wav file, you may see something like this.īare in mind that this is not the original image of the satellite but one modified by the program, for the original image you have to go to Enhancements -> Normal. Record the "tick-tock" sound as the satellite passes over your geographical position and save the. You should hear something like "tick-tock" between a 2400 Hz and a ~1000 Hz tone. Tune to the frequency of the satellite you want to receive and set your filter's width to be at least 34KHz.Īs long as the satellite approaches your location, you should see something like this. Open CubicSDR or else (GQRX, SDR#) and set the modulation to FM. The bandwidth of the emitted signal is ~ 34 KHz and the modulation is FM. The satellites broadcast at 137-138 MHz or more specifically: I work on Elementary OS which is a Linux distribution and I use Gpredit to monitor the NOAA satellites which you can also run on Windows. We see that the simulations agree with the design of the antenna and the filters.
Wxtoimg alternative software#
I also ran simulations for the filters using the software RFSim99. Regarding the gain of the antenna, we can see that it is ~4 dBi for right-hand polarization and "follows" the satellite in its pass from the horizon. We can see that the SWR of the antenna tuns out ~1.24 at 137.5 MHz.Īnd the impedance turns out ~45 Ohm for the real part and ~8.5 Ohm for the imaginary part, ideally the imaginary part of the impedance should be 0 but it's still low and shows us the "inductive attitude" of the designed antenna. I designed the aforomentioned antenna using the software 4nec2. 136.26 + 138.79 = 275.05 and if we divide by 2 we get 137.525 MHz as the antenna's center frequency. For this design, the longer loop consists of 2.2 m wire and tunes at 136.26 MHz (wavelength of 2.2 m) when the shorter loop consists of 2.16 m wire and tunes at 138.79 MHz (wavelength of 2.16 m). The antenna should tune at 137.5 MHz, for this to happen the larger loop should tune to a lower frequency and the smaller loop should tune to a higher frequency. The input impedance of the antenna was measured to be ~50 Ohm. The standing wave ratio (SWR) of this antenna was measured to be 1.27 for 137.5 MHz using an Agilent E5062 vector analyzer. Strip the other end of the line and use the crimping tool to fit it to a RF connector that matches your needs (male RP-SMA for RG174 in my case). Make sure there is no short circuit (the core is completely isolated from the shield).ġ1. Solder the remaining ends with the shield of the line.ġ0.On the top of the antenna, solder one end of the longer loop and one end of the shorter loop with the center core of the coaxial line.Form the helixes in right hand motion as it is shown in the picture below.Be careful and don't apply too much pressure as you may break the wire and hurt yourself! If you want, you can use the drill to straighten the wires after you have placed them to the antenna body.
Fit the printed QFH_BODY parts to the PVC pipe, the distance between the top part and the bottom QFH_BOTTOM part should be 742 mm.Fit the second printed QFH_BOTTOM part to the PVC pipe and place it 45 mm far apart from the first.Fit the first printed QFH_BOTTOM part to the PVC pipe and place it close to the bottom.Ideally you need ~2.20 m (2203 mm) of wire for the longer loop and ~2.16 m (2158 mm) of wire for the shorter loop but it may be easier to cut longer wires and then match them to the body of the antenna.
Wxtoimg alternative download#
Download and print QFH_BOTTOM 2 times, download and print QFH_BODY as many times you need to guarantee that the loops form helixes ( I printed 3) and cut 2 pieces of 2.5 m wire. Since the antenna is used as a receiver, the source should be on the top. A QFH (Quadrifilar Helix) is a circularly polarized antenna and consists of two loops which form four helixes, to receive the APT signal we need a QFH with right-hand circular polarization (RHCP).