[Boatanchors] NEED ANTENNA GURU
garyschafer at ATTBI.COM
Sat Apr 20 23:06:14 EDT 2002
I think the trick is that they need to be harmonically related. In other
words if you have the 80 meter one cut for 3.6 mhz then the 40 meter one
needs to be cut for 7.2 mhz. 20 meters needs to be cut for near 14.4
Operating at 40 meters that part looks like a 40 meter dipole. The 80
meter part looks like a high impedance full wave to 40 meters. If it is
any longer or shorter then it detunes the 40 meter antenna feed
impedance. This is how I understood it anyway.
Glen Zook wrote:
> The parallel dipole arrangement normally works fine.
> In the older versions of the ARRL "Hints & Kinks" book
> there was even one made for 80, 40, 20, 15, and 10
> meters out of 100 feet of the flat ribbon type of
> rotor cable. By proper cutting, you could get the 66
> foot lengths for 80 from each side with the 33 foot
> lengths for 40 adding up to 100 feet of cable. Then,
> you cut one of the 33 feet lengths on each piece to
> size for 20 meters. 15 meters works fine from the 40
> meter section.
> The spacing on that antenna was just a fraction of an
> inch and they work fine. Are you using direct feed
> from your coax or are you trying to use a balun? If
> you have a balun, I would remove it.
> Always cut a dipole a little on the long side so that
> you will have room to trim it to frequency. It is
> much easier to remove wire than to add it.
> I have used parallel dipoles in the past and have had
> no problems at all with them. I would definitely
> check your connections at both ends (make sure that
> the "far" end is not connected to anything and the end
> at the center insulator is definitely connected to the
> 160 meter sections). I know that this is obvious, but
> it is very easy to overlook something (I have done it,
> so I know others have overlooked things as well!).
> Glen, K9STH
> --- Dee Almquist <w4pnt at vaix.net> wrote:
> > Hi Fellow Anchorites
> > Need some help. For years I have seen muti band
> > dipoles used at ham event
> > stations & except for close proximity of ant to
> > equipment (rf feedback),
> > they seem to work well. I got this idea of using one
> > at my shop to cover
> > 160m through 40m starting @ center insulator,one
> > coax, to feed all bands,
> > sagging wire for other bands under main (160m) ant.
> > but insulated by 4 to 6
> > inches with porcelain standoffs. I have done this
> > before with 40m & 80m but
> > seperating wires about 60 deg., anchoring ends in 4
> > different trees & it
> > worked great. This time, however, 160m loads great.
> > but the other 2 bands
> > nothing loads. Got as much reflected pwr as going,
> > or nearly so. Acts like
> > nothing tied to end of coax. Anyone built one of
> > these that can give me some
> > clue where I'm going wrong? Everything is cut to
> > frequency with 468 div by
> > freq. There must be something, somewhere written on
> > this type of antenna.
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