[ARC5] Balanced antenna coupling...

[AKLDGUY .]

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
>