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Antenna dimensions?
Building a small 2.4 GHz detector:
http://www.atvinderby.co.uk/2.4Ghz_SWR_Meter.htm Regarding the dimensions of the wire loops: ant: 28 mm square reflector: 30 mm square separation: 10mm wi 14ga solid (1.6mm dia) Are these dimensions center-to-center of the conductors? Or are these dimensions the space between the conductors? With a conductor diam of 1.6mm, this is more than 10 percent of one dimension (separation), so I think it's important to get it right. Also, is the reflector to be grounded or floating? Thanks. |
Antenna dimensions?
http://www.atvinderby.co.uk/2.4Ghz_SWR_Meter.htm
Regarding the dimensions of the wire loops: ant: 28 mm square reflector: 30 mm square separation: 10mm wi 14ga solid (1.6mm dia) Are these dimensions center-to-center of the conductors? Or are these dimensions the space between the conductors? With a conductor diam of 1.6mm, this is more than 10 percent of one dimension (separation), so I think it's important to get it right. It's probably not actually all that important. Quads are not highly in their dimensioning. Altering the positioning between the driven (active) element, and the reflector, will change the antenna's pattern (gain and front-to-back radio) slightly, and will alter the feedpoint impedance slightly. Neither of these changes is going to be particularly significant (and quite possibly not easy to detect) in this situation. The fact that there's a lot of additional metal in the neighborhood of the antenna (the BNC connector, etc.) is probably going to alter the pattern more than the spacing different will (compared to a theoretically perfect quad in free space). The pattern of a two-element quad is fairly broad, and the front-to-back ratio isn't terribly high. It's not the best design for pinpoint aiming / location of a microwave source... but that isn't really what this device was intended for. As a field-strength meter, it'll work fine (and probably just about equally well) with a 10mm separation edge-to-edge or center-to-center. Also, is the reflector to be grounded or floating? In a quad, it is usual for all of the elements other than the driven one to be floating. Since the article says that the reflector is fastened with a dollop of glue, I think it's safe to assume that it's intended to be floating. That detector is a slick little design - thanks for posting the link! -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Antenna dimensions?
It's probably not actually all that important.
dplatt - - - Thanks for your comments and evaluation of the project. They are helpful to someone not skilled in the black art of wireless :-) I plan to modify the design a bit, eliminating all coax connectors & adapters, using just 2 banana plugs (and supporting plastic block) as the connection to the meter. Is it any more efficient to use copper foil or PCB material as the reflector rather than wire? Thanks. |
Antenna dimensions?
In message .net,
SparkyGuy writes It's probably not actually all that important. dplatt - - - Thanks for your comments and evaluation of the project. They are helpful to someone not skilled in the black art of wireless :-) I plan to modify the design a bit, eliminating all coax connectors & adapters, using just 2 banana plugs (and supporting plastic block) as the connection to the meter. Is it any more efficient to use copper foil or PCB material as the reflector rather than wire? Thanks. A novel bit of kit, looking at the photos it appears to be being used with a DVM, depending on how you want to use it you may find an analogue meter easier. It will show changes better than a DVM. How about buying a movement and a box and building a totally dedicated unit? I'm tempted to make something similar. -- Bill May God defend me from my friends; I can defend myself against my enemies. |
Antenna dimensions?
An interesting design...
Keep in mind that you are building a relative, not absolute measurement device. ie you can calibrate (or not) it anyway you like. Any piece of wire will have a voltage induced into it by a passing EM field! The only real concern is that you may want to ensure that the directivity of the quad is reasonably unidirectional. Some quad designs have pretty bad front to back performance. This may give you erronous results if you start seeing reflections or other TX's of the back of your antenna. The easy way to overcome this is to calibrate the pattern by rotating the unit in an active 2.4GHz field and noting some values. You can then use these in later tests. Cheers Bob SparkyGuy wrote: Regarding the dimensions of the wire loops: |
Antenna dimensions?
Thanks for your comments and evaluation of the project. They are helpful to
someone not skilled in the black art of wireless :-) I plan to modify the design a bit, eliminating all coax connectors & adapters, using just 2 banana plugs (and supporting plastic block) as the connection to the meter. That should certainly work! Is it any more efficient to use copper foil or PCB material as the reflector rather than wire? I believe not. PCB material will probably be less efficient - standard FR-4 fiberglass-and-epoxy has significant losses at 2.4 GHz. Also, the presence of the FR-4 will change the effective length/diameter of the reflector loop... you might have to change the loop diameter to compensate. Foil would probably be bit less efficient than wire, assuming that the width of the foil was the same as the diameter of the wire - less surface area for the current to flow through, and perhaps more current crowding to the edges of the foil due to skin effect. It'd also be significantly less rugged. Once again, neither of these losses of efficiency is likely to be terribly important in this application, but why run the risk? I'd just stick with solid copper wire of a reasonable diameter/gauge, as it'll be electrically efficient and mechanically strong and rigid, easy to get, and inexpensive. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Antenna dimensions?
Dave Platt wrote:
Is it any more efficient to use copper foil or PCB material as the reflector rather than wire? I believe not. PCB material will probably be less efficient - standard FR-4 fiberglass-and-epoxy has significant losses at 2.4 GHz. Also, the presence of the FR-4 will change the effective length/diameter of the reflector loop... you might have to change the loop diameter to compensate. I would think so, at 2.4Ghz there is, no doubt, "only skin effect." Although, I doubt you would notice a great change in efficiency, it should be prove-able, at least on paper. The biquad uses a solid reflector plate for good reason, wire is cheaper/easier to obtain. If the foil side faces the element, I should doubt any rf gets past it to the fiberglass-epoxy to be "lost" in efficiency. Foil would probably be bit less efficient than wire, assuming that the width of the foil was the same as the diameter of the wire - less surface area for the current to flow through, and perhaps more current crowding to the edges of the foil due to skin effect. It'd also be significantly less rugged. My statement above applies here ... all the wire element can "see" is reflector, with foil. Once again, neither of these losses of efficiency is likely to be terribly important in this application, but why run the risk? I'd just stick with solid copper wire of a reasonable diameter/gauge, as it'll be electrically efficient and mechanically strong and rigid, easy to get, and inexpensive. Tear apart some LNA/satellite feeds to the dish, you will not see them using wire reflectors there; I think there is good reason. Just my opinions drawn from my readings/study, looking at commercial equipment and hands-on ... One thing I do totally agree with, it WILL work well with just a wire reflector. Regards, JS |
Antenna dimensions?
