[TowerTalk] Which Balun with the TH7DXX

[Peter Voelpel]

No problem with winding that cable on a 4" pvc pipe. 
And that cable is cheaper for me then four Fair-Rite toroids.

The 40m yagis feed point impedance is 28 ohms.
For the transformation and balun I use a transmission line transformer made
of parallel and single sections of RG142.
All this coax is wound on two large (4.7") stacked 4C65 cores which are
similar to 61 mix.

SWR measured behind 74m of coax (90% 7/8"):

6.930= 1.5
7.000= 1.2
7.120= 1
7.200= 1.2
7.260= 1.5
7.300= 2

73
Peter

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Jim
Thomson
Sent: Dienstag, 23. Juli 2013 11:29
To: towertalk at contesting.com
Subject: [TowerTalk] Which Balun with the TH7DXX

Date: Tue, 23 Jul 2013 00:54:40 +0200
From: "Peter Voelpel" <dj7ww at t-online.de>
To: <towertalk at contesting.com>
Subject: Re: [TowerTalk] Which Balun with the TH7DXX

A solenoid winding made of coax is more effective then those 4 wraps.
I use SCF12-50 Cellfex to wind my choke baluns.
30 turns on a pvc tube of 4-5" diameter do the trick (2000 ohms at 14MHz).

73
Peter

##  This  Cellflex  SCF12-50   is  almost the same as Andrew superflexible
half inch heliax.   
Both have a copper clad solid Aluminum center conductor + corrugated shield.
Min turning radius on this cellflex stuff is 1.3 inchs.
 http://www.rfsworld.com/websearch/DataSheets/pdf/?q=SCF12-50J

##  are you sure you can even wrap this stuff around a 4-5 inch diam PVC
tube ? 
5 inchs  x 3.14 x 30 turns =  471 inchs.  =  39.25 feet required.   That's
one helluva lot
of coax wasted to make a balun.   With its .54 inch outer jacket X 30 turns,
the balun
ends up being  6.08 inchs OD  x 16.2  inchs long.   The balun would have to
be at least
3 inchs away from the boom, and  4-5 inchs would be better. 

##  its unique coax though.  It has the smallest bend radius of all the 1/2
inch cables.
The 1.3 inch min bend radius  is for repeated bending.  They don't list what
the  single bend radius is... which is typ even less than  repeated bending
spec. 

##  peter, what do you use for 40m yagi ?  Is your 40 ma yagi  200 ohm..with
a
1:4 balun.... or is it 50 ohm... with just a choke balun ? 

Jim  VE7RF
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