Although I agree this coax length would work great on 160M and 75M, however
as one goes higher in frequency a fundamental resonance will occur. This is
likely to cause some concern with the performance at frequencies at and
above 20M.
See the following link for additional test data and discussion.
http://www.bcdxc.org/balun_information.htm#Ed,%20WA2SRQ
73
Bob, K4TAX
----- Original Message -----
From: <chip_brown@isp.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Saturday, November 24, 2007 7:27 AM
Subject: Re: [TenTec] balun noise?
>
> This works Great. I used about 50' feet of RG-213 (a piece I had around
> with a connector on one end) and about 24" of 3" PVC. Works fine down to
> 160m.
>
> Also built Rich's Balanced tuner using TT parts (Cap and roller Inductors)
> It also works great into 600 ohm open wire feed to 165' doublet.
>
> KR1P
>
>
>
>> Here's the "balun" solution. These work great, cost little and can
>> handle
>> more power than you can generate. Do note, RG-213 is the coax to use.
>> Don't use the foam stuff. Thanks to Rich Measures, AG6K for the
>> write-up.
>>
>> 73
>> Bob, K4TAX
>>
>> Building a no-grief 1.8MHz to 30MHz 50ohm-balun is easy. No costly
>> ferrite-cores are needed, just a short length of 3 to 5 inch size plastic
>> pipe, about 25 feet of 50ohm coax plus some nylon cable ties.
>> Solid-dielectric coax is best for this application because
>> foam-dielectric
>> has a tendency to allow a change in the conductor to conductor spacing
>> over a period of time if it is bent into a tight circle. This can
>> eventually result in voltage breakdown of the internal insulation. The
>> required length of the plastic pipe depends on the diameter and length of
>> the coax used and the diameter of the pipe. For RG-213/U coax, about one
>> foot of 5 inch size pipe is needed for a 1.8MHz to 30MHz balun. For
>> 3.5MHz
>> to 30MHz coverage, about 18 to 20 feet of coax is needed. This length of
>> coax is also adequate for most applications on 1.8MHz. The number of
>> turns
>> is not critical because the inductance depends more on the length of the
>> wire (coax) than on the number of turns, which will vary depe
>> nding on the diameter of the plastic pipe that is used. The coax is
>> single-layer close-wound on the plastic pipe. The first and last turns of
>> the coax are secured to the plastic pipe with nylon cable ties passed
>> through small holes drilled in the plastic pipe. The coil winding must
>> not be placed against a conductor. The name of this simple but effective
>> device is a choke-balun.
>>
>> Some people build choke-baluns, without a plastic coil-form, by
>> scramble-winding the coax into a coil and taping it together. The problem
>> with scramble-winding is that the first and last turns of the coax may
>> touch each other. This creates two complications. The
>> distributed-capacitance of the balun is increased and the RF-lossy vinyl
>> jacket of the coax is subjected to a high RF-voltage. The single-layer
>> winding on the plastic coil-form construction method solves these
>> problems
>> since it divides the RF-voltage and capacitance evenly across each turn
>> of
>> the balun.
>>
>> A more compact, less ugly, 1 to 1 impedance-ratio, 50ohm trifilar-wound
>> (with wire) ferrite-core balun could also be used but there would be some
>> tradeoffs. Ferrite cores are not cheap. Also, the air-core of the
>> coax-balun can't saturate like the ferrite-core and, unlike ferrite-core
>> wire-wound baluns, single-layer wound coax-baluns almost never have an
>> insulation breakdown problem. Also, a trifilar-wound balun does not like
>> to work into anything but a perfectly balanced load. With an imperfectly
>> balanced load, the coax-balun will not, as does the trifilar balun,
>> generate a differential, third RF-current on the outside of the coax that
>> brings the RF to the input of the tuner. The choke-balun is not fussy. It
>> will work as well into a less than perfectly balanced load as it will
>> into
>> a perfectly balanced load, and do so without the possibility of creating
>> a
>> differential RF-current on the station ground and fricasseeing the
>> operator's fingers.
>>
>>
>>
>> ----- Original Message -----
>> From: "Jim Brown K9YC" <k9yc@audiosystemsgroup.com>
>> To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
>> Sent: Friday, November 23, 2007 2:44 PM
>> Subject: Re: [TenTec] balun noise?
>>
>>
>>> On Fri, 23 Nov 2007 09:46:03 -1000, Ken Brown wrote:
>>>
>>>>Usually a balun is used to connect an unbalanced feed line, such as
>>>>coax, to a balanced antenna such as a dipole. The balun should improve
>>>>the current distribution on the dipole and reduce the current on the
>>>>outside of the coax.
>>>
>>> Most so-called "baluns" of the type Ken describes are really common mode
>>> chokes, and they do exactly what he says.
>>>
>>> See http://audiosystemsgroup.com/RFI-Ham.pdf for a tutorial on many
>>> things,
>>> including these chokes ("baluns".
>>>
>>> 73,
>>>
>>> Jim K9YC
>>>
>>>
>>> _______________________________________________
>>> TenTec mailing list
>>> TenTec@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/tentec
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>>
>
>
>
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