Hello friends of baluns,
Today I thought I’d give it a try and made some Near Field power measurerments with various ferrite materials for my Endfed Baluns. All baluns are type 1:49. Transmitting power 3 W.
The antenna was set up in the garden, a Metro VNA served as powermeter at 15 m distance. Checking for loss in ferrite material should be possible also under nearfield conditions - or am I wrong?
Here are the results (the power levels are given in - dbm, so the lowest negative value is the best):
As VA7JBE and VE6IXD aleady stated, material 61 seems to be a little better, but not as much as I thought. I also tried 77 material, which turned out to be not suitable (although I found information that it could also be used for broadband applications).
At the end I compared with my linked dipole (same height, same position, always one antenna on the mast and the other on the ground). Very surprising the value on 14 MHz. The dipole is 3 dB weaker than the “lossy” endfed. I have to check that again.
Has anyone else got experience in testing antenna efficiency in the near field?
I would be happy if someone could comment on that.
73
Peter