Yep.? While working for a living (I'm retired) the companies we worked for paid for the good, high end, and calibrated antennas, loops (for LF), and peripheral equipment.? I presently have a small set but no LPDA covering below 300 MHz.? We can always fall back on the substitution method with a bit more work.
On Mon, Dec 5, 2022 at 10:00 PM Raphael Wasserman <wassermanr46@...> wrote:
Dave,
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The pleasure stays with me¡
I mentioned that because Martin suggested to use a small transmitting loop antenna at some distance from a constructed receive antenna measuring with VNA S21 parameter of combined antenna and preamplifier arrangement.
In my days I used a good calibrated log-periodic transmit antenna for similar measurements to assess quality of receiving antennae.
Thanks, Raphael!? In the EMC world in which I worked and still consult, we pretty much universally use the 2D^2 / Lamda.? Yes, for antennas which are small as a function of wavelength, wavelength / 2pi is a far better approximation of fr field.
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Dave - W?LEV?
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On Mon, Dec 5, 2022 at 9:39 PM Raphael Wasserman <wassermanr46@...> wrote:
Dave,
Your feedline can be proprely terminated at preamp input but the input of the same feedline is not properly matched to the impedance of your antenna. Of course, when you deal with a reasonable high antenna noise you may turn off light and enjoy a book reading instead... Regarding your second observation, the mentioned by you far field distance is correct for electrically large antennae but for electricaly small antenae the far end region can be esimated as d > wavelength / 2 x pi.
