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Re: [Amps] RF in the Audio

To: "Barrie Smith" <>, <>
Subject: Re: [Amps] RF in the Audio
From: "Jim W7RY" <>
Reply-to: Jim W7RY <>
Date: Sun, 25 Sep 2011 13:51:37 -0700
List-post: <">>
I don't seem to find his web site.

Jim W7RY

From: "Barrie Smith" <>
Sent: Sunday, September 25, 2011 11:11 AM
To: <>
Subject: Re: [Amps] RF in the Audio

> There's a tutorial on building a "truely-balanced" antenna tuner on 
> Sevick's
> web-site.  Schematics for a practical unit, as well.
> After burning out the balun twice in my MBVA, I built one according to his
> plans.
> Works great.  A balun runs from warm to hot to flames.  My tuner doesn't
> even get warm at legal-limit.
> Worth a look.
> 73, Barrie, W7ALW
> ----- Original Message ----- 
> From: "Fuqua, Bill L" <>
> To: <>
> Sent: Sunday, September 25, 2011 11:20 AM
> Subject: Re: [Amps] RF in the Audio
>>   We can perhaps this forum to come up with some ideas on how to achieve 
>> a
>> goal by new design instead of
>> going back and forth with old ideas and currently available equipment.
>> bill wa4lav
>> ________________________________________
>> From: [] On Behalf
>> Of Fuqua, Bill L []
>> Sent: Sunday, September 25, 2011 1:15 PM
>> To:
>> Subject: Re: [Amps] RF in the Audio
>>   Does anyone make a real balanced line antenna tuner? No  toroidal
>> transformer.
>>   If I built one I would couple link couple the TX into a tank and link
>> couple the output with a swinging
>> link with Fariday shield.
>>   You could not get any more balanced than that.
>> 73
>> Bill wa4lav
>> ________________________________________
>> From: [] On Behalf
>> Of Carl []
>> Sent: Sunday, September 25, 2011 12:14 PM
>> To: Rob Atkinson;
>> Subject: Re: [Amps] RF in the Audio
>> The last place I would insert a balun is at any point in a OWL fed
>> antenna.
>> Do the twists as have been the norm since the 30's and live with whatever
>> unbalance remains.
>> Since OWL theses days assumes the use of a tuner then spend the bucks and
>> buy/build a truly balanced one especially if running an amp. Compromises
>> with QRP and barefoot can get away with a barely functional T200-2 iron
>> powder 4:1 balun that comes with the low end tuners.
>> I always use a LPF between rigs and amps and amps and coax feeds. A 12
>> large
>> bead sleeve balun of 43 mix is at the input of each LPF and appears more
>> than sufficient to keep RF inside the coax on any band. More beads are at
>> every antenna feed point. All these conform to or are close to the 1000
>> Ohm
>> impedance rule that has been a sort of ham standard for decades. Im also
>> aware of the 1966 CIA document mentioned by K9YC on his site as I was
>> Tempest cleared at the highest level at Sanders Associates 1969-78, a
>> major
>> DoD supplier and deep into stealth technology even back in the 60's. The
>> CIA
>> and other 3 letter agencies were regular visitors. I didnt remember the
>> 5000
>> Ohm recommendation however which showed some serious thinking that far
>> back.
>> After eliminating all RFI generators in the house using 2.4" 77 or 31 mix
>> cores over several decades as more junk comes into the house Im assured
>> that
>> any digital crud heard on the radios is from external sources. The 
>> HRO-500
>> on a 12V battery in the shack and an AM/SW portable as a sniffer have 
>> been
>> used extensively.
>> Remember also that the initial use of sleeve balun beads was due to TVI
>> and
>> when a dozen 1" beads could tame any tribander or trap vertical it was
>> considered good enough. We didnt have PC's, switchers, digital everything
>> in
>> the house, etc, back then.
>> Switching Beverages and changing directons of other antennas seems to
>> confirm that the sources are thru the air.
>> I have no use for OWL.