John Smith wrote:
... One thing I do totally agree with, it WILL work well with just a wire reflector. Regards, JS I built this, actually, a while back. Toss in a director (what is one more wire?); I found that to be a worthwhile mod ... Regards, JS |
Antenna dimensions?
I built this, actually, a while back. Toss in a director (what is one
more wire?); I found that to be a worthwhile mod ... Regards, JS Suggestions re. dimensions and location of a director? Thanks. |
Antenna dimensions?
Bill wrote:
looking at the photos it appears to be being used with a DVM, depending on how you want to use it you may find an analogue meter easier. It will show changes better than a DVM. The author says he tried that and it didn't work as well: "I tried connecting the antenna directly to a micro amp moving coil meter, however there was very little meter deflection from a Wireless LAN card." Impedance too low, perhaps? Clifford Heath. |
Antenna dimensions?
SparkyGuy wrote:
I built this, actually, a while back. Toss in a director (what is one more wire?); I found that to be a worthwhile mod ... Regards, JS Suggestions re. dimensions and location of a director? Thanks. I believe I tried lengths of a 3% to 5% shorter length with the director, than the drive element (i.e., the one in front of the reflector), settling on a 4% shorter length ... anyway, that is common in HF parasitic arrays ... this is equiv. to a 3-element quad on HF. I just dug it out and measured it, this is what it appears to be, alright. With a spacing between driven element and director of ~0.2 wavelength, center-to-center. Regards, JS |
Antenna dimensions?
SparkyGuy wrote:
... Suggestions re. dimensions and location of a director? Thanks. Had company today, been in and out all day ... sorry I didn't offer more. A wavelength at 2.4Ghz will be approx. 12cm, half-wave ~6cm, 1/4 wave ~3cm. (with a very thin wire 1/2 wave monopole-omni-element I find ~12.25cm works for me, element dia. will affect this, as other factors ...) Anyway, I looked though my old emails for something a friend sent me, thought if you were interested in the 2.4g fsm, you might be interested in this, if nothing else, just because the dude is so complete!: http://www.users.bigpond.com/darren....enna_for_2.htm You will notice, he uses a plate reflector ... Regards, JS |
Antenna dimensions?
I believe I tried lengths of a 3% to 5% shorter length with the
director, than the drive element (i.e., the one in front of the reflector), settling on a 4% shorter length ... So about 26.8mm square? With a spacing between driven element and director of ~0.2 wavelength, center-to-center. So the director should be 25 mm forward (toward the uwave source) of the driven element? (3e8 / 2.4e9) x 0.2 = ~25mm Do these numbers look right? Thanks. |
Antenna dimensions?
On Sun, 07 Dec 2008 21:40:38 -0800, John Smith
wrote: A wavelength at 2.4Ghz will be approx. 12cm, half-wave ~6cm, 1/4 wave ~3cm. (with a very thin wire 1/2 wave monopole-omni-element I find ~12.25cm works for me, element dia. will affect this, as other factors ...) Anyway, I looked though my old emails for something a friend sent me, thought if you were interested in the 2.4g fsm, you might be interested in this, if nothing else, just because the dude is so complete!: http://www.users.bigpond.com/darren....enna_for_2.htm You will notice, he uses a plate reflector ... Regards, JS I also noticed that he cut his elements to a precision of 0.1mm. That would be correct if the boom were an insulator or the elements were inserted in insulating sleeves. However, since the 10mm square boom is metal and effectively "shorts" part of each element, the actual element length includes part of the diameter of the boom, thus adding approximately 5mm to each element length (not including the reflector and driven element). A VSWR sweep test would have shown the problem. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Antenna dimensions?
SparkyGuy wrote:
I believe I tried lengths of a 3% to 5% shorter length with the director, than the drive element (i.e., the one in front of the reflector), settling on a 4% shorter length ... So about 26.8mm square? With a spacing between driven element and director of ~0.2 wavelength, center-to-center. So the director should be 25 mm forward (toward the uwave source) of the driven element? (3e8 / 2.4e9) x 0.2 = ~25mm Do these numbers look right? Thanks. My elements are made from #14 bare copper wire. It is difficult to measure each side, individually, when constructing the antenna. Better to cut the wire to 1 wavelength, then make your bends forming it into a square. Of course, every attempt possible should be made to keep each side 1/4 of this length, exactly. In measuring the one before me, which I constructed, this total length, about the quad, is ~12.5cm. However, here is a calculator I referenced in my constructions: It is a java application, you must have java on your computer. Let me know if you can't access it and I will give you the figures it spits out, 2.4ghz = 2400mhz. Just let me know what wifi channel you wish to center on (frequency.) Regards, JS |
Antenna dimensions?
John Smith wrote:
... However, here is a calculator I referenced in my constructions: It is a java application, you must have java on your computer. Let me know if you can't access it and I will give you the figures it spits out, 2.4ghz = 2400mhz. Just let me know what wifi channel you wish to center on (frequency.) Regards, JS Well, da! It would help if I cut loose with the URL. sheepish smile http://www.n6mrx.com/Antenna/Cubical-Quad1.htm Regards, JS |
Antenna dimensions?
Jeff Liebermann wrote:
... I also noticed that he cut his elements to a precision of 0.1mm. That would be correct if the boom were an insulator or the elements were inserted in insulating sleeves. However, since the 10mm square boom is metal and effectively "shorts" part of each element, the actual element length includes part of the diameter of the boom, thus adding approximately 5mm to each element length (not including the reflector and driven element). A VSWR sweep test would have shown the problem. I have always used #8 wire as a boom on ghz yagis' (constructed a 7 element once.) Since the boom is at a current antinode (voltage node), I ignored the boom. The boom you mention is rather LARGE, give the freqs in question. One of my next projects is a GOOD VSWR meter for ghz ... unfortuantly, on the list of priorities here, it is low on the list ... :-( I have just tended to take the % signal readings on the chans as good enough, and trimmed my antennas accordingly. I know, this does NOT take into account the functioning/power-fluctuations/antenna(s)/etc. of the AP over these ranges ... But, excellent point, glad you mentioned it ... but you are right, my elements end up being filed down a bit from the figures the calculator spits out ... Warm regards, JS |
Antenna dimensions?
