Antenna wire gauge, etc
Locked
 
|
Use care when working with copper-clad
steel wire (Copperweld). The smallest nick in the copper cladding will allow moisture to reach the steel and it will most likely rust through ... sooner or later. Proper insulators have lead-lined holes to "cushion" the wire. A couple of things to keep in mind ... RF flows on/near the surface of a conductor, and the correct length of an antenna made from insulated wire will be slightly different than the formula-calculated length. Building K2 S/N 5665 ... Having the most fun from ham radio in years! Ken Kopp - K0PP [hidden email] or [hidden email] _______________________________________________ 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: Antenna wire gauge, etc
|
|
Ken,K0PP wrote:
Copper-clad steel wire (Copperweld)...Proper insulators have lead-lined holes to "cushion" the wire. A couple of things to keep in mind ... RF flows on/near the surface of a conductor, and the correct length of an antenna made from insulated wire will be slightly different than the formula-calculated length. --------------------- Good points, Ken although lead-lined insulators are going to be hard to come by soon, Hi! Also, the formulas are, at best, approximations. Not only can insulation affect the length, but so does the earth itself (unless it's many wavelengths away) buildings, trees, support poles, etc. The popular formula for 1/2 wave, 468/f(MHz) is only an approximation trying to account for typical end loading caused by capacitance between the ends and support wires through the insulators. A 1/2 wave in "free space" is closer to 492/f(MHz). The bad news is that unless one has non-metallic supports a few hundred feet high and in the clear, the formulas are only going to be an approximation of the right length to be self-resonant. The good news is that it's not important to be self-resonant. The biggest problem with a non-resonant antenna has little to do with the antenna itself. The problem is mostly the rig. Our modern rigs (including the Elecraft rigs) have fixed-tuned output networks. They only work efficiently into a load close to 50 ohms, non reactive, where the old rigs with tuning controls that had to be adjusted as one moved around in frequency worked very efficiently into a large range of impedances. Unfortunately, those tunable output circuits we used in years past don't provide the amount of harmonic rejection now required of our rigs, so you aren't likely to find any new designs using them above QRP levels. So the problem is to match the antenna to the fixed-tuned output network in our rig. Finding the magic length of an antenna is one way, but it's seldom good for much more than one band, and often not even for a whole band. So we use an antenna tuner to match the antenna to the rig. Now we don't care so much about whether we have exactly the right length radiator. Until the SWR gets up fairly high where feeder losses become a concern, it's a non-issue. And the ATU suppresses harmonics and other spurs even more. Ron AC7AC _______________________________________________ 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: Antenna wire gauge, etc
|
|
On August 11, 2006 06:04 pm, Ron D'Eau Claire wrote:
>And the ATU suppresses harmonics and other spurs even more. > Ron AC7AC Does the Elecraft KAT100 Tuner's L network work as a high pass, low pass, or band pass filter? Darrell VA7TO -- Darrell Bellerive Amateur Radio Stations VA7TO and VE7CLA Grand Forks, British Columbia, Canada _______________________________________________ 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: Antenna wire gauge, etc
|
|
They use series inductance with shunt capacitance, so the characteristic is
that of a low-pass filter. Ron AC7AC -----Original Message----- On August 11, 2006 06:04 pm, Ron D'Eau Claire wrote: >And the ATU suppresses harmonics and other spurs even more. Ron AC7AC Does the Elecraft KAT100 Tuner's L network work as a high pass, low pass, or band pass filter? Darrell VA7TO _______________________________________________ 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: Antenna wire gauge, etc
|
|
In reply to this post by Ken Kopp-2
Ken Kopp K0PP wrote:
> A couple of things to keep in mind ... RF flows on/near the surface of a > conductor, and the correct > length of an antenna made from insulated wire will > be slightly different than the formula-calculated length. ------------------------------------------------------------- FWIW a horizontal dipole using plastic covered Flexweave cut to the formula-calculated length is roughly 2-1/2 % too long at 40m and 3 % too long at 6m when in the clear and a half wavelength or more above ground. It needs to be shortened if it has to be resonant at the working frequency. 73, Geoff GM4ESD _______________________________________________ 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 |
«
Return to Elecraft
|
1 view|%1 views
| Free forum by Nabble | Edit this page |