[opendtv] Re: VHF Stations Seek Solutions for Reception Problems, by Doug Lung

  • From: Cliff Benham <flyback1@xxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Wed, 01 Jul 2009 18:17:43 -0400

Ron Economos sent this the other day--a wideband UHF helical TV receive antenna:


-------- Original Message --------
Subject: [opendtv] Re: VHF Stations Seek Solutions for Reception Problems, by Doug Lung
Date:   Tue, 30 Jun 2009 17:23:13 -0700
From:   Ron Economos <w6rz@xxxxxxxxxxx>
Reply-To:       opendtv@xxxxxxxxxxxxx
To:     opendtv@xxxxxxxxxxxxx
References:     <NHEIJNPPCCEBDCJBBJCBKEGCDFAA.dalekelly@xxxxxxxxxxx>


Helical TV antenna. Probably not cheap.

http://www.wade-antenna.com/Wade/WH14-69.pdf



Dale Kelly wrote:
Thanks Ron, good information, your search was obviously more thorough than mine. Unfortunately the referenced yagi antenna ( http://www.m2inc.com/products/vhf/2m/2mcp14.html) has limited bandwidth. The elements are cut and spaced for the desired channel frequency and circularity. Using a Log Periodic modified Yagi provides the required bandwidth but my thinking was that circularity is still an issue; until I found the following abstract info on the IEEE site: (I'm not an IEEE member so can't provide the details) and
unfortunately my searches don't find a commercial LPCP product
Circularly polarized log-periodic dipole antenna for EMImeasurements
This paper appears in: *Electromagnetic Compatibility, IEEE Transactions on* <http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=15>
Publication Date: May 1999

Abstract
Two types of broad-band antennas are widely used for electromagnetic interference (EMI) measurements in the frequency range from 30 to 1000 MHz. Log-periodic dipole antennas (LPDA) are mainly used for the range above 300 MHz and biconical antennas for the range less than 300 MHz. These two antennas have linear polarization. However, EMI measurements can sometimes be more conveniently made with an antenna having circular polarization and so we propose an improved LPDA, which has circular polarization. This LPDA has a second array of dipoles so arranged that each dipole of the second array has a quarter-wavelength phase difference from that of the corresponding dipole of the standard LBDA array for the given radiation field. For this reason, we named it a cross-element LPDA. The cross-element LPDA does not need a broadband 90° hybrid junction to produce circular polarization. We calculated the height pattern and the frequency characteristics of the classical site attenuation (CSA) for the cross-element LPDA when used for both transmitting and receiving, as well as the antenna factor. Moreover, we calculated the normalized site attenuation (NSA) when the cross-element LPDA is used for receiving or for both transmitting and receiving

http://www.m2inc.com/products/vhf/2m/2mcp14.html

Ron




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