Re: KPA500 faulting on high VSWR on power rise

[William Shanney]

I have found that a 4:1 balun is seldom the proper choice for a ladder
line interface. I measure the impedance at the interface and then select
the balun type (usually a 1:1). The biggest problem I've had is the 4:1
transforming the impedance too low for the tuner. This can result in
over stress on the components as the power is increased. If I don't have
an easy to match ladder line interface I add or subtract line length
until I get one.

73

Bill, W6QR

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[Rick WA6NHC-2]

One exception is when the dipole is used on multiple bands, then a 4:1
may be required.  That was the case for my 370' 80M EDZ (two opposing
5/8 wave, center fed).  That is specifically a non-resonant antenna on
any ham band but it performed best with the 4:1 instead of the 1:1.  It
was a compromise either way, this was the better choice since I needed
that antenna to work on all bands.  If it was only 80M, the 1:1 was the
better choice.

While I am not a fan of MFJ so consider it suspect in this case, I also
believe that since the common mode choke (referred to as a balun in this
thread) should GREATLY exceed the voltage expectations for simple
overhead.  The cost differences for higher ratings are not significant. 
In my stations, I use the 10KW rated devices from DX Engineering (KPA500
amp) and I've had no issues with them, even at extreme SWR mismatch (QRO
on 160M into the above dipole, 20:1 unmatched with a Heathkit tuner). 
My new station will be entirely resonant, so a 1:1 CMC will suffice but
I'll still use the high power devices.

The bottom line here is that the antenna in this thread is not resonant
(because of the feed choice, which is understandable for multiband use),
the voltages presented will be extreme, component overkill (and a more
qualified tuner) should be used.  It's not a fault of the amp, but of
the matching network.

It is also KEY that the LEAST amount of coax is used (under 10' to the
final) because the high SWR is present there as well, so the losses will
be extreme and it could even exceed the voltage limits of the coax,
depending on brand, age and type.  Been there, done that (darned HOA
limits).  This also means that the coax should be tested, from time to
time, until proven worthy.

Rick NHC


On 2/24/2018 9:21 AM, William Shanney wrote:
> I have found that a 4:1 balun is seldom the proper choice for a ladder
> line interface. I measure the impedance at the interface and then
> select the balun type (usually a 1:1). The biggest problem I've had is
> the 4:1 transforming the impedance too low for the tuner. This can
> result in over stress on the components as the power is increased. If
> I don't have an easy to match ladder line interface I add or subtract
> line length until I get one.

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[K7TV]

I am not familiar with the protector you use, and how it is specified, but it seems to me that any such device intended for use on a transmission line must strike a fine balance between low breakdown voltage (for protecting your gear) and high breakdown voltage (to accommdate the power level in combination with swr). The higher the swr, the higher the max voltage, for a given power level. So, the manufacturer of the protective device should probably not just tell you a wattage rating, but also the acceptable swr level for that power. The higher swr level that is acceptable, the less protection is provided for your rig and tuner, etc. My guess would be that those protectors are meant for use at low swr. A multiband dipole fed with ladder line + balun + coax will have high swr on the coax at least on some bands, regardless of whether it is 1:1 or 4:1 or whatever. I would not expect the impedance to be close to 50 ohms on the coax. You might want to forget about the protection.
 Or, build a spark gap protector to be located on the ladder line. Or abandon the ladder+balun+coax approach and go to an end-fed dipole with transformer that can provide low impedance coax feed on all bands.

73,
Erik K7TV

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf Of Rick WA6NHC
Sent: Saturday, February 24, 2018 10:41 AM
To: [hidden email]
Subject: Re: [Elecraft] KPA500 faulting on high VSWR on power rise

One exception is when the dipole is used on multiple bands, then a 4:1 may be required.  That was the case for my 370' 80M EDZ (two opposing
5/8 wave, center fed).  That is specifically a non-resonant antenna on any ham band but it performed best with the 4:1 instead of the 1:1.  It was a compromise either way, this was the better choice since I needed that antenna to work on all bands.  If it was only 80M, the 1:1 was the better choice.

