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Re: [Amps] RF in the Audio

To: "Rob Atkinson" <>, <>
Subject: Re: [Amps] RF in the Audio
From: "Carl" <>
Date: Sun, 25 Sep 2011 12:14:16 -0400
List-post: <">>
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.


----- 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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