Attic Antenna
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In a message dated 10/27/06 10:05:38 PM Eastern Daylight Time,
[hidden email] writes: > > B&W makes a "Folded Dipole", 7-30mhz, 45 feet long - > > with supposed flat swr? Like $245. Our attic antenna > > needs to be pretty much left by itself - no trips up > > there to change frequencies. And 40 thru 10 would > > be nice. > > This *is* resistively loaded. It is not a scam like some, but it is less > efficient than an ordinary dipole. It is a version of the T2FD, which has been discussed extensively all over the 'net. The best discussion I have seen is on the W4RNL (Cebik) website. The efficiency of a T2FD varies over its frequency range. At the top end it may be only a few dB less than a dipole of the same size, while at the bottom end it is much less efficient. See the graphs on W4RNL's site - they're not pretty. While it *is* possible to make contacts with an inefficient antenna, remember that the T2FD is much less efficient than a dipole of the same size, erected in the same place. The T2FD isn't new - it's been around since the late 1940s, and was originally meant for receiving applications where its low efficiency wasn't really an issue. It finds use in some military and government applications where its broadband nature is essential (ALE, spread spectrum). The military and government folks get around its inefficiency by running more power. Lots more power! OTOH a T2FD can give you the QRP experience with a 100 watt rig. For normal ham use it is a very poor choice, IMHO. A trap dipole or tuner-fed dipole of the same size will do much better. If you really want to try one in your attic, one can be homebrewed for much much less than $245. Wire, plastic insulators, homemade balun, noninductive resistors. Doesn't have to be weatherproof in the attic. A dipole as long as possible in the > > attic, not parallel to wires/pipes if possible, and fed with ladder line > and a balanced tuner would be close to optimum. > > Agreed. Trap dipole is a second choice. Traps can be made easily from coax and PVC pipe. You need a dip meter, though. 73 de Jim, N2EY _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by PE1E
Peter,
The Impedance range that the KAT2 will match will be greater on the higher bands than the lower (just because of the math in the formulas for impedance of inductors and capacitors). So I hesitate to guess at an answer becuase you did not specify a frequency - I can add up the inductor and capacitor values and give a range for each. With a bit of work with a program like TLW (www.arrl.org), one could determine the impedance range for each band. It is an L network tuner with a series inductor range from 0 to 20.62 uH in 0.16 uH steps; while the shunt capacitor can range in value from 0 to 2423 pf in 10 to 12 pf steps. The shunt capacitor can be at either end of the inductor. Only the min and max values need to be entered for each component and configuration, so there would be 8 calculations for each band of interest. All in all, it is a wide impedance range, but will be more restricted on 160 meters than on 10 meters. This same principle applies to all Elecraft tuners and to other manufacturers of similar L network designs. 73, Don W3FPR > -----Original Message----- > > Is it something like 5-1000 ? > Can't find no indication wherever. > > Peter, PE1E. > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by David Cutter
David, G3UNA, wrote:
> ...My 'doublet' was nearly a loop, ie it followed > the beams around the loft. The ends were left open, about a foot apart... I have some questions for the group. How would one decide whether the ends should be left open, versus connected together to make a loop? (I never could figure out how to model antennas using EZNEC. It should be called HARDNEC.) Does it make a lot of difference? Using a tuner near the feedpoint, which way would give a better match on more bands (160-10m), open or closed ends? Which way would yield stronger signals in the most directions? Is it the case that, below a certain total wire length, the ends should be left open, but above that length, they should be connected together? I guess the only way an indoor antenna of typical length would match on 160m, even with a tuner, would be if the ends were connected together and the whole thing was treated as a very bent end-fed wire working against ground and a counterpoise. Thanks & 73, Jeff, WB5GWB Long Island, NY K2 #821 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
RE: Attic Ant.-Closed Loop vs. Open Ends?