While I am not a fan of MFJ so consider it suspect in this case, I also believe that since the common mode choke (referred to as a balun in this
thread) should GREATLY exceed the voltage expectations for simple overhead.  The cost differences for higher ratings are not significant. In my stations, I use the 10KW rated devices from DX Engineering (KPA500
amp) and I've had no issues with them, even at extreme SWR mismatch (QRO on 160M into the above dipole, 20:1 unmatched with a Heathkit tuner). My new station will be entirely resonant, so a 1:1 CMC will suffice but I'll still use the high power devices.

The bottom line here is that the antenna in this thread is not resonant (because of the feed choice, which is understandable for multiband use), the voltages presented will be extreme, component overkill (and a more qualified tuner) should be used.  It's not a fault of the amp, but of the matching network.

It is also KEY that the LEAST amount of coax is used (under 10' to the
final) because the high SWR is present there as well, so the losses will be extreme and it could even exceed the voltage limits of the coax, depending on brand, age and type.  Been there, done that (darned HOA limits).  This also means that the coax should be tested, from time to time, until proven worthy.

Rick NHC

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[Rick WA6NHC-2]

I’ve always presumed that the ratings were based on 1:1 SWR as there is no reasonable way to define it otherwise.   Actual ratings at other loads can be inferred on that basis.

An end fed dipole is MUCH harder to tame than a dipole (or fan dipole) and inherently challenging to keep the RF away from places like the shack.

Rick WA6NHC

Smell Czech correction happen

> On Feb 24, 2018, at 11:42 AM, Erik Basilier <[hidden email]> wrote:
>
> So, the manufacturer of the protective device should probably not just tell you a wattage rating, but also the acceptable swr level for that power.

> Or abandon the ladder+balun+coax approach and go to an end-fed dipole with transformer that can provide low impedance coax feed on all bands.
>
> 73,
> Erik
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[K7TV]

A lot of users seem pleased with end-fed wire antennas of recent commercial models. Such antennas should not behave much differently compared to end-fed verticals such as the R5 that I have had for many years and which creates no problems even at high power. Like that antenna, the wire models now becoming popular use a high ratio wide-band impedance transformer. The R5 also includes tiny radials and a common mode choke at the feedpoint. The R5 behaves well even at high power with its feedline length of maybe 50ft, and there is not enough RF in the shack to affect the operation of radios or other equipment. However, for good measure I added a second common mode choke in the form of several ferrite snap-on's about 10 ft from the feedpoint and then found a noticeable reduction in shack RF (measured in the shack using an MFJ RF current sensor). I believe there are lots of satisfied users of the Cushcraft endfed verticals. As to the wire end-fed's I am constructing an imitation of a popular commercial version, and will find out for myself if there are any difficulties. I will add a common mode choke placed either at the feed point (like the R5) and a separate counterpoise, or I might try placing the choke a distance away from the feedpoint to let a portion of the feedline act as counterpoise. Again, a second common mode choke further down the feedline will likely be added. Based on the positive reports by so many users of the commercial versions, who apparently don't add any common-mode chokes, I am fairly confident of success.

73,
Erik K7TV

-----Original Message-----
From: Rick Bates (WA6NHC) [mailto:[hidden email]]
Sent: Saturday, February 24, 2018 1:35 PM
To: Erik Basilier <[hidden email]>
Cc: [hidden email]
Subject: Re: [Elecraft] KPA500 faulting on high VSWR on power rise

I’ve always presumed that the ratings were based on 1:1 SWR as there is no reasonable way to define it otherwise.   Actual ratings at other loads can be inferred on that basis.

An end fed dipole is MUCH harder to tame than a dipole (or fan dipole) and inherently challenging to keep the RF away from places like the shack.

Rick WA6NHC

Smell Czech correction happen

> On Feb 24, 2018, at 11:42 AM, Erik Basilier <[hidden email]> wrote:
>
> So, the manufacturer of the protective device should probably not just tell you a wattage rating, but also the acceptable swr level for that power.

> Or abandon the ladder+balun+coax approach and go to an end-fed dipole with transformer that can provide low impedance coax feed on all bands.
>
> 73,
> Erik

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[Rick WA6NHC-2]

I have an R7 (end fed vertical 40-10M).  It and a 80M dipole are my
current antennas, until I plant a tower later this year (55' US Tower,
motor drive, tilt over).  I have to admit that I'm not a fan of vertical
antennas.

