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Antenna tuner
Instead of buying an antenna tuner, is it possible to build one myself.
Nothing fancy, but a rotary switch and some ?capacitors?. Thanks for the advice. Matthew --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.644 / Virus Database: 412 - Release Date: 3/26/2004 |
Matthew&Wendy wrote:
Instead of buying an antenna tuner, is it possible to build one myself. Nothing fancy, but a rotary switch and some ?capacitors?. Thanks for the advice. I prefer pi-net tuners - two variable caps to ground and a variable coil in series in the middle. Easy to build and is a low-pass filter to boot. -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
OK. I am brand new to circuit design. Is there a diagram or picture I could
find to build it. I can solder and get parts, I just don't know the lingo yet. "Cecil Moore" wrote in message ... Matthew&Wendy wrote: Instead of buying an antenna tuner, is it possible to build one myself. Nothing fancy, but a rotary switch and some ?capacitors?. Thanks for the advice. I prefer pi-net tuners - two variable caps to ground and a variable coil in series in the middle. Easy to build and is a low-pass filter to boot. -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.644 / Virus Database: 412 - Release Date: 3/26/2004 |
Matthew&Wendy wrote:
OK. I am brand new to circuit design. Is there a diagram or picture I could find to build it. I can solder and get parts, I just don't know the lingo yet. There are some antenna tuners described in the ARRL Antenna Book. -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
"Cecil Moore" wrote in message
... Matthew&Wendy wrote: Instead of buying an antenna tuner, is it possible to build one myself. Nothing fancy, but a rotary switch and some ?capacitors?. Thanks for the advice. I prefer pi-net tuners - two variable caps to ground and a variable coil in series in the middle. Easy to build and is a low-pass filter to boot. -- 73, Cecil, W5DXP Hi Cecil Hi "Matthew&Wendy" I prefer resonant antennas and transmission lines that match them. You just can't beat a resonant antenna for radiation. Tuners squander AT BEST 1 or 2 db. At WORST (as Cecil has posted here regarding "shootouts") 10 db. So build your antenna resonant, match it, and don't bother with a tuner. If impedance transformation is necessary, use a transformer; That's why they're called transformers. That's what they're for. Just my 2 cents. 73 H. NQ5H PS Wire antennas are CHEAP. |
H. Adam Stevens, NQ5H wrote:
I prefer resonant antennas and transmission lines that match them. I prefer non-resonant antennas and transmission lines that resonant them. :-) You just can't beat a resonant antenna for radiation. Maybe not, but you can equal them. A tuned transmission line resonates the antenna system. Tuners squander AT BEST 1 or 2 db. That's why I don't use a conventional tuner. So build your antenna resonant, match it, and don't bother with a tuner. Or build your antenna non-resonant and match it with a series section transformer. If impedance transformation is necessary, use a transformer; IF impedance transformation is necessary, use a transmission line as the transformer. :-) -- 73, Cecil, http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
On Sun, 4 Apr 2004 22:12:24 -0500, "H. Adam Stevens, NQ5H"
wrote: You just can't beat a resonant antenna for radiation. Eh? You mean a 1¼-wave (non-resonate) dipole radiates less than a ¼-wave resonate dipole? Strange in that a 1¼-wave dipole has 3 dBd gain. Danny, K6MHE |
"Dan Richardson @mendolink.com" ChangeThisToCallSign wrote in message ... On Sun, 4 Apr 2004 22:12:24 -0500, "H. Adam Stevens, NQ5H" wrote: You just can't beat a resonant antenna for radiation. Eh? You mean a 1¼-wave (non-resonate) dipole radiates less than a ¼-wave resonate dipole? Strange in that a 1¼-wave dipole has 3 dBd gain. Danny, K6MHE Danny Do antennas have gain or do they have directivity? Jerry |
"Bill Turner" wrote in message ... On Sun, 4 Apr 2004 22:12:24 -0500, "H. Adam Stevens, NQ5H" wrote: Tuners squander AT BEST 1 or 2 db. __________________________________________________ _______ Nonsense. At 1500 watts, a tuner which "squandered" 1 db would be dissipating about 300 watts and would soon be a smoking mess. 2 db I don't even want to think about. -- Bill, W6WRT QSLs via LoTW Bill This is just something to think about. I would have thought that "squandered" power wouldnt necessarily be "dissipated". Jerry |
