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Jim Higgins wrote:
On Sun, 16 May 2004 21:13:58 GMT, in , R. David Steele /OMEGA wrote: http://www.bwantennas.com/ The military is using these antennas because of ALE (automatic linking) and NVIS. I gather that while they are very broad banded, they have less the best gain? Any feed back? I tend to compare the claims for any antenna to the characteristics of a dummy load and then remember the principle of reciprocity. So for the BW dipole let's see. It's really quiet, esp on the lower frequencies. It's really broad banded. It's not for me. Doh! I guess that was your point! - Mike KB3EIA - |
Jack Twilley wrote in message ...
Out of curiosity, what other antenna provides a better cost-benefit ratio while maintaining the same constraints with respect to power, size, and construction? A well made G5RV, for one. A well-made W3DZZ trap dipole, for another. W5DXP's "linear tuner" dipole, for a third. Or the classic dipole-with-openline-and-a-real-balanced-tuner for a fourth. All are much more efficient than a T2FD of the same size. The B&W/T2FD is discussed in detail on W4RNL's excellent site (which see). In short, its efficiency is quite low on the lower bands and gets to be almost as good as a halfwave dipole on the upper bands. Their one and only advantage is low SWR over the frequency range. 73 de Jim, N2EY |
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Hash: SHA1 "N2EY" == N2EY writes: N2EY Jack Twilley wrote in message N2EY ... Out of curiosity, what other antenna provides a better cost-benefit ratio while maintaining the same constraints with respect to power, size, and construction? N2EY A well made G5RV, for one. A well-made W3DZZ trap dipole, for N2EY another. W5DXP's "linear tuner" dipole, for a third. Or the N2EY classic dipole-with-openline-and-a-real-balanced-tuner for a N2EY fourth. All are much more efficient than a T2FD of the same N2EY size. The only one of those I haven't seen is the "linear tuner" dipole. N2EY The B&W/T2FD is discussed in detail on W4RNL's excellent site N2EY (which see). In short, its efficiency is quite low on the lower N2EY bands and gets to be almost as good as a halfwave dipole on the N2EY upper bands. Their one and only advantage is low SWR over the N2EY frequency range. I've looked, but the T2FD that's discussed isn't the one I'd be buying, and I'm not sure if that matters. N2EY 73 de Jim, N2EY Jack. - -- Jack Twilley jmt at twilley dot org http colon slash slash www dot twilley dot org slash tilde jmt slash -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.4 (FreeBSD) iD8DBQFArEYkGPFSfAB/ezgRApFQAKDmCr5rfAAedd+vbyQ/dYZb+r3azgCg/2oD xgXsm3pVOa95PdaCzXYj6Fo= =wiLd -----END PGP SIGNATURE----- |
Jack Twilley wrote:
The only one of those I haven't seen is the "linear tuner" dipole. It's described at: http://www.qsl.net/w5dxp/notuner.htm -----= 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! =----- |
Jack Twilley wrote in message ...
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 "N2EY" == N2EY writes: N2EY Jack Twilley wrote in message N2EY ... Out of curiosity, what other antenna provides a better cost-benefit ratio while maintaining the same constraints with respect to power, size, and construction? N2EY A well made G5RV, for one. A well-made W3DZZ trap dipole, for N2EY another. W5DXP's "linear tuner" dipole, for a third. Or the N2EY classic dipole-with-openline-and-a-real-balanced-tuner for a N2EY fourth. All are much more efficient than a T2FD of the same N2EY size. The only one of those I haven't seen is the "linear tuner" dipole. http://www.qsl.net/w5dxp/notuner.htm N2EY The B&W/T2FD is discussed in detail on W4RNL's excellent site N2EY (which see). In short, its efficiency is quite low on the lower N2EY bands and gets to be almost as good as a halfwave dipole on the N2EY upper bands. Their one and only advantage is low SWR over the N2EY frequency range. I've looked, but the T2FD that's discussed isn't the one I'd be buying, and I'm not sure if that matters. Which one would you be buying and how is it different? Most of the data in the W4RNL site is for a 90' T2FD. When you look at the gain curves, remember that they're in dBi. A simple halfwave dipole has about 2.2 dBi gain. The T2FD isn't a new invention - it was in QST about 1948 as a *receiving* antenna, and that wasn't the first article on it by any means. Government/military folks wanted a receiving antenna that was essentially omnidirectional and would give a decent match to balanced line over the HF frequency range - possibly feeding several receivers via an active receive coupler. Low efficiency below 8 or 10 MHz was no big deal because the receivers had lots of gain, and atmospheric noise dominates in that part of the spectrum even with a poor antenna. Transmitting is another issue. If you want to spend the money for a T2FD, enjoy. But in the same space (T2FDs are not small!) and for the same or less money you could have a much more efficient transmitting antenna. 73 de Jim, N2EY |
On Sun, 16 May 2004 21:13:58 GMT, R. David Steele
/OMEGA wrote: http://www.bwantennas.com/ The military is using these antennas because of ALE (automatic linking) and NVIS. I gather that while they are very broad banded, they have less the best gain? Any feed back? I have used the BWD-90 for 2 months now, and love it. I live on a city lot, and this antenna fits and performs better than any other antenna I have tried. I've tried shortened 75m dipoles, 40 meter delta loops, and all kinds of slopers. all narrow banded and loaded with city noise. The antenna has made the hobby fun for me again. It is frequency agile, and has a great signal to noise ratio. At 80 meters the antenna is only down 1 db from a standard dipole. At 40 meters it even, there is 1db gain at 20 meters, and 3db at 10m. (B & W,s numbers, not mine). The botton line is if you live in the sticks with all kinds of space, and no noise, you don't need a folded terminated dipole. you can run wire to the cows come home, but it's sure nice in the city. Curt |
Any feed back?
