The Equipment UsedThe EME signal recordings on this page have all been received with equipment described on this site. My antenna is a 4*14 element cross yagi array in the x configuration. The boom length is 10.3 m and the stacking distance 5.2 m. The gain is 21.4 dBd at 144.300 MHz and 21.2 dBd at 144.000 MHz.The mast mounted preamps, one for each polarisation use a single HEMT FET, MGF1425. These preamps give very low noise and high, stable gain (but the dynamic range is poor). The input coil is 12 turns at 10 mm, wound from a 2 mm thick silvered wire. The 50 ohm input is one turn from ground on this coil. The tuning capacitor, and stray capacitances are very small. The output has a much smaller L/C ratio, C is about 30pF, so the output circuit provides a reasonable filter at the much lower impedance present at the drain. The output is matched to 50 ohms by a variable load capacitor, and there is no other load on the drain. The preamps are neutralised, and do not oscillate regardless of SWR. These preamps provide 31 dB Gain, and the 3 dB compression point is at -21 dBm. The preamps are close to the feed point, and the Rx feed loss is 0.15 dB. The usual system check, strength of galactic sources gives the following result at 144.300 MHz:
Cygnus / Leo = 6.80dB
At 144.000 the Y factors are lower by 0.2dB. Because of the large stacking distance, the side lobes are very strong, in the order of 9dB. The noise coming through the side lobes adds to the Y factors and makes a direct comparison with other stations difficult. The two Rx signals are brought to the shack some 50 metres away and fed to a stereo receiver that feeds a computer with digitised data at a bandwidth of 3.5kHz. The computer uses Sliding FFT and adaptive polarisation and presents a signal with about 17 Hz bandwidth to my headphones.
Packed audio filesThe original audio files are ordinary .WAV files recorded at 8kHz in mono with 8 bits per sample. These files are about 0.5 megabytes for a one minute audio sequence, but they are only about 20 kilobytes when packed with WAVPAC. In order to make it easy to download the packed files they are packed once more with PKZIP, because otherwise netscape will present it to you as a text file (I do not know how transfer a .WAP file better).To get the CALL.WAV file, first get the CALL.ZIP into your computer and run PKUNZIP.EXE (If you do not have it, download from some site that you can find by use of Alta Vista).
The command under DOS is:
Then get WAVPAC16.EXE or WAVPAC32.EXE from the corresponding .ZIP files, and run the program under DOS. Give the file name CALL (for CALL.WAP) when prompted by WAVPAC.
Examples of Normal EME signalsDX stations worked during the first hour of the ARRL contest 1996. These are all recordings of the output from the DSP as I was listening during the contest. These recordings were made by playing the wideband stereo DAT recording through the computer again, producing identical signals to those I had in my head phones.
I1ANP.ZIP (16k bytes)
Oct 26 1996, 0007 UT
By playing the same minute as IK2DDR three more times from the tape recorder these recordings from the same minute were obtained in the pile up.
W7FHI.ZIP (14k bytes)
Oct 26 1996, 0100 UT This is one of the easy workable stations I missed in the contest.
How much power is needed for EME?On this page I intend to add some more examples of "normal" EME stations using 1 to 4 yagis and modest output power. I have recordings of most of my contest QSO's during 1996, but I do not have info to calculate the EIRP of the different stations. I am looking for more data to get a more accurate determination of the EIRP required to reach my detect threshold under perfect conditions.A moderate size 4 yagi station PE1OGF recorded during the ARRL contest 1996. The conditions were not particularly good, and the signal level may have been affected by some ground reflections. The ground reflections may add or subtract to the direct signal so the normal level for PE1OGF may be slightly different, up or down. During this EME contact, I was using vertical polarisation for transmit, and the signal from PE1OGF was received at -82 degrees. On a horisontal antenna, this signal would have been 17dB weaker, and therefore not audible even on a very much larger array.
PE1OGF.ZIP (15k bytes)
The EIRP produced by PE1OGF is about 60 kW. The signal is about 4 dB above my detect threshold for random EME contacts at (S+N)/N = 7 dB. Note that S and N add their voltages because the S-meter is a peak detector. From the information above, the EIRP required to reach my detect threshold under perfect conditions can be calculated to be about 10 kW. |
