13dka wrote: ↑Thu Mar 07, 2024 11:02 pm
For a fixed installation - looks like a worthwhile project! For portable usage and small spaces, well -> SULA!
Well, sure, that 4-loops isn't as easy to bring around as the SULA
Oh and if anyone is interested... I was curious to see if I could simplify that project while still having an "electronic steerable" directional antenna, so I started fiddling with NEC and the first thing I did was removing the phasing unit and using resistors on the 4 loops (yep, just like with the SULA) and after adjusting the various parameters, I got a nice result, the antenna takes a 6x6 square, and the apex of the 4 triangles is up 3.2m from ground, the match is good, the pattern is cardioid up to around 14MHz then it becomes omnidirectional (so not good at higher frequencies), gain ranges from -49dBi at 1MHz to -28dBi at 7MHz and -17dBi at 14MHz, adding a 20dB preamp will give an acceptable gain
Just for into, I'm posting a pic showing the antenna pattern and the swr and gain graphs; the triangles have the outer corner at 20cm from ground, the inner bottom corner at 50cm from ground and the upper corner at 3.20m from ground, the antennas are fed at the bottom inner corner and the resistor has a value of 775 Ohm and is placed 1/4 up from the bottom outer corner, the feedpoints are connected to a 9:1 BalUn (one for each loop) and then go to the relay box allowing to select the desired antenna, from there the coax goes to a choke and then to the station
Notice that, with respect to the other 4loop (the one with the phasing unit), this one has the pattern reversed, that is the lobe points toward the center pole and not toward the outside
( full size image here
https://postimg.cc/2bJ4HMky )
![Image](https://i.postimg.cc/J07PhCSN/4-loops.png)