inverted vertical

[Robert "rc"Conley]

Hi All
In preparation to moving into a 3rd floor Seniors apartment.  I wonder
how well a 51' end fed wire suspended [via a fly rod reel so that it may
be retracted and stored when not in use] from the window with a 16'
counterpoise on the apartment floor against the wall. Using my K1-4 with
a KAT1. About two feet of wire to the Banana Plug adapter can be used or
would coax fed be better [center conductor to the End Fed Wire with
shield to the counterpoise] on the K1 to keep RF at a minimum in the
apartment.
72 RC kc5wa
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[Don Wilhelm-3]

RC,

I would think it may work for you that way, but I would be skeptical about
the counterpoise effectiveness on bands other than 20 meters.  I would
suggest a quarterwave counterpoise for each band that you plan to operate to
keep the RF at the K1 location to a minimum - even if it cannot run
straight.  Remember that the the open end of the counterpoise will have a
high RF voltage (yes, even at the K1's QRP power), so keep the far end
isolated and insulated.

The other way to handle the counterpoise on several bands is to tune it with
lumped inductance (or capacitance) so it is an electrical quarterwave on the
band you are operating.  There is commercial gear that does just that, the
MFJ Artificial Ground is one example, but you could easily homebrew an
equivalent, usually a series tuned circuit is all that is needed along with
some indication that the electrical quarterwave tuning has been achieved (an
RF current meter in the counterpoise wire will do - tune for max current).

73,
Don W3FPR

> -----Original Message-----
>
> Hi All
> In preparation to moving into a 3rd floor Seniors apartment.  I wonder
> how well a 51' end fed wire suspended [via a fly rod reel so that it may
> be retracted and stored when not in use] from the window with a 16'
> counterpoise on the apartment floor against the wall. Using my K1-4 with
> a KAT1. About two feet of wire to the Banana Plug adapter can be used or
> would coax fed be better [center conductor to the End Fed Wire with
> shield to the counterpoise] on the K1 to keep RF at a minimum in the
> apartment.
> 72 RC kc5wa
>

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[Ron D'Eau Claire-2]

Run it as close to a half-wave as the KAT1 can handle Actually, you might
consider a small (50 to 100 pf) capacitor in series with the wire. That
should move the reactance to a more manageable level when the length is
really close to 1/2 wave on the band you're using. Wind in wire as need for
higher bands. A shorter 1/2 wave is better than a 1/4 or 3/4 wave without an
extensive "ground" system.

Keeping the radiator near a 1/2 wave keeps the feed point impedance very
high and so keeps the antenna truly "ground independent". That's about 66
feet on 40 meters, 46 feet on 30 meters, 33 feet on 20 meters, etc. The
capacitor in series will make it look shorter to the KAT1 so it can match it
even at the very high impedance presented by a half wave radiator

The pattern will be no different than any other vertical. Expect stronger
signals in the directions away from the building due to the absorption by
the building.

I'd not worry about "RF in the shack" unless you actually have RF in the
shack. I'm presently running a 1/2 wave on 40 meters from a temporary second
floor location with no ground other than the mains. No RF issues at 100
watts. Works FB. If you do find the rig "hot" on some band, connect a 1/4
wave counterpoise wire to the rig case for that band to "tame" it. You can
use very small wire and run it along a baseboard, etc. Just keep the far end
insulated. The building detunes the wire a bit and you'll find that the
optimum length is a little less than half that of the antenna, although it's
not at all critical. It you want to "tune" the wire, put a small flashlight
bulb in series with it and adjust the length for maximum brilliance at a
given power. That's maximum current that will occur when it's exactly 1/4
wave long, electrically. It's easy to adjust: just start "long" and fold the
wire back on itself to "shorten" it. Even if the wire is insulated, folding
it back will be the same is cutting it short since RF flows over the outside
of the conductor. A folded-back wire simply looks like a fatter conductor to
the RF. But I've never had to get so exotic for simply keeping RF off the
rig. However, if you want to operate on a band where your radiator must be
1/4 wave or less long, then you'll definitely want a counterpoise tuned for
maximum current. In that situation the counterpoise will have a huge effect
on how well you get out. But, when the radiator is close to 1/2 wave, the
effect of the counterpoise on the radiated signal is miniscule at the most.

BTW, if you do operate it where the radiator is close to 1/4 wave, it'll
work a bit better than most simple installations using one radial since the
high-current part of your antenna is up in the clear where with most
verticals it's close to the ground!  Indeed you can consider such and
antenna a doublet being fed right at the center with no feedline. I've done
that in second floor apartments with considerable success running QRP on 40
and 20.

Ron AC7AC


-----Original Message-----
Hi All
In preparation to moving into a 3rd floor Seniors apartment.  I wonder
how well a 51' end fed wire suspended [via a fly rod reel so that it may
be retracted and stored when not in use] from the window with a 16'
counterpoise on the apartment floor against the wall. Using my K1-4 with
a KAT1. About two feet of wire to the Banana Plug adapter can be used or
would coax fed be better [center conductor to the End Fed Wire with
shield to the counterpoise] on the K1 to keep RF at a minimum in the
apartment.
72 RC kc5wa

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