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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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