zaterdag 2 mei 2015

Cylinder dipole

I thank Franck F4HFQ for the link from Radioamateur.org to this Blog entry.  Franck writes:

Bert, PA1B, a fabriqué un dipôle cylindrique en remplacement de son antenne défectueuse pour achever un contact QRPp rendu difficile par cette dernière. Résultat ? 1000miles par Watt au premier QSO.

 Red Bull  gives you wings 
This a a catchy one liner, I could NOT resist, LOL.
Please notice that the Cylinder dipole is NOT a joke, but a very short, but working antenna.

Test antenna
A few months ago I built an experimental cylinder dipole with two  Red Bull  cans and a coil, that works as an impedance transformer, to test the properties of symmetrical feeding.
By using symmetrical feeding, the cable doesn't radiate and the cable has no hand effect.

Damaged inverted V
The ribbon of my inverted V is damaged by the wind.  I wanted to make a few nice QSO's in the ARI DX contest, but I was very disappointed by the inverted V. The SWR is constantly changing, even with the slightest bit of wind. The inverted V cracks when the ribbon moves, both on receive and transmit.
I tried to make a QSO with II6T with 360 mW on the damaged inverted. The operator repeated my call immediately correct, but because of the cracking twin lead, my exchange 001 was not received in Italy. Even when I increased my power to 3.6 W, the cracking twin lead spoiled the fun.

Indoor Cylinder dipole
Then I decided to try to use the  Red Bull  antenna. I clamped it between my book shelf.
I connected a 300 ohm twin lead between the coil of the antenna and the symmetrical tuner.
I tuned the antenna with the symmetrical tuner for the lowest SWR.
The resonance frequency of the cans and the coil lays between 21 to 28 MHz, but the  Red Bull  antenna could be tuned easily to 14 MHz, using a symmetrical tuner.

Into the ARI CW contest
After a while I heard II6T again, but now on the cylinder dipole, I answered their CQ with 360 mW. I got an immediate response and the QSO was easily made. WOW.
In total I made about 10 QSO's on the  Red Bull  antenne, with a power of 360 mW to 3,6 watts in the rest of the ARI DX contest.
Please read the interesting details on this amazing 12 inch long  Red Bull  test antenna,
that I used in the ARI DX contest 2015  (Click)

1000 Miles per Watt
Later I realized, that the first QSO with the cylinder dipole is good for 1000 Miles per Watt. hi.

Capacity
Cylinder dipole 4 m above ground @PA1B's shack
The magic of the Cylinder Dipole lies in the large capacity of the the two cylinders.
The coil and the capacity of the cans determine the resonance frequency of the antenna.

Auto transformer
The coil acts as impedance transformer. The 300 ohm ribbon is connected to 2 points on the coil that are 1 turn apart. The coil it self has 14 turns. 

Symmetrical feeder
The twin lead is connected to two connectors one turn apart, at the middle of the coil, to feed the dipole symmetrically
I chose for the symmetrical construction to avoid  hand effect of the ribbon. 


Connections, one turn apart
The Cylinder dipole

7 opmerkingen:

  1. Mooi verhaal Bert.

    Deze antenne werk, en ook nog met qrpp.

    73, Tjeerd
    PA3GNZ

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    1. Hallo Tjeerd, de signalen op de inverted V zijn sterker dan die op de Cylinder Dipole. Daar zijn 4 redenen voor: 1) het hoogte verschil.. de CD op 4 m en de Inv.V op 12 meter. 2 De inverted V is rondom gevoelig en de CD hangt voor sommige richtingen niet optimaal.3) De CD is minder gevoelig door de kortere lengte. 4) Deze versie is niet getuned voor 14 MHz. De spoel is te klein.
      Ik vind het mooi dat hij het doet. 73, Bert

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  2. Zo zie je maar dat alles straalt. Zelfs een paar redbull blikjes. Wel een mooi compacte antenne. Kan je hem niet ergens aan het plafond hangen? Of op zolder? Als noodantenne mocht de inv-V het begeven in de toekomst. Neem aan dat je de inv-V gaat repareren? Of hou je het maar op deze antenne? 73, Bas

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    1. Hallo Bas, Ik was dat gekraak zo zat, vandaar deze wanhoops sprong.
      Ik kon op de inverted V geen QSO maken met verschillende Italiaanse stations. Zelfs niet met 3,6 W.
      Het is een experimentel opstelling en niet afgestemd op 14 MHz. De spoel is te klein.
      Later kon ik wel met 360 mW op de Cylinder Dipole deze zelfde Italiaanse stations werken.
      Ik had niet verwacht dat ik hem met de tuner kon afstemmen. Ik moet nog verder experimenteren.
      Maar nu even niet. Ik ben de laatste tijd wat sneller moe. Dus doe ik rustig aan.
      73, Bert

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  3. Bert,

    Interesting antenna. Is there a formula? how did you determine that you needed 14 turns? How do you determine the spacing for the cans?
    tnx fer yer FB blog, OM

    73,
    DaveL
    KF7JAF

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  4. Hello Dave, Thank you for your fine response. I used this antenna as a test feeding at the center. This feeding hes no hand effect as is the case in EH-antenna's. The test was not done at 14 MHz. I choose 14 turns.
    I will come back on the antenna later. 73, bert

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  5. Hello Dave, I did further measurements on this Red Bull antenna. The resonance frequency is 26 MHz. The distance between the cans is equal to the diameter of the can. I can shift the cans back and for'd. The distance is not that critical.
    I now built and operated with a new antenna with 500 ml cans with a length of 38 cm (15 inches) and found out that detuning to a higher frequency can be done more easily.
    With this antenna (tuned to 16 MHz) I operated at 7 MHz, 14 MHz and 21 MHz. hi.
    Above must be: This feeding has no hand effect on the cable.
    I was surprised to work with New Hampshire with the antenna in the shack with 3.6 W.
    Thanks again, 73, Bert

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