EME Low Power and Channel Characterization Experiments


Low Power EME Data Collection Experiments


The recent MoonNet discussions on low power EME has renewed my interest in development of an optimum waveform for the EME channel. Before the community settles on a particular waveform, we should first determine the channel characteristics. Important characteristics such as coherence bandwidth, selective fading and multipath are best determined by direct measurement with averaging over varying conditions. W3IWI, KA9Q and others have made astute theoretical statements concerning the impact of these perturbations on various modulation techniques. I believe there is an opportunity for the larger EME stations to collect data on the channel characteristics using their radio equipment and a PC equipped with sound card.

Data Collection Approach - Phase 1, Initial Experiments

For the first phase, we need recordings with the strongest signal possible via the EME path. The idea is to transmit various waveforms tailored to allow extraction of key channel characteristics. A one minute transmission is sent by one EME station and the resulting received audio is recorded at the second EME station. Post analysis of the recorded data should provide some interesting insight.

VE7BQH and I ran the first attempt at collecting data on April 28, 1996 using a PC program called TX55a. This program uses the sound card to generate audio waveforms that modulate the transmitter in SSB mode. I am releasing TX55a and its derivatives as a free public program. The program and the data collected is available from this webpage (see next section).

In it's current form, TX55a provides the following:

Data Collection Procedure

Lionel and I used the following procedure for the test:

The stronger the signal, the better the analysis. I suggest that we strive for S/N ratios of at least 15 to 20 dB (100 Hz bandwidth). Each band will have different characteristics, so we need recordings for 144, 432 and above. If you email your recordings to me, I will post them on this webpage.

Results of First EME Channel Characterization Experiments

TX55a - Experiment Weak Signal Data Collection Program available as free public program: tx55a.zip (81 K Bytes)

Spectrogram of Polarity Rotation Test: Spectrogram of Polarity Rotation Test Expand to Full Size (27 Kbytes)

Spectrogram of 1 Minute TX55a EME Reception: Spectrogram of 1 Minute TX55a EME Reception Expand to Full Size (27 Kbytes)

Here is the digitized data file of the TX55a reception in WAV format: tx55a002.zip (850 K Bytes)

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