sigh
"Cecil Moore" wrote in message ... H. Adam Stevens, NQ5H wrote: I prefer resonant antennas and transmission lines that match them. I prefer non-resonant antennas and transmission lines that resonant them. :-) It's "resonate", Cecil, and the antenna still won't be resonant. You just can't beat a resonant antenna for radiation. Maybe not, but you can equal them. A tuned transmission line resonates the antenna system. When you get a lossless line. And the antenna still isn't resonant. Tuners squander AT BEST 1 or 2 db. That's why I don't use a conventional tuner. So build your antenna resonant, match it, and don't bother with a tuner. Or build your antenna non-resonant and match it with a series section transformer. If impedance transformation is necessary, use a transformer; IF impedance transformation is necessary, use a transmission line as the transformer. :-) Not the least lossy approach. Matched impedance = max power transfer. -- 73, Cecil, http://www.qsl.net/w5dxp 73 H. |
"Dan Richardson @mendolink.com" ChangeThisToCallSign wrote in message ... On Sun, 4 Apr 2004 22:12:24 -0500, "H. Adam Stevens, NQ5H" wrote: You just can't beat a resonant antenna for radiation. Eh? You mean a 1¼-wave (non-resonate) dipole radiates less than a ¼-wave resonate dipole? Strange in that a 1¼-wave dipole has 3 dBd gain. Danny, K6MHE Antenna resonance implies a purely resistive impedance at the feed point. Both 1/2 wave and 3/2 wave dipoles are resonant. I don't know what a "1/4-wave resonate dipole" is. A dipole is 1/2 wavelength long at it's fundamental resonant frequency. "Gain" is merely a re-distribution of the radiation pattern. 73 H. NQ5H |
"Bill Turner" wrote in message ... On Sun, 4 Apr 2004 22:12:24 -0500, "H. Adam Stevens, NQ5H" wrote: Tuners squander AT BEST 1 or 2 db. __________________________________________________ _______ Nonsense. At 1500 watts, a tuner which "squandered" 1 db would be dissipating about 300 watts and would soon be a smoking mess. 2 db I don't even want to think about. -- Bill, W6WRT QSLs via LoTW Nonsense huh? OK Load up your rig at 1500 watts key down with a tuner. Measure the tuner's temperature. Icom specifies the insertion loss for the tuners in my 756PROII and PW1. Icom claims less than one decibel. (After tuning) The loss is easy to measure and at 1KW it is indeed well over 100 watts warming the PW1's innards when it could be radiating away from my SteppIR. So I leave the tuners out of line and adjust the antenna for SWR = 1:1. 73 H. NQ5H |
On Mon, 5 Apr 2004 06:30:15 -0500, "H. Adam Stevens, NQ5H"
wrote: "Dan Richardson @mendolink.com" ChangeThisToCallSign wrote in message .. . On Sun, 4 Apr 2004 22:12:24 -0500, "H. Adam Stevens, NQ5H" wrote: You just can't beat a resonant antenna for radiation. Eh? You mean a 1¼-wave (non-resonate) dipole radiates less than a ¼-wave resonate dipole? Strange in that a 1¼-wave dipole has 3 dBd gain. Danny, K6MHE Antenna resonance implies a purely resistive impedance at the feed point. Both 1/2 wave and 3/2 wave dipoles are resonant. I don't know what a "1/4-wave resonate dipole" is. A dipole is 1/2 wavelength long at it's fundamental resonant frequency. "Gain" is merely a re-distribution of the radiation pattern. 73 H. NQ5H Sorry.. a typo should be 1¼-wave non-resonte dipole. Danny |
On Mon, 05 Apr 2004 06:02:56 GMT, "Jerry Martes"
wrote: "Dan Richardson @mendolink.com" ChangeThisToCallSign wrote in message .. . On Sun, 4 Apr 2004 22:12:24 -0500, "H. Adam Stevens, NQ5H" wrote: You just can't beat a resonant antenna for radiation. Eh? You mean a 1¼-wave (non-resonate) dipole radiates less than a ¼-wave resonate dipole? Strange in that a 1¼-wave dipole has 3 dBd gain. Danny, K6MHE Danny Do antennas have gain or do they have directivity? Jerry Both Danny |
On Mon, 5 Apr 2004 06:30:15 -0500, "H. Adam Stevens, NQ5H"
wrote: "Dan Richardson @mendolink.com" ChangeThisToCallSign wrote in message .. . On Sun, 4 Apr 2004 22:12:24 -0500, "H. Adam Stevens, NQ5H" wrote: You just can't beat a resonant antenna for radiation. Eh? You mean a 1¼-wave (non-resonate) dipole radiates less than a ¼-wave resonate dipole? Strange in that a 1¼-wave dipole has 3 dBd gain. Danny, K6MHE Antenna resonance implies a purely resistive impedance at the feed point. Both 1/2 wave and 3/2 wave dipoles are resonant. I don't know what a "1/4-wave resonate dipole" is. A dipole is 1/2 wavelength long at it's fundamental resonant frequency. "Gain" is merely a re-distribution of the radiation pattern. 73 H. NQ5H Well, I'll try it again..... still a typo I meant to say "a ½-wave resonate dipole".. Sorry In other words I press Alt+172 instead of Alt+171 Danny |
