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IK1HGE 432Mhz Quagi

Go to the revised and improved version of the 8 elements quagi

Because of the several pictures, the complete download of this page might require some minutes. Be patient. You might want to read the text, in the meanwhile...

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I like electronics, telecommunications, photography, playing various instruments, programming... There are a couple of recent projects that I'd like to show to you. Let's begin with a 432 Mhz Quagi antenna.

I tried N6NB's project but it didn't work well. Actually, there were some differences from the original project: for the Driven Element and the reflector, I used 1.8mm solid copper wire (the one for coils or transformers) because, at least in Italy, the old insulated #12 TW solid copper wire is too hard to be found. Furthermore, the Directors diameter was 4mm instead of 3mm. Probably these differences resulted in unacceptable Standing Wave Ratio, as you can see here below:

Fig. 1 Experimental SWR curve obtained with N6NB's design (materials as specified in the text above)

Someone suggested me to optimize the antenna through NEC2, and... here you are the first results.

This Quagi is optimized for 432.2Mhz operation, however it works well in a quite wide range of frequency. All following data are obtained through 4NEC2D v. 5.3.2 by Arie.

The protype behaves better than I expected, but it seems that the Driven Element requires a little adjustement due to mounting approximations and to the coating of the copper wire. In my prototype, the Driven Element required to be shortened of about 3mm.

I suggest to:

1) Build the antenna by using the design data here below

2) Run a SWR curve

3) Adjust the DE length. An estimation of the new length is: DE(new) = DE(old) * fSWRmin/432.2

where fSWRmin is the new frequency in MHz of minimum SWR. However the actual length depends on your peculiar construction, thus take it easy and don't cut too much!

I put some experimental results and the pictures of the prototype at the bottom of this page. I only regret that I did not record the SWR curves taken when the Driven Element was 741mm and 738mm long, however you can see that with 735mm the minimum SWR is @ 434.5MHz. You can also see the comparison to a simulated antenna with 735mm DE which includes loss due to non-ideal material.

Have fun!

 Parameter Value Unit (Conditions) Frequency 432.2 MHz Forward Gain 13.77 dBi SWR 1:1.03 (432.2 MHz) SWR (min) 1.01 (432 MHz) Bandwidth 430-434 MHz (SWR<1.4:1) Take off angle 1.8 Degrees above good ground (Height about 8 wavelengths)

Table 1 Antenna performance (MOM simulation)

Fig. 2 Structure of the quagi antenna

 Quads copper wire diameter 0.0018 Directors aluminum rods diameter 0.004 Boom (wood) 1.50 Element Length Position Spacing RE 0.76215 -0.22904 DE-RE 0.22904 DE 0.7413 0 DE-DE 0 D1 0.29365 0.13093 DE-D1 0.13093 D2 0.29213 0.40783 D1-D2 0.2769 D3 0.28042 0.57751 D2-D3 0.16968 D4 0.28618 0.7632 D3-D4 0.18569 D5 0.28384 1.0228 D4-D5 0.2596 D6 0.27414 1.2687 D5-D6 0.2459

Fig. 3 Vertical (Elevation) pattern in free space

Fig. 4 Horizontal pattern in free space

Fig. 5 SWR and reflection coefficient charts

Fig. 6 Impedance charts: Resistance,Reactance (top) and Impedance,Phase (bottom)

Fig. 7 Total Gain vs. Frequency

Fig. 8 IK1HGE 432MHz 8el Quagi - 3D horizontal gain plot

The construction details are described in N6NB's article, in the ARRL Antenna Handbook and in many places on the net. Just search for "Quagi".

Here below, find some suggestions and some pictures of my prototype.

• Use some kind of coating to protect the boom from humidity and sun.
• To hold each square, I used two strips of FR4, that is the normal substrate for Printed Circuit Boards (completely remove the copper foils first!)
• The Driven Element is fed trough a female N connector and a short piece of RG213. Protect the connection points to the square. To make the conection more flexible, I suggest to use a thinner coax instead (like the RG58). You can then use the RG213 for the longer line connecting the RTX to the antenna.
• After the directors are perfectly aligned, you can fix them with a drop of glue.

Fig. 9 IK1HGE 432MHz 8el Quagi - Prototype construction details

I appreciate your comments about this project. For further information or to give me some feedback about your experimental version of this design, e-mail me:

[email protected]

Go to the revised and improved version of the 8 elements quagi