Elecraft

KPA1500 in the IARU Contest Last weekend

Classic

List

Threaded

17 messages Options

Elecraft mailing list

KPA1500 in the IARU Contest Last weekend

A correspondent asked me why I needed to tune a resonant antenna.
The reason was because although the Yagi was tuned to resonate at about 7.130MHz it unfortunately has a rather narrow bandwidth. I needed to operate SSB in this contest in ITU Region 1 SSB, which is between 7.080MHz and 7.200MHZ. At 7.080MHz the SWR (with tuner bypassed) was 1.75:1 & at 7.200 was 1.95:1. I would be operating at power so I preferred to tune for 1.1:1.
Yes I know the Yagi is not very good with that narrow bandwidth, but it is what it is. Normally I operate CW only on 40M & tune it to 7.030 with the bandwidth covering the preferred Region 1 CW portion of the band ie7.000 to 7.040 and the tuner is not needed.
73 Ray G3XLG

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Jim AB3CV

Re: KPA1500 in the IARU Contest Last weekend

Since it is so narrow I suspect it may be a trapped design or have loading
coils which at 1500w may be heating and detuning as a result.

73

jim ab3cv

On Wed, Jul 15, 2020 at 11:45 AM Ray Spreadbury via Elecraft <
[hidden email]> wrote:

>
>
> A correspondent asked me why I needed to tune a resonant antenna.
> The reason was because although the Yagi was tuned to resonate at about
> 7.130MHz it unfortunately has a rather narrow bandwidth. I needed to
> operate SSB in this contest in ITU Region 1 SSB, which is between 7.080MHz
> and 7.200MHZ. At 7.080MHz the SWR (with tuner bypassed) was 1.75:1 & at
> 7.200 was 1.95:1. I would be operating at power so I preferred to tune for
> 1.1:1.
> Yes I know the Yagi is not very good with that narrow bandwidth, but it is
> what it is. Normally I operate CW only on 40M & tune it to 7.030 with the
> bandwidth covering the preferred Region 1 CW portion of the band ie7.000 to
> 7.040 and the tuner is not needed.
> 73 Ray G3XLG
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

john@kk9a.com

Re: KPA1500 in the IARU Contest Last weekend

In reply to this post by Elecraft mailing list

That is quite an assumption. A 2el 40m beam with large efficient
High-Q loading coils will have less bandwidth than for example one of
the popular US manufactured beams that use 68 turns of small wire in
each coil. The latter is more likely to have heating issues. I have
never noticed any SWR changes or amplifier re-tuning with my 40m
OptiBeams during heavy use.

John KK9A

Jim Miller AB3CV wrote:

Since it is so narrow I suspect it may be a trapped design or have loading
coils which at 1500w may be heating and detuning as a result.

73

jim ab3cv

On Wed, Jul 15, 2020 at 11:45 AM Ray Spreadbury via Elecraft <
elecraft at mailman.qth.net> wrote:

Elecraft mailing list

Re: KPA1500 in the IARU Contest Last weekend

Ferrite-cored chokes (balun) heat up and change apparent swr.

