Antenna traps

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

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  1. M1FDZ

    M1FDZ Ham Member

    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 Ham Member

    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.

    Eric
     
  3. M1FDZ

    M1FDZ Ham Member

    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

    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

    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.  
    http://thewireman.com/chemical.html

    SOME inhibitor products (e.g. Ideal Noalox) can ignite and burn vigourously!
    http://www.inspect-ny.com/aluminum/pl2p12.htm

    w9gb
     
  6. M1FDZ

    M1FDZ Ham Member

    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

    [​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

    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

    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

    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
     
  11. W9GB

    W9GB Ham Member

    Almost all electrical high-voltage transmission lines are aluminum or alumnium alloys (instead of copper) -- due to weight and cost.  Check with your major electrical contractors / distributors (or power utility company) in the UK, they will have an appropriate inhibitor.  Lightning rod installers often use both copper and aluminum.  You can also use the "anti-sieze" sold by most antenna manufacturers.

    Want to just order by phone?
    The Wireman can sell you a nice large tube of ICE #602, that should be sufficeint for your antenna project.  
    Here is his web page:
    http://thewireman.com/chemical.html#1
    Conductive Anti-oxidants
    Electrical contact between metal surfaces, especially between dissimilar metals can be rapidly compromised in the presence of oxygen, water, salts, pollutants, and other oxidizing agents. Aluminum antenna element material, copper grounding electrodes and even the integrity of mated galvanized tower section joints can be secured and improved with the application of I.C.E. 600 Series conductive surface coatings.


    BTW, in you current QTH (English Channel - coastal and salt-air) ... you will also want to prep the aluminum with an appropriate clear finish for some additional protection.

    BTW, Aluminum for internal house wiring in USA (tried in early 1970s - with high copper prices), is now prohibited for new construction -- significant number of house fires traced to usage and installation of aluminum house wire !!

    w9gb
     
  12. KG4WPD

    KG4WPD Ham Member

    Burndy Penetrox products can be found at you almost any electrical supply house as well as Home Depot & Lowes in the electrical department, if you have them in your area. . .

    Good Luck,
    Tom - KG4WPD
     
  13. KL7AJ

    KL7AJ Ham Member

    Good point. There is a product called Penetrox, which is a paste that prevents galvanic action between copper and 'luminum. It used to be used on a lot of mixed house wiring up here, before Alaska discovered the National Electric Code. HI.

    Eric
     
  14. KL7AJ

    KL7AJ Ham Member

    That's how they used to keep iron rims on wooden wagon wheels too! Them puppies NEVER came off!

    Eric
     
  15. M1FDZ

    M1FDZ Ham Member

    Thanks for all the info, Until this week I never knew houses in the US were aluminium wired and 55% of house fires are caused by this problem, that's a bit scary, I am glad my house has good solid copper wire. I bet there is a good proportion of American citizens sitting on a potential (excuse the pun) problem without realising it. I will try to get some alloy wire but the copper stuff arrived this morning and I have managed to get all the stainless steel screws and washers now. I am ordering some Penetrox from Tessco Technologies inc. so it will be along shortly too. I will finish the rebuild sometime in the next couple of weeks as all the bits arrive, I will keep you posted. 73 Max
     
  16. KL7AJ

    KL7AJ Ham Member

    Does anyone remember the MUNIMULA (pronounced MOONY MOOLAH) men from the old Ruff and Reddy cartoons? MUNIMULA, of course, is Aluminum spelled backwards.

    Mercy, did I have a wasted childhood.....HI


    eric
     
  17. K9STH

    K9STH Ham Member

    Actually, the vast majority of houses in the United States are wired with copper wire. It was just during the late 1960s and into the 1970s that some houses were wired with aluminum. My house was built in 1969 and was wired with copper. However, the houses on either side were wired with aluminum.

    Before the first house was sold the wiring had to be "pig tailed" with certain adapter wiring to the electrical outlets, light fixtures, etc., before the city would allow it to be sold. Generally problems with aluminum wiring happened where the aluminum wiring was terminated in outlets, etc. Before the second house was sold the code was changed so that the house had to be completely rewired with copper. Then the first house was sold again and it had to be completely rewired with copper. Now this is in Richardson, Texas, a northern suburb of Dallas.

    The electric companies have generally gone to aluminum wiring for transmission and distribution because of the MUCH less weight of the wire. However, those companies definitely have special connectors where the aluminum goes to copper. The diameter of those lines are slightly larger than copper to compensate for the higher "IR" drops in aluminum than copper has. But, aluminum is so much lighter than copper and the cost is also much lower so the trend has been for utility companies to go to aluminum for the past several decades.

    Unfortunately, squirrels like the taste of aluminum and they have been known to actually eat wires in two. My "neutral" was completely destroyed by squirrels about half way between the "pole pig" (transformer) and the entrance to my house. A bad neutral is a number one priority for replacement. When I discovered the open neutral I called TXU and there was a repairman out in well under an hour.

    Glen, K9STH
     
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