The coming BVARC June Newsletter Radio Hotel column is about antenna polarization and height above ground.
The article below is complementary and succinct; found on the TenTen reflector. Enjoy….Rick W5RH HF Antennas: Vertical or Horizontal? Serge Stroobandt, ON4AA Copyright 2013–2015, licensed under <http://creativecommons.org/licenses/by-nc-sa/4.0/> Creative Commons BY-NC-SA <http://hamwaves.com/vertical-horizontal/en/#summary> Summary If you can have only one antenna and can chose between a vertical HF antenna or a relatively high horizontal HF antenna, go for the horizontal antenna. <http://hamwaves.com/vertical-horizontal/en/#modelling-results> Modelling results In January 2008, —as little as three months before his lamented dead— L. B. Cebik, W4RNL (SK) published what was going to be the last entry of his seminal 10-10 News series.1 It turned out to be an interesting gain comparison of <http://w4rnl.net46.net/ant58.html> single element 28.4MHz antennas modelled over various ground types of which a summary is presented here (Table 1). His findings seem to fit well with what John Devoldere, ON4UN modelled and published for equivalent antennas on the lower HF bands.2 All this led me to write up a synopsis which constitutes the remainder of this brief text. Gain & elevation angle of single element 28.4MHz antennas over various ground types1 polarisation antenna hagl salt water very good average very poor vertical 𝜆4 monopole with 32 buried radials 0 4.27dBi 11° -0.56dBi 24° -0.31dBi 27° -1.69dBi 29° vertical 𝜆2 dipole 1ft 5.64dBi 8° 0.69dBi 17° 0.55dBi 18° 0.15dBi 21° vertical 𝜆4 monopole with 4 elevated radials 𝜆4 6.31dBi 7° 0.82dBi 14° 1.15dBi 16° 1.24dBi 19° horizontal 𝜆2 dipole 𝜆2 8.36dBi 29° 7.73dBi 28° 7.24dBi 28° 6.48dBi 27° <http://hamwaves.com/vertical-horizontal/en/#horizontal-hf-antennas> Horizontal HF antennas <http://hamwaves.com/vertical-horizontal/en/#near-by-ground-gain> near-by ground gain At a height of about λ/2, the nearby ground reflection of a horizontal HF antenna will start to be constructive at interesting take-off angles for long- distance ionospheric contacts. This will provide a net gain over the antenna in free-space. <http://hamwaves.com/vertical-horizontal/en/#vertical-hf-antennas> Vertical HF antennas <http://hamwaves.com/vertical-horizontal/en/#near-by-ground-loss> near-by ground loss This is not the case with vertical HF antennas. Nearby ground only contributes loss. This even more so when the ground forms part of the return path of the radiating structure. Even when far-away ground reflections may cause the directivity of a vertical HF antenna at low take-off angles to be much higher than that of a horizontal HF antenna, its net gain will still be lower at those angles. This makes the horizontal HF antenna a clear winner, at least for what transmission is concerned. Note that gain and directivity are not synonyms; gain takes into account losses, directivity does not. <http://hamwaves.com/vertical-horizontal/en/#vertical-hf-antennas-still-remain-useful> Vertical HF antennas still remain useful Vertical HF antennas do have their merit though. At the lower end of the HF spectrum, the λ/2 height requirement for horizontal antennas can become cumbersome (even though horizontal phased arrays have a less stringent minimum height requirement). A vertical HF antenna can get away with a height of only λ/4. Furthermore, if the return conduction current of a vertical radiator flows through salt water, losses will be lower. Finally, the directivity of a vertical HF antenna can be effectively employed at the reception end to cancel out high-angle interference caused by near-by stations. This is why some stations use receive-only phased-arrays of verticals on the low bands. <http://hamwaves.com/vertical-horizontal/en/#polarisation-noise-at-hf> Polarisation & noise at HF Polarisation is not really an issue at HF. This is because the ionosphere is mainly an anisotropic medium, i.e. it messes up polarisation. However, horizontally polarised antennas are again preferred over noisier verticals because of the following considerations pertaining the polarisation of noise signals: 1. Earth-to-cloud lightning (QRN) is vertically polarised. 2. Vertically polarised man-made noise (QRM) propagates longer distances via ground-wave propagation than horizontally polarised man-made noise. Consequentially, the capture area for vertically polarised man-made noise is much larger than that of horizontally polarised man-made noise —actually, by a factor of the difference in propagation distance squared! <http://hamwaves.com/vertical-horizontal/en/#references> References 1. L. B. Cebik, W4RNL. No. 58: the Revere theory of vacation antennas. 2008. Available at: <http://www.cebik.com/> http://www.cebik.com/. 2. John Devoldere, ON4UN. ON4UN’s Low Band DXing. 5th ed. The American Radio Relay League, Inc.; 2010. Available at: <https://www.arrl.org/shop/ON4UN-s-Low-Band-DXing> https://www.arrl.org/shop/ON4UN-s-Low-Band-DXing.
_______________________________________________ BVARC mailing list [email protected] http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org
