He passed away a few years ago. His website is supposed to be still in
operation and maintained by someone else.
I have no idea where it is.
73, Barrie, W7ALW
----- Original Message -----
From: "Jim W7RY" <jimw7ry@gmail.com>
To: "Barrie Smith" <barrie@centric.net>; <amps@contesting.com>
Sent: Sunday, September 25, 2011 2:51 PM
Subject: Re: [Amps] RF in the Audio
>I don't seem to find his web site.
>
> 73
> Jim W7RY
>
>
> --------------------------------------------------
> From: "Barrie Smith" <barrie@centric.net>
> Sent: Sunday, September 25, 2011 11:11 AM
> To: <amps@contesting.com>
> 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" <wlfuqu00@uky.edu>
>> To: <amps@contesting.com>
>> 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: amps-bounces@contesting.com [amps-bounces@contesting.com] On
>>> Behalf
>>> Of Fuqua, Bill L [wlfuqu00@uky.edu]
>>> Sent: Sunday, September 25, 2011 1:15 PM
>>> To: amps@contesting.com
>>> 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: amps-bounces@contesting.com [amps-bounces@contesting.com] On
>>> Behalf
>>> Of Carl [km1h@jeremy.mv.com]
>>> Sent: Sunday, September 25, 2011 12:14 PM
>>> To: Rob Atkinson; amps@contesting.com
>>> 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" <ranchorobbo@gmail.com>
>>> To: <amps@contesting.com>
>>> 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
>>>> Amps@contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>
>>>>
>>>> -----
>>>> No virus found in this message.
>>>> Checked by AVG - www.avg.com
>>>> Version: 10.0.1410 / Virus Database: 1520/3917 - Release Date: 09/24/11
>>>>
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>> _______________________________________________
>>> Amps mailing list
>>> Amps@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>> _______________________________________________
>>> Amps mailing list
>>> Amps@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
>>
>>
>>
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
>
>
----- Original Message -----
From: "Jim W7RY" <jimw7ry@gmail.com>
To: "Barrie Smith" <barrie@centric.net>; <amps@contesting.com>
Sent: Sunday, September 25, 2011 2:51 PM
Subject: Re: [Amps] RF in the Audio
>I don't seem to find his web site.
>
> 73
> Jim W7RY
>
>
> --------------------------------------------------
> From: "Barrie Smith" <barrie@centric.net>
> Sent: Sunday, September 25, 2011 11:11 AM
> To: <amps@contesting.com>
> 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" <wlfuqu00@uky.edu>
>> To: <amps@contesting.com>
>> 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: amps-bounces@contesting.com [amps-bounces@contesting.com] On
>>> Behalf
>>> Of Fuqua, Bill L [wlfuqu00@uky.edu]
>>> Sent: Sunday, September 25, 2011 1:15 PM
>>> To: amps@contesting.com
>>> 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: amps-bounces@contesting.com [amps-bounces@contesting.com] On
>>> Behalf
>>> Of Carl [km1h@jeremy.mv.com]
>>> Sent: Sunday, September 25, 2011 12:14 PM
>>> To: Rob Atkinson; amps@contesting.com
>>> 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" <ranchorobbo@gmail.com>
>>> To: <amps@contesting.com>
>>> 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
>>>> Amps@contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>
>>>>
>>>> -----
>>>> No virus found in this message.
>>>> Checked by AVG - www.avg.com
>>>> Version: 10.0.1410 / Virus Database: 1520/3917 - Release Date: 09/24/11
>>>>
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>> _______________________________________________
>>> Amps mailing list
>>> Amps@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>> _______________________________________________
>>> Amps mailing list
>>> Amps@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
>>
>>
>>
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|