Latest? version? is? now? 3.78
Note? when u? ?go? from? 7? mhz? to? say? 28 mhz...? (for? a? given? inductance)? ?the? XL? will? increase? by? a? factor? of? 4,? since? XL? is? proportional to? F.? ?( XL =? 2pi? x? F? x? ?L)?
However? the? RF? resistance? only? increases? to? the? square? root? of? the? freq? ratio.? ?IE:? ?28/7 =? 4? ? ? ?sq? root? of? 4? =? 2? ? ?(skin? effect).
XL? has? quadrupled.... but? RF? resistance? has? only doubled.?
Since? Q? =? ?XL /? RF? resistance.......? when? u? increase freq to 28 mhz.......? Q? has? now? doubled.? ?Now? with? the? Q? doubled,? joe? ham thinks? he is? doing? really? good with? his? coil? on? 28 mhz.
Fact is,? it's? now? worse,? a? dog's? breakfast on 28? mhz.? ?Heat? being? dissipated? in? the? coil is? now? double !? ? Power is of? course I squared .. x R.? ?Double? the? R...and? u? now? just? doubled? the? heat.? Wait, it? gets? worse.? ?On 24-30 mhz,? typ uh? coil? values? for a PI /? PI-L? are? small.? ? U? end? ?up? dissipating? ?more? heat vs? 7? mhz.....? and? into? ?far fewer? turns!? The? only? fix? is? to? reduce the? RF? resistance of? the coil? on? 24-30? mhz....? by? increasing? the? diameter of? the? tubing used.? Larger? diam tubing? coils (esp? with? smallish ID's)? ?are not? easy? to? wind.? 3/8"? OD? tubing? wound? on a 1.5"? form? is? doable.? ?1/2"? OD? tubing wound on a 1.5"? form? is a real? bitch.? (I? use? the? 1.5"? ID? ?tubing coils? for? the? small? coil between plate? block? cap? assy? and C1? tune? cap.
Plan? B? is? to? use? copper? strap,? and? wind? a? strap? coil.? ?Flat? strap? coils? are? very? easy? to? wind.? You? can? also? wind,? with very? little? spacing? between? turns.? ?With? tubing? coils,? optimum spacing? between? turns? is slightly greater (8-10%)? than? the OD? of? the? tubing? used.? Tubing coils? only? conduct? current? on? the? outside? of? the? coil.? ?Strap? coils (and? also? interconnecting? straps)? conduct on? both? sides.? ?3/4"? wide? strap? has? the same? outer? circumference as? 1/2"? tubing.? ?1.5" wide? strap? as? the? same? circumference as? 1" OD tubing.?
Current? through? the? tank? coil? on a simple? PI? net is? aprx? plate? current? x? Q. (I? have? measured? this,? and? the? simple? formula? was? surprisingly accurate,? within? 1/10? amp,? on? a? RF? ammeter).? ? Double? the? plate current,? and? RF? current? doubles...(for? the? same? loaded? Q).? ? Double? the? RF? current, and? heat? dissipated? in? the? tank? coil? quadruples.? ? ?High plate? current? and? high? loaded? Q? is a bad? combo.? Hence? the use? of a? small coil? between plate? block? cap? and? C1? tune? cap....? to? reduce? the plate? load? Z? to a manageable number.? (that? small? coil? has? lotsa? current? through? it,? treat? it? the? same as? the? main? tank? coil.)
Avoid? ferrous? steel....and? also? SS? in? tank? circuits.? Use? brass /? bronze /? phosphor? bronze? for? fasteners...? (all 3? can? easily be silver? plated? with? cool-amp? glop).? Ditto? with? RF? connections? at at? feed points,? tuners,? remote? switch? boxes? etc.?
Using? coil? 3.78,? ?you? can? see? at? a? glance? what? the? exact? RF? resistance? of a given? coil? will? be.? Knowing? the? RF? current,? the? heat? dissipated in? the? coil is? easily? calculated.?
Knowing the OD? of? the? tubing? being? used...and? the? coil? diameter..and? length,? and? number? of? turns,? it's a few? simple? calcs? to? determine the? exact surface? area of? the? entire? coil.? ?
Take? the? watts? dissipated....? and? divide? by? the? surface? area.... and? the? result? will? be...? "watts? per? square? inch" .? ?My? way to? deal? with? heat? is to? try? and? ?generate? less? heat? as? possible.?
Cu? tubing is? cheap? at? home? depot.? ?I? silver? plate? all? my? coils? with? cool-amp? glop....mainly for? aesthetic? reasons.? ? Copper? strap? comes? from? local? metal? store.? I typ? get? em? to? shear 3'? lengths? ?of? 1/2", 3/4",? and? 1".....and? sometimes? wider.? ?Typ? .035"? thickness? used,? easy? to? work? with.? For? rigid? strap? coils, .049"? thickness? is? used.??
Later....? Jim? ?VE7RF
