[Antennas] Dipole

Thu, 9 Jan 2003 20:13:33 -0600

Before I would do that I would put up what I did. I needed an antenna for 20
meters with lowest radiation angle possible from an antenna height of 25'. After
modeling several dipole and inverted vee center fed antennas, I finally found
what I needed, an off center fed antenna, 40 meter length, actually 69' long
fed at 22' from end, long end 47', 25' at center, 15' at ends. Has about 27
Deg radiation angle on 20 meters. Antenna is fed with coax with a 4:1 balun
at feed point and about 25' of coax on round form for choke for common mode
current. SWR is around 2:1 on 40 and 20 meters, around 3:1 on 10 meters, about
4:1 on 17 and 12 meters, and highest on 15 meters, 5:1 plus or minus. Antenna
is veed both vertically and horizonally and has some gain in one direction.
I was surprised how well the modeling program, EZNEC, matched the real antenna.
Biggest problem is common mode, make sure choke is big enough, and antenna can
be matched with most tuners in radios. I just checked 20 meters, about 2:1 at
bottom of band and 1.5:1 at top, I have used it on that band without the tuner
in line. Another advantage is all coax feed. Hope this is of interest.
Darryl, KK5IB
>This a great job for antenna modeling. You can model
>this puppy and sweep and prune and stuff without
>looking dumb in the backyard.
>>The height of the antenna will be crucial to this
>model as will all dimensions, spacing, etc.
>>I'm sure someone has said this before, but really you
>should feed a 40m dipole w/ balanced line and use an
>in-shack transmatch w/ balun to tune all bands.
>>However, you can certainly feed this with coax but
>expect a LOT of tuning interaction if you can't fan
>the elements out.
>>73, Steve N4SL
>>--- Mike Rhodes <[email protected]> wrote:
>> Mike,
>> Not quite sure what you said but if I interpret it
>> correctly, you stated
>> the problem with your theory in the last line. The
>> longest antenna will
>> undoubtedly change length at some point in time if
>> you are starting the
>> tuning process with the shortest antenna. Therefore,
>> all shorter antennas
>> are more likely to change as you tune the longer
>> elements (i.e., the longer
>> elements affect the shorter elements much more than
>> the shorter elements
>> effect the longer).
>>>> Mike / W8DN
>>>> ----- Original Message -----
>> From: "Mike Olbrisch" <[email protected]>
>> To: "'Wes (N7WS) and Linda'"
>> <[email protected]>; "'WD8OKN de
>> Michigan'" <[email protected]>; <[email protected]>
>> Cc: <[email protected]>
>> Sent: Thursday, January 09, 2003 7:11 PM
>> Subject: RE: [Antennas] Dipole
>>>>>> > Hmmmm... I disagree, but I could very well be
>> wrong. I would tune the
>> > shortest element first. Once it is done, it will
>> have little further
>> > CHANGING effect on the longer one. OTOH, since
>> the longer one will
>> continue
>> > to be longer, it's effect on the shorter ones will
>> remain constant no
>> matter
>> > what the change (unless it becomes at long or
>> shorter).
>> >
>> > Someone correct me if I am backwards.
>> >
>> > Mike. KD9KC
>> > El Paso, TX.
>> >
>> > > -----Original Message-----
>> > > From: [email protected]
>> > > [mailto:[email protected]]On Behalf
>> Of Wes
>> > > (N7WS) and Linda
>> > > Sent: Thursday, January 09, 2003 11:42 AM
>> > > To: WD8OKN de Michigan; [email protected]
>> > > Cc: [email protected]
>> > > Subject: Re: [Antennas] Dipole
>> > >
>> > >
>> > >
>> > > You can run the wires parallel to each other but
>> you should
>> > > expect more
>> > > interaction between them. In other words, they
>> will be
>> > > harder to prune to
>> > > resonance. Start with the longest element and
>> work up.
>> >
>> >
>> > - - -
>> >
>> > Your moderator for this list is:
>> > Larry Wilson KE1HZ [email protected]
>> > _______________________________________________
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>> >
>>>> - - - 
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