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Jeff,
I agree with you. I cannot figure out Eznec.... Could be my brain doesn't work the same way as the creator. I am a PC builder tech and etc., but that program is designed for a different brain than mine. SO many use it but I don't have the time or patience to figure it out. I worked in a usability lab while designing desktop software for a very large corporation and this would not satisfy us. It is NOT intuitive in my opinion! There's way too much learning and putzin' to get it to work. Bill K9YEQ K2-35 & 5279; KX1-35/3080 ___________________________________ Subject: [Elecraft] Attic Ant.-Closed Loop vs. Open Ends? David, G3UNA, wrote: > ...My 'doublet' was nearly a loop, ie it followed > the beams around the loft. The ends were left open, about a foot apart... ...(I never[WJ] could figure out how to model antennas using EZNEC. It should be called[WJ] HARDNEC.) Does it make a lot of difference? [WJ] ... Thanks & 73, Jeff, WB5GWB _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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I agree with you. I cannot figure out Eznec.... Could be my brain doesn't work the same way as the creator. ...(I never[WJ] could figure out how to model antennas using EZNEC. It should be called[WJ] HARDNEC.) Does it make a lot of difference? [WJ] ... I had the same problem until I went to the HELP menu. Under HELP there are three tutorials. If you go through each one then you get a good feel on how the program works. 73, Larry, KB5DXY K1 #2269 (in progress) _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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ok, we have established that many of you cannot, like me, use the
software. (smile) Who can answer the topic: "closed loop or open ends"? Ron, wb1hga Larry wrote: > I agree with you. I cannot figure out Eznec.... Could be my brain doesn't > work the same way as the creator. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Fred (FL)
In a message dated 10/27/06 4:38:23 PM Eastern Daylight Time,
[hidden email] writes: > The Diamond bottom tube may, (and likely) contains a broad band ferrite > cable choke. Probably - to keep RF off the outside of the coax. Such a choke would cost a few dollars at most. Or there may be a combination trap/ loading coil such as used > > on some tri band beams for multibands. > No, that wouldn't work. Traps are used in the radiator itself, not at one end. The BB7 claims SWR of less than 2:1 over the entire range. Traps and loading coils won't do that. It's resistively loaded. 73 de Jim, N2EY _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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[hidden email] wrote:
> In a message dated 10/27/06 4:38:23 PM Eastern Daylight Time, > [hidden email] writes: > > >> The Diamond bottom tube may, (and likely) contains a broad band ferrite >> cable choke. > > Probably - to keep RF off the outside of the coax. Such a choke would cost a > few dollars at most. Actually, a choke on the coax would *prevent* the antenna from working unless it was mounted on a metal mast. It needs a counterpoise and the coax shield provides it unless a mast or radials are present. This is actually similar to the 'e-h' antenna, in which the alleged 'antenna' at the end of the feedline serves to tune the shield of the feedline to resonance. The shield actually does the radiating. Adding a bead balun to an e-h antenna causes the antenna to stop working and the balun to get hot! No, I don't want to start a thread on this antenna either! In the Diamond antenna, the feedline is only half of the antenna, with the 22-foot radiator being the other half and the resistor smoothing out the SWR variations. -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Fred (FL)
In a message dated 10/29/06 11:12:34 AM Eastern Standard Time,
[hidden email] writes: > [hidden email] wrote: > > In a message dated 10/27/06 4:38:23 PM Eastern Daylight Time, > > [hidden email] writes: > > > > > >> The Diamond bottom tube may, (and likely) contains a broad band ferrite > >> cable choke. > > > > Probably - to keep RF off the outside of the coax. Such a choke would cost > a > > few dollars at most. > > Actually, a choke on the coax would *prevent* the antenna from working > unless it was mounted on a metal mast. It needs a counterpoise and the > coax shield provides it unless a mast or radials are present. Agreed. Note that in the literature, the unit is shown on a metal mast. > > This is actually similar to the 'e-h' antenna, in which the alleged > 'antenna' at the end of the feedline serves to tune the shield of the > feedline to resonance. The shield actually does the radiating. Adding > a bead balun to an e-h antenna causes the antenna to stop working and > the balun to get hot! No, I don't want to start a thread on this > antenna either! > Good idea. > In the Diamond antenna, the feedline is only half of the antenna, with > the 22-foot radiator being the other half and the resistor smoothing out > the SWR variations. > Or the mast. So what's probably in the "matcher" is really just a resistor. $400 for 22 feet of tubing, a mast clamp, and a nice noninductive resistor. 73 de Jim, N2EY _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: Attic Ant.-Closed Loop vs. Open Ends?
