It is very easy to create a simple 1/2 wave dipole, all you need is some lengths of wire such as the core of some mains flex or even a straightened out metal coat hanger, some co-ax cable and a connector for your scanners antenna input (usually BNC or SMA).

The formula to calculate the length of the antenna is *147/frequency in MHz*, this gives the total length of the dipole in metres. For example, to make a 150MHz dipole: 147/150 = 98cm so each element of the dipole should be 49cm

Connect one end of each cut wire to one side of a piece of choc block and to the other sides connect the core and shield of a length of 75 ohm co-ax. Put a suitable connector for your scanner onto the other end of the co-ax and hang the antenna in a suitable position with the element that is connected to the center core of the co-ax pointing upwards.

The balanced 75 ohm impedance of a dipole should really be matched to the unbalanced impedance of the co-ax using a balun but this is not as important for receiving only as it would be for transmitting. The mismatch will degrade the performance a little as it will reduce the overall sensitivity and possibly allow the co-ax feeder to act as an antenna and pick up some noise generated from within the building (eg. computers).

Dear All,

I am designing a VHF antenna for AIS devices. The frequency used is 162MHz. as formula, the length of antenna is 90.7cm. because we have not measure equipment, i want to measure the gain specification. so please let me know how to measure this gain specification and how to increase this specification?

Thanks and looking forward to receiving your reply.

i have the dipole antenna for 1.8GHZ .

the length is 78 mm .

How to calculate the balun for this.

and how to connect balun to Antenna and Connector.

where this choc block is ?

What is a balun, duh..? Where will I get one? Thanks.

I am designing an antenna frame to observe radio signals coming from jupiter.Why should the length of antenna be given a particular value? and how do we check what value should be given?

Thanks for a neat little tip. It’s saved me a bit of cash because I have the wire and a choc block so all I need to do is get into the loft and set it up. I’m only using this for receiving at the moment – so my question would be is bigger better?

Hello, y have this antenna made and it works great.

Y have a 6m and a 10 m monobander

Now y will combine them to a dualbander and see what happens

Pa3cuu

73

please, how do i calculate for the frequency of my transmitter in order to make a dipole antenna for it?

Hello, how do i calculate for the frequency of my transmitter in order to make a dipole antenna for it? Explain it simple, pls

Copy paste:

The formula to calculate the length of the antenna is 147/frequency in MHz, this gives the total length of the dipole in metres. For example, to make a 150MHz dipole: 147/150 = 98cm so each element of the dipole should be 49cm

A standard Di-Pole (not off-centered!) is 75 ohm impedance. Your radio is 50 ohm. This means you need a 1.5:1 balun or a choke. However, I’ve read elsewhere that care must be taken when using baluns on certain types of di-poles (primarily off centered di-poles) when operating on the 2nd harmonic (eg. 40 meters on a 80 meter di-pole!), so you may want to double check that before using a balun. In either case, when calculating the frequency for the di-pole, one generally picks a frequency that is exactly halfway down the band they are wanting to build the antenna for. Some bands (higher in frequency) are too hard to tune for the entire band, so its best to pick the portion of the band you will use most, then use a tuner to get the rest of the band. 6 meters is an excellent example of that!

i have sine wave of frequency 100 mhz.

how i feat the signal to the dipole antenna