Posted by: Rivai | January 5, 2009

KA3DPW – Sobat Dari Negeri Seberang Samudra

Membaca email hari ini diwarnai dengan tawaran simpatik dari sobat saya John Harp KA3DPW untuk membantu saya menghiasi blog ini dengan bantuan cuma-cuma tanya jawab mengenai apa saja yang John bisa bantu jawab. Tentu ini sebuah tawaran yang luar biasa, terutama untuk membuat blog YB3TD ini semakin menarik dan berguna bagi pembacanya. Dan tentu saja saya terima tawaran itu dan segera saya post hari ini meski hari ini bukan jadual saya melakukan posting di blog ini.

Saya memulai bertukar email dengan John KA3DPW lewat milis mengenai antenna vertikal dimana John sering sekali membantu teman-teman disana dan bertukar pikiran. Pertemanan dilanjutkan via japri dengan berbagai topik. John tinggal di Pennsylvania state (semoga bener nih nulisnya) dan berlatar belakang suku beraneka ragam. Memang dia nampak sebagai kulit putih, tetapi menurut dia, dia adalah contoh dari sebuah kerukunan antar ras.

John senang dengan radio-radio yang komponennnya masih besar-besar (radio tahun 80 an) dan dia memiliki koleksi skema-skema radio Kenwood cukup lengkap. Meskipun bukan seorang montir radio, KA3DPW senang kotak-katik sendiri dan membangun ulang sendiri  radio lamanya. Hamshack dibangun berdasarkan tema green living, yaitu sebanyak mungkin menggunakan bahan-bahan alam dan bahkan power supply didapat dari solar panel.

Bagi temen-temen yang kepengin berbagi cerita dengannya, bertanya ataupun sekedar say hello ke John, silahkan menuliskannya di bagian komentar. Pake Bahasa oke karena akan saya terjemahkan untuk John, pake english malah lebih baik. KA3DPW sudah janji akan merespon semua. Ngga usah sungkan ya, kayak sama siapa aja sih.


Responses

  1. Dear John & OM Rivai, I wanna install some vertical antenna for WARC band, especially on 30m, let me inform you also that my space is not allowed me to spread the radial or counterpoise.
    Sure I need the antenna for dx-ing.
    Any information will be much appreciated.

    ’73 de yb2ecg-Jon.

  2. Greetings and yes I will try to answer your questions.

    I am answering by translation from english.

    I am not perfect but will do my best for you. John.

  3. you have decided on vertical polarization. Do you want ground mounted vertical, a vertical up in the air with a few radials, vertical dipole or vertical polarized loop? These are the most common choices.

  4. Dear John, due to my location maybe the suitable antenna for me is ground mounted vertical and I think radials is not my options.
    My primary band actually is WARC but 30m is my first choice.
    Thanks for any helps.
    I’ll much appreciated.

    73 de yb2ecg-Jon

  5. You chose the ground mounted vertical which will need an area at least 15 meters by 15 meters.

    It may be made smaller but may compromise your signal strength some.

    There are other ways to deal with this. Such as many radials cut to smaleer lengths and the radiating element can be made smaller also by using loading coils or capacity hat or using the T or -L antenna.

    Radials may be placed under the soil instead of on top.

    You can also raise the antenna high enough to use just a few radials so it is above your head. This may work a little better sometimes.

    Riv says you like contesting. That tells me you like a challenge.

    Do you live in an apartment or do you operate portable? There are options for these.

  6. Dear John,
    Let me tell you that I have no 15×15 area, my area is only 14x8m.

    I just look at to WA3WSJ’s Black Widow Vertical antenna and I believe it’ll compromise with my location.
    What’s your opinion, John.
    Thanks for any informations.

  7. If you are interested in 30 meters it should do well enough in a compromise.

    It has other bands. and for the more closer equatorial locations where the higher frequencies open more frequently it should serve you well.

    For 40 meters you might look a little high on SWR for a solid state radio but if you have a tube final reciever the SWR should be reasonable.

    I believe you will find if you give this antenna a good ground in that 14×8 area as long as you keep the surrounding objects as far away as you can, you should be ok.

    Objects coming in close will absorb some energy from the radiation pattern and may cause a mismatch for your feeding. This could be bad or it might seem to help a little.

    Give it a good ground. The better your ground the better you’ll radiate the signal.

    Being on the ground or just under the soil will work well and that you will find you won’t need to prune your radials to resonance. That’s a plus for you.

    It’s portable which is another plus it has for you. You can take it in when the antenna is not in use.

    16 wave radials placed just on the ground or better just under the soil will be 3.75 meters and you will want many of them for a good ground.

    But better yet, buy some metal screen and bury it. It will seem easier than just laying one radial at a time or you might just let the grass grow a little higher through the screen and cut the grass a little higher than you normally would. In a year you would be suprised at how the grass will pull the screen down to the soil.

    Don’t just go for matching SWR. Go for lowest radiating resistance you can get. Here’s why.

    That screen is returning small currents as the radiating element radiates. So give it a good match at the feed point instead and let your ground radiation resistance go as low as you can get it.

    Remember that it is a physically shortened vertical with a base loading coil and that you will want a low loss coilwith a high Q to minimize loss.

    In this design being as large a radiating element, you probably will be ok.

    Feed it with a good coax and remember that the 30 meter band will be a narrow band. It’s only 10 mhz to 10.15 mhz. You probly won’t need a tuner for this but you could place one under the radiator if 30 meters is all you will need. Buy a cheap one and weather proof it.

    Here is the reason. It is better to adjust it at the base to minimize coaxial line loss for using mono band on 30 meters. The better the ground the better your signal will get out. Likewise the lower the ground resistance and the farther you will be away from 50 ohms. Also, the shorter the radiating element is the lower the radiation resistance will become.

    This is not to say you cannot get out as well, many time a shorter well designed antenna can work almost as good.

    A good operator can do well with a setup like what you are considering. You being a contester knows this all to well.

    Antenna tuner good ground and a good ground plane this antenna will serve you well.

    Only one drawback I see is that this antenna is that it can only withstand winds up to 40 miles an hour. That is not very strong.

    My full size vertical for 40 meters is 9.75 meters tall, hinges is self supporting and withstands winds to 110 miles an hour. I live on top of the highest point in my area and I get wind gusts that may get to 90 occasionally. A flag is usually moving here and you will almost always feel air flow on your face. A gale force wind will likely ruin this antenna. If a flag shouldn’t fly you will definitely want this down fast.

    Make that antenna more able to with stand high winds and you should do well. Otherwise, put it up watch the weather as you operate and take it down when you are done.

    I will soon be sending Riv some pictures of my vertical and I invite you to look at them Jon.

    I spent some money and it took me 3 years from concept to actal operation. I am still improving on it. But this one will defintely stand the test of time for at least one full sunspot cycle.

    So look at mine go for yours consider my advice on your antenna and enjoy the QSO’s. For the amount of maney you will invest, take good care of it and it will serve yor compromised situation well.

    Hopefully I talk with you on the air some time.


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