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In reply to this post by Jeff-229
Jeff
Answering your last question first: for top band and 80m mainly (actually, it worked on all bands) I joined the feeders together into one terminal of my Drake tuner and the other I took thro some tv coax (shorted) back up thro the ceiling, out to the soffit board and straight down to a ground spike (brass curtain rods) and lots of radials in the front garden. This was then a heavily top loaded vertical and worked very well. The single outdoor brown wire spaced off the brick wall about a foot was almost unnoticeable and a friend thought it was just the tv coax that had come unclipped. Back to the invertedV/doublet/loop bird's nest: I could model it in EZNEC if I had a few minutes, but I am sure the results will be impenetrable: there will be lobes going in all sorts of directions at all sorts of angles. What will be a problem is modelling the house and structure which is beyond me. Frankly, as the man said: I don't give a d*mn. As radio amateurs we are interested in getting signals in and out and the performance of simple antennas is just the joy of working the world and that's what I did. Be aware of the noise picked up from the house mains and the interference you can put into the mains. I used to modulate the lights on 20m. Look out for high voltages - use heavy gauge insulated house wire (it's more efficient) and insulate any bare wire ends. As to shorting or opening the ends: it changed the range of frequencies that could be matched. I started making a table of strength of signals from various directions with open or short and with feeding from corners or apex, but the combinations were endless and of course change endlessly with frequency and band conditions. I gave up after a few trials. In its vertical configuration I got more dx which was to be expected and I think I left it like that. Just enjoy getting out. David G3UNA ----- Original Message ----- From: "Jeff" <[hidden email]> To: <[hidden email]> Sent: Saturday, October 28, 2006 9:19 PM Subject: [Elecraft] Attic Ant.-Closed Loop vs. Open Ends? > David, G3UNA, wrote: >> ...My 'doublet' was nearly a loop, ie it followed >> the beams around the loft. The ends were left open, about a foot >> apart... > > I have some questions for the group. How would one decide whether the > ends > should be left open, versus connected together to make a loop? (I never > could figure out how to model antennas using EZNEC. It should be called > HARDNEC.) Does it make a lot of difference? Using a tuner near the > feedpoint, which way would give a better match on more bands (160-10m), > open > or closed ends? Which way would yield stronger signals in the most > directions? Is it the case that, below a certain total wire length, the > ends should be left open, but above that length, they should be connected > together? I guess the only way an indoor antenna of typical length would > match on 160m, even with a tuner, would be if the ends were connected > together and the whole thing was treated as a very bent end-fed wire > working > against ground and a counterpoise. > > Thanks & 73, > Jeff, WB5GWB > Long Island, NY > K2 #821 > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Fred (FL)
Looking like ELECRAFT should consider getting into the STEALTH ANTENNA game. A stealth vertical perhaps, one could just lean up against the home. Or a gutter-shaped antenna, that would easily attach to one's home front facia. There's certainly interest and need for one. Fred N3CSY ....displaced Buffalonian ____________________________________________________________________________________ Access over 1 million songs - Yahoo! Music Unlimited (http://music.yahoo.com/unlimited) _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Hi antenna challenged fellow hams. You can do your own stealth gutter
antenna these days. Two easy ways: 1) Get a combination of metal gutter and one short section of plastic gutter to join two metal halves of a dipole. Remember, you can use shorter than quarter wave lengths of elements, since their cross section is large compared to wavelength. 2) Even easier: Get all plastic. Lay dipole elements in bottom of plastic gutter. Even hook up wire can be used for elements. Glue them to corner of gutter bottom that will be furtherest from the house. Better still, glue them UNDER the gutter corner, so water in gutter will not stand on antenna wire. Use 1/4 inch coax feed to feedpoint, or twin lead, again glued to underside of gutter. Run it into soffit, and then to rig. An all band tuner, will facilitate operations on multiple bands, especially if the dipole is at least 60 per cent of a half wave for the lowest frequency of interest. Your nearest Lowe's or Home Depot is already a stealth antenna store, and you did not know it. Even coax can be purchased there! I regularly use insulators and standoff's from Home Depot's electric fence department for various home antenna projects. They have a compression spring for electric fence gates that is ideal for relieving stress in a dipole element tied to a tree. Unlike a door spring which is extension type, this spring will not elongate with use. At least, not as much as extension springs. Stuart K5KVH _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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