>> Just last month a new and very loud noise showed up on 160; turns out one
>> of
>> the companies renting tower space changed to a new repeater and required
>> several pounds of ferrite to tame.
>> About 30 years ago I had a friend who owned a 2 way shop ask me to help
>> him
>> locate an IMD source that was driving him crazy at a repeater site. After
>> I
>> eliminated everything in the building....solid coax and other 
>> connections,
>> no change in recordered VSWR's, etc we sat and studied the display on the
>> service monitor. Remembering a USN experience from around 1962 I asked 
>> him
>> to go outside and beat on the guy anchors and terminations with a tire
>> iron
>> from his van. That was the source of the problem, corrosion was causing
>> diode joints and rectification of the RF. Back to the house for several
>> dozen Snap-On chokes Id been stocking and selling for Yuri, VE3???, and
>> they
>> were put over the guys and taped in place. No more IMD. Later Yuri
>> contracted with RatShak to stock them. Since the 160' tower belonged to
>> the
>> site owner we were not about to disconnect the guys and use the large
>> beads!
>> Ive since done that here to all 4 towers.
>> While K9YC's site has a lot of very good information there is also a bit
>> of
>> disagreement with what others have published and I dont see that changing
>> much in my lifetime. He hasnt bothered to reply to my request for a test
>> of
>> a balun feeding OWL fed dipole covering 160-10M and at 1500W. Lets try
>> this
>> with a 4:1 and 9:1 as those are the common ones in use as well as
>> deliberately varying feed line lengths to present worse case scenarios on
>> different bands.
>> One test I rarely see mentioned is to test your coax first.
>> Leave in place and terminate the far end in 50 or 75 Ohms and then tune
>> the
>> bands recording any crud frequencies. Then add a bead balun and
>> reterminate.
>> Record any differences in signal levels. If you have a quiet receiver 
>> then
>> any pickup with the antenna is likely in "antenna mode" as I like to call
>> it. Many get confused with all the technical terms used. Any additional
>> crud
>> picked up in "interference mode" will be small and easily eliminated at
>> the
>> shack end with another bunch of beads and hopefully a decent RF ground.
>> This
>> is no different than the Beverage coax procedure as has been in ON4UN's
>> Low
>> Band DXing and various web pages for awhile.
>> The expense of DXE or other overpriced Beverage "boxes" is a waste of
>> money
>> unless you are incapable of following the well documented alternatives
>> that
>> can be tailored to individual requirements. A one size fits all box can
>> have
>> a wide range of performance in the real world.
>> Carl
>> KM1H
>> ----- Original Message -----
>> From: "Rob Atkinson" <>
>> To: <>
>> Sent: Sunday, September 25, 2011 8:27 AM
>> Subject: Re: [Amps] RF in the Audio
>>> The perceived problem with parallel balanced feedline has nothing to
>>> do with the ability to achieve an acceptable balance in the system and
>>> everything to do with the way most hams use the line and type of
>>> matching network employed.  Roughly 90% of so-called balanced tuners
>>> are either non-symmetrical, inadequate in design or (this is the
>>> closest to honesty) make no claim of being balanced but somehow claim
>>> to handle balanced systems.   The Johnson Matchboxes are genuine
>>> balanced tuners that do the job right by putting RF currents in the
>>> line that cancel and collapse the field.  I've tested this with my
>>> system using current meters and field strength measurements around and
>>> in between my line in several random points.  A better tuner is the
>>> very hard to fine TMC TAC tuner, probably the best commercially
>>> manufactured tuner ever made available to hams.  But many hams express
>>> dissatisfaction with the Matchboxes usually over their alleged limited
>>> matching range.  That gets us into a separate discussion about the
>>> education of hams regarding tuners and their expectations, and is a
>>> topic for TowerTalk.
>>> The common mode problem exists where you have a balanced system, but a
>>> noise point source is closer to one side of the system than the other,
>>> so while you have equal and opposite transmit currents, you can have
>>> c.m. on receive from a local point source near the antenna, such as
>>> noise from a router or power supply in a neighboring home.
