Build a twin-lead j-pole for ten meters and use the tuner on 15 and 20. It'll be about 23 feet long, I think. Flexible, so you can roll it up for storage. Just dump it off the balcony and let it hang. Pass the coax at the near end through a toroid (mix 31 or maybe 43) to keep RF off the outside conductor and to reduce local noise. No ground plane required.
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-- Carl
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