Oblong loop formulas
Posted: Wed Apr 30, 2025 2:15 pm
the antenna is similar to the one described here
https://qrper.com/2023/11/a-portable-ob ... -2-meters/
the calc formulas (in meters) are
Lambda=300/MHz
perimeter=Lambda*1.05
semip=perimeter/2
shortside=semip/3
longsidd=semip-shortside
the antenna offers low takeoff angle and a gain over 8dBi if the lower short side (horizontal) is placed at 0.66 Lambda from ground ( or ground plane), the size is manageable down to the 15m band and btw the antenna works fine at V/UHF
The impedance is an almost perfect match to 50 Ohm so it can be fed with a simple 1:1 BalUn (a w2du choke/balun will do fine at V/U, a voltage bslun is ok for HF)
https://i.sstatic.net/neGbo.png
example for 29MHz
Lambda=300/29=10.34 meters
Perimeter=Lambda*1.05=10.86
the remaining calcs give us a semi perimeter of 5.43 meters which in turn gives us a short side of 1.81 which results in a quite manageable antenna plus, the bidirectional pattern the low takeoff angle and the gain over 8dBi will allow some nice DX and squeeze out the most from QRP power
the voltage balun below used at HF, will "float" the loop keeping it w/o a direct reference to ground
https://qrper.com/2023/11/a-portable-ob ... -2-meters/
the calc formulas (in meters) are
Lambda=300/MHz
perimeter=Lambda*1.05
semip=perimeter/2
shortside=semip/3
longsidd=semip-shortside
the antenna offers low takeoff angle and a gain over 8dBi if the lower short side (horizontal) is placed at 0.66 Lambda from ground ( or ground plane), the size is manageable down to the 15m band and btw the antenna works fine at V/UHF
The impedance is an almost perfect match to 50 Ohm so it can be fed with a simple 1:1 BalUn (a w2du choke/balun will do fine at V/U, a voltage bslun is ok for HF)
https://i.sstatic.net/neGbo.png
example for 29MHz
Lambda=300/29=10.34 meters
Perimeter=Lambda*1.05=10.86
the remaining calcs give us a semi perimeter of 5.43 meters which in turn gives us a short side of 1.81 which results in a quite manageable antenna plus, the bidirectional pattern the low takeoff angle and the gain over 8dBi will allow some nice DX and squeeze out the most from QRP power
the voltage balun below used at HF, will "float" the loop keeping it w/o a direct reference to ground