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Re: [Amps] RF in the Audio

Subject: Re: [Amps] RF in the Audio
From: Richard Solomon <>
Date: Sun, 25 Sep 2011 10:47:37 -0700
List-post: <">>
Johnson Matchbox ??

73, Dick, W1KSZ

On Sun, Sep 25, 2011 at 10:20 AM, Fuqua, Bill L <> wrote:

>   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
> 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>>
> > _______________________________________________
> > Amps mailing list
> >
> >
> >
> >
> > -----
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