Jerry Martes wrote:
Do antennas have gain or do they have directivity? From Balanis: "Although the gain of an antenna is closely related to the directivity, gain is a measure that takes into account the efficiency of the antenna as well as the directional properties of the antenna, and it is therefore controlled only by the pattern." -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Someone sed,
"You just can't beat a resonant antenna for radiation." =================== PHOOEY! Some of the best antennas are NOT resonant, and shouldn't be. I use my 130-ft doublet on 40 m where it is one wavelength long. Has theoreitical gain of about 1.8 dB. This is NOT a resonant antenna. 73 de Jack, K9CUN |
"Do antennas have gain or do they have directivity?"
============================ What a wierd question! These are not mutally exclusive properties. 73 de Jack, K9CUN |
H. Adam Stevens, NQ5H wrote:
"Cecil Moore" wrote: Maybe not, but you can equal them. A tuned transmission line resonates the antenna system. When you get a lossless line. And the antenna still isn't resonant. So what? If you move off the resonant frequency, your antenna still isn't resonant. I'd rather have a resonant antenna system on many frequencies and many bands than an antenna system resonant on only one frequency. IF impedance transformation is necessary, use a transmission line as the transformer. :-) Not the least lossy approach. Matched impedance = max power transfer. Depends upon how much money you want to sink into your coax. Open-wire line with an SWR of 10:1 will beat RG-213 in the loss department on 80m. It takes 9913 to equal the performance of open-wire line with an SWR of 10:1 on 80m and 9913 costs about three times as much as open-wire line. And with open-wire line, one can enjoy all eight HF bands immediately, and not have to spend two days cutting and trying a fan dipole. -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
On Sun, 04 Apr 2004 21:12:51 -0700, Bill Turner
wrote: On Sun, 4 Apr 2004 22:12:24 -0500, "H. Adam Stevens, NQ5H" wrote: Tuners squander AT BEST 1 or 2 db. _________________________________________________ ________ Nonsense. At 1500 watts, a tuner which "squandered" 1 db would be dissipating about 300 watts and would soon be a smoking mess. 2 db I don't even want to think about. -- Bill, W6WRT QSLs via LoTW Dear Bill, Your figures and your terminology are 100% correct. Anyone who has an amplifier capable of delivering 1500 watts of carrier power, continuously, for any appreciable amount of time would, indeed, encounter a smoking mess. Fortunately, hams don't usually run that kind of power, but it does explain why so many tuners found at hamfests have very obvious damage to the variable inductor coil. Bob, W9DMK, Dahlgren, VA http://www.qsl.net/w9dmk |
H. Adam Stevens, NQ5H wrote:
"Dan Richardson @mendolink.com" ChangeThisToCallSign wrote: Strange in that a 1¼-wave dipole has 3 dBd gain. I don't know what a "1/4-wave resonate dipole" is. Look again, Danny said a 1.25 WL dipole, a non-resonant length dipole known as an extended-double-Zepp and known to have about 3 dB gain over your 1/2WL resonant dipole. With about a 0.2WL series section transformer made out of open-wire line, the non-resonant EDZ resonates as a system and will beat your resonant 1/2WL dipole in its favored direction. -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
JDer8745 wrote:
"Do antennas have gain or do they have directivity?" ============================ What a wierd question! These are not mutally exclusive properties. Guess the answer is 'yes'. :-) Seriously, directivity doesn't include efficiency. Gain includes efficiency. If an antenna could be 100% efficient, the directivity and gain would be the same. -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Sure. check virtually any ARRL Handbook for plans, and start making the
rounds of local ham swap meets... 73, Mike KI6PR El Rancho R.F., CA "Matthew&Wendy" wrote Instead of buying an antenna tuner, is it possible to build one myself. Nothing fancy, but a rotary switch and some ?capacitors?. Thanks for the advice. Matthew --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.644 / Virus Database: 412 - Release Date: 3/26/2004 |
No gain in a pure isotropic source?
