...My intended operating is SSB, 500 to 1000 mile radius on 75/40m...
A vertical should for the outer part of that range, but for for closer stuff you'll want a horizontally
polarized antenna. That's a problem, because you probably don't have much horizontal space to
string it out. There are a number of shortened horizontal antennas on the market, including the
Tak-Tenna, Buddi-Pole, and various sorts of dipoles made from mobile antennas.
Whenever you shorten a dipole from a full half wavelength, you encounter a range of effects:
(1) the antenna is no longer resonant. You have to add loading coils, capacity hats, or some
combination of those or similar methods to make it resonant. Loading coils have losses.
(2) the radiation resistance decreases. This has two effects - first, the SWR will be high unless
you employ some sort of matching and/or the antenna has high losses. Second, the currents
are higher at the center (leading to higher losses for the same diameter wire) and the voltages
are higher at the ends than a straight wire dipole.
(3) The bandwidth narrows. This is a side effect of (1) and (2), because there is more reactance
in the system and less resistance, therefore a higher loaded Q. Tuning becomes more critical, and
even a nearby branch blowing in the wind will cause the SWR to vary.
Antenna length should be considered in wavelengths: for the same physical length (say 10') the
electrical length is longer for 40m (0.07 wavelengths) than for 80m (0.035 wavelengths). Many
of the shortened antennas that work reasonably well enough on 40m are extremely difficult to
get working in practice on 80m just because the size reduction is so great.
As N3OX pointed out if a Tak-Tenna really worked as advertised and did all the radiating itself it
would have a feedpoint impedance of 2.7 ohms (SWR = 18 : 1) and 6 kHz bandwidth on 40m.
Clearly, many of the smaller antennas rely on radiation from the coax for their performance:
this makes some sense, since in many cases the coax is longer than the antenna, but it also
means that the antenna tuning varies as the coax is rerouted between the antenna and the
shack. Since the coax runs closer to most of the electronic devices in your home than the
antenna is, using the coax as part of the antenna tends to pick up more noise from those
While 40m and especially 75/80m operation is very difficult under such circumstances, it
isn't impossible in all cases. The best antenna I've strung up for such use was a loop of
wire (insulation chosen to match the exterior colors) tossed over the roof and brought
down each side of the building, then in the ground floor windows to an antenna tuner right
at the rig. True, it was coupled closely to the house electronics and was prone to various
RFI problems, but the transmitting efficiency on 40m and 75m was higher than what could
be achieve with any of the commercial shortened antennas on the balcony.
A high-Q tuned loop (sometimes called a "mag loop") can also provide high efficiency in
a small space using large-diameter conductors. They also have a narrow bandwidth,
but are tunable to any spot in the band (or in some cases, across several bands in a
2 : 1 frequency range.)