Since I moved here last year and haven't gotten the tower up yet, the R7
is 'adequate' for a temporary antenna, but dipoles are more effective. 
It also provides decent diversity reception with a horizontal dipole. 
(The new antenna, when it gets up, is a SteppIR DB-42 at 60', resonant
80-6M then I'll add in a Beverage for RX only since I have the space now
or a K9AY.  I have a 160M inverted L up too (bend at about 90'), using
the underground water pipe as the counterpoise, buried down 4-5', 1:1
CMC at the base, it was quick and simple.  I'm adding a tuning network
to that so that will be a 80/160M resonant vertical, giving me another
option on 80M.)  The beautiful part is that with only 2 resonant
antennas, I can cover 160-6M once I'm done, perfectly matching the new
KPA1500.  Simple ROCKS!

The R7 (like the R5, 8, 9) has a matching network (torroids mostly) in
the black box and trap and capacitive elements on the main element and
short radials at the base to get it to load, but that doesn't meant that
it's efficient; it means it presents a load that is acceptable (so does
a dummy load).  The EDZ at my last QTH beat  the R7 in almost all
scenarios on any band, unless the other station was off the ends of the
dipole, then it was even money; which left the R7 being used for diversity.

So it works, but I wouldn't rate it highly unless one is limited by
space, HOA or similar.  It reacts badly when near (w/in 10' of) any
metal and the base must be at least 10' AGL.  Adding more choking is
very wise.  I would expect similar results from a non-commercial
antenna, unless used only on one band (and it's still a challenge to tame).

Dipoles are much simpler, even when used for multiband operations.  Cut
the antenna to the desired (available) length, add the feedline,
measure, adjust for local conditions (add/cut feedline for open wire or
antenna for single band) then see how it plays.  Add common mode choke
transformation (1:1 vs 4:1) to keep the currents outside the shack, feed
with no more than 10' of coax to the final; have fun.

Reality beats textbook every time since the textbook doesn't know about
the septic field, tree proximity or the dog kennel fence, let alone
actual height above ground which isn't always the top layer of dirt.  Go
play, have fun, it's part of the long tradition of ham radio.

73,
Rick NHC


On 2/24/2018 3:45 PM, Erik Basilier wrote:
> A lot of users seem pleased with end-fed wire antennas of recent commercial models. Such antennas should not behave much differently compared to end-fed verticals such as the R5 that I have had for many years and which creates no problems even at high power. Like that antenna, the wire models now becoming popular use a high ratio wide-band impedance transformer. The R5 also includes tiny radials and a common mode choke at the feedpoint. The R5 behaves well even at high power with its feedline length of maybe 50ft, and there is not enough RF in the shack to affect the operation of radios or other equipment. However, for good measure I added a second common mode choke in the form of several ferrite snap-on's about 10 ft from the feedpoint and then found a noticeable reduction in shack RF (measured in the shack using an MFJ RF current sensor). I believe there are lots of satisfied users of the Cushcraft endfed verticals. As to the wire end-fed's I am constructing an imitation of a popular commercial version, and will find out for myself if there are any difficulties. I will add a common mode choke placed either at the feed point (like the R5) and a separate counterpoise, or I might try placing the choke a distance away from the feedpoint to let a portion of the feedline act as counterpoise. Again, a second common mode choke further down the feedline will likely be added. Based on the positive reports by so many users of the commercial versions, who apparently don't add any common-mode chokes, I am fairly confident of success.
>
> 73,
> Erik K7TV
>
>


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[K7TV]

Rick,

I didn't mean to imply anything about the efficiency of the R5/R7; they are quite short with lots of compromises, and there are certainly ways a vertical antenna in general may, in a given installation, have specific limitations. Certainly I rarely use mine as I get much better results with my horizontal beam (Sommer XP708). My comments regarding the R5 were meant to be only about issues with matching and rf in the shack etc.

