An antenna comparison
Summary
An end-fed half wave antenna that Thomas Riedle, DD4TR brought was compared with an upper and outer antenna by me, DJ3EI, on the 20 m band and on the 40 m band.
I thank Thomas for allowing me to publish this.
We did the comparison by operating WSPR on both transceivers simultaneously.
The two antennas were only a few meters apart. I was a bit afraid of frying receiver pre-amplification stages, so we carefully restricted our transmit power to 17 dBm or 50 mW on both transceivers.
We used one way to determine output power at first and double-checked (with small adjustments) using a measurement instrument we had available later. I’m confident that at all times, both stations transmitted with the same power within ±1 dB, probably better.
Short wave propagation conditions were generally pretty lousy that day.
The ground was a lawn. The area has very high ground water just a short distance below the surface.
We used wspr.rocks to extract data that enabled us to compare.
The type of SQL we can be seen via the sample SQL file. The fields starting with “dd” pertain DD4TR data, those starting with “dj” DJ3EI. The SQL has been done in quick and dirty session, it generates redundant columns.
Our TX
Find stations that have heard both Thomas’ signal and mine in the same time slot, and compare the two SNR reports given by such stations. The raw data is available as TSV-file (“tab-separated file”, can be viewed as a variant of CSV) tx_compare.tsv. LibreOffice Calc will happily read such a TSV file and convert it as a spreadsheet.
Initial result: On 20 m, the upper and outer was received 4.6 dB louder on average. On 40 m, the dipole was received 3.5 dB louder on average.
Our RX
Find stations that have been heard by both Thomas’ and my TRX in the same time slot, and compare the two SNR reports given by Thomas and my station. The raw data is available as TSV-file rx_compare.tsv.
Initial result: On 20 m, the upper and outer received with -9.2 dB lower SNR on average, on 40 m, with -5.4 dB.
The antennas
Thanks to Eva, the youngest participant of that meeting, who diligently helped me measure antenna lengths and heights!
The EFHW antenna
The end that was fed was 3.56 m above ground, the far end 2.78 m above ground. The lowest point was 2.32 m above ground. This is a commercially available antenna, with description available from the manufacturer. The total length is 15.5 m. Accordong to a German description by Werner Schnorrenberg, DC4KU, it has one coil 9.8 m from the feedpoint and another 12.2 m from the feedpoint. The inductance values are not known (to me).
The upper and outer antenna.
The feedpoint of the antenna is 1.29 m above ground. Both the radiator and the radial are 7.19 m long each. The radial starts at the feedpoint 1.29 m above ground, in the middle, it is 1.05 m above ground and at its far end 1.08 m.
It is fed by a home-made two-wire “chicken ladder” feed line of some length I still have to determine and via a QRO Z-match tuner.
At some point, the fiberglass telescope rod supporting the vertical radiator of this antenna collapsed partially, leaving the antenna in a less-than-optimal configuration. This problem was rectified (shortly) before 13 UTC.
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