David G3UNA/G6CP

> On 15 July 2020 at 17:36 [hidden email] wrote:
>
>
> That is quite an assumption. A 2el 40m beam with large efficient
> High-Q loading coils will have less bandwidth than for example one of
> the popular US manufactured beams that use 68 turns of small wire in
> each coil. The latter is more likely to have heating issues. I have
> never noticed any SWR changes or amplifier re-tuning with my 40m
> OptiBeams during heavy use.
>
> John KK9A
>
>
> Jim Miller AB3CV wrote:
>
> Since it is so narrow I suspect it may be a trapped design or have loading
> coils which at 1500w may be heating and detuning as a result.
>
> 73
>
> jim ab3cv
>
> On Wed, Jul 15, 2020 at 11:45 AM Ray Spreadbury via Elecraft <
> elecraft at mailman.qth.net> wrote:
>
> >
> >
> > A correspondent asked me why I needed to tune a resonant antenna.
> > The reason was because although the Yagi was tuned to resonate at about
> > 7.130MHz it unfortunately has a rather narrow bandwidth. I needed to
> > operate SSB in this contest in ITU Region 1 SSB, which is between 7.080MHz
> > and 7.200MHZ. At 7.080MHz the SWR (with tuner bypassed) was 1.75:1 & at
> > 7.200 was 1.95:1. I would be operating at power so I preferred to tune for
> > 1.1:1.
> > Yes I know the Yagi is not very good with that narrow bandwidth, but it is
> > what it is. Normally I operate CW only on 40M & tune it to 7.030 with the
> > bandwidth covering the preferred Region 1 CW portion of the band ie7.000 to
> > 7.040 and the tuner is not needed.
> > 73 Ray G3XLG
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

Jim Brown-10

Re: KPA1500 in the IARU Contest Last weekend

On 7/15/2020 11:46 AM, CUTTER DAVID via Elecraft wrote:
> Ferrite-cored chokes (balun) heat up and change apparent swr.

Not if they are properly designed and properly applied. And not all
antennas can be choked -- in general, only resonant antennas can be
effectively choked. Chokes applied to non-resonant and/or poorly
balanced antennas (like OCF wires) are, in general, NOT effective, and
WILL likely overheat.

I suggest a study of
k9yc.com/RFI-Ham.pdf and
http://k9yc.com/2018Cookbook.pdf

73, Jim K9YC
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Elecraft mailing list

Re: KPA1500 in the IARU Contest Last weekend

Elecraft mailing list

Re: KPA1500 in the IARU Contest Last weekend

In reply to this post by Jim Brown-10

Size is the most important parameter.

I've read your tutorials several times and they are an inspiration but it's just like linear amplifiers: you can't say an amplifier designed for intermittent service like ssb or cw is poorly designed because it doesn't pass the BOK test. It's horses for courses. A properly designed choke for an ocfd will not over-heat but these are few and far between it seems.

David G3UNA/G6CP

> On 15 July 2020 at 21:07 Jim Brown <[hidden email]> wrote:
>
>
> On 7/15/2020 11:46 AM, CUTTER DAVID via Elecraft wrote:
> > Ferrite-cored chokes (balun) heat up and change apparent swr.
>
> Not if they are properly designed and properly applied. And not all
> antennas can be choked -- in general, only resonant antennas can be
> effectively choked. Chokes applied to non-resonant and/or poorly
> balanced antennas (like OCF wires) are, in general, NOT effective, and
> WILL likely overheat.
>
> I suggest a study of
> k9yc.com/RFI-Ham.pdf and
> http://k9yc.com/2018Cookbook.pdf
>
> 73, Jim K9YC
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

Jim Brown-10

Re: KPA1500 in the IARU Contest Last weekend

In reply to this post by Elecraft mailing list

On 7/15/2020 1:36 PM, CUTTER DAVID wrote:
> It's all about size. Bigger core helps,

Dave,

No, it is NOT about size. It is about design of the entire antenna
system, including the antenna, the feedline, and other parts needed to
make the SYSTEM work. The principal characteristic of a common mode
choke is the resistive component of its common mode impedance at the
operating frequency(ies) where it will be used. Further, dissipation in
the choke occurs at least as much in the WIRE that is wound around the
core as in the core itself.

There is another fundamental error in many antenna systems that ONLY
looks at matching to the transmitter at the transmitter, ignoring the
match between the antenna and the transmission line, using high
impedance, parallel wire line, and using a random center-fed or
off-center fed horizontal wire on all bands. Yes, the transmitter can be
made to supply power to the feedline, yes, it will get to the antenna,
and yes, it will radiate. But it may not receive all that well due to
common mode current on the line from noise sources in our own homes and
those of our neighbors. THAT is the problem with using a decades-old
design for a world where there was 20 dB less noise than most of us face
today.

so a core that is OK for ssb
> and cw might be undersized for AM or some data modes. Just like linear
> amplifiers.

