On Mar 21, 10:02 am, Artem wrote:
On Mar 21, 6:26 pm, K7ITM wrote:

On Mar 21, 3:08 am, Artem wrote:

Sources is not grounded.

Yes, unfortunately noise that is generated more than one or two
wavelengths away from your antenna will be almost entirely
electromagnetic by the time it reaches your antenna. Antennas do not
differentiate between "electrically generated" and "magnetically
generated" noise, when you are far enough that the electromagnetic

I did not hear nothing about electrically or magnetically photons.
It's just photons.

:-) Oh, no, not photons again! When you are near to a source -- to a
transmitting antenna or to a computer radiating noise -- the fields in
general have not developed fully into electromagnetic waves -- photons
if you wish. It is quite usual that, close to the source, either the
electric or the magnetic field will dominate. Often from noise
sources, the near field is predominantly electric, and a properly done
loop antenna will reject that, responding only to the, um, photons.

field dominates over any near-field electric or magnetic field. The
balanced small loop is good for rejecting electric-field noise only if
(1) the noise is generated close to the antenna and

Yes. Computer, lamps etc close to antenna.

(2) the antenna is
close to the ground (so the electric field is guaranteed to be nearly

15 floor of 16-floor building. But I think that in this case "ground"
are building walls.

There is a hint he it is common that tall buildings incorporate a
lot of steel, and that will likely act as a shield. I hope this
antenna is not mounted inside!

vertical) -- -- where "close" means relative to a wavelength. So the
small balanced loop is especially good for LF and VLF work.

my reason was make narrow-band antenna. For reject all out of band
noise.

A reasonable thing to do, though a good receiver with a low-distortion
and fairly narrow-band front end should not have trouble with out-of-
band signals (noise). Do you have a quantitative measure of just how
strong this out of band noise is? I'd personally much rather use a
preselection filter separate from the antenna, and close to my
operating position, to reject out-of-band signals. Even though the
antenna you have described has very high Q, I believe I could do
better with a two or three resonator filter running at lower Q, since
the slope of the attenuation versus frequency is much greater. Unless
there was some especially strong signal in the band, I would at least
consider a fixed-tuned bandpass filter that covered my band of
interest, assuming that band is fairly narrow such as 7.0-7.1MHz.

Can you tell that you are getting the expected antenna bandwidth,
about 3kHz at the 3dB points at 7MHz?

If the amplifier at the antenna has a tendency to oscillate, it very
likely also has poor intermodulation performance. Be careful that it
doesn't destroy the benefits you are trying to obtain.

Cheers,
Tom