Telescopic antenna question

[Gadgeteer2000]

Hello all, I have two questions about telescopic antennas.

First, is there a calculator to tell me what should be the antenna length (so how far should I extend it) for a particular frequency?

Second, are all telescopic antennas fundamentally the same as they are all basically just a (shorter or longer) metal rod? If not, what is the reason for any difference? (I am talking about electrical difference - not about how robust, durable etc they are).

Thank you for any explanations.

For context - this is for wideband scanners (so receiving only). I have several telescopic antennas (some wideband, others for particular frequency bands) and I would like to find out the best way to use them

 

[Dog]

radio frequency calculator

 

[dlwtrunked]

Hello all, I have two questions about telescopic antennas.

First, is there a calculator to tell me what should be the antenna length (so how far should I extend it) for a particular frequency?

For a simple quarter-wave antenna, like you are after, skip specialized calculators and just use any calculator (like the one on your cell phone or PC) to calculate
7500/f, or in other words find 7500 divided by the frequency. where f is the frequency in MHz and the answer will be in centimeters
(divide that answer by 2.54 if you insist on an answer in inches).

 

[Gadgeteer2000]

For a simple quarter-wave antenna, like you are after, skip specialized calculators and just use any calculator (like the one on your cell phone or PC) to calculate
7500/f, or in other words find 7500 divided by the frequency. where f is the frequency in MHz and the answer will be in centimeters
(divide that answer by 2.54 if you insist on an answer in inches).

Thank you. This is helpful. So in general I should use the same length for any telescopic antenna, correct? (I use metric so cm is good 👍)

 

[dlwtrunked]

Thank you. This is helpful. So in general I should use the same length for any telescopic antenna, correct? (I use metric so cm is good 👍)

I would start with what you get from the calculation and then see if varying the length makes any difference. Since the antenna will not "in the clear", some local effects may influence things. But I am not expect that to make much difference.