[Elecraft] ladderline and balun question

[Don Wilhelm]

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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