If you desire a single antenna with excellent SWR match at many bands, then I am of the opinion that there is value here. Even the most efficient horizontal dipole is almost useless for DX--the assumed need, not NVIS-- unless it is high up. This is because all low dipoles have low gain at low elevations: Their launch angle is quite high. I would suspect that typical ohmic losses on the BW are 2-5 dB. The mismatch lsses are negligible. Getting this well over a wave high at the lowest freq of operation will afford at least that, and probably more, in a gain differential at low angles, compared to an efficient, low dipole. The point: a high BW antenna will work well. Any low dipole will work poorly. The in-between is a valid issue to ponder. 73, Chip N1IR |
"Fractenna" wrote in message
... Any feed back? If you desire a single antenna with excellent SWR match at many bands, then I am of the opinion that there is value here. Even the most efficient horizontal dipole is almost useless for DX--the assumed need, not NVIS-- unless it is high up. This is because all low dipoles have low gain at low elevations: Their launch angle is quite high. I would suspect that typical ohmic losses on the BW are 2-5 dB. The mismatch lsses are negligible. Getting this well over a wave high at the lowest freq of operation will afford at least that, and probably more, in a gain differential at low angles, compared to an efficient, low dipole. The point: a high BW antenna will work well. Any low dipole will work poorly. The in-between is a valid issue to ponder. 73, Chip N1IR Chip, how did we digress to comparing a "high B&W" to a "low dipole"? When the two are each at their optimal height (and why would we ever compare anything else..) then the dipole has it all over a B&W. I use my (amost 1/2 wave height) dipole only for DX, without a tuner on it's two resonant frequencies and with a tuner on two bands well above, with amazing results. 5, 8, 11 and 15 mhz to Alaska, Equador, Venezuela and Canadian Maritimes, if that qualifies as "DX". 73 Jack Painter Virginia Beach, Va |
Chip, how did we digress to comparing a "high B&W" to a "low dipole"? When
the two are each at their optimal height (and why would we ever compare anything else..) then the dipole has it all over a B&W. I use my (amost 1/2 wave height) dipole only for DX, without a tuner on it's two resonant frequencies and with a tuner on two bands well above, with amazing results. 5, 8, 11 and 15 mhz to Alaska, Equador, Venezuela and Canadian Maritimes, if that qualifies as "DX". 73 Jack Painter Virginia Beach, Va Hi Jack, It seems relevant to me in two big contexts: (1) why do some folks do well (relatively) with the BW antenna; (2) what does it replace? My response clearly explains (1). In the case of (2), I can think of many circumstances where it is preferable to put one dipole (BW) up high than a slew of dipoles up high. If you have neighbors, you know what I mean:-) Don't know what DX is to me anymore; I have DXCC #1 Honor Roll and haven't been active on the low bands in several years. To someone else, DX is what you haven't heard or worked yet:-) I say go for it. Some folks don't live in a perfect world, Jack, and its good to know when a compromise is a true degradation. A BW antenna, up high, is a good antenna for DX across many bands. It is hardly a dummy load. Hope this helps on this question. 73, Chip N1IR |
With all the hoopla going on for this antenna I was surprised that no
one reported any calculated antenna efficiencies. So I modeled the antenna in free space - to remove environmental influences other than those contained within the antenna itself (terminating resistor and wire loss) - NEC reported the following: Freq. MHz. Efficiency Average Gain Peak Gain MHz % DBi DBi 3.5 9.6 -10.43 -8.49 7.15 41.24 -3.85 -1.33 14.2 23.21 -6.36 -1.59 21.2 30.01 -5.23 -1.36 29 53.81 -2.69 2.17 73 Danny, K6MHE |
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