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Need To Homebrew Traps for 40/30 dipole

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WB9SBD, Feb 7, 2011.

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  1. WB9SBD

    WB9SBD Ham Member QRZ Page

    I need to make a trap dipole for 40 & 30 meters. But in an un usual way.

    Yes here are many coaxial trap programs out there and others. But i need the traps to be as light as possible. Power is not to worry about it may see at the absolute most power of 5 watts, and more likely 1 to 2 watts really. but may go as high as 5.

    I have never made a trap dipole before and from what I have been learning, it seems to be mainly a L and C circuit. that has some stray resistance.

    So can low power traps be made from lumped components? like fixed capacitors and home made coils of tiny wire?

    Remember the power is very low.

    and i need these to be as light weight as possible every ounce counts.

    Joe WB9SBD
  2. KA9UCN

    KA9UCN Ham Member QRZ Page

    Yes you can build simple light traps. The question is how durable do they need to be? You start with a fixed capacitor. ( at 5 watts it can be relatively low voltage) I like to use pvc for the coil form but you can use anything non conductive, Styrofoam? Wrap the inductor a bit larger than required and then trim it to resonance. Here is a small program that may help. it will do the math for resonance at a acceptable Q You will have to look for one that will give coil diameter choices to fit your needs.
  3. KH6AQ

    KH6AQ Ham Member QRZ Page

    Pill bottles will work. The cap can be 100 pF and the inductor 2.5 uH. Give me the coil form diameter and I'll use the K6STI coil program to come up with some close-wound coils using thin enameled wire. I'll include the wire lengths beyond the trap to make it resonant on 40 meters.
  4. WB9SBD

    WB9SBD Ham Member QRZ Page

    does the coil diameter effect the efficiency? I'll probably use something like styrofoam for the coil form so almostany diameter can be done.

  5. KA9UCN

    KA9UCN Ham Member QRZ Page

    Coil diameter does have an effect. I have built many traps using 1 ¼ ( aprox. 1 ½ OD) pvc thin wall drain pipe with no.14 stranded wire spaced 1 wire diameter between each winding. I have also used 2 inch pvc with the same spacing for 20 and 40 meter traps. My personal opinion was that the 1 ¼ inch thin wall drain pipe worked best although I never made a side by side comparison. On the 2 inch I used caps and screw eyes. They looked good on the bench but were heavy and made for a lot of sag in the antenna. The 1 ¼ thin wall had no caps on the end only a ¼ inch hole on each end that the wire tied to. They were very light and held up well. I only had them up for about a year. For caps I used duel sided PCB with the edges etched off to stop coronal discharge. The traps held up to over a KW with no signs of arcing. At the time I built them I had no intent of going over 100 watts. You might consider building your traps for at least 100 watts. You will have to use capacitors that will handle that but they are easy to build or cheep to buy. They will not significantly increase the weight.
  6. WB9SBD

    WB9SBD Ham Member QRZ Page

    wattage is not a concern max it will ever get to is 5 watts.

    But this is for a balloon project, where every ounce counts. thats why i'm trying to make them efficient as possible (because of the only 1 or 2 watts) and as light as possible because it's going on one of our balloon flights.

  7. KA9UCN

    KA9UCN Ham Member QRZ Page

    That is great! Good to know that someone is putting this kind of effort in a project for the youth of today. Styrofoam fishing sane floats would work well.
  8. KB9BVN

    KB9BVN Ham Member QRZ Page Terry WA0ITP about the antenna ideas...he works with the Iowa High Altitude Balloon projects. He designed the HF beacon and keyer setup. I bet he'd be glad to help you out.
  9. WB9SBD

    WB9SBD Ham Member QRZ Page

    I don't need that I got a transmitter and an awful cool one at that. it will run RTTY and domino to send out position reports like APRS does, but in those modes, the domino is incredible I have had perfect copy 27 db into the noise where I cant even hear it, and the waterfall barely can see it yet perfect position reports. and this transmitter will do on both bands on 40 as well as 30 meters alternating. I'm just trying to make a dual band antenna. that weighs nothing.

    I'm one of the original guys stat started all this ballooning back in the 80's been doing them for since 1988. done HF beacon flights all the time. just trying to save every ounce for a very special flight.
  10. KH6AQ

    KH6AQ Ham Member QRZ Page

    A balloon project?. No PVC plumbing trap for you. Don't worry too much about the trap coil Q. 100 is fine and is what is used, for example, in the 4BTV trap vertical. Close wound enamel wire will work.

    I use #26 AWG steel clad stranded wire from The Wireman for 160 meter balloon verticals. A 'safety' line is attached between the top end of the wire and the balloon. The safety line is fishing line sized to break before the wire.
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