Please treat this reply to the below thread where an emphasis on linear loading being mo betta than a loading coil as a dialectic discussion. Something about that posit - linear loading is more efficient than a loading coil - didn't ring true with me so I did a little digging. Now, keep in mind that what I paste below may not follow, exactly, the thrust of the discussion, based on the types of antennas being considered.......see what these two fellas had to say as the choice of one over the other, sorta depends (see the last quoted writeup by W8JI): This from a fella at M2: extensive modeling with AOP (antenna optimizer, professional) shows that linear loading designs using decent diameter loading component work very well and are very efficient. Coil loading using wire size and fabrication techniques that maintain a Q of at least 300 works very well and are very efficient. The results of the multiple years of simultaneous, on the air testing shows no detectable difference in forward gain or front to back performance using linear loading on one antenna and coils with a Q of 500 on the other antenna. Modeling of each antenna showed virtually identical results meaning gains within .2 dB and F/B of 24 dB plus/ minus 2 dB. So it comes down to personal choice based on your local weather and esthetics Go here for the full story (about the third write up down the page) And this from that W8JI fella: Linear Loading is really nothing other than a poor form-factor inductor. The radiation from the linear loading does NOT change the radiation resistance of the antenna except as the effective position of the load might change from the direction of fold. In all cases, a proper form-factor inductor would have less loss, and provide the same radiation resistance. And another posit by that W8JI fella: Remember one thing, linear loading is like replacing a loading coil with a very low Q coil.
The claim it is "low loss" or worse yet "lossless" stems from advertising by antenna manufacturers that have brainwashed the public. A typical well-constructed open wire line with large gauge copper wire configured as a stub with 450 ohms inductive reactance has a Q of about 300-400 or just over 1 ohm loss resistance at 7MHz. This isn't exceptionally good, it is just OK. (Coil Q will typically range from 200-800.) If you move down to #18 copper wire, Q is 50-150, pretty poor. Factually, the same wire size wound into a conventional coil has LESS loss and higher Q. It also isn't necessarily true the stub is more stable with weather. It is more stable if you do nothing at all to weatherproof a coil, but a coil is much easier to weatherproof and so is much more stable than a stub that is exposed to weather. A #18 AWG air-wound coil of reasonable form factor generally has a Q of 250 or more, compared to a stub of the same guage having a Q of maybe 75 to 100. So the coil has 1/3 the loss for the same reactance. If you research 75 meter Yagi's, you will see people are paying big bucks to convert them from linear loading back to coils!! If the required inductance is small, it makes no difference what you use. If the required inductance is high, better use a coil or the losses will eat you up. 72, Jim Rodenkirch, K9JWV > Date: Mon, 18 Jun 2012 07:18:54 -0400 > From: w3...@embarqmail.com > To: nskou...@talisman-intl.com > CC: elecraft@mailman.qth.net; qr...@mailman.qth.net > Subject: Re: [QRP-L] [Elecraft] Antenna Question > > Neil, > > When you see an antenna element folded back on itself like that, think > "linear loading" (look it up in the ARRL Handbook or similar). There is > no "magic", but it is one way of shortening an antenna. It is not as > efficient as a full length antenna, but is more efficient than using > loading coils. Everything is relative. > If you have the space to put up full size half wave dipole antennas, > that is the way to go. If you need shortened antennas for the lower > bands, linear loading is one way to achieve resonance with shortened length. > > 73, > Don W3FPR > > On 6/17/2012 11:26 PM, Niel Skousen wrote: > > I'm pretty sure I've seen this antenna on the net, but don't recall the > > name nor have I been able to find a link to a description / design data. > > > > The county ERC has a 'shortened fan dipole' with three parallel elements, > > spaced about 18-24" apart on each side. the longest element folds back > > around the mid-length element toward the shortest element. The antenna > > end insulator / guy rope is attached to the long element, where it folds > > back. There appears (from the ground) to be a 6~8" insulator / gap > > between the end of the shortest element, and the longest element where its > > been folded back. no traps, loading coils, or loading resistors that I can > > see. > > > > I'm assuming three or four band coverage (80, 40, 20, and 15 ??) with a 75m > > dipole, a 40m dipole (with 15m as a freebie), and a 20 m dipole. but > > would be interested in more technical details if anyone can decipher my > > text description above… > > > > Thanks > > Niel > > > > ______________________________________________________________ > QRP-L mailing list > Home: http://mailman.qth.net/mailman/listinfo/qrp-l > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:qr...@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