Butch KF5DE Cecil Moore wrote: Jerry Martes wrote: Do antennas have gain or do they have directivity? From Balanis: "Although the gain of an antenna is closely related to the directivity, gain is a measure that takes into account the efficiency of the antenna as well as the directional properties of the antenna, and it is therefore controlled only by the pattern." -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
On Wed, 07 Apr 2004 12:16:45 -0500, Butch wrote:
No gain in a pure isotropic source? Hi Butch, There is no gain in any antenna. An isotropic source represents a reference. One may choose any other antenna, a dipole being a common basis of comparison. In this sense of comparison, gain as a term then becomes an indicator of differences between the subject at hand and the reference. 73's Richard Clark, KB7QHC |
"Butch" wrote in message ... No gain in a pure isotropic source? If there was one, it wouldn't have any. That's part of the definition, since it radiates in all directions equally. You get gain by adding directivity. |
Dave VanHorn wrote:
"Butch" wrote in message ... No gain in a pure isotropic source? If there was one, it wouldn't have any. That's part of the definition, since it radiates in all directions equally. You get gain by adding directivity. Those statements illustrate several misconceptions about gain and directivity. The first is that gain is an absolute figure -- that a particular antenna, like an isotropic radiator, has an immutable, single, value of gain. That isn't true. Gain is always a relative term. It's the ratio of two numbers. One of those two numbers is the field strength from the antenna, the other is the field strength from the reference antenna in the same direction. You can get just about any gain you want from an antenna simply by changing the reference. For example, a dipole in free space has 0 dB gain relative to a dipole in free space in its most favored direction. It also has 2.15 dB gain relative to an isotropic source, something like -6 dB gain relative to a 3 element Yagi in free space, and about -5 dB relative to the most favorable direction of a dipole mounted over ground. So the same dipole has a gain of 0, 2.15, -5, and -6 dB in its most favored direction. It also has an infinite number of other gains. This hasn't been lost on antenna manufacturers, who are often very creative in their choice of reference. People who believe that gain is an absoulte value independent of the reference are their rightful prey. The second misconception is that the gain of an antenna is a single value, even if the reference is given. The gain of a dipole in free space varies from 2.15 dBi (dB relative to an isotropic source) to - infinity, depending on the direction. It makes sense to look only at the maximum gain if you're able to rotate or construct the antenna so you can point the most favored direction at the station you want to communicate with. Otherwise, it's a meaningless number. Who cares how strong a signal the antenna radiates straight up (unless you're using it for NVIS propagation) or at some azimuth or elevation angle other than the one you're using to communicate? An extended double Zepp (EDZ) has gain over a dipole -- but only over a rather narrow range of angles. At all other angles, the gain is negative. If the station you're working is at one of those other angles, you're better off with a dipole -- because it has more gain than the EDZ at that angle. And if you're equally likely to work stations in any direction, you'd do better with a dipole most of the time. Whenever the antennas have different pattern shapes, their gains will be different in different directions when compared to the same reference or to each other. The third misconception is that the gain and the directivity are the same. If two antennas are equally efficient, then the one with the greater directivity will have the greatest gain (by the amount of the directivity) in its most favored direction. But there's more to gain than just directivity, and that added something is efficiency. Two antennas can have equal directivities but different gains relative to the same reference. For example, a free space dipole with a 73 ohm resistor at the feedpoint will have a gain of -3dB -- in all directions -- compared to one without the resistor, even though both have the same directivity. (Here, I've used the antenna without the resistor as a reference. I