So it is NOT the size of the core, it's the design of the antenna
system. HFTA author and retired ARRL Antenna Book and Handbook editor
Dean Straw, N6BV, published an excellent piece in QST 6-8 years ago
called "Don't Blow Up Your Balun," in which he pointed out the
differential mode dissipation in chokes, which can be extremely high if
the choke is at a very high current point in a mismatched line. When he
passed it to me for review, I noted that these losses were in addition
to the common mode dissipation, and he revised the piece to reflect that.

you can't
> label something poorly designed because it doesn't pass the BOK test.

BOK?

73, Jim K9YC

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Vic Rosenthal

Re: KPA1500 in the IARU Contest Last weekend

Re open-wire fed antennas:

If the antenna is well-balanced and fed via a true balanced antenna
tuner (preferably link-coupled) then there shouldn't be a problem with
common mode currents.

Yes, you have to worry about nearby objects unbalancing the antenna,
which is less of a problem with a choked coax-fed dipole. But being able
to use a very simple single antenna from (for example) 7 to 28 mHz. with
relatively good efficiency is advantageous.

My experiments with baluns seem to indicate that just using a current
balun to go from an unbalanced transmitter or tuner to a balanced line
works poorly unless you cancel out the reactance with a balanced network
on the antenna side of the balun. All these tuners with "balanced"
outputs provided by a balun (often a voltage balun) do not work well at all.

My best result with balanced lines has been with the Johnson Matchbox.
It's a shame that there doesn't seem to be an equivalent available today
(and it wouldn't be easy to procure the parts to build one).

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
On 16/07/2020 6:26, Jim Brown wrote:

> On 7/15/2020 1:36 PM, CUTTER DAVID wrote:
>> It's all about size. Bigger core helps,
>
> Dave,
>
> No, it is NOT about size. It is about design of the entire antenna
> system, including the antenna, the feedline, and other parts needed to
> make the SYSTEM work. The principal characteristic of a common mode
> choke is the resistive component of its common mode impedance at the
> operating frequency(ies) where it will be used. Further, dissipation in
> the choke occurs at least as much in the WIRE that is wound around the
> core as in the core itself.
>
> There is another fundamental error in many antenna systems that ONLY
> looks at matching to the transmitter at the transmitter, ignoring the
> match between the antenna and the transmission line, using high
> impedance, parallel wire line, and using a random center-fed or
> off-center fed horizontal wire on all bands. Yes, the transmitter can be
> made to supply power to the feedline, yes, it will get to the antenna,
> and yes, it will radiate. But it may not receive all that well due to
> common mode current on the line from noise sources in our own homes and
> those of our neighbors. THAT is the problem with using a decades-old
> design for a world where there was 20 dB less noise than most of us face
> today.
>
> so a core that is OK for ssb
>> and cw might be undersized for AM or some data modes. Just like linear
>> amplifiers.
>
> So it is NOT the size of the core, it's the design of the antenna
> system. HFTA author and retired ARRL Antenna Book and Handbook editor
> Dean Straw, N6BV, published an excellent piece in QST 6-8 years ago
> called "Don't Blow Up Your Balun," in which he pointed out the
> differential mode dissipation in chokes, which can be extremely high if
> the choke is at a very high current point in a mismatched line. When he
> passed it to me for review, I noted that these losses were in addition
> to the common mode dissipation, and he revised the piece to reflect that.
>
> you can't
>> label something poorly designed because it doesn't pass the BOK test.
>
> BOK?
>
> 73, Jim K9YC

Elecraft mailing list

Re: KPA1500 in the IARU Contest Last weekend

In reply to this post by Jim Brown-10

Jim
We're drifting off topic and you're pushing at an open door.

I accept that wire size has an influence, but in my experience on smaller cores (UK limit is 400W) wound with RG316 I have observed the core getting hotter than the wire.

