The first thing I would do before calling the yagi wrong would be to compare it against a known standard. IE: a dipole at the same frequency. the 15dbi means that it has 15db gain over an 'isotropic dipole' (standards dipole mounted in 'freespace')
maybe your dish is not what it's supposed to be??
Then, after seeing the difference when comparing the dipole to the yagi you would have a difinitive answer as to the yagi gain,
In ham radio circles, MFJ is not known for quality products. That antenna might be suitable for temporary installation, but the exposed copper driven element and unprotected connector is just asking for problems outdoors. Also, I made no attempt to price shop or optimize the cost/dB ratio. Interestingly, at one time, the yagi was the most expensive, while the omni was the cheapest. I can do it again using approximately the same gain antennas, which should produce more useful results, but I was just hoping that the OP would do her own calculations based on prospective antennas.
Well, the maximum gain of a dish is very easy to calculate.
Gain(dBi) = Pi^2 * Dia^2 / wavelength^2 * feed-efficiency where Dia and wavelength are in the same units and efficiency is a function of feed illumination accuracy and is no more than 50% at best for typical small dish antennas.
Climbing onto my roof and trying the numbers on a PacWireless 24dBi dish: Gain = 9.87 * 68cm^2 / 12.5cm^2 * 0.50 Gain = 9.87 * 4624 / 156.25 * 0.5 = 146 = 21.6dBi Close enough to 24dBi.
The gain of a yagi is approximately the gain of a dipole, 1.66 scalar (or 2.2 dBi) times the number of elements (including the driven element). So, the MFJ yagi should have a gain of: 1.66 * 16 = 14.2dBi Close enough to 15dBi.
Basically, if the antennas were built perfectly, they would be sufficiently close to theory to make the advertising correct. However, this is rarely the case. Manufacturing tolerances, surface coating inefficiency, connector losses, sloppy construction, VSWR losses, boresight errors, effects of the mounting hardware, local reflections, and sloppy installations all conspire to reduce the gain below the maximum. Your mileage and gain may vary.
It's not fraud. You might try the better biz burro or Federal Trade Commish. I doubt that they care.
It's not 5dB short. There are plenty of other abominations in the antenna business. I've often considered going into the commercial antenna business because few people can understand how they work, make valid comparisons, and have the necessary test equipment. Perfect for an evil exploiter like me. Anyway, I can do without hand drawn antenna patterns, unrealistic free space antenna patterns, non-standard scales on antenna patterns, claims of range improvement (compared to what?), forgetting about coax cable and pigtail losses, ignoring bandwidth issues, failing to measure up-tilt on omnis, crappy mounts, use of easily corroded materials for unsealed outdoor antennas, etc. It's not really distorting the numbers as much as conveniently forgetting to mention some important items.
I like to prototype things first with disposable parts. For all I know something else might pop up that would prevent the whole idea from working well. If I spent too much time trenching and buying special outdoor cable I'd feel really stupid. Indoor cat-5 is so cheap I wouldn't even think twice about running a 150ft run knowing that it would have to be redone with higher quality parts once all the other details had been worked out.
One trick I learned from the cable guys when they installed my athome connection many years ago is to use the soft black fountain hose as poor-man's conduit. That method did have its problems as water tended to pool in the low parts of the conduit. I wonder if small bleed holes in the conduit would have helped. Thoughts? Or just go for direct burial/gel and forgo the conduit?
Thanks for that tip! I'm sure I'd have fallen for that.
Sounds like the goop ma-bell used to put into the phone electronics. You could wash your hands 10x and the crap would still be stuck to your fingers.
The 15dbi bbq dish I have is only the small 12"x16" 15dbi one from Sharper-Concepts.
It has a N-female just like the MFJ antenna so I can move the pigtail from one antenna to the other. The difference between the two antennas was 5db in signal strength. The test source was the mystery "Mt Allison" wifi source which came in with 2db above the noise floor with the yagi and 7db with the dish. Both claimed to be 15dbi antennas. I supposed the dish could be vastly better than it is rated, but what is the chance of that?
I can't afford to do that for my customers. They don't want to pay me to do things twice. I have to get it right the first time. However, at home, I can experiment.