could also use the other as a reference and say that the antenna without the resistor has a gain of 3 dB relative to the one having it. Or I could have said that the one without the resistor has a gain of 2.15 dB relative to isotropic in its most favored direction, and the one with the resistor has a gain of -0.85 dB relative to the same reference. All are equally valid.) A Beverage antenna typically has high directivity but considerably lower gain than antennas with lower directivity such as a Yagi of a few elements, or even a dipole. An inefficient antenna with a perfectly isotropic pattern has a negative gain (in dB) in all directions relative to the theoretical, perfectly efficient isotropic source. There is one unambigous way of stating gain without describing the reference, and that's to give the gain in dBi. If you do this, it's understood that the gain is relative to a 100% efficient isotropic source. Of course, you still have to say whether that's in the antenna's most favored direction or in some other direction unless it's obvious from the context. If you don't use the isotropic reference, you need to clearly describe the reference, or any gain figure you quote is meaningless. "dBd" is a popular term among hams, and a windfall for less scrupulous antenna manufacturers. Often defined as gain relative to a dipole in free space, it's just as often defined, understood, or misunderstood to mean gain relative to a dipole over ground at the same height as the test antenna. The 5 or so dB difference between these two meanings of the same catchy term offers ample opportunity to confuse the consumer and make an antenna look much better than it really is. So be very wary if you see this term, and don't make any assumptions about what it might mean. Roy Lewallen, W7EL |
Butch wrote:
No gain in a pure isotropic source? Of course there's gain: zero dBi gain, :-) Gain can be zero, positive, or negative. -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Richard Clark wrote:
There is no gain in any antenna. There you go again, contradicting Balanas, Kraus, Jasik, Terman, et al. From Balanis: "Absolute gain of an antenna (in a given direction) is defined as "the ratio of the intensity, in a given direction, to the intensity that would be obtained if the power accepted by the antenna were radiated isotropically." This is the exact definition of antenna gain given in the IEEE Dictionary. Balanis goes on to give ten equations for gain in the next two pages. -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Bill Turner wrote:
Richard Clark wrote: There is no gain in any antenna. Wow! Wait till the engineering world hears about this! What do you expect from someone who doesn't know that the glare from a red laser is the same frequency as the laser? -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Bill Turner wrote:
On Wed, 07 Apr 2004 17:42:58 GMT, Richard Clark wrote: There is no gain in any antenna. __________________________________________________ _______ Wow! Wait till the engineering world hears about this! -- Bill, W6WRT QSLs via LoTW If it is a passive device, which it is, there is no gain. There is vector addition and subtraction of EXH fields to form a beam. That's math!! However, I don't know of any Yagi, Quad, 4-square, that with 100 watts into the antenna and 100 watts radiated, assuming 100% efficiency, has any gain!! It has directivity!! Now, my Ameritron 80B takes 65 watts in and delivers 900 watts out. That's gain! It converts 1400 watts plate power to 900 watts rf [key down conditions]. |
Dave Shrader wrote:
However, I don't know of any Yagi, Quad, 4-square, that with 100 watts into the antenna and 100 watts radiated, assuming 100% efficiency, has any gain!! It has directivity!! Hey Dave, crack out your trusty IEEE Dictionary and reference their definition of gain. It's not the same as yours. According to the IEEE and Balanis, the only difference between directivity and gain is the antenna efficiency. A 100% efficient antenna would have gain equal to directivity. Sorry, that's the definition. -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
I don't have an IEEE dictionary so I stand corrected. However, 100 watts
