[Antennaware] center loading versus ground loading

Sun Jan 31 19:34:21 PST 2010

Dave,

Sounds promising...and making more sense than my idea of using irrigation
pipe.

First off, since you obviously understand more about this than I do, thank
you.  Second, you might enjoy this calculator and discussion:

http://hamwaves.com/antennas/inductance.html

In order to minimize coil losses, would a more square design (length to
diameter) be preferable?  Or are you concerned about the coil having too
great a Q and therefore limited bandwidth?

In my "envisioning" of using the coil to choke the radiator around 65 feet
or so, I was thinking of a large coil, perhaps 4 or 5 inch diameter.  I run
the Hy-Gain AV640 and notice the coils do warm up, so assume that such heat
is loss.

The 2" diameter coil would be about 8 inches long, right?  This program
shows a Q of about 400 ohms at 1.8mhz, which surprised me.  Is there any
advantage or disadvantage, electrically, to a coil that was similarly wound
but 3.5" x 5"?

Thank you for working this through...it sounds great and do-able.  I am
curious as to your thoughts on different coil design methodologies.

Art

-----Original Message-----
From: antennaware-bounces at contesting.com
[mailto:antennaware-bounces at contesting.com] On Behalf Of DAVID CUTHBERT
Sent: Sunday, January 31, 2010 7:56 PM
To: aa4nn
Cc: antennaware at contesting.com
Subject: Re: [Antennaware] center loading versus ground loading

Gary,

The Battlecreek is a good antenna. However, It looks like a lot of work
though to get the tubing lengths correct before and after the 40 meter trap
as well as to tune the 160 meter wire.

Here is two band vertical that is easier to tune up. It is for 80 and 160
meters and it tuned from the base. Put up the antenna one time and tune at
the base. No relays. Direct feed with coax.

We can write an article on the antenna for QST, CQ, or AntenneX if you'd
like. Here is the antenna:

*160 meters:*
A 67' mast. This can be the long vertical kit from DX Engineering (about
$200).  On top is a top hat consisting of six 0.5" aluminum tubes 6' long.
Right below the top hat is a 70 uH inductor. It is made of 2 inch PVC pipe
with close wound #14 THHN wire (from the hardware store). To adjust it to
resonance on 160 meters a 10 uH base coil is adjusted.

The top hat mass can be reduced by using the DX Engineering top hat with the
long spokes. The inductor will need to be sized for this. I can do this in
EZNEC.

*80 meters:*
A 64' wire spaced 2' from the mast. It is base tuned with a loading coil.
About 2 uH. The bottom of this coil connects to the bottom of the 160 meter
tuning coil. The coax attaches there.

Put up the vertical. Tune 160 meters. Tune 80 meters. Done.

    Dave WX7G

On Sun, Jan 31, 2010 at 1:23 PM, aa4nn <aa4nn at earthlink.net> wrote:

> HI Gary,
> All you need do is emulate the Battle Creek Special.
> You can google to get specifics.  The BCS uses only
> one wire to top load for 160m and only one wire to top
> load for 80m.  Excellent antenna...no switches, no tuning,
> just change bands and go.  If you are unable to find
> specs, let me know.
> 73 & all the best.
> de Joe, aa4nn
> Lake Wylie, SC
>
> ----- Original Message -----
> From: "Gary K9GS" <garyk9gs at wi.rr.com>
> To: <antennaware at contesting.com>
>  Sent: Sunday, January 31, 2010 2:41 PM
> Subject: Re: [Antennaware] center loading versus ground loading
>
>
> I have been contemplating an antenna design to cover 40, 80, 160M.
> Basically ~32 ft of aluminum tubing/mast, a trap, then more tubing/mast to
> ~60 ft (possibly using a capacity hat to tune on 80M) and then a second
> trap
> above the capacity hat with a T-top loading wire to tune on 160M.  My goal
> would be no switching/control lines at the antenna.  I work almost
> exclusively CW so I don't need to cover the entire 80/160M band.
>
> Thoughts??
>
> 73,
>
> Gary K9GS
> ++++++++++++++++++++++++++++++++++++++++++++++++
> K9GS
> Gary Schwartz           email: k9gs (at) arrl.net
> Check out K9NS on the web: http://www.k9ns.com
> Society of Midwest Contesters (SMC)     http://www.w9smc.com/
> GMDXA http://www.GMDXA.org <http://www.gmdxa.org/>
> ++++++++++++++++++++++++++++++++++++++++++++++++
>
> ----- Original Message -----
> From: "Art Trampler" <atrampler at att.net>
> To: <antennaware at contesting.com>
> Sent: Friday, January 29, 2010 10:48 PM
> Subject: [Antennaware] center loading versus ground loading
>
>
> I live on a fairly small lot and use a Hy-Gain AV640 for 40 through 10 and
> currently have no antenna for 80 or 160.
>
>
>
> My backyard is about 90 x 70 but has some ill-placed and ill-shaped trees
> for either wire antennas or a tower.
>
>
>
> So I am thinking of another vertical, but this one ¼ wave with a radial
> field.  I would like to get 80 and 160 out of it.  I don't mind having to
> guy it, or even having to pour a concrete base for it.
>
>
>
> My first thought is to use aluminum irrigation pipe as others have, and
> have
> about 60 to 65 feet of it, an insulator and inductor and high voltage
> relay,
> and then perhaps 15 to 20 of much smaller aluminum tubing, with a sloping
> capacity hat of four wires going partially down the four top guys.  I
don't
> know if I could get away from the relay, and put up a trap instead but am
> wary of using a true trap (coil & capacitor) rather than just a large,
high
> Q coil.
>
>
>
> As you can see this idea is full of possibilities and mechanical
drawbacks,
> so the question is, is there that much to gain from the center-loaded
> design
> with capacity hat, versus a switchable tuning network at the base of the
> antenna?
>
>
>
> Your input is appreciated.  I am hoping to make this a summer project and
> reward myself with 80 and 160 in the winter.
>
>
>
> 73,
>
> Art
>
>
>
> Art Trampler, KØRO
>
>
>
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