I agree that reality isn't always in agreement with the theories at hand. That is why I plan to compare the end-fed with a center-fed before I commit to it for personal use. In a previous thread I have outlined my planned comparison, "side by side", trying my darnedest to notice any performance loss resulting from the endfeed. We shall see about that. I won't take up space here to repeat all the discussion about that testing. What I have tried to say in this thread, is that I am rather confident that I can "tame" the end-fed in the sense that it won't cause problems with rf in the shack, and regarding performance I will assume there is no problem until my comparison shows that there is.

The original poster had a problem with coaxial protection devices, and if I understood his configuration correctly, such problems could be anticipated in that configuration. I pointed to end-feed with tunerless low swr as a potential approach to make those protection devices work as intended, with a radiator that is the same length wire as what he had.

Your antenna farm is a separate subject, as is mine, and in this thread I will just comment briefly on those subjects. I got interested in SO2R, but don't have space for two towers/beams. You may not be thinking about SO2R, but if you are, and if you too can't put up a second tower/beam, then you might want to think twice about using SteppIR. With a beam that can work multiple bands without retuning, I use a multiplexer that allows two transmitters to use the same beam as if I had two separate ones. (Minus the capability to point them in different directions!). If an end-fed wire antenna works well without tuner on multiple bands, it can also be used with a multiplexer to perform instantly on another band, without retuning. Not so with a simple center-fed dipole (but a fan or trapped dipole would be ok). My other comment is about your verticals fed against a pipe in the ground. When I was using inverted L's for 160 and 80, I first tried them against a single, 4" wide copper s
 trap going part way around the house and tied to a few ground rods here and there. Then I tried it against two zigging wires used as elevated radials. This worked much much better. Like others have said so often and so well: If you are going to bury radials, it will take many of them.

73,
Erik K7TV

-----Original Message-----
From: Rick WA6NHC [mailto:[hidden email]]
Sent: Saturday, February 24, 2018 10:30 PM
To: Erik Basilier <[hidden email]>
Cc: [hidden email]
Subject: Re: [Elecraft] KPA500 faulting on high VSWR on power rise

I have an R7 (end fed vertical 40-10M).  It and a 80M dipole are my current antennas, until I plant a tower later this year (55' US Tower, motor drive, tilt over).  I have to admit that I'm not a fan of vertical antennas.

Since I moved here last year and haven't gotten the tower up yet, the R7 is 'adequate' for a temporary antenna, but dipoles are more effective. It also provides decent diversity reception with a horizontal dipole. (The new antenna, when it gets up, is a SteppIR DB-42 at 60', resonant 80-6M then I'll add in a Beverage for RX only since I have the space now or a K9AY.  I have a 160M inverted L up too (bend at about 90'), using the underground water pipe as the counterpoise, buried down 4-5', 1:1 CMC at the base, it was quick and simple.  I'm adding a tuning network to that so that will be a 80/160M resonant vertical, giving me another option on 80M.)  The beautiful part is that with only 2 resonant antennas, I can cover 160-6M once I'm done, perfectly matching the new KPA1500.  Simple ROCKS!

The R7 (like the R5, 8, 9) has a matching network (torroids mostly) in the black box and trap and capacitive elements on the main element and short radials at the base to get it to load, but that doesn't meant that it's efficient; it means it presents a load that is acceptable (so does a dummy load).  The EDZ at my last QTH beat  the R7 in almost all scenarios on any band, unless the other station was off the ends of the dipole, then it was even money; which left the R7 being used for diversity.

So it works, but I wouldn't rate it highly unless one is limited by space, HOA or similar.  It reacts badly when near (w/in 10' of) any metal and the base must be at least 10' AGL.  Adding more choking is very wise.  I would expect similar results from a non-commercial antenna, unless used only on one band (and it's still a challenge to tame).

Dipoles are much simpler, even when used for multiband operations.  Cut the antenna to the desired (available) length, add the feedline, measure, adjust for local conditions (add/cut feedline for open wire or antenna for single band) then see how it plays.  Add common mode choke transformation (1:1 vs 4:1) to keep the currents outside the shack, feed with no more than 10' of coax to the final; have fun.

Reality beats textbook every time since the textbook doesn't know about the septic field, tree proximity or the dog kennel fence, let alone actual height above ground which isn't always the top layer of dirt.  Go play, have fun, it's part of the long tradition of ham radio.

