Topband: Forms for traps/coils

[Dennis OConnor]

For 160 I make my coils 6 inches dia. mainly...  I usually aim for my coils to come out roughly square, i.e. 6" dia. X 6" long...  My rationale here is that this gives the best Q with least dissipation, though it may be gilding the lily a bit...
4 inch dia. will work also and thin wall PVC septic drain field tubing comes in this size - so Lowes, etc... My 6 inch plug form is home made with end plugs circle cut from plywood, 4 oak formers making the tube and then wrapped with galvanized steel (heating duct) to get a nice round plug...  If you know anyone with a wood lathe ask them to turn a 6" X 12" plug for you...

Cebik, W4RNL, on his web site will have discussion of how to calculate coil dimensions, i.e. length X turns for a given uH...  There are other coil calculators available on line, just do a search...

Wire size is depending upon the power you are running... #10 solid wire will work nicely for traps and general matching..  #8 solid for series tuned coils with more current flowing in it, high power contesting, etc... Since these are spaced turns bare wire from stripping the insulation off THHN, Romex, or similar, will work nicely...  The easist way to strip wire is with a box knife.. Clamp the end of the wire in a vice, hold the wire stretched with one hand, hold the box knife almost parallel to the wire, then back up sliding the wire through your hand as you slide the knife along the wire... 30 seconds of practice will make you an expert...

I use quarter inch, dead soft, refrigeration copper tubing for my tuner coils - even though I mostly contest CW in the low power catagory I get a percent or two more efficiency - but when I do decide to run RTTY with the amp into a low impedence antenna I don't have to worry about over heating.....

denny  ...  k8do

 		
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