(75 watts total for the 3X13 Array - no ground gain involved)
Two days ago, in order to collect additional evidences of what TARP is capable of delivering performance-wise, I decided to conduct an "extreme" Moon Echo experiment where I completely bypassed my power amplifier and ran "barefoot", i.e. using only the 100 watts that my ICOM 746 PRO is capable of producing at 144MHZ.
In order to have a more accurate picture of the power making it to the actual antennas, I measured the power at the input of the power divider which is located close to the array in the tower. My Daiwa CN-801 power meter measured 80 watts PEP, which is equivalent to about 75 watts of available power once the cable loss going to the antenna feed point is accounted for. Since there are 3 antennas to feed, we are talking about only 25 watts making it to each antenna! The ultimate emerging question: can Moon Echos be realistically detected using so little power? Can TARPpull this off?
Initially, I really did not have much hope for anything to come out of this experiment. First of all, since I use the same array to transmit and receive, any sizable polarity mismatch penalty due to Faraday Rotation would most certainly wipe out any chance of detecting anything. Considering the magnitude of the challenge at play, if at all detectable, it is clear that the echos produced would be extremely faint and practically invisible. In order to mitigate that and allow the "Echo Trail" to become somewhat visible, I decided to run the experiment during 45 minutes with a few short pauses and recorded everything.
***WARNING: For Acceptable Video Resolution, it is critical to select 720p HD resolution in the youtube "settings" at bottom right of the player. The 360p default setting won't yield good enough resolution to see the details. It will take several seconds before the High Resolution kicks in, so you will need to restart the video from the beginning when the High Resolution is active and select to view the video in "Full Screen Mode" for best experience...***
The events that unfolded were absolutely stunning to me. As shown on the video, not only it was possible to detect and clearly see some good echo traces, but some of them were quite strong relatively speaking, i.e. in the -20dB to -24dB range. It is important to note that during the experiment, in addition to the most visible traces, I could also clearly see a lot of very "faint" echo traces on my PC screen. However, due to the recording and video processing which caused a loss of definition/resolution at the pixel level, most of the faintest traces do not reveal themselves very clearly on the video so we can only see the most obvious ones which produce "white dots" on the waterfall.
In the post-experiment analysis that followed, I calculated the corresponding EIRP and ended up with a figure of 7200 watts. Based on the examples of low EIRP QSO shown in Section 52, it made perfect sense that I could see my own echos at that EIRP level since it was estimated that TARP was capable of detecting and decoding EME signals in the most likely range of 2100-8100 watts EIRP.
This experiment is a good validation of the results obtained and presented in Section 52. Clearly, TARP is capable of "hearing" extremely weak signal below 8000 watts EIRP. In the current example, this corresponds to only 25 watts at the feed points!