What is a qfh antenna?

What is a qfh antenna?

This is where the QFH Antenna comes in, it’s actually two antennas, a small one inside a bigger one, that is of the proper dimensions so that it blocks out surrounding interference and receives signals very well on the 137.5 MHz frequency band that the NOAA satellites transmit around.

How do I measure for the right size antenna?

For the antenna it is important to be somewhat precise, so measure three or four times before drilling or cutting. First choose the “up” side of the frame and mark a point about 10cm from the top. This will be the upper part of your antenna.

What is the shape of the antenna?

Fig 1. illustrates the antenna which consists of two vertical loops at right angles to each other, resonant at slightly different frequencies, twisted into a half turn helix. Correctly made it will provide true all round coverage with circular polarization at all angles.

Does changing the diameter of the antenna affect the frequency?

Changing the diameter changes the resonant frequency only a little. More importantly, it changes the impedance of the antenna. We have made many loops with different diam- eters and, for example, an 8 mm pipe diameter antenna shows an impedance of about 21 ohm, whereas a 15 mm antenna is about 30 ohms impedance .