73,
Rick NHC


On 2/24/2018 3:45 PM, Erik Basilier wrote:
> A lot of users seem pleased with end-fed wire antennas of recent commercial models. Such antennas should not behave much differently compared to end-fed verticals such as the R5 that I have had for many years and which creates no problems even at high power. Like that antenna, the wire models now becoming popular use a high ratio wide-band impedance transformer. The R5 also includes tiny radials and a common mode choke at the feedpoint. The R5 behaves well even at high power with its feedline length of maybe 50ft, and there is not enough RF in the shack to affect the operation of radios or other equipment. However, for good measure I added a second common mode choke in the form of several ferrite snap-on's about 10 ft from the feedpoint and then found a noticeable reduction in shack RF (measured in the shack using an MFJ RF current sensor). I believe there are lots of satisfied users of the Cushcraft endfed verticals. As to the wire end-fed's I am constructing an imitation
 of a popular commercial version, and will find out for myself if there are any difficulties. I will add a common mode choke placed either at the feed point (like the R5) and a separate counterpoise, or I might try placing the choke a distance away from the feedpoint to let a portion of the feedline act as counterpoise. Again, a second common mode choke further down the feedline will likely be added. Based on the positive reports by so many users of the commercial versions, who apparently don't add any common-mode chokes, I am fairly confident of success.
>
> 73,
> Erik K7TV
>
>


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[Rick WA6NHC-2]

Hi Erik,

I'll keep this short as the thread will likely be closed soon (or
should).  What I have up now is Field Day style, simple antennas (the
inverted L for example, an 80M dipole, R7) shot into the trees so I
could get on, pending the install of 'the real station', hi.  The water
pipe (300+' in two directions, deep enough to never freeze) is the L
counterpoise, for now.  It isn't ideal but it works and isn't meant for
forever.

I will be installing a lightning protection and counterpoise system with
lots of copper, ground rods etc, which will come to box (for feed line,
rotor control) at the tower end of the conduit to the shack (AND tie
into the house grounding per code).  The box will have hardline from the
house, coax for the tower, matching network for the Inverted L and the
surge and lightning devices on each feed (static or lightning stays
OUTside).  I'll also put an AC power outlet at the base, for occasional
power tool use and a wifi web cam (may as well, I have to power the
electric winch motor).

I DX, I don't contest, so I don't need SO2R (other than the second rx
for DX chasing on splits).  Should that someday change, I'm blessed with
the space for a tower farm or I'll put the EDZ up (kind of a favorite, I
worked a LOT of DX on that dipole).  With the KAT500 (or KPA1500), rapid
QSY isn't an issue on the EDZ.

No slam was inferred or taken on the Cushcraft; only that the
compromises add up to make it work, but not as well as a tuned dipole.

I'm not sure that an end fed wire antenna will work well on multiple
bands without a fair amount of effort (remote tuner at least, absolutely
a CMC to back that up).  The voltages at radical SWR (non-resonant
afterall) can be high.  Isolating the radiation to the wire is a major
issue, that antenna tends to want the feedline (coax commonly) as the
counterpoise, bringing RF into the shack (and why I went with the
inverted L which partly warms the worms).

73,
Rick NHC


On 2/24/2018 10:53 PM, Erik Basilier wrote:
> Your antenna farm is a separate subject, as is mine, and in this thread I will just comment briefly on those subjects. I got interested in SO2R, but don't have space for two towers/beams. You may not be thinking about SO2R, but if you are, and if you too can't put up a second tower/beam, then you might want to think twice about using SteppIR. With a beam that can work multiple bands without retuning, I use a multiplexer that allows two transmitters to use the same beam as if I had two separate ones. (Minus the capability to point them in different directions!). If an end-fed wire antenna works well without tuner on multiple bands, it can also be used with a multiplexer to perform instantly on another band, without retuning. Not so with a simple center-fed dipole (but a fan or trapped dipole would be ok). My other comment is about your verticals fed against a pipe in the ground. When I was using inverted L's for 160 and 80, I first tried them against a single, 4" wide copper strap going part way around the house and tied to a few ground rods here and there. Then I tried it against two zigging wires used as elevated radials. This worked much much better. Like others have said so often and so well: If you are going to bury radials, it will take many of them.
>
> 73,
> Erik K7TV
>
>


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[K7TV]

Hi Rick,

I distinguish between the radiator and the feed method, and therefore I would not say "the compromises add up to make it work".

