# Homework Help: Adjusting Telescoping Antenna Length

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1. Apr 1, 2012

### Sevendust

1. The problem statement, all variables and given/known data

"Your vacation cabin in the woods is at the very fringe of the reception area for the FM radio station in the previous question (that broadcasts at 100 mHz). In order to maximize your chances of receiving your favorite tunes clearly from this station, you should adjust the telescoping antenna of your portable radio to ____ meters in length."

2. Relevant equations

I missed class, so after some googling I found an equation online that stated that 143/frequency gives me the length in meters.

3. The attempt at a solution

143/100mhz = 1.43
I entered this and it was incorrect. Any help/equations I can use?

Last edited: Apr 1, 2012
2. Apr 1, 2012

### Staff: Mentor

Hi Sevendust! http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

Did you find what fraction λ is best for the whip antenna? Won't you need to know whether the answer should be in feet or metres, before entering it in an online quiz?

http://en.wikipedia.org/wiki/Whip_antenna

Last edited by a moderator: May 5, 2017
3. Apr 1, 2012

### Sevendust

Hey :), the answers going to be in metres, sorry if I made that vague in my first post. I'm not exactly sure what you mean by finding the fraction λ: can you explain?

4. Apr 1, 2012

### Staff: Mentor

fraction of λ = fraction of wavelength

5. Apr 1, 2012

### tms

You shouldn't use random formulas without understanding them. You should review your textbook before trying the problem.

The kind of antenna in question is usually 1/4 of the wavelength of the expected signal. You know the frequency, so you can calculate the wavelength. You may also need the rule of thumb that the electrical length of an antenna is about 95% of the physical length.

6. Apr 1, 2012

### Sevendust

Got it: thanks for your help guys. I need to find a classmate with the notes so I can review for the test. Cheers.