BOK = Brick On Key. I think it was Alpha that used this in their advertising.

So, in the protagonist's system, if he finds his swr climbing for no apparent reason, rather than blaming the linear it might simply be the core of the choke getting too hot with continuous use. A bigger core (or doubling up) helped me and it might help him.

David G3UNA

> On 16 July 2020 at 04:26 Jim Brown <[hidden email]> wrote:
>
>
> On 7/15/2020 1:36 PM, CUTTER DAVID wrote:
> > It's all about size. Bigger core helps,
>
> Dave,
>
> No, it is NOT about size. It is about design of the entire antenna
> system, including the antenna, the feedline, and other parts needed to
> make the SYSTEM work. The principal characteristic of a common mode
> choke is the resistive component of its common mode impedance at the
> operating frequency(ies) where it will be used. Further, dissipation in
> the choke occurs at least as much in the WIRE that is wound around the
> core as in the core itself.
>
> There is another fundamental error in many antenna systems that ONLY
> looks at matching to the transmitter at the transmitter, ignoring the
> match between the antenna and the transmission line, using high
> impedance, parallel wire line, and using a random center-fed or
> off-center fed horizontal wire on all bands. Yes, the transmitter can be
> made to supply power to the feedline, yes, it will get to the antenna,
> and yes, it will radiate. But it may not receive all that well due to
> common mode current on the line from noise sources in our own homes and
> those of our neighbors. THAT is the problem with using a decades-old
> design for a world where there was 20 dB less noise than most of us face
> today.
>
> so a core that is OK for ssb
> > and cw might be undersized for AM or some data modes. Just like linear
> > amplifiers.
>
> So it is NOT the size of the core, it's the design of the antenna
> system. HFTA author and retired ARRL Antenna Book and Handbook editor
> Dean Straw, N6BV, published an excellent piece in QST 6-8 years ago
> called "Don't Blow Up Your Balun," in which he pointed out the
> differential mode dissipation in chokes, which can be extremely high if
> the choke is at a very high current point in a mismatched line. When he
> passed it to me for review, I noted that these losses were in addition
> to the common mode dissipation, and he revised the piece to reflect that.
>
> you can't
> > label something poorly designed because it doesn't pass the BOK test.
>
> BOK?
>
> 73, Jim K9YC
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

Jim Brown-10

Re: KPA1500 in the IARU Contest Last weekend

In reply to this post by Vic Rosenthal

On 7/16/2020 1:14 AM, Victor Rosenthal 4X6GP wrote:
> If the antenna is well-balanced and fed via a true balanced antenna
> tuner (preferably link-coupled) then there shouldn't be a problem with
> common mode currents.

Few ham antennas are perfectly balanced -- they are often unbalanced by
their surroundings. For example, ground slope, unequal heights of the
two halves, other conductors around the antenna, even vegetation. And
yes, all elements of the antenna system, including the feedline, the
antenna, and matching at both ends, contribute to the balance of the SYSTEM.

THAT'S why it's wrong to talk about "balanced line," using "parallel
wire" or 2-wire" line instead.

73, Jim K9YC
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

k6dgw

Re: KPA1500 in the IARU Contest Last weekend

Indeed! Probably the least unbalanced of "balanced" antenna systems
that ever existed were the HF point-to-point rhombics and V-beams at the
RCA, Mackay, and Marconi shore stations in the first 60 or so years of
the 20th century. Despite very precise engineering to make them
balanced, the RF currents in each side of the open feeders were never
exactly the same.

As a teenage ham, I tended to think in absolutes and exactitudes. If my
Heath MM-1 multimeter said the screen voltage was 176.5 V, I believed it
was, exactly, and if the spec said 177.5 V, I needed to do something to
"fix" it. If the ARRL Handbook said the two halves of my 40 meter
dipole needed to be exactly 32.9114 feet, I believed that the antenna
would not work if I didn't assure my dipole was exactly 32.9114 on each
side. As I grew older, both in age and ham longevity, I realized my
Elmer was right when reminded me on multiple occasions, "We're
amateurs. Most often, 'close' is good enough."

