[Elecraft] ladderline and balun question

[Don Wilhelm]

Don,

I gave you the antenna feedpoint impedances for a 2 wavelength loop and 
a 4 wavelength loop from L B Cebik's simulations.  Those impedances are 
as close a one might get.

73,
Don W3FPR

On 1/12/2012 9:39 PM, goldtr8 at charter.net wrote:
> Thanks Don,
>
> I installed the SW that came with the Antenna Book.
>
> My problem is I dont know how to model stuff so I dont have the
> feedpoint impedance.
>
> I am lucky someone is being kind enough to mentor me so I can learn this
> stuff.
>
> Cheers
> Don
>
> ~73
> Don
> KD8NNU
>
>
> On Wed, Jan 11, 2012 at 5:30 PM, Don Wilhelm wrote:
>
>> Don,
>>
>> If you don't have TLW, you might have to invest in the ARRL Antenna
>> Book - it is on the CD that comes with that book.
>> It is "Transmission Line for Windows", and you can plug in the antenna
>> feedpoint impedance, the type and length of feedline and the program
>> tells you the impedance at the other end.
>>
>> 73,
>> Don W3FPR
>>
>> On 1/11/2012 5:11 PM, goldtr8 at charter.net wrote:
>>> 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.
>>>>>
>>>>>
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