[TenTec] OCF antennas evolution

Fri Jul 12 11:45:45 EDT 2013

You read too much into what I said.  All I was doing was giving a case 
for where a 4:1 balun was better than a 1:1 balun.  I wasn't talking 
about using coax.  I was talking about 600 ohm open wire line with a 4:1 
balun at the antenna end.  And I was actually talking about a 4:1 
transformer that was balanced on both ends.

I really don't want to get into this discussion, but there are many 
cases where a 4:1 transformer is less loss than a 1:1.

Carl Moreschi N4PY
121 Little Bell Dr.
Hays, NC 28635
www.n4py.com

On 7/12/2013 11:23 AM, Rick - DJ0IP / NJ0IP wrote:
> Let's consider that one again, Carl.
>
> If we place a 4:1 balun at the feedpoint of the 80m antenna, then we have
> 625 Ohms "Unbalanced" at the feedpoint on 40m. the math is correct, but
> normally we would attach the coax to the bottom side of the balun, not
> openwire.  The 625 ohms is a 12:1 SWR for the coax.  So we don't want to do
> that.  And if we are going to run openwire, then we attach it directly to
> the antenna, we don't use a balun at that point.
>
> If we attach the openwire at the antenna and run it to the shack, into a 4:1
> balun at the tuner, just what value the antenna system exhibits at that
> point will depend on the length of the feedline.  Granted it appears a 4:1
> balun would be a better match and usually it would be from an impedance
> standpoint.  However if the SWR happens to be above 3:1 or so, the 4:1 balun
> quickly loses its ability to impede common mode current and that is very
> bad.  The 1:1 current balun does not.  Again as Jim says, we should be
> calling it a choke, not a balun but old habits die hard.  So as long as your
> matchbox is capable of matching whatever mismatch there is in the antenna
> system, it's better to use a 1:1 balun (for the sake of impeding CMC) and
> let the matchbox do the matching.
>
> The real problem is the other way around, when you attach openwire feedline
> to a 40m dipole and attempt to match it on 80m.
> Now I know they recommend not to do this, but I've had a few QTH's where it
> was my only way of getting on 80m.  I didn't have enough space for anything
> else, so I ran this and worked lots of DX with it on 80. But it creates some
> real challenges for the balun and the matchbox:
>
> In this case the impedance is likely to be less than 10 Ohms at the
> matchbox, but it also depends on the length of the feedline. Let's call it
> 12 Ohms for the sake of easy math.  The 4:1 balun at that point transforms
> it in the wrong direction, down to 3 Ohms.  ALL matchboxes have high losses
> when trying to deal with such low impedance.  Just read any ARRL test of any
> matchbox and check the internal loss at this impedance.  Clearly the 12 Ohms
> will be easier to match than 3 Ohms.  AND the 1:1 balun/choke (assuming it
> is adequate for the job) will do its job of impeding the common mode
> current, whereas the 4:1 balun will fail miserably.
>
> On top of that, the voltage balun fails in any case.
> The 238 has the wrong type of balun (voltage) and the wrong ratio (4:1).
> Don't use it.
> Use an external 1:1 current balun capable of dealing with the power level
> you are using.
> Jim (K9YC) has written an excellent paper on this topic. It is well worth
> reading.
>
> 73
> Rick, DJ0IP
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Carl
> Moreschi
> Sent: Friday, July 12, 2013 4:56 PM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] OCF antennas evolution
>
> Let's say you are running a 80 meter dipole on 40 meters.  The impedance
> will be about 2500 ohms or higher.  Let's also say you are using 600 ohm
> ladder line.
>
> Then by placing a 4:1 balun at the antenna, the 2500 ohms becomes 625 ohms.
> That means you have an excellent match on the 600 ohm ladder line.  You then
> match the 600 ohm line to the rig with a tuner.
>
> The 4:1 balun in this case ends up with less loss than the 1:1 balun.
>
> It all depends on what you are matching as to which one is better.
>
>
>
> Carl Moreschi N4PY
> 121 Little Bell Dr.
> Hays, NC 28635
> www.n4py.com
>
> On 7/12/2013 9:15 AM, Bob McGraw - K4TAX wrote:
>> I commented recently where there is indeed a good application for 4:1
>> balun usage. I think you have also indicated the correct use for 4:1
>> baluns in some of your OFC antenna discussions. In most other cases,
>> typically 1:1 ratios are preferable. I know that Jim , K9YC, has some
>> good information and history on correct balun usage. To complicate the
>> topic, there are current baluns and voltage baluns both in 1:1 and 4:1