To me, moving a dipole's feed from center to the end (or to somewhere in between) doesn't change its radiating characteristic as a dipole. Whether the feed method is free of loss, or free of diverting power off of the dipole are complicated questions better answered by serious testing of an individual design than by simple rules of thumb. I haven't recently looked into the "box" of my Cushcraft vertical, but it has been reported that there is a separate impedance transformer and a separate common mode choke. A very low swr is achieved without a tuner, at full legal power (within bandwidth limitations; people have blown up toroids when going outside bandwidth on 40m on the R7). There is obviously not a high level of power lost in the "box", or it would not survive full legal power. Thus this is not like some antennas that sacrifice efficiency by swamping in order to achieve low swr. Therefore most of any observed loss of performance can be attributed to the radiator and its en
 vironment, in combination with some rf going on the outside of the feedline (which is not completely prevented by the one CMC in the box). Some end-fed antennas use a non-resonant radiatior. This invariably results in swr high enough to require a tuner. Since the R5/R7 has low swr and not very high losses in the "box", the radiator obviously is resonant on all bands, presenting a non-reactive impedance at the end. That impedance must be very high since it is at the end. The very high non-reactive impedance makes it comparable to the end impedance of a resonant halfwave wire dipole even if the Cushcraft radiator is in other respects different. That is my basis for assuming that the Cushcraft "box" can be compared to what you would put at the end of a wire dipole when moving the feed from its center to one end.

An end-fed dipole can be resonant and present a very high but non-reactive impedance on multiple (higher) bands. This can allow a fixed, broad-band impedance transformer to provide low swr on multiple bands without a tuner. Yes, one has to be suspicious of possible losses in the transformer, and it takes a fight to stop rf from going onto the outside of the feedline. But since one avoids swr-caused losses in coax, and balun losses, and tuner losses with end-feed, I consider it an alternative worthy of serious consideration. If optimal protection against high voltages on the coax is a main goal, that just might tip the scale to make the end-fed dipole the winner.

73,
Erik K7TV
 

-----Original Message-----
From: Rick WA6NHC [mailto:[hidden email]]
Sent: Sunday, February 25, 2018 2:52 AM
To: Erik Basilier <[hidden email]>
Cc: [hidden email]
Subject: Re: [Elecraft] KPA500 faulting on high VSWR on power rise

Hi Erik,

I'll keep this short as the thread will likely be closed soon (or should).  What I have up now is Field Day style, simple antennas (the inverted L for example, an 80M dipole, R7) shot into the trees so I could get on, pending the install of 'the real station', hi.  The water pipe (300+' in two directions, deep enough to never freeze) is the L counterpoise, for now.  It isn't ideal but it works and isn't meant for forever.

I will be installing a lightning protection and counterpoise system with lots of copper, ground rods etc, which will come to box (for feed line, rotor control) at the tower end of the conduit to the shack (AND tie into the house grounding per code).  The box will have hardline from the house, coax for the tower, matching network for the Inverted L and the surge and lightning devices on each feed (static or lightning stays OUTside).  I'll also put an AC power outlet at the base, for occasional power tool use and a wifi web cam (may as well, I have to power the electric winch motor).

I DX, I don't contest, so I don't need SO2R (other than the second rx for DX chasing on splits).  Should that someday change, I'm blessed with the space for a tower farm or I'll put the EDZ up (kind of a favorite, I worked a LOT of DX on that dipole).  With the KAT500 (or KPA1500), rapid QSY isn't an issue on the EDZ.

No slam was inferred or taken on the Cushcraft; only that the compromises add up to make it work, but not as well as a tuned dipole.

I'm not sure that an end fed wire antenna will work well on multiple bands without a fair amount of effort (remote tuner at least, absolutely a CMC to back that up).  The voltages at radical SWR (non-resonant
afterall) can be high.  Isolating the radiation to the wire is a major issue, that antenna tends to want the feedline (coax commonly) as the counterpoise, bringing RF into the shack (and why I went with the inverted L which partly warms the worms).

73,
Rick NHC




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