why poor transmission at lower frequencies

At lower frequencies,generally the length of the conductor is high.hence due to losses poor tranmission occur.

You need to clarify your question.
What frequency you are refering to as LOW?
What experiments you done to conclude with the above quote?
Are you using same VFO for higher freqencies and the lower?
Are you using same tunning sections for higher freqencies and the lower?
Are you using same buffer and amplifier for higher freqencies and the lower?
Are you using same antenna for higher freqencies and the lower?
What power are you using
What antenna are you using?
Cloudy and too much sunlight will too affect low frequency transmissions

You may expect better replies when you answer these questions first
Cheers

i have started first course in Electronic communication

and it is mentioned there in "KENNEDY" book in first chapter but there was no explanation given so i queried but did not find any conclusive answer yet

"Re: why poor transmission at lower frequencies" wrong!, thats why nuclear submarines use 9 - 16KHZ to get world wide communications.
Frank

Coz books are books and practical is practical...too answers to your question will be still a question unless my questions are answered...:::)))

Good example..