[TowerTalk] Type 31 baluns

[Jim Thomson]

Apparently array solutions is now using type 31 material for their
w1JR style baluns.    The original stacked cores used type 61 material.

Both the new style and  the old style use  several wraps of  RG-393 teflon coax
and  a 7-16 DIN. It's rated for 160-10m. . 

Another version is rated for  80-6m 

The box appears to be a 6" x 6" x 6"  nema box... and the stacked cores are up
off the bottom of the box.  This is done, so when used on a yagi... the nema box
is bolted to an Aluminum plate 1st... and the AL plate is then u bolted to the boom.
That keeps the stray  C  between balun and al plate to a minimum.  A non conductive
plate would be the ticket... [ provided it's uv resistant..and strong]  

On the balanced side... he uses 2 x big ceramic stand off's......with concentric rings on em..
to stop water.  Weep holes are on the bottom of the box.. to drain any condensation that gets
into the box.  
Also... a compensation  cap [HV type]  is wired across the balanced output.  This is used to 
cancel some of the stray internal lead XL.

The ...'line isolator' version of these baluns is just a 2nd 7-16 Din.. instead of the balanced ceramic
stand off's. 

You can't blow  up any of the version's either.  For anybody homebrewing these things... be careful
with the max turns of coax used on the cores.   In one of em.. with I think about 7-9 turns of RG-400
[small teflon coax]  wound on 8 x type 43 cores. [4 on the left.. 4 on the right]   it arced between
2 x adjacent turns.. on the inside of the core hole... where the turns are close together.   That's arcing
between one braid of one turn.. and the braid of the adjacent turn... and the voltage  punched right
through 2 x sets of insulation.. which is pretty good on RG-400.  Jay at AS.. had warned me of this
effect, called parasitic arcing.. caused when too many turns of coax on the cores.. and high power used.

393 teflon coax may fare better..since it uses a FEP-9  jacket.. which I think has teflon in it.  Better
to use more cores..and less coax.     When I see these notes, where as  many as 12 x turns of coax are used
... it  makes me shudder.   Testing on a HP Z meter is one thing.  Stuffing RF into it is another matter.  

I like the idea of the wrapped torroids in a self contained box.. with connector's on each end..[which is why
the cross over winding is used.. in either the balun version or the line isolator version] .
Then wind can't get at the coax..eps if there is lots of space between turns.. and change the C between
turns.  If you decide to leave the wrapped torroids flopping in the breeze.. they have to hang below.. and
away from the boom. ...otherwise stray C  from boom to balun will affect it's performance.       

later.... Jim   VE7RF