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#17 03-13-2012, 10:57 AM

LOL , i didn't get the memo

Needle Bender · #18 03-13-2012, 11:03 AM

Those antennas you mentioned are current-fed so current should be highest at the feed point, diminishing more as you go away from that point toward the ends of the half wave or car body.

A bottom-fed 1/2 wave is voltage fed and that's why the feed point impedance is so high, around 2000-5000 ohms.

Marconi · #19 03-13-2012, 03:53 PM

Quote:

Originally Posted by BOOTY MONSTER

since the merlin base antenna and most mobile antennas are less than 7 ft tall above their feed-point ...... does that mean the current is highest 2 feet (or lower on shorter verticals) below the feed-point on the ground planes or car body ?
does it mean when my 3 ft lil will in on the 6 ft high roof on my vehicle that the current is highest just under the tires ? if it were on a trunk , would it be 3 ft under ground ?

Your reasoning here is silly, and you missed NB's point completely. Go sit in the corner and put on the dunce cap.

#20 03-13-2012, 04:02 PM

can you explain why it's silly and what point i missed ?
BTW , i'm always in the corner wearing my dunce hat

Needle Bender · #21 03-13-2012, 04:02 PM

Quote:

Originally Posted by Marconi

Your reasoning here is silly, and you missed NB's point completely. Go sit in the corner and put on the dunce cap.

LOL!

Quote:

Originally Posted by BOOTY MONSTER

can you explain why it's silly and what point i missed ?
BTW , i'm always in the corner wearing my dunce hat

Is that the one you stole from me? - HEY, I need it BACK!

Quote:

Originally Posted by Needle Bender

isn't the current highest about 1/4 wave down from the top?

I was referring to the 22 1/2' 5/8 wave Marconi had modeled.

#22 03-13-2012, 04:28 PM

i earned the dunce hat today

you can have it back when you earn it

#23 03-13-2012, 07:20 PM

from OGP's link
G3ZPS HF radio antennas

"The 'Zepp' name came from the use of the antenna on Zeppelins in the 20's and 30's. Its a non resonant antenna which provides arounnd 3dB of gain over a dipole if mounted at the right height. Around 0.6 of a wavelength is ideal .

Each leg of the Zepp is 0.64 Wavelength (5/8) and must be fairly accurately cut, the formula I use is 599/f in MHz."

i thought antennas were supposed to always perform better when they were resonate . and this one is supposed to have more gain over a dipole than a 5/8 or .64 . the formula looks to be a bit shy of whats commonly thought of as a 5/8 WL , let alone a .64 .

599 / 26.965 = 22 ft 2 1/2 inches for channel 1
599 / 27.405 = 21 ft 10 1/4 inches for channel 40

it ain't easy being a dunce

Needle Bender · #24 03-14-2012, 02:02 AM

Quote:

Originally Posted by BOOTY MONSTER

from OGP's link
G3ZPS HF radio antennas

"The 'Zepp' name came from the use of the antenna on Zeppelins in the 20's and 30's. Its a non resonant antenna which provides arounnd 3dB of gain over a dipole if mounted at the right height. Around 0.6 of a wavelength is ideal .

Each leg of the Zepp is 0.64 Wavelength (5/8) and must be fairly accurately cut, the formula I use is 599/f in MHz."

i thought antennas were supposed to always perform better when they were resonate . and this one is supposed to have more gain over a dipole than a 5/8 or .64 . the formula looks to be a bit shy of whats commonly thought of as a 5/8 WL , let alone a .64 .

599 / 26.965 = 22 ft 2 1/2 inches for channel 1
599 / 27.405 = 21 ft 10 1/4 inches for channel 40

it ain't easy being a dunce

Well, since the Germans probably used insulated, braided wire for strength & shorting resistance, I bet the velocity factor made it electrically longer than .6, perhaps .64?

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