Topband: KLM antennas on shunt fed towers

[John Harden, D.M.D.]

I still have two Telrex 10 meter monobanders (a 3 el and a 5 el at 65 ft 
and 35 ft) that are part of a 3 high stack. They both have T-Matches 
with coaxial baluns. I'm running maximum legal power to a 160 meter 
Omega match on the 45G 100 ft tower that these antennas are on.

In my particular situation I have not had any baluns fail as yet. 
However every situation is different. The driven elements are insulated 
from the boom on both of the antennas.

73,

John, W4NU


On 12/26/2012 2:13 PM, Tom W8JI wrote:
>> Anyone have problems running a KLM antenna with the 4:! balun and 
>> elements insulated from the boom (stock KLM config) on a shunt fed 
>> tower for 160? I ask because I have a 6 element 10 on the top of my 
>> shunt fed tower and now, after running a kw on 160, the antenna's swr 
>> has gone over 2:1 where before it was pretty flat at about 1.2:1 or 
>> so. Any ideas?
>
> You probably ruined the balun from 160 current. The best cure would be 
> installation of RF chokes from elements to boom on all of the 
> elements. Anything over a few dozen ohms on 10 meters works for the 
> parasitic elements. They are not critical.
>
> For 10 meters, I would use a good 4:1 voltage balun with the coax 
> grounded to the boom, or you can use a 4:1 current balun if you use a 
> center tapped choke of at least 1000 ohms and less than 2000 ohms on 
> ten meters with tight mutual coupling across the winding.
>
> It would not be difficult to build some.
>
> Remember the half-wave of coax makes a voltage balun, so you might as 
> well just save space and get more bandwidth by using a standard 
> compact 4:1 voltage balun.
>
> 73 Tom
> _______________________________________________
> Stew Perry Topband Distance Challenge coming on December 29th.
>