Yagi Antenna and other types of directional antenna
Also I am living in Chennai, India. Where can I buy yagi antenna and what would be the minimum cost of that antenna?
Thanks in advance.
May be you can build your own antenna. yagi's are easy to build and effective apart from yagi's there are a plethora of other antenna's that can be used.
Depending on your frequency? whats the frequency you are interested in
Regards
Elchachito
iVenky,
If time is short and you have access to wire and coaxial cable, I have use a simple dipole to do "DF" work before, usually to locate 'noise' RF sources, like at 30 MHz where a Yagi is not practical because of the wavelength size at that frequency!
To use a dipole for Direction Finding, when one 'points' to the location of the transmitter a deep null in signal is obtained, a null that is much sharper than than the broad main 'beam' of any Yagi as well. One has to keep in mind, though, that the null can be off either end of the dipole (180 degree ambiguity) so one must take a second 'bearing' from another location and observe where the two null 'lines' intersect: there is your transmitting source ...
It might be advantageous to have one of each, a Yagi (for when signals are weak) and a dipole (for fine bearing resolution).
I have use Yagi for DF at 450 MHz where the size of the antenna is very manageable. At 145 to 150 MHz a Yagi cut for these frequencies starts to get large, and a dipole is still manageable.
Various 'loop' antennas can be used below 30 MHz, as for DF at 3.8 or 7.2 MHz or even 15 MHz, but these take a little more construction time and expertise than cutting a simple self-resonant structure like a dipole for the frequency of interest.
Hope this give you some ideas.
Jim
PS. - An example using a small loop designed and tuned for noise DFing at 15 MHz:
DFing Pole with RF Noise at 15MHz using Degen and 1 foot Tuned Loop, MVI4763 - YouTube
Frequency is 150 Mhz.
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Also what would be the minimum cost of a Yagi antenna?
Thanks in advance
Minimum cost = almost zero.
As stated, all you need is a dipole. For DF it doesn't have to be complicated, just a co-axial cable, one end to the receiver and the other split into two equal-length wires facing opposite directions. For 150MHz you could use a half wavelength dipole so from end to end the two wires would total 1 metre. Almost any length will work to some extent. You could clip the co-ax and the wires to a wood pole to keep them rigid.
At the receiver, when you rotate the dipole you will get a peak when the dipole is long side facing the signal and a null when the wires are in line with it. Usually, it's easier to find the null because receivers use AGC to adapt to strong signals and this hides the peak position. When you have the null, the source is in line with the wires, all you have to do is move elsewhere, find the null again and triangulate the two angles.
Brian.
Try this one
HB9CV