Open wire fed dipoles having enough length to cover to 3.5 MHz (minimum 140
feet, center fed), really work well.
I make mine 175 ft long (split in the middle for the open wire feed). At this
length (longer than 1/2 wave at 80 meters), it is two 5/8 wave lengths in phase
for 40 meters. It has real gain
on 40.
Although the 4:1 balun followed by lengths of coax method works, I really
prefer the Johnson matchbox for matching the open wire fed dipole direct to the
radio (or amplifier) with minimum
coax after the tuner.
This is a great antenna with gain above 7 MHz and a efficient (low loss feed
system) that can be tuned from 3.5 to 30 MHz with a good openwire (balanced)
tuner.
73!
Tim K3LR
http://www.k3lr.com
"James C. Hall, MD" wrote:
> Hi Lee:
>
> There is a huge amount written on the simple dipole antenna. I would first
> consult any ARRL Handbook as well as the Antenna Book. One of my all time
> favorite web sites is that of Dr. L. B. Cebik, W4RNL at
> http://www.cebik.com/radio.html . You can spend absolutely hours reading and
> absorbing all manner of antenna subjects.
>
> During our Field Day operations, we have several 135 foot center-fed dipoles
> up. They are fed with ladder-line (just the standard 'window' line, not the
> 'tuned-feeders' of y'or). We bring the ladder line to fairly near the shack
> and attach a 4:1 balun. Then a short run of RG8X completes the run. With an
> antenna tuner, you can match very well to frequencies of 75M and above. We
> use them for 40 and 80M during FD. Works great !
>
> At the frequencies we're talking about, it would seem to me to make little
> difference whether you wrap or solder the dipole ends - I've done both with
> no perceived difference. If you use the ladder-line technique above, you
> don't have to worry about the diameter (and weight) of the dipole wire
> itself.
>
> Good Luck !
>
> 73, Jamie
> WB4YDL
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of Lee Buller
> Sent: Tuesday, August 30, 2005 1:54 PM
> To: TowerTalk Reflector
> Subject: [TowerTalk] Dipole questions for the Liberal Arts Major
>
> Towertalkians....
>
> As I am sitting here waiting for a huge programto load
> into the file server I started asking myself about the
> simple dipole...or Inverted-Vee (I know there is a
> difference.)
>
> Although my dipoles seem to radiate, I am somewhat
> dismayed at the "bandwidth" of a typical 40 or 80
> meter dipole. Lets just talk 40 meters for now....
>
> I was always instructed by an Elmer to cut the dipole
> long and then use a tuner to tune the higher part of
> the band. Others have instructed me to cut the dipole
> for about 100 Khz up from the bottom and get as much
> use as possible (not quite possible on 80 or 75
> meters). Another Elmer cautioned me to make sure I
> solder the ends of the dipole because the wire wrapped
> at the end acts as a inductor with a capacitor in the
> loop of the wire around the insulator which would make
> the resonate point different than calculated. And yet
> another told me to build a large wire diameter dipole
> (out of RG58 or 59 or even RG8) to get some bandwidth.
>
> So, with those comments that I have made...what do you
> do when working with dipoles to get them to the point
> where you get good bandwidth?
>
> Lee Buller
> Liberal Arts Major
> K0WA
>
> Common sense is in short supply - get some and use it.
> If you can't find any common sense, ask for help from
> somebody that has some common sense. - Lee Buller
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
> questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
> questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|