Seems like many today are convinced that 32.9114 ft will work but
32.9000 ft won't.

73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 7/16/2020 1:00 PM, Jim Brown wrote:

> On 7/16/2020 1:14 AM, Victor Rosenthal 4X6GP wrote:
>> If the antenna is well-balanced and fed via a true balanced antenna
>> tuner (preferably link-coupled) then there shouldn't be a problem
>> with common mode currents.
>
> Few ham antennas are perfectly balanced -- they are often unbalanced
> by their surroundings. For example, ground slope, unequal heights of
> the two halves, other conductors around the antenna, even vegetation.
> And yes, all elements of the antenna system, including the feedline,
> the antenna, and matching at both ends, contribute to the balance of
> the SYSTEM.
>
> THAT'S why it's wrong to talk about "balanced line," using "parallel
> wire" or 2-wire" line instead.
>
> 73, Jim K9YC

Charlie T, K3ICH

Re: KPA1500 in the IARU Contest Last weekend

Yeah, I remember as a new ham of 14, I asked my dad to buy a 50 foot piece of RG-58/u at Electronics Wholesalers in Washington DC.
He came home with 50 feet of RG58C/u which has a stranded center conductor and a characteristic Z of 53Ω.

I politely asked him to return it since it wasn't the correct impedance.
The counter clerk tried to explain that it was "better" because of the more flexible center and the very slight difference in characteristic impedance wouldn't make ANY difference in performance, but he insisted and came away with a new piece of RG-58/u. I think l I used it to string up a 15M dipole between our two chimneys.

Never DID get that %$#@ Globe Chief to work on 15 though.
For some reason, it had more output on 14 MHz than 21 even when I had the bandswitch on 15M
My entire Novice career was spent on 40M CW and 2M AM back when Novices had 145 to 147 MHz.

73, k3ICH (ex KN3ICH in1959)

-----Original Message-----
From: [hidden email] <[hidden email]> On Behalf Of Fred Jensen
Sent: Thursday, July 16, 2020 5:41 PM
To: [hidden email]
Subject: Re: [Elecraft] KPA1500 in the IARU Contest Last weekend

Indeed! Probably the least unbalanced of "balanced" antenna systems that ever existed were the HF point-to-point rhombics and V-beams at the RCA, Mackay, and Marconi shore stations in the first 60 or so years of the 20th century. Despite very precise engineering to make them balanced, the RF currents in each side of the open feeders were never exactly the same.

As a teenage ham, I tended to think in absolutes and exactitudes. If my Heath MM-1 multimeter said the screen voltage was 176.5 V, I believed it was, exactly, and if the spec said 177.5 V, I needed to do something to "fix" it. If the ARRL Handbook said the two halves of my 40 meter dipole needed to be exactly 32.9114 feet, I believed that the antenna would not work if I didn't assure my dipole was exactly 32.9114 on each side. As I grew older, both in age and ham longevity, I realized my Elmer was right when reminded me on multiple occasions, "We're amateurs. Most often, 'close' is good enough."

Seems like many today are convinced that 32.9114 ft will work but
32.9000 ft won't.

73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

donovanf

Re: KPA1500 in the IARU Contest Last weekend

In reply to this post by k6dgw

Hi Skip,

Conceptionally you're correct about rhombics and V-beams but your time frame is way off.

Edmond Bruce's rhombic antenna patent was filed in 1931.

www.aktuellum.com/mobile/circuits/antenna-patent

ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=1685103

The heyday for the rhombic ran from the 1930s through the 1970s with
the advent of satellite communications. The 200 foot tower for my
40 meter stacked 3 element Yagis came from a decommissioned
Laport Rhombic installed at the NSS receive site in Cheltenham MD.
We removed it in 1985, but it hadn't been used for years.