On Mon, 08 Dec 2008 08:37:34 +1100, Clifford Heath
wrote: Bill wrote: looking at the photos it appears to be being used with a DVM, depending on how you want to use it you may find an analogue meter easier. It will show changes better than a DVM. The author says he tried that and it didn't work as well: "I tried connecting the antenna directly to a micro amp moving coil meter, however there was very little meter deflection from a Wireless LAN card." Impedance too low, perhaps? Clifford Heath. Maybe, but more likely, not enough RF to do anything useful with an un-amplified meter. What's missing from everyone's posting is what they plan to do with this field strength meter. Let's play with the numbers. The average wi-fi access point belches about +12dBm (32 mw) RF into an antenna with perhaps 2dBi gain. The FSM has a gain of perhaps 0dB. At a distance of about 3 meters (10ft) the path loss at 2.4GHz is about 50dB which will deliver about -30dBm to the diode. On the most sensitive voltage range, the DVM has an input impedance of at least 1Mohm and can be treated like an open circuit load to the detector. -30dBm into 50 ohms is 0.224 vrms. Transforming linearly from 50 ohm reference to perhaps 150 ohms loop antenna impedance yields about 600mv rms. (Note: I know this is a bad guess but it's midnight and I'm tired). Resonating the loop probably raises the impedance even higher, thus resulting in even more rectified voltage. The resultant DC voltage will be about the same at about 600mv DC. However, for wi-fi use, the xmit duty cycle is quite low, sending just beacons, when there is no traffic moving. The 1000pf cap will need to be paralleled with a much larger cap in order to form a usable peak detector. So, with a high imput impedance DVM the antenna and detector is quite efficient and can generate quite a bit of voltage. However, when the DVM is replaced with a non-amplified meter, the relatively low impedance of the meter shorts out the diode and signifigantly reduces the Q of the resonant loop antenna, resulting in much lower detected voltage. I've built several transmitter hunt "sniffers" using almost exactly the same circuit, except that I use a hot carrier Schottky diode for the RF detector, and the cheapest Harbor Freight DVM (because it always gets destroyed or lost during the hunt). For 2.4GHz, I use a dish antenna, RF amplifier, step-up xformer (coax balun), diode detector, and DVM. I also made a really ugly hack that uses a satellite TV signal meter. http://www.sadoun.com/Sat/Products/Accessories/Meters/SF95L-DSS-FTA-Satellite-Signal-meter.htm These work from about 900 to 1800MHz with a minimum detectable meter sensitivity of about -70dBm. They are comatose at 860 (cellular) and 2.4GHz but are great for 900 and 1900MHz (PCS) sniffing. The input port is connected to a 900MHz or 1.2GHz antenna of any sorts. The output goes to a 75 ohm load and a 12V battery (gel cell) through an RF choke. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Antenna dimensions?
John Smith wrote:
Jeff Liebermann wrote: ... I also noticed that he cut his elements to a precision of 0.1mm. That would be correct if the boom were an insulator or the elements were inserted in insulating sleeves. However, since the 10mm square boom is metal and effectively "shorts" part of each element, the actual element length includes part of the diameter of the boom, thus adding approximately 5mm to each element length (not including the reflector and driven element). A VSWR sweep test would have shown the problem. I have always used #8 wire as a boom on ghz yagis' (constructed a 7 element once.) Since the boom is at a current antinode (voltage node), I ignored the boom. The boom you mention is rather LARGE, give the freqs in question. One of my next projects is a GOOD VSWR meter for ghz ... unfortuantly, on the list of priorities here, it is low on the list ... :-( What about surplus directional couplers and a bolometer set (various military versions used to be quite affordable)? Used to show up at hamfests regularly too, covered 1 to 20 GHz or so in the kit; sorry I forget the AN number at the moment, but it came with half a dozen directional couplers for the various bands and lots of adapters. Michael |
Antenna dimensions?
On Mon, 08 Dec 2008 00:23:16 -0800, John Smith
wrote: One of my next projects is a GOOD VSWR meter for ghz ... unfortuantly, on the list of priorities here, it is low on the list ... :-( http://pe2er.nl/wifiswr/ I've built several. They work nicely and are a very important tool. My main inspiration was blowing up my Wiltron Model something SWR bridge and discovering the exhorbitant cost of a repair or replacement. The designs are sufficiently similar that I can substitute. Of course, it's not flat over many decades of bandwidth, but for fairly narrow bands, it's quite adequate. I have just tended to take the % signal readings on the chans as good enough, and trimmed my antennas accordingly. I know, this does NOT take into account the functioning/power-fluctuations/antenna(s)/etc. of the AP over these ranges ... I have a handy distant reference signal for 2.4GHz. It's line of sight and creates no Fresnel Zone issues, so it's useful for antenna testing. I start with my "standard" gain panel antenna and take a measurement. I then take the antenna under test, and compare. I rarely make an absolute level measurement. It's always relative to some other antenna of known characteristics. The only problem is that I have to climb onto my roof to do the measuring. I'm currently at the tail end of radiation oncology (no big deal), which makes me kinda tired. I find myself somewhat tipsy on the roof, so no antenna measurements for a few more weeks. One might also suggest that it affects my math and memory, but they're currently just as bad as always. But, excellent point, glad you mentioned it ... but you are right, my elements end up being filed down a bit from the figures the calculator spits out ... Suggestion: I always build a 3 element yagi first. Just the director, driven element, and reflector. With the antenna on the bench (after clearing off the chain saw and bicycle repair debris), I run a fairly wide sweep using a reflection coefficient bridge or VSWR bridge to an oscilloscope. I then trim the various elements for resonance. My sweeper has a marker generator, but an external generator (or wi-fi trash generator) can also be used. Adding additional elements does change the tuning a bit, but the really big frequency determining elements are the first 3 elements. http://802.11junk.com/jeffl/pics/home/slides/lab.html Incidentally, don't forget the mounting bracket. I just hate it when I prototype an antenna, and then find that the bracket, radome, potting foam, serial number sticker, or other irrelevent hardware detune the antenna. Another trick that I use with wire rod type of antennas is to thread the end of the rods. Attached to these are threaded standoffs. These can be rotated to adjust the length of the elements. Also, don't forget to round off or chamfer the ends of each element to improve the bandwidth. 1AM. Time to give up before I start babbling nonsense. Warm regards, JS Bah-Humbug (T'is the season). -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Antenna dimensions?