Yep. I have several runs of black poly something flex water pipe running under the road and buried along the shoulder. However, I spent quite a bit of effort to keep it waterproof. I originally had it pressurized but the later decided that it was a waste of effort. No water inside that I can find.
No, a drain hole won't work because there's not enough pressure inside the pipe to eject the water through the small hole. Small holes require pressure to get past the surface tension of the water drops. The obvious question is why is there water inside? Condensation? Capillary action? Siphon action? Keep the water out and you won't need to worry about drainage.
Yep, that's the goo. Some type of silicon greasy gel. The state of the art waterproof cable now uses "Poly-Gel" which is a white powder. I've never played with the stuff and know nothing about it.
That's a 15dBi dish antenna. I have several similar ones from PacWireless. They work well enough.
That's the same general method that I use except that I have a convenient line-o-sight signal from Loma Prieta. It's a good way to do it. A stronger test signal might be a bit better.
There's a big difference between a high gain yagi and a dish. The dish feed is a relatively broadband device when compared to the yagi. If the yagi were mistuned even slightly, the gain will drop like a rock. That's another reason why I like dish and panel antennas. They're not overly frequency sensitive. Also, all of these antennas will have some variation in gain with frequency withing the 2400 to
2483.5MHz band. 1 - 3 dB gain variations are typical.
If you want, I can crank out some 4NEC2 simulations for the two antennas. However, I'm lazy and don't wanna do anything tonite.
On Tue, 4 Jul 2006 11:03:49 -0400, "Peter Pan" wrote in :
Increase coverage by adding access points (network bridges), not routers. You want only one router on the typical small network. Otherwise you'll likely run into problems of multiple NAT and DHCP conflict. You use additional routers to increase coverage if you configure them as access points rather than routers, as described in the How To wiki below. That means connecting LAN port on the router to LAN (not WAN) port on additional routers configured as access ports.
On Tue, 4 Jul 2006 15:19:26 -0400, "Peter Pan" wrote in :
You want only one router on the typical small network. Otherwise you'll likely run into problems of multiple NAT and DHCP conflict. You use additional routers to increase coverage if you configure them as access points rather than routers, as described in the How To wiki below. That means connecting LAN port on the router to LAN (not WAN) port on additional routers configured as access ports.
Using the same SSID is the best way to have wireless clients connect automatically to the best access point, but using the same channel is a bad idea, because of possible interference. It's best to use different channels with minimum overlap (1, 6, 11).
Other options to consider for wiring additional access points:
I've used a similar product for mains-voltage cabling and its quite annoying to work with, though about as flexible as 10mm soft-annealed copper central heating pipe, if you're familiar with that (you can tie knots in it). Special glands required at the ends of course, and special units at any junctions / connectors etc.
A heck of a lot cheaper to run cat5 and replace it every few years, I've had a length of cat5 bought from Maplin running round the outside of my house (south and west elevations) for about three years now, with no discernible signal degradation. I'll tell you in about another three years whether the 40m running to my garden shed causes problems... :-)
Install a compatible WAP (wireless access point) in your shed with another directional antenna pointing toward the one at your house. The WAPs will connect to each other, and the one in the shed will then relay to your laptop. (Your wireless router is a WAP.) No wires needed.
On Thu, 06 Jul 2006 01:35:09 -0000, firstname.lastname@example.org (Gary Heston) wrote in :
Unfortunately, it's not that simple. You either need (a) a wireless client bridge connected to an access point, which works fine with a directional antenna, or (b) a repeater (e.g., WDS), which generally has to be the same make and model as the host, and which won't work terribly well with a directional antenna.
John is correct. A receiving antenna, when matched, reradiates half the power it receives. An impinging field induces current in the antenna. This causes radiation, just like the current in a transmitting antenna. As it turns out, when the antenna is matched, the amount of power radiated equals the amount of power delivered to the load, and that's the best you can do. If you'd like a more in-depth and mathematical explanation, you can find it in any antenna text, often discussed as "scattering".
If a receiving antenna did absorb all the impinging power, it would be a lot easier to make a shield or a stealth aircraft.