Hi Neil,
Yes, absolutely computer modeling. I don't think I ever would have found
that point by experimenting.
It's not exactly 85/15... I think 83/17 or something like that. I don't
recall if the exact measurements are on my web site or not. If not I can
send them to you. Pse write me directly: Rick@dj0ip.de
The modeling was done for me by DJ1AT. He does all of my modeling for me.
I'm a bit of a novice at modeling, he's very good. When I get wild ideas, I
ask him to model them and he gives me the results in short order. Then I go
to the field, build it, then first adjust the overall length and then begin
moving the feedpoint one inch at a time. I found the 80m quite quickly.
Took a bit longer with my 40m OCFD.
Tip: If you want to build multiband antennas, don't full around with an
MFJ-259B or similar. Get yourself a scanning analyzer that can scan the
entire hf spectrum in on go, such as the RigExpert AA-54. You will save
light-years of time that way.
I ran an extensive test on common mode current last summer.
I found that the farther away from the center you move the feedpoint, the
worse problems you get with common mode current. (duh).
When you use such a radical split as I did, it is imperative that you use a
good balun AND also a good 1:1 RF choke directly attached to the balun. The
balun should be dual-core with each transmission line wrapped on its own
separate core. In my case, my power level (600w) and with the antenna in
the clear, a 1:1 Maxwell was good enough. If more power or antenna located
near other objects, it is better to use a 1:1 Guanella.
If you plan to run very high power, you should use 4 cores (piggy back two
pairs) for your balun.
Beware of people selling baluns. Very few have any clue what they are doing
and pass out bad advice.
Best is to build your own. (cheapest too).
If you have never built any baluns, I suggest you begin by reading a couple
of documents (in this order).
1) "Baluns: what they do and how they do it." By Roy, W7EL
2) "RFI Ham" by Jim, K9YC. (read it 2 or 3 times, unless you're a lot
smarter than I am)
Finally, don't let anyone tell you that a good 4:1 balun (for antennas) can
be built on a single core; it can't.
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Neil
Martinsen-Burrell
Sent: Saturday, May 24, 2014 12:20 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] The Next Flagship
Rick,
I have enjoyed the antenna articles on your site before. (Up next for me is
your 40m monoband delta loop.) The 80m OCF article looks very interesting,
but can you say how you found the 85/15 location for the feedpoint? Was it
using computer modeling or by actually moving the feedpoint while measuring
the VSWR? Or, to ask another way, if I wanted to duplicate your multiband
SWR results, how would I proceed?
Thanks again for the nice articles on your website.
-Neil KD0UKC
On Fri, May 23, 2014 at 4:15 PM, Rick - DJ0IP / NJ0IP <Rick@dj0ip.de> wrote:
> My favorites are similar to Carl's:
>
> 1: 130 to 136 foot wire, fed in the middle with openwire
> 2: Off-Center-Fed Dipole such as the one I currently use (see:
> http://www.dj0ip.de/off-center-fed-dipole/80m-ocf/)
> 3: Inverted L, 130 to 136 ft. long as Carl described
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt am Main)
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Carl
> Moreschi
> Sent: Friday, May 23, 2014 11:06 PM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] The Next Flagship
>
> I also agree if I could only have one antenna it would be a 130 foot
> dipole set up as an inverted V and fed with open wire line to an in shack
tuner.
> And my second choice is an end fed 130 wire in an inverted L with an
> outdoor automatic tuner and coax from the tuner to the shack.
>
> Carl Moreschi N4PY
> 58 Hogwood Rd
> Louisburg, NC 27549
> www.n4py.com
>
> On 5/23/2014 4:57 PM, Rick - DJ0IP / NJ0IP wrote:
> > Jim, I can't agree. Sorry.
> > You are not on the same page as I am.
> > You push a resonant antenna, but that's a monoband antenna.
> > You sell the "all band dipole" much too short.
> >
> > YES you are correct about its many nulls on the high bands. They
> > are definitely not as bad as you make it out to be.
> > I've seen your current and past QTH (in Chicago).
> > You are a lucky man. Compliments for making best use of the space
> > available for an antenna farm - especially in Chicago!
> >
> > Many people, possibly most, can have just one single antenna at
> > their
> QTH.
> > They will never have what you have or have had in the past.
> > Many use the non-resonant or openwire fed dipole - the one you say
> > is not a good antenna.
> >
> > You do it a big injustice to say it is a bad antenna.
> > Many experts, including W1ICP (Lew McCoy) and W4RNL (L.B. Cebik)
> > have said "if I could only have just one antenna, it would be the
> > openwire fed dipole."
> >
> > My own experience: go to CQWW DX Contest, "All Time Records" (CW).
> > Do a search on "DJ0IP".
> > I'm on the list as an all time record holder (high power assisted)
> > in one European country, set using this antenna that you claim does
> > not work. My record has stood for over 20 years. You don't set
> > records with antennas which do not work.
> >
> > So yes, there are lots of better mono-band antennas, but I don't
> > know of any multiband antenna that works better.
> > If you do, PLEASE share it with us. I will gladly be proven wrong
> > in this case! (hi)
> >
> > 73 - Rick, DJ0IP
> > (Nr. Frankfurt am Main)
> >
> >
> > -----Original Message-----
> > From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Jim
> > Brown
> > Sent: Friday, May 23, 2014 6:45 PM
> > To: 'Discussion of Ten-Tec Equipment'
> > Subject: Re: [TenTec] The Next Flagship
> >
> > On 5/23/2014 3:06 AM, Rick - DJ0IP / NJ0IP wrote:
> >> I agree with all of that, but you leave one point out. "Openwire."
> >> As you well know, the impedance of an openwire dipole varies from
> >> band to band and can be all over the map, up to a couple thousand Ohms.
> >
> > Rick,
> >
> > I didn't leave it out at all -- it's one of the non-resonant
> > antennas I talked about. This is a lousy antenna, a bad idea. Yes,
> > the Handbook says it "works" on all bands. So does a light bulb. That
"all band"
> > dipole has a pattern that varies widely from band to band, with deep
> > nulls in some directions where there are stations you would like to
work.
> >
> > The place for antenna match boxes is to make a dipole cut for 80CW
> > work on the phone band, to load a random long wire that ends in the
> > shack, to correct for a dipole that isn't quite the right length.
> >
> > I'm a big fan of fan dipoles, which are easy to build, which work
> > really well, and which have very predictable patterns. If you have
> > room for a 20M dipole, you can hang a 20/15/10 fan. Barry at Hypower
> > Antenna Company sells very nice loaded dipoles that also cover 30
> > and
> > 40 and can fit 80M into about 100 ft. That was my low band antenna
> > in Chicago. He makes a version for 160 and 80 with a fan element for
> > 40 that
> also works very well on 30M.
> >
> > 73, Jim K9YC
> > _______________________________________________
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> >
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> >
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