Jeff Liebermann wrote:
... Maybe, but more likely, not enough RF to do anything useful with an un-amplified meter. What's missing from everyone's posting is what they plan to do with this field strength meter. Let's play with the numbers. The average wi-fi access point belches about +12dBm (32 mw) RF into an antenna with perhaps 2dBi gain. The Hmmm, max power for a wifi router is 1 watt! Here is a full power one: http://www.wirelessnetworkproducts.c...OD&ProdID=1425 The router I presently use is "belching" 500mw into a 7.5db antenna (well, I might question the 7.5db ...) Throw out your access point man! Get a decent one ... Regards, JS |
Antenna dimensions?
On Mon, 08 Dec 2008 00:59:16 -0800, John Smith
wrote: Jeff Liebermann wrote: ... Maybe, but more likely, not enough RF to do anything useful with an un-amplified meter. What's missing from everyone's posting is what they plan to do with this field strength meter. Let's play with the numbers. The average wi-fi access point belches about +12dBm (32 mw) RF into an antenna with perhaps 2dBi gain. The Hmmm, max power for a wifi router is 1 watt! I said "average wi-fi access point". 1 watt routers are relatively rare among the common home wireless routers. Most run about 32mw. Some Buffalo models run about 250mw. 2wire 2701 can run up to about 450mw. I think Enginius also makes one at around 1 watt. The problem with this is what I call the "alligator" effect. An alligator is an animal with a big mouth and small ears. Running a 1 watt access point will make the xmitter heard over a much wider area than it can hear the responses from the clients. Unless the other end of the link (i.e. client radios) are also running the same high power level, the range will be limited by the clients tx power. In other words, the system gain and power levels in both directions have to be evenly matched to avoid turning the high power access point into what I consider to be no better than a jamming transmitter. If you need a slogan, you should use "only as much power as necessary" which doesn't mean crank it up to the max. Please print this slogan on a large sign and plaster it in front of your desk until the meaning sinks in. Also, note that most modern communications technologies includes automatic transmit power control (usually based on RX SNR or BER) to prevent alligators and systems like yours from becoming a problem. Here is a full power one: http://www.wirelessnetworkproducts.c...OD&ProdID=1425 The router I presently use is "belching" 500mw into a 7.5db antenna (well, I might question the 7.5db ...) Turn down the power to about 100mw. The antenna is fine because it results in a symmetrical improvement in system gain. Also, give yourself a slap on the wrist, repent your evil ways, and pray for forgiveness. Throw out your access point man! Get a decent one ... You haven't seen my office. I never throw anything away. Regards, JS -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Antenna dimensions?
Jeff Liebermann wrote:
... Turn down the power to about 100mw. The antenna is fine because it results in a symmetrical improvement in system gain. Also, give yourself a slap on the wrist, repent your evil ways, and pray for forgiveness. Throw out your access point man! Get a decent one ... You haven't seen my office. I never throw anything away. Regards, JS Yes, my AP's software allows for power control. Indeed, the AP will, automatically, only supply enough power to make a, almost, error free transmission link. Having one side of transmission link error free is MUCH superior to have both sides error prone! However, although I have a pocketfull of various USB dongles, my external USB wifi "card" is the highest output I could find which is cost effective (@ 500mw.) External USB being powered off the USB buss must stay 500ma (@ 5v) or below, total consumption. And, would more than allow for a 1 watt USB dongle. Here is a USB card to match my router: http://www.data-alliance.net/servlet...802.11n/Detail Try one, you'll like it, "Mikey does!" grin Regards, JS |
Antenna dimensions?
http://www.n6mrx.com/Antenna/Cubical-Quad1.htm
Thanks for the link. The calculator works for me. One remaining Q: how do I take into account the "pigtails" of the driven element? A nice square loop is nice, but I've got to connect it to the (relatively) big diode, and this requires a bit more wire from the loop to the diode (on the + side of the loop) and to the meter connector (on the - side). Do I include these wire lengths in the loop size calculation? Or ignore them? Or does the 1000pF cap effectively terminate the loop (re. size)? Thanks. |
Antenna dimensions?
On Mon, 08 Dec 2008 01:51:53 -0800, John Smith
wrote: Jeff Liebermann wrote: ... Turn down the power to about 100mw. The antenna is fine because it results in a symmetrical improvement in system gain. Also, give yourself a slap on the wrist, repent your evil ways, and pray for forgiveness. Throw out your access point man! Get a decent one ... You haven't seen my office. I never throw anything away. Regards, JS Yes, my AP's software allows for power control. Indeed, the AP will, automatically, only supply enough power to make a, almost, error free transmission link. I beg to differ. Unless I missed something in my post-midnight scan of the specs, the wireless router's TX power is set and forget. If it receives an extremely strong signal level report in the 802.11 management packet, the power remains the same. The ability to do power control is there (because each device reports its RX signal strength and SNR) but very few access points even try. Having one side of transmission link error free is MUCH superior to have both sides error prone! I beg to differ. You're creating un-necessary interference. Let's play with the numbers. The commodity wireless router belches about +12dBm. Yours is allegedly +27dBm. Range doubles for every 6dB increase in TX power. Therefore, your TX range is: (27 - 12) / 6 = 7.5 time more than would be with a commodity wireless router. In terms of coverage area, that's: 7.5^2 = 56.3 times the area. Assuming a uniform density of WLAN users in your vicinity, you're trashing 56.3 times as many users or systems as necessary. You're also partly wrong about asymmetrical systems being superior. The transition between a fairly good BER or PER (packet error rate) is rather abrupt. What happens is that the AP simply slows down the data rate until the PER improves. Since the connection speed can be different in each direction, you'll get very good speed in one direction, and probably very slow speed in the other. In addition, things go insane above 54Mbits/sec connection speed. You might have enough signal to go faster than 54Mbits/sec in one direction, but if it's lacking in the other direction, the AP will simply revert to 802.11g and limit the speed in the stronger direction to 54Mbits/sec. That's not a problem as few systems can operate reliably at 54Mbits/sec beyond a few meters range and in the presence of interference. Meanwhile, you're operating an alligator, jamming 56 times as many users as necessary, and polluting the airwaves with your overpowered xmitter. It's like operating a kilowatt xmitter in the middle of the QRP frequencies. Your stuff gets through, but nobody else's. I suggest you do the math, repent your evil ways, offer sacrifice to the radio gods on the hibachi, slap yourself on the wrist several times for penitence, and stop playing with the dark side. However, although I have a pocketfull of various USB dongles, my external USB wifi "card" is the highest output I could find which is cost effective (@ 500mw.) External USB being powered off the USB buss must stay 500ma (@ 5v) or below, total consumption. And, would more than allow for a 1 watt USB dongle. You would do better with a directional antenna, so as to not both pickup and deliver interference from other systems. Antennas with gain also improve the system gain in both directions, thus preventing the creation of an alligator. Here is a USB card to match my router: http://www.data-alliance.net/servlet...802.11n/Detail Try one, you'll like it, "Mikey does!" grin Nope. Instead, I was instrumental in convincing at least one mesh wi-fi vendor to reduce their poletop TX power, as they were causing most of their own interference. Asymmetric systems suck. Regards, JS Bah-Humbug (T'is the season). -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Antenna dimensions?
