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Re: ½ λ dipoles

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Charlie T, K3ICH

Re: ½ λ dipoles

I'm curious as to when the concept of a ½ λ dipole became the norm?

In other words, the idea of the current distribution as exists on a dipole.

Early pictures of typical ham antennas looked more like a set of parallel
clothesline wires.

What I gather from reading early articles, it seemed that the more wire you
had in the air, the better it would "capture" (and radiate) the signals.

Feel free to reply directly if you don't want to clutter the forum.

(k3ich at arrl dot net)

73, Charlie k3ICH

-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of Phil
Wheeler
Sent: Friday, August 05, 2016 10:58 AM
To: [hidden email]
Subject: Re: [Elecraft] OT:. G5RV's

Alas, the poor G5RV. Now that its been flogged to death, maybe we need a
new target -- say the Windom?

Phil W7OX

On 8/4/16 10:22 PM, Wes Stewart wrote:

> The tuner loss also depends on how it is adjusted. For example the
> very popular high-pass Tee with three adjustable elements has an
> infinite number of possible combinations that will effect a match on
> the same load Z. One of them is the lowest loss solution, all of the
> others aren't.
>
> As I said earlier, in a letter to Dean Straw dated February 2, 1994 I
> offered an example where the SPC tuner, then current in the handbooks,
> could be used to match an impedance of 4.34 +j46 to 50 ohm. (I forget
> where this came from but it was a real possibility) I assumed Qc =
> 1000 and Ql = 300 (generous). I used Touchstone to calculate the
> minimum loss and maximum loss solutions The best case was 1.6 dB and
> the worst case was 7.8 dB.
>
> With lower Q components, Qc = 500, Ql =200, the losses were 2.4 to 9.5
> dB!
>
> Wes N7WS
>
>
> On 8/4/2016 2:00 PM, Alan Bloom wrote:
>> > It's a pity that too many newcomers, as well
>> as many oldsters, are
>> > enamored by this piece of wire.
>>
>> The G4RV is definitely a compromise antenna.
>> However its advantage is that is has low-enough SWR to be easily
>> matched by most tuners on a number of bands.
>>
>> > ... the horrific losses that could be
>> incurred even
>> > with high quality tuners,
>>
>> It's true that tuner losses are the
>> manufacturers' dirty little secret. Loss is rarely specified, partly
>> because it can be pretty bad, and partly because it is hard to
>> measure, but also because it is not constant - it depends on the
>> particular impedance being matched.
>>
>> One exception is the old Drake tuners. Their Pi-L topology makes the
>> loss almost independent of the load impedance. If you can get it to
>> match, you know that almost all the power is going into the feed
>> line. For example, the
>> MN-2700 that I designed when I was at Drake was specified at 0.5 dB
>> maximum insertion loss and I did a lot of testing and tweaking to
>> achieve that on all bands.
>>
>> Alan N1AL

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riese-k3djc

Re: ½ λ dipoles

early on the antenna would help define the operating frequency
spark made RF everywhere and the tank and antenna coupled
the RF to the operating frequency

Bob K3DJC

On Fri, 5 Aug 2016 18:41:57 -0400 "Charlie T, K3ICH" <[hidden email]>
writes:

> I'm curious as to when the concept of a ½ λ dipole became the norm?
>
> In other words, the idea of the current distribution as exists on a
> dipole.
>
> Early pictures of typical ham antennas looked more like a set of
> parallel
> clothesline wires.
>
> What I gather from reading early articles, it seemed that the more
> wire you
> had in the air, the better it would "capture" (and radiate) the
> signals.
>
> Feel free to reply directly if you don't want to clutter the forum.
>
> (k3ich at arrl dot net)
>
> 73, Charlie k3ICH
>
>
>
> -----Original Message-----
> From: Elecraft [mailto:[hidden email]] On Behalf
> Of Phil
> Wheeler
> Sent: Friday, August 05, 2016 10:58 AM
> To: [hidden email]
> Subject: Re: [Elecraft] OT:. G5RV's
>
> Alas, the poor G5RV. Now that its been flogged to death, maybe we
> need a
> new target -- say the Windom?
>
> Phil W7OX
>
> On 8/4/16 10:22 PM, Wes Stewart wrote:
> > The tuner loss also depends on how it is adjusted. For example the
>
> > very popular high-pass Tee with three adjustable elements has an
> > infinite number of possible combinations that will effect a match
> on
> > the same load Z. One of them is the lowest loss solution, all of
> the
> > others aren't.
> >
> > As I said earlier, in a letter to Dean Straw dated February 2,
> 1994 I
> > offered an example where the SPC tuner, then current in the
> handbooks,
> > could be used to match an impedance of 4.34 +j46 to 50 ohm. (I
> forget
> > where this came from but it was a real possibility) I assumed Qc
> =
> > 1000 and Ql = 300 (generous). I used Touchstone to calculate the
> > minimum loss and maximum loss solutions The best case was 1.6 dB
> and
> > the worst case was 7.8 dB.
> >
> > With lower Q components, Qc = 500, Ql =200, the losses were 2.4 to
> 9.5
> > dB!
> >
> > Wes N7WS
> >
> >
> > On 8/4/2016 2:00 PM, Alan Bloom wrote:
> >> > It's a pity that too many newcomers, as well
> >> as many oldsters, are
> >> > enamored by this piece of wire.
> >>
> >> The G4RV is definitely a compromise antenna.
> >> However its advantage is that is has low-enough SWR to be easily
> >> matched by most tuners on a number of bands.
> >>
> >> > ... the horrific losses that could be
> >> incurred even
> >> > with high quality tuners,
> >>
> >> It's true that tuner losses are the
> >> manufacturers' dirty little secret. Loss is rarely specified,
> partly
> >> because it can be pretty bad, and partly because it is hard to
> >> measure, but also because it is not constant - it depends on the
> >> particular impedance being matched.
> >>
> >> One exception is the old Drake tuners. Their Pi-L topology makes
> the
> >> loss almost independent of the load impedance. If you can get it
> to
> >> match, you know that almost all the power is going into the feed
> >> line. For example, the
> >> MN-2700 that I designed when I was at Drake was specified at 0.5
> dB
> >> maximum insertion loss and I did a lot of testing and tweaking to
>
> >> achieve that on all bands.
> >>
> >> Alan N1AL
>
> ______________________________________________________________
> Elecraft mailing list
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> Please help support this email list: http://www.qsl.net/donate.html
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> delivered to [hidden email]
>
> ______________________________________________________________
> Elecraft mailing list
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> Post: mailto:[hidden email]
>
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Don Wilhelm

