I am not a big believer in published gain figures of antennas. Marketing superlatives claim astronomical gain figures with unlimited front/back ratios. One of the claims, which I have heard and read on multiple occasions is the performance of quad antenna versus yagi.
Earlier I was referring to my HRSQ listening performance against a yagi antenna, but let us have a view what to expect when doing on-the-air comparison tests between the three element yagi and HRS quad.
As the baseline for my HRS quad development I used groundbreaking work of dk7zb. I built the HRS quad model based on dk7zb quad, and modified the design for material selections I was using. I further improved the model to take material and feed losses into account to optimize the tower setup.
From the my previous it may have already become already clear that I am a big believer in computer modeling. Having said that, it is important to understand the drawbacks and potential problems of various modeling software.
The following models can be compared, but the real life performance due to material losses, nearby structures, etc. can be significantly different i.e. less than the model indicates.
Please note on my dB practice: All gain figures are dBi, front/back etc. absolute figures are dB. When ground reflection is included in dBi figures I try to note that clearly.
HRSQ vs. 3 element Yagi
Myth: “Two element quad beats three element yagi”.
I have described the HRSQ, there is a way to improve the performance on 20m, but for this comparison the radiator is one lambda length on 20m band. But how about the yagi? First thing we have to set is to define the yagi to be compared against HRSQ.
The most significant factor of yagi performance is the length of the boom, not the number of elements as many marketing guys want you to believe. A typical 3 element yagi for 20m band in my opinion would be about 0,4 lambda long. There are similar monobanders available from several manufacturers and they are reasonably easy to construct. In my model I used three element yagi with 5.6 meter boomlength.
Free Space Performance
Elevation
Free space elevation patterns are very similar. Yagi is 0,3dB better in gain, but quad is 3dB better in front to back performance. 3dB beam angle is very close to each other.
Azimuth plot
Since the azimuth is the different projection of the elevation discussed above the gain and f/b are the same. The horizontal 3dB beam angle is a bit better (5 degrees) on HRSQ than with yagi.
Summary
Free air performance of two antennas is very close to each other.
But.. so far I have never seen HF antenna being in use in free space. There is always ground reflection and the antenna height to be accounted for. For the next model I used Eznec standard average ground, and placed both antennas at 10 meters above the ground. For the HRSQ the 10 meter point was the center of the quad structure.
Performance With Ground
Elevation patterns
Now we start seeing a little more differences between the antennas. The gain for yagi is 0,6dB better, the f/b is 3dB better, and the beamwidth is also slightly better, as the free space comparison would indicate.
Azimuth patterns
Here yagi wins with 4dB f/b, 6dB f/s. The only area where quad is better is 3dB beamwidth winning that by slight 7 degree margin.
Summary of part 1
Both antennas are solid performers. There are no grounds for the claim that the two element quad would beat well designed three element yagi. Free space figures would suggest that quad would beat yagi on all of the areas (f/b, f/s, horizontal 3dB beamwidth) but when modeled above real ground the yagi is a solid performer beating quad in all of the figures except horizontal beamwidth, where quad is 7 degrees better.
But that is not the end of the comparison, part 2 will follow… with some analysis on antenna bandwidth, construction accuracy requirements, and final notes.
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