I recently performed an experiment similar to the Schmidt (1980) experiment, and unlike Schmidt, I got something that looks like a positive result, but only after numerous unsuccessful attempts.
This is part of the abstract of the Schmidt (1980) paper; A Search for Advanced Fields in Electromagnetic Radiation:
An experiment to search for an advanced component of electromagnetic radiation, as suggested by the time symmetry of Maxwell's equations was conducted. A dipole transmitting antenna was driven periodically with 10.2 GHz microwave pulses of 12 ns duration and 4 watt instantaneous power. A receiving dipole antenna at a distance R = 10m away was instrumented to search for power above noise received in a time gate at a time r/c prior to transmission of each pulse. Data were integrated over 10 to the 7th power pulses. The experiment was performed at Lick Observatory, atop Mt. Hamilton, CA, to enable placement of the antennas so that a line connecting them, when extended to infinity in both directions, encounters no local complete absorber.
In the Schmidt experiment configuration I also got negative results. After at least 2000 runs in which no statistically significant signal above the level of the noise were detected in the advanced time window, I introduced three important changes in the experiment. The positive result was obtained only when all three changes are implemented simultaneously:
1. The experiment is carried out at wavelengths greater than 21 cm. It is possible that, due to the red shift in the distant future, microwaves of shorter wavelengths become stretched to the wavelength of 21 cm and absorbed by interstellar hydrogen, as suggested by Fearn (2014).
2. The detection is done with a λ/20 antenna, as suggested by Niknejadi (2015). The advanced signal disappears when antenna of ≈λ/6.7 or bigger is used for detection.
3. The antennas are placed so that a line connecting them, when extended behind the receiving antenna, points to the sky at an angle of ≈10° above the horizon. The advanced signal disappears in conditions of high relative humidity of the air and overcast sky at angles of less than ≈5°.
Even though the SNR of the signal measured in the advanced time window defined as μ/σ reaches 30.9, the possibility that the real cause of the signal is an unknown source of systematic error cannot be completely ruled out.
If perhaps someone is interested to reproduce the experiment to confirm or refute the results, here can find more details about the experiment:
Measurement of Advanced Electromagnetic Radiation - http://doi.org/10.5281/zenodo.247283
From the above working paper:
The block diagram of the basic experiment is shown in Figure 1. RF signal generator Signal Hound VSG25A generates pulses in duration of 6 ns to 24 ns (FWHM) and 10 mW (CW) power. Signal is supplied with an 8 cm long coaxial cable to the RF amplifier Mitsubishi M57796MA from which the signal amplified to ≈100 mW (CW) is supplied to a λ/10 monopole transmitting antenna, placed 200 cm above the surrounding terrain. At a distance of 430 cm, a receiving λ/20 monopole antenna is placed at the height of 300 cm above the ground. Angle between the horizon and the line connecting the two antennas is ≈10°. Received signal is supplied by 60 cm long coaxial cable through simple high pass filter to 50Ω input of 300 MHz oscilloscope Rigol DS2302A and a 100 MHz wide digital band-pass filter is applied to the signal. Horizontal scale is set to10 ns/div, vertical scale is set to 500 μV/div, while the mathematical scale in which the filtered signal is shown is set to 200 μV/div.
Figure 2 A shows a signal measured in the above described configuration at an angle of ≈10°. Peak of the retarded pulse, 12 ns FWHM, wavelength of 167 cm is at 0 ns. Peak of the advanced signal is at -28.6±0.2 ns. Average value (Vrms) of advanced signal after 1000 pulses is 252.3±9.5 μV. Error is the standard deviation. As shown in Figure 2 B, by raising the transmitting antenna by 50 cm and thereby by reducing the angle to ≈ 3.5°, the advanced signal weakened to 35.4±5.1 μV. Runs were made 5 minutes apart at clear skies and low relative humidity. Same effect can be achieved by lowering the receiving antenna to the height of the transmitting antenna. In conditions of high relative humidity of the air or cloudy weather, the signal completely disappears at angles smaller than ≈5°.
I'm not a professional physicist (obviously), so it is possible that I made some big mistake that I did not aware of. Any criticism is welcomed and appreciated.