Posted by
K9MA on
Jan 06, 2019; 8:17pm
URL: http://elecraft.85.s1.nabble.com/KAT-500-and-open-wire-tp7647776p7647781.html
Using a balun with balanced line is risky. Window line or open line can
be used with reasonable losses up to at least a 10:1 SWR, but that means
the impedance at the balun output could be anywhere from 30 to 3000 Ohms
(for 300 Ohm line). The current balun should work if the impedance at
the balun output is low, not much over 50 Ohms. This is hard to measure,
but modeling should give a close enough value. On the other hand, the
impedance could be thousands of Ohms, and that kind of balun will be
ineffective. Transformer-type baluns have limitations at both high and
low impedances.
While a transformer type balun could overheat and/or generate harmonics,
I suppose the worst thing a current balun could do is to upset the
balance. I've you're not seeing a lot of "RF in the shack", you're
probably good.
The only really reliable way to feed unmatched balanced line is with a
truly balanced tuner, a seriously endangered species. I'm still using
the one I built almost 50 years ago.
73,
Scott K9MA
On 1/6/2019 13:42, Bob McGraw K4TAX wrote:
> Yes I use a balanced feed line being the "window" type line. It
> feeds a 250 ft wire in the center at 50 feet. I have about 75 ft of
> feed line from the center of the antenna then, through the attic eve
> vent, supported on some wooden hangers I made and attached to the roof
> rafters. Then it drops through the ceiling to the balun which sits
> on the shelf above the KPA500 and the KAT500. The balun is a Balun
> Designs 1:1 ATU current balun rated at 5 kW being model 1171t. I
> use a common mode choke, being model 8232 purchased from The Wireman.
> It runs from the balun to one of the tuner 3 outputs. Works great
> from 160M through 10M.
>
> Of note, I am on the 2nd floor of a wood frame house more in the
> center. No windows or walls to the outside. I do not use any type
> of "station ground" to the outside. I do have lightning protection
> devices where the feed lines and rotor lines enter the house. As the
> antenna and feed line is quite well balanced, there is no RF radiation
> in the shack an thus no RF issues with computers, phones, TV's,
> surround sound systems, and such. Each piece of station equipment is
> bonded to the station power supply ground terminal using a dedicated
> ground jumper. The 3rd pin AC ground is maintained and the amp runs
> from a dedicated 240 VAC circuit.
>
> Works great!
>
> 73
>
> Bob, K4TAX
>
>
> On 1/6/2019 10:59 AM, Viggo Magnus Nilsen Nilsen wrote:
>> Hello Elecrafters,
>>
>> Do some of you using KAT500 with open wire,ladder line feed to ur wire
>> antennas with balun (outside the tuner) ? working ok ?
>>
>> 73' LA9NEA Viggo M.
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