Moonraker antenna?

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Bton-FM
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Re: Moonraker antenna?

Post by Bton-FM » Thu Dec 05, 2019 7:14 am

teckniqs wrote:
Thu Dec 05, 2019 12:18 am
Sorry but what is that supposed to be?? !

....it looks like some kind of Dildo
A very scientific drawing

s2000
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Re: Moonraker antenna?

Post by s2000 » Thu Dec 05, 2019 12:39 pm

I must admit I've always been curious about Harrys antenna, it may be time to try and build one! Just a bit of confusion over some parts..

I know the antenna has to be scaled so the elements and transmission line are the right length for the new freq, what about the 5cm gap? Has that gotta be scaled or is it non critical?

It says on the drawing to connect the coax 15cm from the short (which looks like a 1:4 balun of some sort), are you esentially looking to try and find the 200 ohm point on the 1/4 transmission? Im assuming it would be at a different point for a new freq.

Harry mentions his initial readings were so good he didn't bother tuning, but if you had a poor reading, are you supposed to slide the two elements back and forth on the 1/4 to get the best reading?

I think maybe you could use some kind of braid for a good connection between the elements and the transmission.

Albert H
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Re: Moonraker antenna?

Post by Albert H » Fri Dec 06, 2019 1:58 am

  • The 5 cm gap doesn't really need to be scaled, but on my version, the gap was about 7.5 cm.
  • Yes - you're looking for the 200Ω resistive point on the ¼-wave transmission line.
  • The coax loop is a 4:1 impedance matching transformer.

    At Band II, the bandwidth of the antenna is about 500 kHz. The SWR rises sharply either side of resonance. I think that he's somewhat optimistic with his gain figure, but I find that this antenna far outperforms a twin-stack of dipoles every time. It's also more compact. It also doesn't look like a dipole!

    A friend of mine has been building an end-fed version of this aerial, with groundplanes, and it was only when I pointed out the "Super-J" that he realised what he was doing!
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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Undercover Neckz
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Re: Moonraker antenna?

Post by Undercover Neckz » Sat Dec 07, 2019 8:25 am

I just wonder what it's like to use a rake on the moon?

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