[Elecraft] ladderline and balun question

[goldtr8 at charter.net]

HI Don,

I wish to look into the TLW application you mention.  However, I am not 
what it is exactly.  Would you please be so kind as to point me in the 
proper direction.

I most likely will be going back to the 1:1 balun but the promise of swr 
of 1.3 on 160m was nice, which I have on the 4:1.   Also it is a current 
balun.

Thanks

~73
Don
KD8NNU


On Wed, Jan 11, 2012 at 5:02 PM, Don Wilhelm wrote:

> Don,
>
> According to L B Cebik's modeling, a 2 wavelength horizontal loop will 
> have a feedpoint impedance of 180 - j125 ohms, and a 4 wavelength loop 
> (the same loop used on 80 meters will have a feedpoint impedance of 
> 235 - j135.
> Both are good candidates for the use of a 4:1 balun - but that only 
> applies if you mount the balun right at the antenna feedpoint.  The 
> fact that you have 60 feet of 450 ohm feedline changes the situation 
> drastically - that is about 1/8 wavelength on 160 and close to 1/4 
> wavelength on 80 - so the feedoint impedance at the end of that 60 
> feet of feedline is quite a bit lower - that is most likely why your 
> 1:1 balun worked so well.  You can work with L B Cebik's antenna 
> feedpoint impedances and the TLW application available from the ARRL 
> to find the feedpoint impedance at the end of the 60 foot feedline, 
> but I think you will find it closer to 50 ohms than to 200 ohms.
>
> The other question is what type of balun is your 4:1 balun - if it is 
> a voltage type, it has no chance of stopping common mode current.
>
> My guess for why your current choke did not work is either that you 
> did not place it at the right point on the coax, or it was at a point 
> where the RF voltage was high, and in light of a high RF voltage 
> (think impedance equal to 2000 to 4000 ohms, a choke of 5000 ohms 
> impedance does not have much of a chance to stop any current.
>
> So bottom line - go back to what you had before, or put the 4:1 balun 
> at the antenna feedpoint where it should work if your antenna is 
> anything like L B Cebik's simulations.
>
> 73,
> Don W3FPR
>
> On 1/11/2012 4:12 PM, goldtr8 at charter.net wrote:
>> Gents,
>>
>> I have a ladder line and balun question that I hope someone can guide 
>> me
>> thru.
>>
>> I had a good working antenna system with two antennas.  First being 
>> an
>> Alpha Delta Dipole and the second a 2WL 160m loop antenna at 40 ft in
>> the air strung in trees.  So the wire does touch the trees.
>>
>> Dipole is fed with coax and choked at the feed point and the loop was
>> fed with 60 ft of ladder line to a 1:1 current balun then 25ft coax 
>> to
>> the shack tuner.  Then the amp and radio.   This combination was 
>> working
>> real well no RF problems in the shack.
>>
>> I was advised that I would obtain better results for better SWR at
>> resonance and easier matching if I removed the 1:1 balun and went to 
>> a
>> 4:1 balun.  I made this change with everything else being the same. 
>> I
>> now had RF in the shack again.
>>
>> I then added an isolation balun to the system by adding 6ft coax from
>> the output of the 4:1 to a balun designs 116du which is supposed to 
>> have
>> 4500 ohms of choking impedance on 160m and over 5000 ohms choking
>> impedance  on 80 and 40 meters.   This did not eliminate the RF and I 
>> am
>> still having problems.
>>
>> So here is the question, is it possible that with the combination of
>> length of the ladder line at 60ft plus the 6 ft plus 25 ft of coax I 
>> am
>> at a feed line length that will be a problem no matter what I do. 
>> I
>> keep looking at the internet to try and figure this out but I am
>> confused as some information I find says it only applies to 1:1 
>> baluns
>> or other factors.
>>
>> So anyone who can help me understand this feed line question I will 
>> be
>> greatly appreciative.
>>
>>