pdf from here

formatting link

I didn't find a schematic.

--
This email is free from viruses and malware because avast! Antivirus protection is active. 
http://www.avast.com
Reply to
amdx
[snip]

I have a whole set of tuning tools, in their original pocket protector. (I grew up in a Radio/TV repair shop in the late 50's, when there were IF cans aplenty :-) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.