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help with an attic antenna design

Discussion in 'Amateur Radio Antennas' started by Dutchman II, Jan 25, 2021.

  1. HomerBB

    HomerBB Sr. Member

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    It may be too late... at least for me. ;)


     

  2. Dutchman II

    Dutchman II New Member

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    Have you ever experimented with taking a wire and making several large loops, say 12 feet across in the shape of a hexadecagon, and then spiraling the wire downward so the loops were 10 or so inches apart, having 7 loops in total ? 7 loops would be around 263 feet, that would hit the 80 meter band, if it worked.

    Just trying to think outside the box, being close to circular that is
     
    #17 Dutchman II, Feb 7, 2021
    Last edited: Feb 7, 2021
  3. HomerBB

    HomerBB Sr. Member

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    Nope. Never done any circular polarity stuff.
     
  4. Dutchman II

    Dutchman II New Member

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    That makes two of us.

    I am curious as to how they expect you to build a full wave vertical circular loop ???? A horizontal hexadecagon is doable.

    https://rechneronline.de/pi/hexadecagon.php
     
    #19 Dutchman II, Feb 8, 2021
    Last edited: Feb 8, 2021
  5. Beetle

    Beetle Sr. Member

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    Attic antennas seem to work acceptably for some, but I have to ask about metallic structures like water/gas piping, foil faced insulation batts, home electrical / TV wiring and cabling and so forth.

    The antenna you finally decide to build and install may be fine; just remember to watch for the little things.
     
  6. Dutchman II

    Dutchman II New Member

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    Insulation in the floor, bare rafters above, cast iron stack pipe around 9 feet away, no electrical wiring above the attic floor, no TV wiring or cabling. The attic peak is probably close to 9' high.

    That is the thinking, build as precise as possible paying attention to the little things, then it is what it is.
     
  7. Dutchman II

    Dutchman II New Member

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    Still not exactly understanding here, using the 11 meter antenna as an example.

    If the antenna (radiator) I construct is built as close to precise as possible by adjusting the length of the wire so that the wire resonates mid-band then that means that most of the energy that reaches the wire will be radiated outward as an radio frequency energy wave.

    If I construct a ladder line feed, again as close to precise as I can, the ladder line, because it is a balanced component, will help prevent any energy that was not radiated by the antenna from traveling back down the ladder line feed and back into the transmitter.

    At this point, if I use an antenna tuner with a balanced input then the antenna tuner will match the 50 ohm transmitter impedance to the ladder line/antenna impedance regardless what that impedance is, within a certain range, is there a large loss of energy matching these two opposing impedances, or not ?

    Question, what happens to the energy that is not being radiated from the wire that was created from the transmitter ? At what points in this particular antenna system is this energy converted to heat, assuming this is what happens to the energy ? Seems like the goal here is to prevent as much of the energy created from the transmitter from being turned into heat on the transmitting side of the system and to radiate outward as an energy wave.

    I went ahead and purchased an ATR-30, priced well in good condition, I was bidding on an ATR-10 on Fleabay but was outbid, hoping that the ATR-30 is not too big for my use with lower power. I wanted to go manual tuning figuring less likelihood of noise being introduced into the system, hopefully this was not a mistake.
     
    #22 Dutchman II, Feb 16, 2021
    Last edited: Feb 16, 2021
  8. Riverman

    Riverman Old Member

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    I have all of that plus my home’s AC/Heating unit and box upon box of Christmas decorations and the such. Despite this, I’ve always had good luck with attic antennas. Keeping them above all that stuff helps. The only one that didn’t perform well up there was my Tak-tenna.
     
  9. The DB

    The DB Sr. Member

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    The antenna tuner, when adjusted properly, creates something called a "conjugate match", which is technical jargon for letting the power from one side (the radio/amplifier side) pass while reflecting the power coming in from the other side (the antenna side) back towards the antenna. This is what happens to that extra power that is reflected from the antenna, namely it gets sent back towards the antenna. If you want to know more I highly recommend looking up a freely available .pdf file called "Another Look at Reflections" by M. Walter Maxwell.

    The reason ladder line and other forms of balanced feed line is used is when it comes to losses is the worst of them, 300 ohm twinlead, has about the same loss characteristics as what some see as the "almighty" LMR-400, and the best, a well made ladder line, makes LMR-400 look like RG-58 in comparison. When working with antenna tuners where there is a high SWR between the antenna tuner and the antenna, feed line losses also increase, so this more efficient feed line and its better efficiency pays back in spades.

    Most antenna tuners aren't actually inefficient, unless they are used near the edges of their limits, or you overpower some component within it. At worse, they are only slightly less efficient than the specialized antenna tuners at the feed point of antennas (ok these are more commonly called matching circuits, but they do the exact same thing as antenna tuners in the exact same way, and in fact are sometimes the exact same circuits.)

    Antenna tuners do have some losses to heat, but even when running large amounts of power they don't tend to warm up enough notice, so I woudn't worry about it unless the case the antenna tuner is in warms up noticeably.


    The DB
     
    Slowmover likes this.
  10. Dutchman II

    Dutchman II New Member

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    Very happy with the antenna tuner, although I never owned one before and I have nothing to compare it to, it seems to work good. Experimenting on the 11 meter band (with a magnet mount antenna on a washing machine), I have the " transmitter " and " antenna " capacitors adjusted to a fixed position, I can swing the inductor dial from the 11 o'clock position (channel 1) clockwise to the 9 o'clock position (channel 40) and have a flat match (according to the meter on the tuner) on every channel, I can also achieve maximum output power (according to the meter on the tuner) on every channel as well, however, I only have one jumper cable so I am unable to connect another meter to verify these readings.

    Odd thing is, with this adjustment the output meter on the radio (TRC-490) also peaks to near maximum ( 80% of scale), however, with different settings of the capacitors and the inductor I can have a flat SWR, according to the meter on the antenna tuner, and a high power output, according to the meter on the antenna tuner, but the output meter on the radio will only read about 40% of scale ?

    Have been busy working extra hours to pay for all of this stuff so I have not had a chance to do the antenna build, yet, but so far I have a good feeling about this working well. Ordered some Browning BR-8X jumper cables to interconnect the radio and tuner and an external power/modulation/SWR meter purchased off Ebay, price of this project really jumped up quick.
     
    #25 Dutchman II, Feb 23, 2021
    Last edited: Feb 23, 2021
    Slowmover likes this.

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