On Mon, 8 Dec 2008 08:24:55 -0800, SparkyGuy
wrote: Q: how do I take into account the "pigtails" of the driven element? A nice square loop is nice, but I've got to connect it to the (relatively) big diode, You don't need to include diode lead length in the quad antenna calculations. The "loop" in the quad driven element is just an LC tuned circuit. It's as bit less than one wavelength around the loop and resonated to 2.4GHz by the tuning cap. The diode and other components do add some capacitance, which will lower the frequency somewhat, but the adjustment cap is substantially larger than these capacitances. For example, the off capacitance of a Schottky diode is about 0.5pf. You do need to keep lead length short as the added inductance will act as an RF choke. However, instead of the giant diode, I suggest something smaller and better, such as a Schottky diode: http://www.adsemi.com/diodes/schottky_barrier_mixer_detector.shtml http://www.macom.com/psc/jsp/ListParts.jsp?dataFile=mixing_detector_diodes.txt -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Antenna dimensions?
You don't need to include diode lead length in the quad antenna
calculations. Thanks, Jeff. Very much appreciated. |
Antenna dimensions?
In article ,
The problem with this is what I call the "alligator" effect. An alligator is an animal with a big mouth and small ears. Running a 1 watt access point will make the xmitter heard over a much wider area than it can hear the responses from the clients. Unless the other end of the link (i.e. client radios) are also running the same high power level, the range will be limited by the clients tx power. In other words, the system gain and power levels in both directions have to be evenly matched to avoid turning the high power access point into what I consider to be no better than a jamming transmitter. A not-uncommon scenario, I think. I've seen APs which put out a signal that has useful strength for blocks, and yet you have to be within about 100 feet of them to establish contact with a typical client system. This same issue is significant in other bands, as well. My area's ham-radio VHF/UHF repeater coordination group has a firm principle... a coordinated repeater's transmit coverage and receive coverage should be consistent. Having an ultra-high-powered transmitter simply causes interference well outside the repeater's practical use range. Having overly-sensitive receivers can also be a problem, albeit a lesser one, as it means that the repeater can be "keyed up" by remote stations too far away to hear the repeater properly. It's less of a problem, though, as most repeaters use CTCSS tone squelch these days and won't respond to signals intended for co-channel repeaters with a different CTCSS tone. I don't think this is an issue for 802.11 access points at all. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Antenna dimensions?
Jeff Liebermann wrote:
I beg to differ. Unless I missed something in my post-midnight scan of the specs, the wireless router's TX power is set and forget. If it receives an extremely strong signal level report in the 802.11 management packet, the power remains the same. The ability to do power control is there (because each device reports its RX signal strength and SNR) but very few access points even try. You are speaking of the specs on the USB card, I am speaking access point ... and actually, I have never searched for power-throttling in the USB card, I simply would not use it ... when the wife and I go out and I search for APs, I want every possible mw in action, at a clients, hotel, hospital, etc. Having one side of transmission link error free is MUCH superior to have both sides error prone! I beg to differ. You're creating un-necessary interference. Let's play with the numbers. Let's not, I said what I meant, and meant what I said, one side error free is better than two sides error prone. The commodity wireless router belches about +12dBm. Yours is allegedly +27dBm. Range doubles for every 6dB increase in TX power. Therefore, your TX range is: (27 - 12) / 6 = 7.5 time more than would be with a commodity wireless router. In terms of coverage area, that's: 7.5^2 = 56.3 times the area. Assuming a uniform density of WLAN users in your vicinity, you're trashing 56.3 times as many users or systems as necessary. No problem. I don't live in a dorm, trailer park, high-rise or apartment building ... the software will automatically adjust to find the best chan and recheck this decision, from time-to-time. If others don't have that capability, they may wish to upgrade ... like I have strongly implied, already, "If your AP is crap, toss it out!" I can't imagine anyone here who failed to read specs before purchasing, however ??? You're also partly wrong about asymmetrical systems being superior. The transition between a fairly good BER or PER (packet error rate) is rather abrupt. What happens is that the AP simply slows down the data rate until the PER improves. Since the connection speed can be different in each direction, you'll get very good speed in one direction, and probably very slow speed in the other. In addition, things go insane above 54Mbits/sec connection speed. You might have enough signal to go faster than 54Mbits/sec in one direction, but if it's lacking in the other direction, the AP will simply revert to 802.11g and limit the speed in the stronger direction to 54Mbits/sec. That's not a problem as few systems can operate reliably at 54Mbits/sec beyond a few meters range and in the presence of interference. The equip can do b/g/n (b&g for the usb card in question, multiple computers here) With a windows widget to monitor my ap/card connection (transfer rate, errors, signal strength, etc.), I see it rise and fall from time to time. Sometimes I have seen the connection renegotiate from n to g to b ... however, at this same time AirSnare has went nuts. Seems wardriving teens are to blame ... grin I was a teen once, so long ago, I fear I may forget ... :-( But, I will tell you, if ever I notice a problem with the errors (just looked, 3 errors), I will remember your words. Meanwhile, you're operating an alligator, jamming 56 times as many users as necessary, and polluting the airwaves with your overpowered