Short Antenna for 4m range

[Mr_Programmer]

I've to build a portable receiver for the 4m range, how can I decrease the antenna length? I want to use a PLL for channel selection, any suggestions for my problem?

 

[zubair]

U did not mentioned ur frequency of operation.If possible use high frequency.I can gave u a better advice if u gave ur frequency of operation iif u r working on low frquency perhaps helix or monoploe could be a choice.

 

[Mr_Programmer]

As I mentioned before, 4m range 68MHz - 88 MHz, Thanx

 

[papyaki]

Hi

Basic solution would be to use lambda/4 antenna, that means 1 meter height. You can add a loading coil at the base of the antenna and then reduce the it's length.


See this topic :

h**p://www.elektroda.pl/eboard/ftopic73718.html

This give some links to antenna's basics

 

[flatulent]

With the short 4m range you could use any short length of wire. Do an experiment and see if your basic transmitter circuit without any antenna connected will get across the 4m.

 

[Mr_Programmer]

hmm, I have to build a pocket receiver. So I got not much space, the case should be something like a pager. So I think lambda/4 is a little bit, hmm ... to much :wink:
Well I've seen antennas with ferrite core, maybe somebody has some formulas or even better practical knowledge. Would be nice, really...

 

[papyaki]

Hi

I agree with Flatulent when the output level of your transmitter is low, for about < 100mW. Otherwise you take the risk to burn your output transistor.

What you can do is to add a PI filter between your output transistor and the antenna. This PI filter will act as an impdance adapter. The length of the antenna can then be the one you want and the antenna can also be printed on you PCB.

 

[IICCEE]

In fact,this is a system question.So you may think something about the PA in your reciever system.

other suggestion: you may design a high derective antenna so the gain is high,get a goo match,in the other hand,you may also use high input impedance not 50ohm to get high sensitive.

In nomal,the gain is limit the antenna phisical size.