>> configurations as well as other ratio version. You are correct in that
>> the topic is rather complex and there's widely varying opinions,
>> approaches and results.
>>
>> In my case balun usage is in the 50 ohm to 50 ohm unbalanced to
>> balanced configuration where a matched condition always exist. Thus
>> being on the input of the tuner.
>>
>> 73
>> Bob, K4TAX
>>
>>
>> ----- Original Message ----- From: "Rick - DJ0IP / NJ0IP"
>> <Rick at DJ0IP.de>
>> To: "'Discussion of Ten-Tec Equipment'"<tentec at contesting.com>
>> Sent: Friday, July 12, 2013 1:26 AM
>> Subject: Re: [TenTec] OCF antennas evolution
>>
>>
>>> Mike,
>>>
>>> I don't think anyone here is going to be able to explain to you in a
>>> single email why the 1:1 balun is better.
>>> However I can show you how to learn about this in a systematic way,
>>> using material from 4 of the experts in this field.
>>> It will probably take you about 10 hours to do this, but then you
>>> will know.
>>> (otherwise, just take our word for it.)
>>>
>>> This is a 4 part training course:
>>>
>>> PART-1: View GM3SEK's online presentation on common mode current
>>> problems, especially the first half of it. View all of it but at this
>>> point, you only need to understand what all can be causing us
>>> problems. Ian's presentation is a good introduction to that. See:
>>> http://www.ifwtech.co.uk/g3sek/in-prac/
>>> (Note: it is a challenge just to bring the file up. You have to right
>>> click Ian's link and save the link to your computer. Then
>>> double-click the link on your computer and it brings the PowerPoint
>>> file up.)
>>>
>>> PART-2: Read W7EL's excellent paper on "Baluns: What They Do and How
>>> They Do It". These 8 pages will give you a good understanding of
>>> Baluns (which Jim rightly called Chokes), and begin to answer your
> question. See:
>>> http://www.eznec.com/Amateur/Articles/Baluns.pdf
>>>
>>> PART-3: View G3TXQ's excellent page on "Tuner Balun Ratios":
>>> http://www.karinya.net/g3txq/tuner_balun/
>>>
>>> PART-4: Now that you have a fairly good understanding of all of this,
>>> Read K9YC's paper, "RFI-Ham". Although this is the most comprehensive
>>> paper, I don't recommend beginning with this one. This is like the
>>> graduate course.
>>> It is 66 pages long, but it has everything in it. See:
>>> http://audiosystemsgroup.com/RFI-Ham.pdf
>>>
>>> If you haven't a clue about all of this and view these resources in
>>> this order, you will probably understand most of what Jim wrote,
>>> though if you're like me, you'll have to read it two or three times.
>>>
>>> SHORTCUT for your question, MIKE: Go straight to PART-3.
>>>
>>> However I recommend anyone asking this type of question, take the
>>> time to work through all of this. It will be very beneficial.
>>>
>>> 73
>>> Rick, DJ0IP
>>>
>>>
>>> -----Original Message-----
>>> From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Mike
>>> Bryce
>>> Sent: Friday, July 12, 2013 3:51 AM
>>> To: Discussion of Ten-Tec Equipment
>>> Subject: Re: [TenTec] OCF antennas evolution
>>>
>>> I quite aware that open line is generally considered lost less feed line.
>>>
>>> What threw me was the use of a 1:1 balun instead of a 4:1.
>>>
>>> That's the head scratcher.
>>>
>>> Mike wb8vge
>>>
>>> Sent from my iPhone
>>>
>>> On Jul 11, 2013, at 9:32 PM, k6jek<k6jek at comcast.net>  wrote:
>>>
>>>> Mike,
>>>>
>>>> You're matching the antenna system, the antenna and the feed line.
>>>> You
>>> just can't separate the two. When the antenna impedance at a
>>> particular frequency is different from the feed line characteristic
>>> impedance, the impedance on the line is different every place on the
>>> line. You're matching whatever it happens to be at the shack end of
>>> the feed line.
>>>>
>>>> Losses are the reason to put the balun near the station instead of
>>>> near
>>> the antenna. Open wire line has much lower losses than coax under
>>> conditions of very high SWR. That's the reason we put up with the
>>> stuff which is a royal pain in the arse, just so we can have a
>>> ridiculous SWR and not care about it. And very high SWR is exactly
>>> what we have at almost all frequencies when using a doublet as a
>>> multi-band antenna. The only reason we can get away with such a thing
>>> is the low loss of open wire line.
>>> So you
>>> want to run that stuff as far as you can before switching to coax. As
>>> long as you can is ideally right into a balanced tuner, no balun at
>>> all.
>>>>
>>>> Jon
>>>>
>>>>
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>>
>>
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