Re: ½ λ dipoles

In reply to this post by Charlie T, K3ICH

Charlie,

A bit of history ---

Most of those ham antennas that used parallel wires were folded dipole
antennas - yes they were mostly 1/2 wavelength long. The feedpoint
impedance for that antenna is 300 ohms. Add a 3rd wire or a 4th and the
impedance increases. So to my mind, that was an attempt to match the
feedline to the antenna which in early days was open wire line which for
normal spacing has a characteristic impedance near 600 ohms.
By the time I became a ham, TV twinlead was common with a characteristic
impedance of 300 ohms. Many ham antennas were created using that
twinlead. A folded dipole was made from the twinlead and fed in the
center with additional twinlead serving as the feedline.

With the migration to coax feedlines, those older techniques have faded
from memory, but those antenna *did* work just fine although many hams
did not really understand why.

At that time we had PA tank circuits with swinging link coils and could
match most any impedance. The tuning sequence was to start with the
link lightly coupled to the PA inductor and then to "dip the plate" to
resonance - then slowly increase the coupling between the PA inductor
and the antenna link to increase the PA current. That was done in an
iterative manner until the plate current was at the desired point.
That process could match most any load that the antenna and feedline
might present to the transmitter.

Then came television. Many ham transmitters were interfering with TV
reception, so transmitters became shielded devices, and the shift to
coax rather than open transmitters with the older parallel feedline
connection direct to the antenna slowly became a product of the past.
Swinging links and plug in coils inside a shielded enclosure were
possible, but a PITA.
So the advent of the Pi-Network in ham transmitters was born. It
allowed band switching and could match a reasonable range of antenna
impedance. The shielded coax feedlines provided the chassis shield to
be extended all the way to the antenna feedpoint (or so the story goes,
but that is not entirely true).

The bottom line of what I am trying to communicate is that much of ham
radio antennas, transmission lines and transmitter construction changed
drastically in the 1950s with the advent of television and that was done
primarily to reduce ham interference to TV viewing (TVI).
As an example of that effort, my first novice transmitter which I built
from a design in a 1955 ARRL Handbook was in a completely shielded
enclosure and used shielded wiring throughout with bypass capacitors at
each end of the shield wire. That included all the wiring, filaments
and DC power circuits and anything else. If you find a 1955 ARRL
handbook it was the 75 watt transmitter with a 5763 crystal oscillator
and 6146 final included in that book. Nostalgia urges me to again build
that transmitter, but practical sense says that it would be
prohibitively expensive these days and some components are no longer
available.

73,
Don W3FPR

On 8/5/2016 6:41 PM, Charlie T, K3ICH wrote:

> I'm curious as to when the concept of a ½ λ dipole became the norm?
>
> In other words, the idea of the current distribution as exists on a dipole.
>
> Early pictures of typical ham antennas looked more like a set of parallel
> clothesline wires.
>
> What I gather from reading early articles, it seemed that the more wire you
> had in the air, the better it would "capture" (and radiate) the signals.
>
> Feel free to reply directly if you don't want to clutter the forum.
>
> (k3ich at arrl dot net)
>
>

Elecraft mailing list

Re: ½ λ dipoles

In reply to this post by Charlie T, K3ICH

Fascinating discussion. Anybody know of any noteworthy books that cover the subject? Especially tube transmitters and their antennas. Given my love for Steam trains, breadboard receivers and Ham Radio, I sometimes think I was born about 50 years too late!
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Elecraft mailing list

Re: ½ λ dipoles

Try any handbook before 1957 when transistors became available. If you can't find them at the ARRL, try E-BAY as they are only available used.K5EWJ (original 1956 issued call sign)

From: rick jones via Elecraft <[hidden email]>
To: "[hidden email]" <[hidden email]>
Sent: Saturday, August 6, 2016 1:00 PM
Subject: Re: [Elecraft] ½ λ dipoles

Fascinating discussion. Anybody know of any noteworthy books that cover the subject? Especially tube transmitters and their antennas. Given my love for Steam trains, breadboard receivers and Ham Radio, I sometimes think I was born about 50 years too late!
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