[ARC5] Balanced antenna coupling...

Thu Dec 25 12:48:22 EST 2014

Hello Neil,

At 5' max height your short doublet is going to be largely omnidirectional
anyway at the bands of interest so don't worry about orientation.

You might consider a short vertical with top loading.  Put up a five foot
pole with adjustable loading coil in the middle.  The top loading would be
nothing more than wires to the four corners of your yard.  They don't have
to be equal length or equally spaced or even as many as four.  Drive in a
good ground stake (like a piece of Cu conduit) and lay in radials if you
can.  It any case spread a good layer of iron rich fertilizer (in the US we
call this product Ironite) around the base and water it in well.  You can
base feed this antenna via coax or center feed it balanced style via the
centered loading coil.  It will probably radiate better than a 5' high
horizontal wire.

Merry Christmas!

Dennis AE6C

On Wed, Dec 24, 2014 at 11:39 PM, AKLDGUY . <neilb0627 at gmail.com> wrote:

> Hi Kenneth
> Sorry for the delayed reply (been out all afternoon).
>
> > You might consider making that an inverted-vee dipole,
>
> Nope, there are tenants on the next floor above me. The 5 foot fence around
> my property is the practical height limit.
>
> >... or even going "diagonally" from fence corner to fence corner. That
> would
> > give you a bit more length to play with.
>
> Nope, 6 metres (more like 20 feet) is the limit because the yard is not
> square
> and longest length would result in a North-South orientation which would
> make
> for worst directivity (New Zealand is a long thin country and East-West
> antenna
> orientation is best).
>
> > However, if you make the link tunable by adding a fairly high capacitance
> > tuning cap in series with the coil to ground, it will make it
> considerably
> > quicker to set up for a particular frequency or band.
>
> Very good suggestion.
>
> > You may wish to make the link coil adjustable for inductance, less
> inductance
> > for higher frequencies.
>
> Nope, it's too much like hard work to make something like that, especially
> if the
> much easier link tuning cap suggestion above is already implimented.
>
> > Actually, if you diagram the entire link-coupling system, including the
> coax
> > and the final tank Pi-network circuit, you will find that it is actually
> two
> > parallel-tuned circuits that only LOOK series tuned where two of the
> tuning
> > capacitors in the link circuit (the Pi-network loading cap and the
> link-tuning
> > cap) are in series across the link coil, with the center-connection of
> those two
> > capacitors grounded.
>
> But the BC-230 doesn't have a pi-network output. It has a parallel tuned,
> series
> fed tuned circuit with an antenna coil wound over the top. The antenna
> picks
> off from a movable tap. I see your point though.
>
> > The way I operated my coupler was to center the Pi-network loading cap,
> the
> > splt-stator cap, and the link cap, then resonate the final with its plate
> tuning
> > cap, then adjust the taps on the balanced output coil for a minumum SWR,
> > then go back and tweak the other three caps for maximum output and
> > minimum SWR.
>
> Yes it's going to be a tedious process, but I'm looking forward to
> experimenting.
> In fact, I don't care if I make no contacts. The aim is to have fun and
> play with
> the BC-230.
>
> 73 de Neil ZL1ANM
>
>
>
> On Thu, Dec 25, 2014 at 1:35 PM, Kenneth G. Gordon <
> kgordon2006 at frontier.com
> > wrote:
>
> > On 25 Dec 2014 at 8:38, AKLDGUY . wrote:
> >
> > > Some of us have not enough space for a full size dipole, so
> > > a 50 or 72 ohm match is impossible. In my case, there's only
> > > about 6 meters,
> >
> > A little over 18 feet for us "'muricans".
> >
> > > from fence to fence so I'll be forced to set up
> > > a very short dipole.
> >
> > You might consider making that an inverted-vee dipole, or even going
> > "diagonally" from fence corner to fence corner. That would give you a bit
> > more length to play with. I used that combo, at a height of about 30 feet
> > (10
> > meters) for many years as my only station antenna when I lived in
> Missoula,
> > Montana. I was quite pleased with its performance.
> >
> > Mine was about 130 feet long, however.
> >
> > > What I want to try is an (unbalanced) 2-wire feed from the
> > > BC-230 to a link coil wound at the centre of a matching coil.
> >
> > Yes. I used that too.
> >
> > However, if you make the link tunable by adding a fairly high capacitance
> > tuning cap in series with the coil to ground, it will make it
> considerably
> > quicker to set up for a particular frequency or band. You may wish to
> make
> > the link coil adjustable for inductance, less inductance for higher
> > frequencies.
> >
> > In my case, I wound the link-coil out of 1/4" copper tubing and mounted
> it
> > INSIDE the main balanced coil. That coil had two sets of taps: one for
> the
> > open-wire line, and a second set to adjust the coil "length".
> >
> > > The bottom end of the link (connected to the G terminal of
> > > the BC-230) will form a 'ground' terminal.
> >
> > Or to the rotor of a tuning cap, with the stator grounded.
> >
> > > There will be a split stator capacitor across the coil with its
> > > frame connected to the 'ground'. Taps on each side of the
> > > coil's centre will go out via 300 ohm ribbon cable to the dipole.
> > > The capacitor may need to be made up of 2 separate units
> > > and a gearing arrangement, as split stator capacitors of the
> > > expected size are not readily available.
> >
> > VERY true. I had a main tuning split-stator capacitor from a Wilcox 96A
> > which I used in my coupler. The Wilcox 96A used a pair of 450TLs at over
> > 3KW plate modulated AM, so it is pretty substantial. It is a real "bread
> > slicer".
> >
> > > This classic balanced matching system of the 1930s before
> > > coax came into widespread use should work,
> >
> > Yes. It will work very well. The only thing making it less common these
> > days
> > is that it is very "un-handy", requiring a lot of manual energy entry to
> > make it
> > work correctly.
> >
> > > but I'm not
> > > expecting DX contacts. I'll be happy with local NVIS contacts.
> >
> > I expect you will find that it will work better than you suspect it
> would.
> >
> > Actually, if you diagram the entire link-coupling system, including the
> > coax
> > and the final tank Pi-network circuit, you will find that it is actually
> > two
> > parallel-tuned circuits that only LOOK series tuned where two of the
> tuning
> > capacitors in the link circuit (the Pi-network loading cap and the
> > link-tuning
> > cap) are in series across the link coil, with the center-connection of
> > those two
> > capacitors grounded.
> >
> > The Pi-network is built the same way, in fact.
> >
> > I would think that a circuit-analysis of what amounts to two Pi-networks,
> > connected end-to-end, might prove to be very entertaining. ;-)
> >
> > Or maybe it is simply a Pi-L network. I dunno. Anyway, it worked
> extremely
> > well for me.
> >
> > The way I operated my coupler was to center the Pi-network loading cap,
> the
> > splt-stator cap, and the link cap, then resonate the final with its plate
> > tuning
> > cap, then adjust the taps on the balanced output coil for a minumum SWR,
> > then go back and tweak the other three caps for maximum output and
> > minimum SWR.
> >
> > I went through all the bands and MARS frequencies on which I expected to
> > operate, and wrote up a chart with all the appropriate settings. Moving
> > from
> > band to band didn't take long after that.
> >
> > In point of fact, the link-tuning cap is simply an extension of the
> > loading cap,
> > and can be used as a loading cap.
> >
> > Ken W7EKB
> >
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