Cebik antenna and other short limited space dipole antennas (was:
RE: Re: [SECC] K4OGG, CWSS)
ku8e at bellsouth.net
ku8e at bellsouth.net
Tue Nov 9 09:14:51 EST 2004
I think he is talking about a dipole fed with 50 ohm coax.... not 450 ohm open wire. Open wire has little or no loss....
Jeff
>
> From: "Matt Lee, K4AQ" <Matt at HiWAAY.net>
> Date: 2004/11/08 Mon PM 08:26:39 EST
> To: <ku8e at bellsouth.net>,
> "'Tommy'" <aldermant at alltel.net>
> CC: <SECC at contesting.com>
> Subject: Cebik antenna and other short limited space dipole antennas (was: RE: Re: [SECC] K4OGG, CWSS)
>
>
> Here is W8JI's take on the noted subject:
>
> http://www.w8ji.com/short_dipoles_and_problems.htm
>
>
> Some key points:
>
> "While pattern looks excellent on higher bands, lowest band performance
> of a short dipole (in this case 88 feet long on 80 meters or 44 feet
> long on 40) certainly leaves a great deal to be desired when feedline
> and tuner losses are included. It isn't the efficiency of the antenna
> that is in question, it is feedline efficiency and high voltages in the
> matching system that become problems.
>
> "Short dipoles and verticals will almost always model with very good
> efficiency, because a model is a perfect lossless system if we do not
> include feedline losses and matching losses.
>
> ".... (It makes very little difference by the way if the balun is on the
> tuner input. Don't think moving a current or choke balun to the input of
> a tuner is a solution. The balun is under the same common mode
> stresses.)
>
> "The lower limit in size of a multiband dipole, before feed system and
> matching losses move to the edge of severe problems, is about 200 feet
> on 160 meters, 100 feet on 80 meters, 50 feet on 40 meters, and so on.
>
> "A good rule of thumb is to multiply the band in meters by 1.25. The
> result is the minimum dipole length you can use without using a good
> matching system in, at, or near the antenna!
>
> "As an antenna is shortened from that length, losses in the feed system
> (even what Hams consider a good one) climb rapidly. 88 feet is just too
> short for an 80 meters antenna, because...it is at the limit of what
> most tuners will match. It also places most tuners at their power limit
> at a few hundred watts of applied power.
>
> (Take heed of the above paragraph if you are running HP! --Matt, K4AQ)
>
> "The optimum length for a multiband dipole is near 1/2 wl on the LOWEST
> band, and the optimum open-wire feedline length is any odd multiple of
> 1/8th wavelength on the lowest band. This means an optimum 80-meter
> dipole would be about 125ft long, and the feedline would be 25-30ft,
> 75-90ft, or 125-150ft long. The longer the feeder, the more likely you
> are to having to trim it for optimum tuner performance.
>
> "Most tuners like to see impedances HIGHER than 50 ohms, and inductive
> loads at low impedances. Pi's and L's are NOT a solution to matching
> problems. They actually are significantly more restricted in matching
> range than a conventional T using the same general style and quality
> components."
>
> --
> Matt Lee, K4AQ
> Atlanta, GA USA
> <K4AQ at arrl.net>
>
>
> > -----Original Message-----
> > From: secc-bounces at contesting.com
> > [mailto:secc-bounces at contesting.com] On Behalf Of ku8e at bellsouth.net
> > Sent: Monday, 08 November, 2004 11:40
> > To: Tommy; SECC at contesting.com
> > Subject: Re: Re: [SECC] K4OGG, CWSS
> >
> >
> > Tom,
> >
> > If you are using a 130 foot antenna with open wire feeder....
> >
> > On 80 meters it acts like a dipole
> >
> > On 40 meters if is two half waves in phase broadside to the
> > antenna giving you about 3 db gain over a dipole
> >
> > On 20 meters you have a clover leaf pattern.
> >
> > On 15 meters you have about 8 lobes
> >
> > On 10 meters you have a whole bunch of lobes !!!
> >
> >
> > If you can only put up one antenna this is the one. you
> > could short the feeders together and run it as a "T" on 160
> > and put down some radials. You should get out good enough
> > (running the amp) to be dangerous !!!
> >
> > See http://www.cebik.com/88.html
> >
> >
> > 73, Jeff
> >
> >
> > >
> > > From: "Tommy" <aldermant at alltel.net>
> > > Date: 2004/11/08 Mon AM 10:37:44 EST
> > > To: <SECC at contesting.com>
> > > Subject: Re: [SECC] K4OGG, CWSS
> > >
> > > My Titan 3 blew up, sitting in stand-by on the desk. Just got it
> > > back from Ten Tec on Thursday.
> > >
> > > When testing it, could only get 1200w max into the dummy load.
> > > Taking it apart and inspecting it, I found the same old problem of
> > > poor assembly. A screw from the tube section was protruding to the
> > > below compartment, partially shorting out the RF input line on a PC
> > > board. I went through this with Ten Tec back in November and found
> > > the problem after they told me "you must have a bad interface coax
> > > cable". Still an on-going problem with practically NO QC at Ten Tec.
> > >
> > > Anyway after replacing the screw, I still expected to have problems
> > > with the amp, but it just sat there, purring at 1500w.
> > >
> > > Was going to add an HF (20&15m) antenna, but the way this silly 80m
> > > dipole is working...WHY?
> > >
> > >
> > > Tom - W4BQF
> > >
> > > ----- Original Message -----
> > > From: "Macie, Gordon" <GMacie at innotrac.com>
> > > To: "'Jay Pryor'" <jpryor at uga.edu>; <SECC at contesting.com>
> > > Sent: Monday, November 08, 2004 10:13 AM
> > > Subject: RE: [SECC] K4OGG, CWSS
> > >
> > >
> > > > I ran my amp also. Strange experience people actually hearing me.
> > > > I had very few fills compared to what I'm use to.
> > > >
> > > > Gordon
> > > >
> > > > -----Original Message-----
> > > > From: Jay Pryor [mailto:jpryor at uga.edu]
> > > > Sent: Monday, November 08, 2004 10:05 AM
> > > > To: SECC at contesting.com
> > > > Subject: [SECC] K4OGG, CWSS
> > > >
> > > >
> > > > This was my first part-time CWSS in a long time. And the first
> > > > time I have
> > > > ever entered any contest in the high power category. But there's
> > > > no question that my score is higher than it would have been
> > > > otherwise. Anyway, it took me a while to figure out how to hook
> > > > up and
> > > > load up the amp. I really don't use it much. After I got it up
> > > > and
> > > > running though I enjoyed a laid-back SS. It was good to run into
> > > > many SECC folks, and other contesters who are "regulars."
> > > >
> > > > Here's what it looked like:
> > > >
> > > > BAND Raw QSOs Valid QSOs Points Mults
> > > > __________________________________________________
> > > >
> > > > 80CW 64 64 128 30
> > > > 40CW 48 48 96 18
> > > > 20CW 103 103 206 14
> > > > 15CW 95 95 190 9
> > > > 10CW 12 12 24 1
> > > > __________________________________________________
> > > >
> > > > Totals 322 322 644 72
> > > >
> > > >
> > > > Final Score = 46368 points.
> > > >
> > > > 73,
> > > >
> > > > Jay/K4OGG
>
>
>
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