I moved into a retirement community several months ago and I don't have many alternatives for a SWL antenna and earth ground either by the HOA antenna regulations, no dirt for an earth ground rod, no metal water pipes for grounding or any perceptible grounding rod for the electrical service panel on the side of my house. Only thing I have done is I constructed a stealth dipole slinky antenna in the overhead inside my garage. For a ground, I have been utilizing an old and not recommended trick of using the neutral contact on an AC outlet. It actually works but a crummy way for a ground. I could use counterpoise grounding but there is no area around my house as it is all concrete walkway. If there are any alternative DIY antennas and grounding ideas that I have missed, please let me know.
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Interesting that you should mention using an antenna tuner. I have been considering buying a MFJ-959 antenna tuner with preamp made especially for SWL. Also, a MFJ-918 1:1 balun for my slinky antenna.
If you could use two slinkys connected as a dipole, fed with balanced feedline, and an antenna tuner to match that to your radio, that should work reasonably well, even for transmitting. Or for receive only you could try one of the active broadband antennas mounted in your attic - maybe one that has a tuned amplifier separate from the antenna element.
I would think your electrical system has to have some type of ground. I'm not an electrician, but I think neutral has to be bonded to earth at the panel. Regardless, I would probably feel better about using the green ground wire rather than the neutral.
73,
Win W5JAG
I forgot to mention: another highly effective small antenna for shortwave listening -- perhaps the best small antenna, in fact -- is the small tuned loop. See here for an example: http://www.kr1st.com/swlloop.htm . The disadvantage is that it is narrow-banded and you have to re-tune it with a capacitor for every station. The advantage is that it delivers a fairly strong signal to your receiver because of the relatively high loop currents that flow when the loop is turned to resonance. The narrow-bandedness also helps cut out unwanted interference.
Although the KR1ST loop linked above uses a copper tube for the loop element, it will also work with a copper strap (like 5 cm wide copper tape, which I used) or even thick wire, though signal levels will be lower.
It's also possible to replace the variable capacitor in the small tuned loop with a varactor (variable capacitance diode), which will allow you to remotely tune the antenna (though the varactor will have lower Q than the variable capacitor). This can be done very simply -- use one varactor, with an isolating 100k resistor on each side of it, connected to a long two-wire cable. At the other end of the cable, hook up a potentiometer wired as a variable voltage divider on a 9-volt battery. Finally, connect each end of the varactor to the loop through a 100 nF capacitor. This is an unbalanced arrangement -- a better arrangement would use two varactors back-to back, as shown in the tuned loop at https://www.randombio.com/loopantenna.html .
To get fancier, you can also even try to add regeneration to the loop antenna. Here's an example of a remotely-tuned, regenerative loop antenna: https://www.transkommunikation.ch/dateien/schaltungen/diverse_schaltungen/radio_circuits/Universal%20LF-MF%20Preamplifier.pdf .
For shortwave listening, you might want to try the M0AYF active loop antenna. It's a broadband design that requires no tuning. I have built it and it works pretty well. It is a small, balanced antenna and needs no ground.
https://www.qsl.net/m0ayf/active-loop-receiving-antenna.html
I used 2N3904 transistors. For the loop, I've used a strip of copper tape about 3-4 meters long, or some household electrical cord of about the same length.
G8JNJ has done some comparisons of various active loop antennas. The M0AYF is not the best, but is simple to construct.
For a high-performance active loop antenna, the LZ1AQ design seems to be good. I haven't built this one.
http://www.lz1aq.signacor.com/docs/wsml/wideband-active-sm-loop-antenna.htm
If you need to go even smaller, you can also try an amplified ferrite rod antenna. That will need to be tuned with a variable capacitor. See here for an example: http://www.lz1aq.signacor.com/docs/fa-eng/Weak_signals-mag_loop_engl.htm
Finally, you can also try an active whip antenna, also described on G8JNJ's site linked above. A popular one is the PA0RDT "mini whip" antenna. I tried this and it worked okay, but tended to pick up a lot of noise at my location. I find that an active loop antenna is much better and quieter in my environment. The downside is that the loop antenna gives a little weaker signal.