Hi Rasid,
The optimum height above the ground or roof depends upon the frequency and the distance (take off angle) you desire.
Regardless of how high the antenna is, a roof, especially a metal roof, will have a negative effect on the antenna pattern if the roof is 1/8 wavelength away or closer. (35' on 75M.)
If there is no roof, then 1/4 wavelength above ground is good for higher angle local skip work. For DX work, you want the antenna up at least 3/8 wavelength and the best is 1/2 wavelength high. (130' for 75M) If a roof is involved, the house wiring and plumbing can have an unpredictable bad effect on the pattern. This holds true for 40-10M too, except 1/2 wavelength becomes a smaller number.
So to answer your question, 4-5 meters high is a good height for 10M DX or 20 M local work. (Local being higher angle signals into Europe from Turkey, etc) On 40M this is about 1/8 wavelength high and very good for closer in work. You will still be able to work stateside, but you may be 10db weaker than if the antenna were up at 1/2 wavelength or higher.
Can you download EZNec software? You will have fun trying different antennas and learn a lot too.
Hope this helps.
Tom, K1JJ
Leave it to JJ to confuse everyone.
Tom, after reading your answer, I forgot what the OP's question was.
Makes me want to go outside and spray Miracle Grow on my tower.
Fred