xmitter. It's like operating a kilowatt xmitter in the middle of the QRP frequencies. Your stuff gets through, but nobody else's. I suggest you do the math, repent your evil ways, offer sacrifice to the radio gods on the hibachi, slap yourself on the wrist several times for penitence, and stop playing with the dark side. Although, I am sure one or two of my neighbors are savvy enough to set their routers into non-broadcast mode of the SSID, and have WPA and filter on mac addresses, I just don't see the traffic/jam you speak of. But, like I say, if I do, I shall remember your words. However, although I have a pocketfull of various USB dongles, my external USB wifi "card" is the highest output I could find which is cost effective (@ 500mw.) External USB being powered off the USB buss must stay 500ma (@ 5v) or below, total consumption. And, would more than allow for a 1 watt USB dongle. You would do better with a directional antenna, so as to not both pickup and deliver interference from other systems. Antennas with gain also improve the system gain in both directions, thus preventing the creation of an alligator. No, I would NOT. When I take my laptop and USB antenna analyzer out to the antenna(s), I appreciate my omni. When I take my laptop and USB ODB II out to the car (in another direction), I appreciate my omni. When teens go by wardriving and trigger AirSnare warnings (and giving me one-hell-of-a-kick!), I appreciate my omni. You hang around with the old men here, beware the cynicism, it IS contagious! Here is a USB card to match my router: http://www.data-alliance.net/servlet...802.11n/Detail Try one, you'll like it, "Mikey does!" grin Nope. Instead, I was instrumental in convincing at least one mesh wi-fi vendor to reduce their poletop TX power, as they were causing most of their own interference. Asymmetric systems suck. Beware. Again you risk being controlled by the control freaks here. Glad it works for you, attempt to enforce it for me, we have a battle .... you know, there is equip and hacks available to open up chans far in excess of what is legal, I am sure some are savvy and use them ... perhaps teenagers? straight face I have even heard of some flashing their ap/cards with the foreign version of the software for them and exceeding power/chans ... shame on them! :-| Regards, JS Bah-Humbug (T'is the season). However, you provide good discussion, and have valid arguments, I am sure--some will agree with and appreciate--perhaps even some which are state-of-the-art! Personally, I would NEVER suggest purchasing an AP/card with less than 350mw capability. And, only then if you get one-hell-of-a-buy. Warm regards, JS |
Antenna dimensions?
John Smith wrote:
... Personally, I would NEVER suggest purchasing an AP/card with less than 350mw capability. And, only then if you get one-hell-of-a-buy. Warm regards, JS Sorry to have been so verbal. I could have summed that up rather quickly, nicely and sweetly, I choose not to ... You see millions of cell phones; You see a LOT of problems? Regards, JS |
Antenna dimensions?
SparkyGuy wrote:
http://www.n6mrx.com/Antenna/Cubical-Quad1.htm Thanks for the link. The calculator works for me. One remaining Q: how do I take into account the "pigtails" of the driven element? A nice square loop is nice, but I've got to connect it to the (relatively) big diode, and this requires a bit more wire from the loop to the diode (on the + side of the loop) and to the meter connector (on the - side). Do I include these wire lengths in the loop size calculation? Or ignore them? Or does the 1000pF cap effectively terminate the loop (re. size)? Thanks. You MUST take into consideration every single mm of the loops length! Leads (apparently "pigtails") ARE the loop ... But, nothing stops you from being creative. The guy whos' construction(s) we are following did have about optimum parts to work with--you will just have to be "creative" ... good-luck. Warm regards, JS |
Antenna dimensions?
Jeff Liebermann wrote:
... However, instead of the giant diode, I suggest something smaller and better, such as a Schottky diode: http://www.adsemi.com/diodes/schottky_barrier_mixer_detector.shtml http://www.macom.com/psc/jsp/ListParts.jsp?dataFile=mixing_detector_diodes.txt SMC sounds good ... Regards, JS |
Antenna dimensions?
Jeff Liebermann wrote:
You don't need to include diode lead length in the quad antenna calculations. The "loop" in the quad driven element is just an LC ... Hmmm, perhaps I read him wrong, you ARE correct here ... that clarification is appreciated. Regards, JS |
Antenna dimensions?
On Mon, 08 Dec 2008 11:35:12 -0800, John Smith
wrote: You see millions of cell phones; You see a LOT of problems? Oh yes, I certainly do see problems. They're well hidden and mitigated in various ways. For example, if the error rate climbs, the adaptive tx power control cranks up the power on both the handset and the cell site end. If it persists, you get disconnected. Rather than have the user sound like they're talking while gargling ball bearings, the cell site just pulls the plug. Incidentally, the tx power control algorithm is rather messy as it has to handle different data types, at different rates, all while doing its best not to drain the handset battery. One the cell site end, it's no better as the power consumption of a typical cell site is non-trivial. Problems? Well: http://www.roughlydrafted.com/2008/08/28/the-inside-deets-on-iphone-202-and-dropped-calls/ Hmmm... power control algorithm again. Todays typical cell phones run about 150mw max average power output (according to the FCC ID data). Some are even less. None are anywhere near the 600mw legal maximum. If they could, you would have a dead battery within about an hour. (Do the math). Back to wi-fi and your setup. Sure, you'll have fairly good preformance with a high power setup. 14 times the usual power is bound to do some good. However, I suspect your neighbors are not so thrilled and will probably also be shopping for higher power hardware. It will be like an arms race, where the biggest bomb allegedly wins. Dealing with mutual interference is no fun, especially with only 3 available non-overlapping channels. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Antenna dimensions?