>>> Jim,
>>> I don't think I'd employ DX Engineering as some sort of imprimatur or
>>> validator for your work, as they are in the business of making and
>>> selling products for hams.
>>> Having read the rest of your email, I understand your points and your
>>> statements are convincing, on paper at least, but such a choke as you
>>> describe seems to be a solution to a problem that doesn't have to
>>> exist, if an operator were to employ a method of impedance matching
>>> and transfer from balanced feed to unbalanced that would allow for the
>>> isolation of the balanced feed to prevent a complete common mode
>>> circuit.
>>> I can see such a choke being worth a try for someone trying to force a
>>> transfer with an unbalanced network, or with one of the symmetrical
>>> tuners that contain a pair of synchronized roller inductors and a
>>> single common capacitor.  I operated with one of those for a few years
>>> and did in fact experience c.m. issues such as conducted out of band
>>> RF (a very strong electric service spark gap) detuning a vswr
>>> analyzer, but in my case all these problems vanished once I started
>>> isolating the balanced feed lines with inductive coupling (the
>>> aforementioned Matchboxes).  I believe that is a more robust and
>>> reliable solution.
>>> 73
>>> Rob
>>> K5UJ
>>> <<<MANY of the DX Engineering so-called baluns are common mode chokes --
>>> indeed, what is commonly called a "current balun" IS a common mode
>>> choke. Many DXE baluns that transform impedance are ARRAYS of common
>>> mode chokes connected in series and parallel.   If you open up some of
>>> these you will clearly see chokes would not with coax, but with parallel
>>> wires.  And DXE DOES sell a common mode choke. I haven't bought one,
>>> because I can rolll my own that are probably better for one-sixth of the
>>> cost.
>>> I HAVE inserted the bifilar chokes between the output of a Titan 425 and
>>> the antenna tuner and tested at 1.5kW keydown for several minutes from
>>> 1.8 MHz to 28MHz. At that point, the choke sees ONLY the differential
>>> field, and there is VERY little heating because the field from one
>>> conductor cancels the field from the other.  Dissipation due to common
>>> mode current is a very different matter, and is discussed at length in
>>> the tutorial. In essence, if the choke as sufficiently choking high
>>> impedance and the antenna is not very poorly balanced, the common mode
>>> current, and thus the common mode dissipation, is reasonably small.  If
>>> conditions of the application (for example, impedance transformation)
>>> place very high common mode voltage across a choke, the common mode
>>> impedance must be much higher.  In a testing situation, I have set up
>>> very high common mode voltages and placed two chokes in series to
>>> withstand them.  DXE builds some of their impedance transforming arrays
>>> of chokes that way.
>>> As to mismatch -- a study of the fundamentals of transmission lines
>>> would lead one to the conclusion that the loss due to mismatch in the
>>> short length of 100 ohm line that comprises the choke is quite small.
>>> After all, one of the most common uses of parallel wire line (notice
>>> that I do NOT repeat the fiction of calling it a balanced line) is to
>>> minimize the loss due to mismatch when feeding antennas that are wildly
>>> mismatched, like the "one-size'fits-all" dipole that is nowhere near
>>> resonance on most frequencies where it is used.  Think about this --
>>> we're connecting an antenna that could be anything from 5 ohms to 5,000
>>> ohms, plus reactance, to a feedline  that is, perhaps, 400 ohms.  The
>>> insertion of a 24 inch piece of 100 ohm line simply modifies (and not
>>> very much) the impedance of the antenna as seen by the line. And, if
>>> wound using #12 copper, as the chokes I have described are, the loss is
>>> VERY VERY small, as confirmed by my tests.
>>> Now, I'm a guy who plays by the rules, and shares my work FOR those who
>>> play by the rules, and my testing is done at that power level, at duty
>>> cycles consistent with serious contesting. Someone who wants to run more
>>> than 1.5kW can design and test his own solutions. :)
>>> 73, Jim Brown K9YC>>
>>> _______________________________________________
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