HF propagation

Discussion in 'Radio Propagation Questions' started by mahmoudshakra, Aug 10, 2017.

  1. mahmoudshakra

    mahmoudshakra New Member

    Hello , i need to know what is the restriction in the height of the surrounding obstacles (building ,....) to the HF propagation for inverted V antenna if i have data about the radiation pattern of the antenna ,,, and this levels are measured to sea level or ground level ??
  2. Hi Mahmoud, I'm not sure that I am the right person to answer this, but since nobody else has popped up yet, and I'm in the Forum, here are a few starting pointers. I'm sure somebody will come along who can give a full technical answer.

    As you already know the effects of buildings at HF are very much less than at VHF and UHF ( getting a signal on a mobile indoors ), so I am assuming that you are talking about an HF inverted V.

    In general we all have to operate with compromised antennas due to the height of the mast available or nearby objects. Usually the primary goal is to get the antenna apex as high as possible and in an open location. However, most of us live surrounded by other buildings, and to a greater or lesser extent these will affect the close-in radiation pattern.

    The antenna radiation patterns as calculated in the handbooks etc. usually assume a perfect location and the vertical plot showing the take-off angle of the main lobe will be referenced to the station local ground (not sea level) since this is what interacts with the radiation to give the ground reflections to form part of the lobe. I suspect as a starting point you could look at the surrounding area and see how many tall buildings are 'seen' by the lobe at the theoretical take-off angle. I am not sure if some of the antenna modelling programs allow you to enter details of nearby objects, but I'm sure someone will know the answer to that...

    Overall Mahmoud, I would say that 99% of amateurs have to operate from a restricted environment with the real world putting trees and buildings in the 'wrong place' for our antennas, which are invariably compromised in some way. If its not too critical for you, I would say just try the antenna, however imperfect you think the exposure is, since most of us do that anyway and manage to get plenty of QSOs regardless. By the way, I know that operating portable /P from a proper open site can be very rewarding and gets rid of the problems of noise from domestic sources like broadband and solar panels.

    I hope that helps a little, but I imagine that others will be able to add some more detailed technical comments.

    Good luck with your transmitting attempts and good DX
    73 de Jim

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