In article ,
Jeff Liebermann wrote: Good plan but there are problems. Most hams these daze use walkie talkies with perhaps 1 watt of TX RF. The typical repeater is running perhaps 10 to 40 watts out (after the duplexer). The walkie can hear the repeater almost anywhere, but when trying to talk, they drop in and out all the time. The mobiles, which run more power, are usually well matched to the repeater's tx power. I've suggested adaptive tx power control (to preserve battery power) on our 2 meter repeater, but nobody wants it. Seems to me that would introduce another set of incompatibilities. People out on the fringe area of the repeater's coverage would be able to hear repeated signals from weak transmitters (e.g. HTs), but if the repeater saw a strong input signal from a mobile (or an HT near the site) and dropped its transmitter power, the repeater coverage area would shrink abruptly and those users out around the edges could lose coverage. This could re-create the "hidden node" problem in a new way! I don't think adaptive power management can work reliably in the absense of a signal-quality feedback from each station which is accessing the repeater/AP. We had a co-channel user that was running carrier squelch. It took only about 7 years of constantly pounding on the trustees before they would install PL. They lied on their NARCC application claiming they had a functional PL system. Grrr. Worf "Romulans have *no* sense of honor." /Worf Our system (W6ASH, SPECS, at El Camino Hospital in Mountain View) switched over to PL-tone-only years ago, and it helps in numerous ways... the absence of noise-initiated kerchunking is a real blessing. I've preserved the ability to switch the repeaters over to carrier-sense-only in an emergency but really don't expect to ever need to use this feature. The experience taught me a few things, one of which is that hams generally make lousy RF neighbors. Some are lousy neighbors, lazy and self-centered. Others hold themselves and their equipment and operation to very high standards. I think it depends very much on the individuals involved, on their attitudes, and on their level of prior experience in supporting a real-world user community. No, it's not for most home systems. There's a similar coexistence problem with mesh networks and municipal networks. Neither of these scale very well. They work ok with a small number of repeaters, but rapidly foul up as the usage, traffic, and number of repeaters increases to the point of mutual interference. Details and a rant on request. I believe you! My impression is that a limited set of mesh repeaters, and a plentiful set of direct backhaul links on a different (non-interfering) band, works out rather better. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Antenna dimensions?
Jeff Liebermann wrote:
On Mon, 08 Dec 2008 11:35:12 -0800, John Smith wrote: You see millions of cell phones; You see a LOT of problems? Oh yes, I certainly do see problems. They're well hidden and mitigated in various ways. For example, if the error rate climbs, the adaptive tx power control cranks up the power on both the handset and the cell site end. If it persists, you get disconnected. Rather than have the user sound like they're talking while gargling ball bearings, the cell site just pulls the plug. Incidentally, the tx power control algorithm is rather messy as it has to handle different data types, at different rates, all while doing its best not to drain the handset battery. One the cell site end, it's no better as the power consumption of a typical cell site is non-trivial. Yes, hackers (well, you may prefer programmers/software-engineers?) do a very nice job, they have done it with wifi too, still doing it actually, personally--I suspect viagra! LOL Problems? Well: http://www.roughlydrafted.com/2008/08/28/the-inside-deets-on-iphone-202-and-dropped-calls/ Hmmm... power control algorithm again. Todays typical cell phones run about 150mw max average power output (according to the FCC ID data). Some are even less. None are anywhere near the 600mw legal maximum. If they could, you would have a dead battery within about an hour. (Do the math). Yeah, personally, I could handle a cell phone 2x to 3x the size, most of it battery ... my cellphone is 300mw out (max, but variable, as needed, as you state), I read those specs before purchasing, also. 4 hours max talk time (like if your sitting right under the tower?) is no problem for me, mine averages 2-3hrs, but I have a pocket charger, takes two AA high output recharge-ables (you can chuck alkaline in if needed) and is quick, chat while charging, so never without power (did I mention 2 week standby time?), now ask the wife, you get another answer ... Back to wi-fi and your setup. Sure, you'll have fairly good preformance with a high power setup. 14 times the usual power is bound to do some good. However, I suspect your neighbors are not so thrilled and will probably also be shopping for higher power hardware. It will be like an arms race, where the biggest bomb allegedly wins. Dealing with mutual interference is no fun, especially with only 3 available non-overlapping channels. My son and I, once or twice a year, attend a game fest. There is more high power equip set up than you can shake a whatever at ... doom, heretic, diablo, etc. (you can tell, I like the old ones :-( ) nets all off separate APs, the wifi cards are simply uncountable--if you think thats nuts, attend a gaming convention in Nevada, frankly, I would have to state, from REAL hands-on, the problems you state just don't exist to a REAL degree ... if they/it did, they would be fixing that now (more chans, tighter packet packing/encryption, more-adaptable, spread spectrum, etc. Remember, networking has NOT EVEN reached its' infancy, yet!) Without a doubt, there are conflicts and lost packets--you just never notice them--now, if everyone there started, separately, watching a HD movie, most-likely no joy ... :-( Besides, my neighbors are idiots (technical idiots, I admit, I like a couple of 'em), I doubt they do anything but email/surf and download an illegal movie/song now-and-then -- well, I suspect them of porn--but I am like that yanno? Suspicious. But hey, if everyone agreed with me, I would NOT be here, and this would NOT be fun--did I mention it would be boring? wink Warm regards, JS |
Antenna dimensions?
Dave Platt wrote:
In article , The problem with this is what I call the "alligator" effect. An alligator is an animal with a big mouth and small ears. Running a 1 watt access point will make the xmitter heard over a much wider area than it can hear the responses from the clients. Unless the other end of the link (i.e. client radios) are also running the same high power level, the range will be limited by the clients tx power. In other words, the system gain and power levels in both directions have to be evenly matched to avoid turning the high power access point into what I consider to be no better than a jamming transmitter. A not-uncommon scenario, I think. I've seen APs which put out a signal that has useful strength for blocks, and yet you have to be within about 100 feet of them to establish contact with a typical client system. This same issue is significant in other bands, as well. My area's ham-radio VHF/UHF repeater coordination group has a firm principle... a coordinated repeater's transmit coverage and receive coverage should be consistent. Having an ultra-high-powered transmitter simply causes interference well outside the repeater's practical use range. Having overly-sensitive receivers can also be a problem, albeit a lesser one, as it means that the repeater can be "keyed up" by remote stations too far away to hear the repeater properly. It's less of a problem, though, as most repeaters use CTCSS tone squelch these days and won't respond to signals intended for co-channel repeaters with a different CTCSS tone. I don't think this is an issue for 802.11 access points at all. All the problems you state would disappear with the correct algorithms controlling the packets/encryption/compaction ... there is just not enough interest to put together a team together to do it, and a for-profit organization would go broke doing it ... and, you can't get everyone to agree. The (A)ncient (R)etarded (R)adio (L)aggards) don't see a need--you see, no brass is required ... :-( Regards, JS |
Antenna dimensions?
