[OKDXA] Dipole Antenna Question

[kd5gho]

Okay I hafta ask.
say our home brew ladder line hainging from the center insulater is
pruneable, and it is.
Would their be any way to tune the little bugger remotly?
Say their are 2 pullys sort of like a block and tak, and the bottom pullys
were able to roll the ends of our home brew ladder until we hit the sweet
spot?
Just sounds to simple.
Q#2: a dipole should be about 75 ohms at the feed point?
So changeing the spaceing of our spreaders will change the feed point
resistance?
Thies questions make the toss and tune method sound okay, but we all love to
play and learn.
For sure wire lingth tuned for res freq = RX db.
Ok now on to Daves Rombic farm.
Jim   ad5kd


-- Original Message -----
From: "Nelson Derks" <ac5up@vei.net>
To: <okdxa@mailman.qth.net>
Sent: Thursday, October 31, 2002 9:15 PM
Subject: Re: [OKDXA] Dipole Antenna Question


> > I have $20 worth of wire and a 300 foot lot.
>
> Here's your plan for World Domination on 40 Meters...
>
> Buy a 500' spool of 10 gauge solid insulated THNN house wire from your
> favorite hardware mega-store. That's about a $40 bill, but if you have
220'
> of good sturdy antenna wire on hand, you can skip that part. Divide 1,500
by
> the absolute lowest frequency in MHz of the band you're interested in.
Let's
> say 1500 / 6.9 = 217.4' so you'll cut 220' of wire. Find the exact center
of
> this wire and cut it again. That's your feed point. Then you'll divide
1,200
> by the frequency in MHz of the band segment you're most interested in.
Let's
> say 1200 / 7.1 = 169', but since you don't like dealing with fractions
(and
> it really doesn't matter), you'll arrange the center insulator so you have
> 170' of wire across the horizontal top section. The balance of your wire
> will hang from the center feed point and be arranged into something
> resembling ladder line.
>
> A 10' length of 1/4" C-PEX plastic tubing (plumbing aisle, it's used to
hook
> up water coolers and such) runs about $4.00 and can be chopped up into
1.5"
> spacers with a tubing cutter. Cut plenty of them. You'll also need a bag
of
> 6" black nylon Ty-Raps that you'll thread through the C-PEX spacers and
> cinch around the two wires you're turning into a ladder line. Once you
have
> all of that done, haul the wire up to a comfortable working height with
the
> bottom of the feeder maybe 5' off the ground (4' if you're N5UW, OKDXA Ham
> Of The Year, 2002). Connect your 1:1 current Balun to the feeder (Reisert
or
> Guanella type), then run any length of coax back to your rig.
>


> Key up at the absolute bottom of the band (or maybe a little lower if you
> dare) and take an SWR reading at the rig. It should be 1:1. Prune 2" or so
> off the bottom of the feeder and check your SWR. If it's still 1:1,
repeat.
> As soon as the bottom of the band shows any SWR rise, no matter how
slight,
> stop pruning and check the top of the band. If it's a little higher than
you
> like, prune just a hair more but keep a close eye on the bottom end.
You'll
> find the low end has a very steep SWR rise while the mid to top segment
has
> a much slower SWR rise. A slip of the cutters can ruin the CW section
before
> you realize it, so go slow and watch the bottom end 'real close'.
>
> Weatherproof your connections, haul the wire up to its final height, then
> wait for that magic moment when you hear K8FU trying to bust a pileup for
a
> card he really, really wants...
>
> Feel free to key up and show Mr. Frogg exactly how it's done.
>
> As a bench project, you might consider whipping together a simple battery
> charger that connects to your antenna switch and tops off the HT NiCd
> battery while you're not on the air. You'll have a volt or three to play
> with at the PL-259 and a voltage tripler should get you there, so I say
'go
> for it'. You'll also find the AM broadcast band has a bunch more stations
> than it used to, even during the day, and at night the weak ones will be
20
> Over... Big wires are truly amazing.
>
> - AC5UP
>
> _______________________________________________
> OKDXA mailing list
> OKDXA@mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/okdxa