73
Frank
W3

----- Original Message -----

From: "Fred Jensen" <[hidden email]>
To: [hidden email]
Sent: Thursday, July 16, 2020 9:41:21 PM
Subject: Re: [Elecraft] KPA1500 in the IARU Contest Last weekend

Indeed! Probably the least unbalanced of "balanced" antenna systems
that ever existed were the HF point-to-point rhombics and V-beams at the
RCA, Mackay, and Marconi shore stations in the first 60 or so years of
the 20th century. Despite very precise engineering to make them
balanced, the RF currents in each side of the open feeders were never
exactly the same.

As a teenage ham, I tended to think in absolutes and exactitudes. If my
Heath MM-1 multimeter said the screen voltage was 176.5 V, I believed it
was, exactly, and if the spec said 177.5 V, I needed to do something to
"fix" it. If the ARRL Handbook said the two halves of my 40 meter
dipole needed to be exactly 32.9114 feet, I believed that the antenna
would not work if I didn't assure my dipole was exactly 32.9114 on each
side. As I grew older, both in age and ham longevity, I realized my
Elmer was right when reminded me on multiple occasions, "We're
amateurs. Most often, 'close' is good enough."

Seems like many today are convinced that 32.9114 ft will work but
32.9000 ft won't.

73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 7/16/2020 1:00 PM, Jim Brown wrote:

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

k6dgw

Re: KPA1500 in the IARU Contest Last weekend

They were around somewhat before the patent in several forms, and they
were around in 1960, which is the last time I looked hence my estimate
of 60 years. Lots of other "balanced" antennas fed with open line were
also in use commercially during that rough period, they too exhibited
the same characteristic ... while carefully engineered to be balanced,
RF currents in the two wires never were exactly balanced, which was the
original and only point.

I still have an RF ammeter in my junk box, from some airborne WW2 radio
I think. It's probably an antique by now.

73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 7/16/2020 5:47 PM, [hidden email] wrote:

> Hi Skip,
>
> Conceptionally you're correct about rhombics and V-beams but your time
> frame is way off.
>
> Edmond Bruce's rhombic antenna patent was filed in 1931.
>
> www.aktuellum.com/mobile/circuits/antenna-patent
> <https://www.aktuellum.com/mobile/circuits/antenna-patent/>
>
> ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=1685103
> <https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=1685103>
>
> The heyday for the rhombic ran from the 1930s through the 1970s with
> the advent of satellite communications. The 200 foot tower for my
> 40 meter stacked 3 element Yagis came from a decommissioned
> Laport Rhombic installed at the NSS receive site in Cheltenham MD.
> We removed it in 1985, but it hadn't been used for years.
>
> 73
> Frank
> W3
>

Vic Rosenthal

Re: KPA1500 in the IARU Contest Last weekend

In reply to this post by k6dgw

I took great care in the construction of my rotary dipole and feed
system to make it as balanced as possible. I made a clamp-on device from
a split ferrite bead that I can use to measure the relative currents in
the open line conductors, and they are very close.

There is one direction in which there is measurable unbalance due to a
nearby object, but unfortunately this is also the direction of my major
source of noise, another building 100m away, so it's not possible to
tell whether the unbalance contributes to the noise or not.

Someone else said that balanced lines don't reject common mode noise.
It's true that common mode noise currents can flow on the feedline, but
they are rejected by the balanced link-coupled tuner at the transmitter end.

I unfortunately don't have a choked coax-fed dipole to compare it to,
but it is much quieter than the previous antenna, a coax-fed multiband
vertical. And it is also a far better transmitting antenna.

Let's hear it for 1930s technology!

