Antenna traps

Discussion in 'General Technical Questions and Answers' started by M1FDZ, Sep 12, 2006.

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  1. M1FDZ

    M1FDZ Ham Member QRZ Page

    I am needing to replace some traps on a beam antenna, the original traps are 2.55mm dia aluminium wire and 30 turns, on a former of approx 3/4 inch. problem is I cannot get 2.55mm aluminium wire, the nearest is 2.50mm enamelled copper wire. what if any difference is this going to make to the traps bearing in mind the resistances of the two metals are slightly different? 73 Max
  2. KL7AJ

    KL7AJ Premium Subscriber QRZ Page

    I think your copper wire might actually work a bit better. Copper is almost twice as good a conductor as aluminum (though I've forgotten the skin depth difference.) I think you'll do just fine. Keep in mind that the total inductance will be a bit different....keep the overall coil length the same, even if the spacing between turns is a bit more, to minimize this.

  3. M1FDZ

    M1FDZ Ham Member QRZ Page

    Thanks Eric, I have ordered the new enamelled wire and I will proceed with the repairs. I am sure the diameter is not going to make any significant differences, after all being commercial traps I am sure they are not resonated to exact frequencies, moreso somewhere in between 10 and 15 or 15 and 20m. 73 Max
  4. W8JI

    W8JI Ham Member QRZ Page

    The biggest problem with the copper will be getting a good connection. Most traps use aluminum wire because the rest of the trap is aluminum.

    You'll have to use a stainless buffer or the wire will eat the aluminum right up and make powder ay the contact point.

    73 Tom
  5. W9GB

    W9GB Ham Member QRZ Page

    Tom is correct.  Several suitable inhibiting products are available from electrical contractors / distributors for mating aluminum and copper --
    remember that dissimilar metals do "react" to each other (galvantic effects).

    The inhibitor used should be one that does not ignite and flame readily.  Burndy Penetrox A is one such inhibitor product.

    SOME inhibitor products (e.g. Ideal Noalox) can ignite and burn vigourously!

  6. M1FDZ

    M1FDZ Ham Member QRZ Page

    Thanks, That is interesting, I had not thought about that, I had been putting the antenna together with copperslip, anti seize / squeal compound the stuff you put behind brake disc pads on vehicles, only because the guy who I bought another antenna from had done so, maybe I'll have to clean all that off and replace it with something alloy based, I don't want this antenna turning into some weird 'son et lumier' that would drive the neighbours and my XYL a bit wild. they think I'm crazy enough as it is without provoking the situation, LOL. I can get some stainless steel washers to barrier the CU/AL situation I don't think the 'Burndy penetrox a' is available here but I'll see if there is a similar compound. 73 Max
  7. KE4FES

    KE4FES Ham Member QRZ Page

    [​IMG] Don't be concerned about the difference in diameter of 0.00191685". YOUR HAIR IS PROBABLY THICKER THAN THAT ! For your application, disreguard the DC OHMIC difference of the materials, you are working with AC [RF] IMPEDENCE. Be concerned with; coil diameter, turns and wire spacing.It should be "easy" to duplicate the original coil . CLEAN THE CONTACT AREAS AND APPLY THE PROPER "LUBE/SEALANT" MATERIAL. Air and moisture are your enemy ! [30 TURNS, should be about 71+ '' of # 10 awg. wire]. [​IMG] *** power utilites use multi conductor alum. transmission wires, several paralleled conductors. They scrap excess ends, sell to scrap yards. There is a source ! Be careful straightening
    as soft alum. will stretch easily, reducing the diameter.
    It is bare, clean and coat it, for LOW voltage a clear
    plastic or lacquer areosol spray coating will work.
  8. M1FDZ

    M1FDZ Ham Member QRZ Page

    Thanks KE4FES, I was going to use copper wire as I can get enamel coated here, The coils are easy as there are proper formers, so it is just a matter of taking the old wire off and rewinding the new onto the old former after cleaning it, just making sure it is tightly wound. my concern now is where to find the Burndy penetrox A in the UK, I cannot find an equivalent substance as we (as far as I know) do not have aluminum wire in houses. so there is not such a big demand. I was going to use copperslip, anti seizing compound but I am not so sure now, maybe it will react with the alloy? any ideas..
  9. VK2TIL

    VK2TIL Ham Member QRZ Page

    To make a tight winding, warm the wire before you wind it onto the form; secure the ends whilst it's warm.

    When it cools & contracts you will have a nice tight winding.

    If you are using bolts/nuts/ washers to secure the winding ends, get stainless steel. A stainless washer separating the copper from the aluminium will prevent corrosion; no special compound will be required.

    All-stainless hardware is best but, if you can't get S/S bolts & nuts, zinc will be OK; just separate the different metals with stainless as I said.

    Boating places sell stainless bolts but you are a fair way from the sea. Refrigeration places use stainless. Try to get stainless if you can, it's the best for antennas.
  10. M1FDZ

    M1FDZ Ham Member QRZ Page

    Thanks VK2TIL, the antenna originally had steel self tapping screws and they were mostly slightly rusted so I was going to replace them anyway, Thankfully I have a fastener centre and a Chandlers not far from here (QTH is Christchurch UK) plenty of yachts in the marina here. hence the reason for the corroded antenna in the first instance. The salt air gets into the holes in the traps and corrodes the alloy coils. I shall go and get all the stainless hardware this afternoon. The antenna is a Hi-gain TH-5 mk2 and it is an excellent antenna not only in its performance but also in it user friendly manufacture, everything is, or appears to be, repairable, just what you need really. When you undertake a project like this it is truly amazing how much you can learn. Thanks for all the help so far. 73 Max
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