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#11
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"AM200" wrote in message ...
What does "Q" actually stand for as i can't find anyone that can explain this. Q is generally taken to "stand for" quality factor. The definition I like to go back to when all else fails is "energy stored divided by energy dissipated per radian." Q really only makes sense when you are talking about single resonators. This definition of Q applies to LC tanks, coaxial cavities, hollow cavities, acoustic resonators, pendulums, or any other singly resonant structure. High Q resonators "ring" for a long time, a lot of cycles. Low Q resonators dissipate energy rapidly and the ringing fades quickly. Cheers, Tom |
#12
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#13
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Tom's comment below -
For an example of the VSWR bandwidth achievable in an HF design, check the antenna described at this link http://www.tcibr.com/PDFs/613tfwebs.pdf. Nominal input VSWR is 2:1 from 2-30MHz . No input tuner is used. Good VSWR bandwidth in an antenna is not limited to VHF and above. RF Visit http://rfry.org for FM broadcast RF system papers. ______________________ "Tom Bruhns" wrote Just because one person wants to use a tuner, and retune after any QSY greater than 20kHz doesn't mean another who wants to use a broadband system should be discouraged from doing so. |
#14
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#15
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You have choices here, and I don't much care for generalities that
unnecessarily limit the choices. Just because one person wants to use a tuner, and retune after any QSY greater than 20kHz doesn't mean another who wants to use a broadband system should be discouraged from doing so. Hi Tom, The thread was "wire thickness versus bandwidth" As you know, to scale an antenna from one frequency to another, you need to scale the wire diameter as well. This will keep the bandwidth pretty much the same. I thought I was commenting on the bandwidth as one changes the frequency and length of an antenna, but keep the effective wire diameter constant. Of course if you vary the effective diameter, 3 parallel pieces of #8 a foot apart on 1.8 mhz, you change the effective bandwidth. you have choices here, and I don't much care for generalities that unnecessarily limit the choices. I did not mean to be general and limit choices, sorry. 73 Gary N4AST |
#16
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JGBOYLES wrote:
The thread was "wire thickness versus bandwidth" As you know, to scale an antenna from one frequency to another, you need to scale the wire diameter as well. This will keep the bandwidth pretty much the same. . . When you scale an antenna's dimensions, including the wire diameter, the *fractional* bandwidth remains the same. So if you scale it for twice the frequency, the bandwidth doubles. This is assuming that loss is negligible. If loss is appreciable, it becomes a factor in determining the bandwidth. And in order to preserve the loss characteristics when scaling, you've also got to scale the conductivity (as the square root of frequency). This is generally impossible or at best highly impractical, so the bandwidth of a lossy antenna won't scale like it will for a low-loss one. Roy Lewallen, W7EL |
#17
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At HF, increasing wire diameter has an absolute negligible effect on antenna
bandwidth. Multiply effective conductor diameter by 100 or 1000 and you are getting somewhere on one band only. But it can be completely spoiled by use of a tuner. ---- Reg, G4FGQ |
#18
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When you scale an antenna's dimensions, including the wire diameter,the
*fractional* bandwidth remains the same. So if you scale it for twice the frequency, the bandwidth doubles. Hi Roy, I have never heard of *fractional* bandwidth. Not unusual that I have never heard of stuff. If one has a band that is 100khz wide and the 2:1 swr bandwidth is say 20khz, what is the fractional bandwidth, and the bandwidth? If you scale the antenna to double the frequency (neglecting losses, or assuming negligible) and scale the dimensions, what are the 2 bandwidths? I hope you enjoy Dayton, first time in 5 years I won't be there. It rains too much when I am up the-( 73 Gary N4AST |
#19
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JGBOYLES wrote:
I have never heard of *fractional* bandwidth. Fractional bandwidth is bandwidth in Hz divided by the center frequency in Hz. Multiplying by 100 gives a percentage bandwidth. Both are normalized bandwidth. -- 73, Cecil http://www.qsl.com/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! =----- |
#20
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By fractional bandwidth, I mean the fraction of the operating frequency
that the bandwidth is; or in other words the ratio of the bandwidth to the operating frequency. For example, if the operating frequency is 10 MHz and the bandwidth is 1 MHz, the fractional bandwidth is 0.1 (1 MHz / 10 MHz). If you scale the antenna to 20 MHz, the bandwidth of the scaled antenna is 2 MHz. The fractional bandwidth is 2 MHz / 20 MHz = 0.1, the same as before it was scaled. I don't have enough information to answer your question, since you didn't give the operating frequency. I hope the example I gave will clarify what I meant. I always enjoy Dayton. It's a pleasure to meet EZNEC users, potential EZNEC users, and some of the many people who read this newsgroup. And if rain bothered me, I sho' 'nuff wouldn't live here in Oregon! Roy Lewallen, W7EL JGBOYLES wrote: When you scale an antenna's dimensions, including the wire diameter,the *fractional* bandwidth remains the same. So if you scale it for twice the frequency, the bandwidth doubles. Hi Roy, I have never heard of *fractional* bandwidth. Not unusual that I have never heard of stuff. If one has a band that is 100khz wide and the 2:1 swr bandwidth is say 20khz, what is the fractional bandwidth, and the bandwidth? If you scale the antenna to double the frequency (neglecting losses, or assuming negligible) and scale the dimensions, what are the 2 bandwidths? I hope you enjoy Dayton, first time in 5 years I won't be there. It rains too much when I am up the-( 73 Gary N4AST |
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