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
.
On 17/07/2020 0:41, Fred Jensen wrote:

> Indeed! Probably the least unbalanced of "balanced" antenna systems
> that ever existed were the HF point-to-point rhombics and V-beams at
> the RCA, Mackay, and Marconi shore stations in the first 60 or so
> years of the 20th century. Despite very precise engineering to make
> them balanced, the RF currents in each side of the open feeders were
> never exactly the same.
>
> As a teenage ham, I tended to think in absolutes and exactitudes. If
> my Heath MM-1 multimeter said the screen voltage was 176.5 V, I
> believed it was, exactly, and if the spec said 177.5 V, I needed to
> do something to "fix" it. If the ARRL Handbook said the two halves
> of my 40 meter dipole needed to be exactly 32.9114 feet, I believed
> that the antenna would not work if I didn't assure my dipole was
> exactly 32.9114 on each side. As I grew older, both in age and ham
> longevity, I realized my Elmer was right when reminded me on multiple
> occasions, "We're amateurs. Most often, 'close' is good enough."
>
> Seems like many today are convinced that 32.9114 ft will work but
> 32.9000 ft won't.
>
> 73, Fred ["Skip"] K6DGW Sparks NV DM09dn Washoe County
>
> On 7/16/2020 1:00 PM, Jim Brown wrote:
>> On 7/16/2020 1:14 AM, Victor Rosenthal 4X6GP wrote:
>>> If the antenna is well-balanced and fed via a true balanced
>>> antenna tuner (preferably link-coupled) then there shouldn't be a
>>> problem with common mode currents.
>>
>> Few ham antennas are perfectly balanced -- they are often
>> unbalanced by their surroundings. For example, ground slope,
>> unequal heights of the two halves, other conductors around the
>> antenna, even vegetation. And yes, all elements of the antenna
>> system, including the feedline, the antenna, and matching at both
>> ends, contribute to the balance of the SYSTEM.
>>
>> THAT'S why it's wrong to talk about "balanced line," using
>> "parallel wire" or 2-wire" line instead.
>>
>> 73, Jim K9YC
>
> ______________________________________________________________
> Elecraft mailing list Home:
> http://mailman.qth.net/mailman/listinfo/elecraft Help:
> http://mailman.qth.net/mmfaq.htm Post:
> mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net Please help support this
> email list: http://www.qsl.net/donate.html Message delivered to
> [hidden email]

Elecraft mailing list

Re: KPA1500 in the IARU Contest Last weekend

In reply to this post by k6dgw

Skip

Was any attempt made to redress the imbalance?

David G3UNA

> On 17 July 2020 at 03:19 Fred Jensen <[hidden email] mailto:[hidden email] > wrote:
>
>
> They were around somewhat before the patent in several forms, and they
> were around in 1960, which is the last time I looked hence my estimate
> of 60 years. Lots of other "balanced" antennas fed with open line were
> also in use commercially during that rough period, they too exhibited
> the same characteristic ... while carefully engineered to be balanced,
> RF currents in the two wires never were exactly balanced, which was the
> original and only point.
>
> I still have an RF ammeter in my junk box, from some airborne WW2 radio
> I think. It's probably an antique by now.
>
> 73,
> Fred ["Skip"] K6DGW
> Sparks NV DM09dn
> Washoe County
>
> On 7/16/2020 5:47 PM, [hidden email] mailto:[hidden email] wrote:
>
> > > Hi Skip,
> >
> > Conceptionally you're correct about rhombics and V-beams but your time
> > frame is way off.
> >
> > Edmond Bruce's rhombic antenna patent was filed in 1931.
> >
> > www.aktuellum.com/mobile/circuits/antenna-patent
> > <https://www.aktuellum.com/mobile/circuits/antenna-patent/>
> >
> > ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=1685103
> > <https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=1685103>
> >
> > The heyday for the rhombic ran from the 1930s through the 1970s with
> > the advent of satellite communications. The 200 foot tower for my
> > 40 meter stacked 3 element Yagis came from a decommissioned
> > Laport Rhombic installed at the NSS receive site in Cheltenham MD.
> > We removed it in 1985, but it hadn't been used for years.
> >
> > 73
> > Frank
> > W3
> >
> > > ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email] mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email] mailto:[hidden email]
>