[TowerTalk] 6M coax balun

[Roger (K8RI)]

On 8/31/2010 10:33 PM, Jim Thomson wrote:
> Date: Tue, 31 Aug 2010 18:37:35 -0400
> From: "Roger (K8RI)"<K8RI-on-TowerTalk at tm.net>
> Subject: Re: [TowerTalk] 6M coax balun
>
>
>
> On 8/31/2010 5:10 PM, Hector Garcia XE2K wrote:
>> Tony
>>
>> if you want to read more about the baluns for the 6m band and the antennas  go
>> to this web page
>>
>> http://www.g0ksc.co.uk/creatingabalun.html
>>
>> I just build the Hybrid for the LFA's and was very easy.
> Part looks good, but the "air core" 5 turns on the paint can is unlikely
> to be very effective.
>
> 73
>
> Roger (K8RI)
>
> ###   14 x  of the  large  type 43 beads..  [ 1" OD x .5"  ID  x 1.125"  long]    will give you 2083 ohms  on 6m.  If you use RG-393 coax,
> you can then stuff  5 kw CCS all day long into it.   If you use large  type 31 beads,  you will get  just over 2 k ohms, resistive, with 10 x large
> beads... and  just over 4 k ohm, resistive, with 20 x large beads. [3 k with 15 x beads]
I figured 3 t on 7 cores for 6-meters should give about 5K
> ##  If you opt for a few turns of coax in a solenoid air wound config..... or coax wound on type 31  2.4"  OD cores.... make damn sure you keep the
> outside of the coax well  away from the boom... as in at least the OD of the coax coil.     IE:  3"-4" OD coil.... keep it 3-5" away from the boom...
Using Davis BuryFlex or even LMR400 to it's minimum bend radius you can 
get some fairly small coils.
Again, I'd mount them in the NEMA PVC box as you mention below.
> or the stray C  from the coax to boom  will screw up the balun really fast.   On these 80-40  baluns, made from coax wrapped onto type 31 cores,
> depending on how tight the turns are wrapped onto the core..... it's not easy to get the coax  turns away  from the boom  [ or mast if a 80m rotary dipole is used] .
>
> ##  This is where a large size nema box comes in handy.... then the cores and coax can be suspended in mid air, dead center in the nema box...and away from metal.
> The string of large beads on RG-213/393  coax has an advantage too....easier to install..and zip windload.  You also don't have a stray C to boom problem.  You can't blow
> up the large type 43 beads..on any band..with YC-156 power levels.    The large type 31 beads will also work.. but the choking Z has to be a lot higher, since the type 31
> material  is mostly resistive.  I squared x Resistive ohms  = real heat     I squared  x  reactive ohms = reactive power =  'wattless power' .    It amounts to a 2 x edged sword.
> Modern thinking dictates a predominantly resistive component, but to pull that off, the Z has to be real high... like 2-3+ K  ohms.    A type 31 choke balun that's only 1 k ohm,
> and predominantly resistive, will go off like a bomb.  A  2 k ohm choke, also made from type 31 material, will  dissipate exactly  1/2  the power of a 1 k ohm/type 31  choke.
>
I use 5t on 5 cores which should be around 4 to 5K on 75 and 40.
> I will be doing some experiments this fall/winter, where type 43 beads are used at the feedpoint... and type 31 beads are used 1' downstream.
>
I'd like to experiment with the beads as well. The large heatshrink 
tubing will just nicely fit over them.

BTW, I finished painting the two 24', 2" OD (1/4" wall DOM) and the 25G 
tower base this afternoon.  It was 93F in the shade and it was bright 
sunshine.  Man but that paint dried fast. By the time I had sprayed the 
second mast section the first was dry enough to handle, but a bit too 
hot to comfortably hang onto.


73

Roger (K8RI)
> Later... Jim   VE7RF
>
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