[TowerTalk] Which Balun with the TH7DXX

[Jim Thomson]

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