Hi Mike,
Rhombic antennas -- with few exceptions -- were not usually designed for high gain. They were usually designed as a compromise between gain and typically one octave of bandwidth (e.g. 14-28 MHz). To compound the design compromises, the r hombic termination resistor throws away nearly 3 dB of whatever gain it might achieve. Because of this, high gain transmitting rhombics have very narrow beamwidth, typically 20-30 degrees. A high gain rhombic designed for 14-28 MHz -- competitive with a pair of stacked large triband Yagis -- might be 300 feet wide, 700 feet long and supported by four 100 foot towers. In order to achieve this gain, the rhombic beamwidth would be only about 25 degrees, requiring at least a dozen huge reversable rhombics to cover most of the compass. I visited many rhombic antenna farms many years ago (as far as I know they've now all been dismantled). They were typically at least one square mile sites with fifty to a hundred towers with heights of 50 to more than 200 feet. Dismantled VOA Site C in Greenville, NC is a good example, a 1.5 square mile site with pairs of massive rhombics -- the biggest I've ever seen -- for diversity reception. To the extent these facilities are still operating (the vast majority are not), the rhombics were replaced by rotatable log periodic antennas, perhaps with higher power transmitters to make up for the slightly reduced gain. That approach replaces a one square miles ( in some cases much larger) with a few acres or perhaps 100 acres for very large site. This is a good reference: www.w8ji.com/rhombic_antennas.htm 73 Frank W3LPL ----- Original Message ----- From: "Mike Markowski" <[email protected]> To: [email protected] Sent: Friday, September 13, 2019 10:24:32 PM Subject: Re: [Elecraft] Rhombic antenna "gain" Can you expand on this, Ken, or if easier, a reference? I'm curious what tradeoffs are made. I used a rhombic at Ft. Monmouth, NJ before the Army base was closed in 2011, and used to boom into Europe and Russia. It was amazing. I also got copies of WWII manuals on rhombic construction while there. You know, just in case I became wealthy with tens of acres of land. :-) 73, Mike ab3ap On 9/13/19 5:57 PM, Ken G Kopp wrote: > Rhombic antennas derive their well-known gain by "throwing away" some of > the design's gain. Ditto for the infamous "inverted vee". Use is made of > the lobes from the four wires while disregarding others. > > 73 ! > > Ken Kopp - K0PP ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
