good long range antenna for HF around 40 m

[pasha]

Hello everyone, please excuse me if i missed something obvious, but i was unable to find this (seemingly simple) information in several searches.

I live in Ukraine, and am in the process of trying to get my license. I am building a small qrp transmitter for CW, and i have a short wave radio that reads all the way to 30 Mhz. I want to build my own antenna that would be mounted either in the house of on the roof of the 5-story building i live in. I want to know what antennas are considered cheap to build and are not huge while still being able to transmit(receive) over long distances. I would like to be able to transmit to the states(chicago area), but i don't know how realistic that is. I have good experience with electronic circuits so i think i should be able to build an amplifier if that is necessary. What types of antenna could allow me to do what I want, and how many watts of power should i be able to output (cw) for this to work? thank you in advance.

[5B4AJB]

Verticals are fairly easy to build & have a low angle of radiation, trouble is, a 40m vertical is pretty long to have "vertical".
They do work horizontally, but you lose half the ERP.

Anyway, take about 6 feet of insulator (WHITE or GREY plastic pipe, BLACK has carbon in it) wrap a quarter wavelength of (speaker) wire into an evenly spaced coil around it, about a quarter wavelength of "tail" on the end of the coil.

You will have to experiment a bit with radials and the coil, but once it is resonant, you should pull in some good signals...

If you have room (and the building is orientated correctly) you could try a 2 element wire beam, the ultimate in simplicity, cheapness and gain (also pretty big!).

Power output will vary according to the radio conditions, but 40m holds the world distance/Watt record...

[pasha]

Thank you I will try. Can you tell me anything about folded dipoles? I built one this afternoon using 10 M of electrical wiring soldered the ends to each other, and put the output to an rca plug on the back of my sw radio to test it on 20M bands, but it didn't work well.
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Gnd on rca Rca Center
< = soldered together ___ = wire.
this was layed out east west on the floor of our appartment. it appeared to work worse than the built in antenna. do you know why?
thanks in advance

[5B4AJB]

First of all, an antenna touching the ground will not resonate properly, even a few inches away will make a huge difference. There are certain fractions of a wavelength above ground which are a "sweet spot", depending on the type of antenna.

For a folded dipole, the two wires have to be evenly spaced throughout it's length, the total length of the fold is important too.

If your radio has 50Ω antenna impedance and the antenna is 300Ω impedance, you'll need a transformer or balun (or an ATU) to connect it together.