into a Yagi, Quad, Log Periodic, or 4-square and 100 watts radiated is still 0 dB gain. Gain = 10 * Log[Pout/Pin] = 10 * log [100/100] = 10 * 0 = 0 dB. It also has 0 dB attenuation!!! NB: Valid over either 4*Pi or 2*Pi steradians. Cecil Moore wrote: Dave Shrader wrote: However, I don't know of any Yagi, Quad, 4-square, that with 100 watts into the antenna and 100 watts radiated, assuming 100% efficiency, has any gain!! It has directivity!! Hey Dave, crack out your trusty IEEE Dictionary and reference their definition of gain. It's not the same as yours. According to the IEEE and Balanis, the only difference between directivity and gain is the antenna efficiency. A 100% efficient antenna would have gain equal to directivity. Sorry, that's the definition. -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Bill Turner wrote:
SNIP Ask any Top of the Honor Roll DXer whether his beam has "gain". Don't be surprised if his eyes glaze over as he contemplates what must be the world's rawest newbie. -- Bill, W6WRT QSLs via LoTW With all due respect Bill I am not a newbie! [see below] His beam, assuming 100% efficiency, is only 0 dB gain. Gain [dB] = 10 * Log[Pout/Pin] = 0 dB. The Honor Roll holder, much to his chagrin, still has a 0 dB gain antenna. He may have an amplifier that puts out 1500 watts, no feedline loss and a 100% efficient antenna. He is still radiating 1500 watts and that is by definition 0 dB gain. The double integral of ExH across theta from 0 to Pi and Phi from 0 to Pi is constant in both cases. Therefore 0 dB gain!!! Deacon Dave, W1MCE [for 50 years] Program Chief Engineer, USAF MX Missile, RS/RV |
Dave Shrader wrote:
I don't have an IEEE dictionary so I stand corrected. However, 100 watts into a Yagi, Quad, Log Periodic, or 4-square and 100 watts radiated is still 0 dB gain. Dave, that's true for the entire surface of a sphere at 100% efficiency but you are still not using the IEEE Dictionary definition of antenna gain. From Balanis: "... the power *gain* is usually taken in the direction of maximum radiation." i.e. not over the entire sphere but over a small area where the radiation intensity is at a maximum. The gain over isotropic would then be based on the ratio of maximum radiation intensity per unit area from the beam to the average radiation intensity per the same unit area from an isotropic antenna. To obtain the (G)ain, one can calculate the (D)irectivity and multiply by an efficiency term. G(theta,phi) = e(cd)[D(theta,phi)] where anything in parentheses is a subscript. e(cd) is an efficiency term based on conduction and dielectric losses. If efficiency equals 100%, gain equals directivity. (theta,phi) are vertical and horizontal angles related to a chosen area on the surface of a sphere. -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
On Thu, 08 Apr 2004 08:32:58 -0700, Bill Turner
wrote: Try this: 1. Attend a meeting of your local DX club. 2. Announce in a loud voice that all their fancy beams have exactly zero dB gain. 3. In addition, announce that when feedline losses are included, their fancy beams actually have less gain than a dummy load (because of the shorter feedline). 4. See how long it takes to receive an invitation to join the club. :-) All simply an argument for engineering through democratic vote. I wouldn't cross a bridge designed that way. I have a 100W transmitter, name me one antenna that will radiate more than 100W from this source. Then we can put a "gain" figure to it. 73's Richard Clark, KB7QHC |
Richard Clark wrote:
I have a 100W transmitter, name me one antenna that will radiate more than 100W from this source. Then we can put a "gain" figure to it. The ONLY difference between antenna directivity and antenna gain, by definition, is efficiency. Therefore, it logically follows that you are asserting that no antenna possesses directivity. Care to prove that outrageous assertion? Maybe you better stick to optics? -- 73, Cecil, W5DXP |
Dave Shrader wrote:
I don't have an IEEE dictionary so I stand corrected. However, 100 watts into a Yagi, Quad, Log Periodic, or 4-square and 100 watts radiated is still 0 dB gain. Gain = 10 * Log[Pout/Pin] = 10 * log [100/100] = 10 * 0 = 0 dB. It also has 0 dB attenuation!!! NB: Valid over either 4*Pi or 2*Pi steradians. What you've calculated here is efficiency, not gain. It's important to understand the difference between the two if you want to communicate with others about antennas. Roy Lewallen, W7EL |
Richard Clark,
I fully support your "All antennas have zero gain" campaign. Why not join the "There's no such thing as an SWR meter" campaign? ---- Reg, G4FGQ |
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