On Mon, 8 Dec 2008 14:18:49 -0800, (Dave Platt)
wrote: In article , Jeff Liebermann wrote: Good plan but there are problems. Most hams these daze use walkie talkies with perhaps 1 watt of TX RF. The typical repeater is running perhaps 10 to 40 watts out (after the duplexer). The walkie can hear the repeater almost anywhere, but when trying to talk, they drop in and out all the time. The mobiles, which run more power, are usually well matched to the repeater's tx power. I've suggested adaptive tx power control (to preserve battery power) on our 2 meter repeater, but nobody wants it. Seems to me that would introduce another set of incompatibilities. People out on the fringe area of the repeater's coverage would be able to hear repeated signals from weak transmitters (e.g. HTs), but if the repeater saw a strong input signal from a mobile (or an HT near the site) and dropped its transmitter power, the repeater coverage area would shrink abruptly and those users out around the edges could lose coverage. This could re-create the "hidden node" problem in a new way! Good point, but that's not what I had in mind. I was aware of the problem and suggested that the power control be run by a micro. The algorithm needs to be worked out, but basically, the weakest signal sets the power level. The range of power adjustment also will not be huge or large enough to have much of an effect on distant stations. Our current 60 watt amplifier might have the power output reduced to about 20 watts or 4.5dB power reduction. That's less than one S-unit and probably wouldn't be noticeable even by distant stations. However, it will make a huge difference in power consumption and battery operation run time. There are a few other economies that can be thrown in, such as having the repeater always ID in low power. Of course, there are complications, such as the mobiles and handhelds not reporting their RX signal quality, which makes deciding the repeater power output somewhat problematic when dealing with the traditional broken radios. (Same people, same radios, same problems, same club net, every time). Incidentally, this was suppose to be a minor feature of a proposed repeater voting system, which is another can of worms. I don't think adaptive power management can work reliably in the absense of a signal-quality feedback from each station which is accessing the repeater/AP. Yes it can. I intentionally reduced the repeater TX power during a club net from 60 watts (before the duplexer) to about 20 watts. Nobody said anything, there were no complaints, and nobody noticed, even after I mentioned it after the close of the net. As long as I don't run the power output to near zero, it can me made to work, even if the power level is set manually with a touch tone command. We had a co-channel user that was running carrier squelch. It took only about 7 years of constantly pounding on the trustees before they would install PL. They lied on their NARCC application claiming they had a functional PL system. Grrr. Worf "Romulans have *no* sense of honor." /Worf Actually, it was far more stupid than it appears. We had several of the club politicians pounding on the alleged trustee of the repeater, who literally didn't care, didn't communicate with the rest of the organization, broke numerous promises to take it up with the board, and so on. Complaints to NARCC went to the trustee with predictable results. We were simply talking to the wrong person. One day, we caught the right person on the air working on the repeater. He was informed of the situation, after a few emails and the usual miscommunications, the PL decoder magically appeared. As would be expected, the initial transistion was slow. First there was no-PL during their club nets. Later, it became full time. There was also some work done on placing a notch in the antenna pattern in the direction of Santa Cruz. That has worked quite nicely. Our system (W6ASH, SPECS, at El Camino Hospital in Mountain View) switched over to PL-tone-only years ago, and it helps in numerous ways... the absence of noise-initiated kerchunking is a real blessing. I've preserved the ability to switch the repeaters over to carrier-sense-only in an emergency but really don't expect to ever need to use this feature. That alleged benefit is that no PL allows visitors and hams with antique hardware to use the repeater. We have a control code that is available to anyone that will temporarily disable the PL for a specified time period. It actually does get used by some hams who apparently plan on being buried with their ancient radios and have no intention of ever selling them. The experience taught me a few things, one of which is that hams generally make lousy RF neighbors. Some are lousy neighbors, lazy and self-centered. Others hold themselves and their equipment and operation to very high standards. I think it depends very much on the individuals involved, on their attitudes, and on their level of prior experience in supporting a real-world user community. It varies. I consider myself a good example of one of the lousy RF neighbors, so I know they exist. My impression is that a limited set of mesh repeaters, and a plentiful set of direct backhaul links on a different (non-interfering) band, works out rather better. Sure, but that's not the way most municipal wireless networks are umm.... engineered. Most are single channel, store and forward repeaters. The problem is that if you're perhaps 3 nodes away from where it hits the wired internet, you will have 4 identical duplicated packets flying through the air. If everyone can see everyone else (as is the case with omni antennas on office rooftops), only one of those radios can be transmitting at a time. That means that you would be hogging at least 3 times the shared bandwidth (airtime is shared) to deliver one lousy packet. Add the problem of trying to create the ultimate geographic routing algorithm, and mesh networks have a propensity to fill the airtime with duplicates, retransmissions, and junk. The worst of the worst are broadcasts, noteably ARP requests, which go everywhere. I was monitoring what was coming out of Google's Mtn View network and finding about 60% of the airtime occupied by ARP requests. Of course, when the proponents of municipal wireless find that there are holes in their coverage, they just add yet another store and forward mesh repeater. Eventually, the density is high enough for the mesh repeaters to start interfering with each other. Since this is difficult to diagnose, the usual solution is to increase the TX power of the mesh node. That does the opposite of what might be expected, but until the numbers are in for availability testing, everyone just assumes that more power is more better. It took quite a bit of arguing to convince one mesh operator to reduce their power and even more to demonstrate that it worked. As an example, see the data and conclusions from the old MIT RoofNet at: http://pdos.csail.mit.edu/roofnet/doku.php?id=interesting Note the probabilies of actually delivering a packet through just one hop. Yech. I couldn't resist and just had to rant. But, it was worth it. Onward to another thrilling day of doing battle with QuickBooks and my traditional end of the year billing nightmare... -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com # http://www.LearnByDestroying.com AE6KS |
Antenna dimensions?
Jeff Liebermann wrote:
Good point, but that's not what I had in mind. I was aware of the problem and suggested that the power control be run by a micro. The algorithm needs to be worked out, but basically, the weakest signal sets the power level. The range of power adjustment also will not be huge or large enough to have much of an effect on distant stations. Our current 60 watt amplifier might have the power output reduced to about 20 watts or 4.5dB power reduction. That's less than one S-unit and probably wouldn't be noticeable even by distant stations. However, it will make a huge difference in power consumption and battery operation run time. Would it? A lot of amplifiers don't change their power consumption all that much, especially if they're designed for saturated operation (i.e. if you reduce the input drive, they either distort, or drop into linear mode and dissipation goes up). if you have an amplifier designed for variable power output, then what you say might be a good idea. |
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