The Mighty Rhombic, the King of Antennas (AD #128)

Published 2018-04-11
There was a time, back in the 1930s and 1940s, when the rhombic antenna was the king. A remarkable antenna that had phenomenal directivity and an extraordinarily low elevation angle made it the antenna of choice for point-to-point HF links. Here's a little history, plus an exploration using EZNEC+. Phenomenal antenna! Subscribe: youtube.com/davidcasler. Ask Dave Playlist: goo.gl/inaQeB. Tip Jar: ke0og.net/tip-jar

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All Comments (21)
  • @ricpla6930
    You are an excellent presenter and speaker. Clear and concise, packed full of information with no filler bs. A true teacher.
  • @jrpefx
    Hello David, John here with some old field notes from my father a Major in the U.S.Army during WW II. He informed me that during the war he was stationed in North Africa. And his job was to transmit via short wave to parts of Europe and back to New York. He told me that he would use Rhombic Antennas to do the job. One funny aside was that the local inhabitants would climb the poles and steal the copper wire that made the antenna. So he went into the town and spoke with the local leader, and made a deal, once a month the locals would get one spool of wire and they in turn would protect and leave the antennas alone. He too said that this type of antenna worked very well. Take care 73 de KM6LBW
  • @grs6262
    As a Morse intercept op, USASA, 1966-1970 we employed rhombics to listen to 'everyone' from our listening posts (small dets to large field stations) worldwide.. Our unofficial motto was; In God we trust. All others we monitor.. The rhombic tended to business.. you could hear a gnat sneeze in western china from a monitoring station in okinawa..
  • @johncliff5417
    Great video Dave. I was a "Boy Soldier" in the Brit army from 15 years old. On leaving Boys service I went to 224 Signal Sqn. to train as a "Spec Op" I had to learn all about the good old Rhombic before being allowed to use one for listening to our friends overseas on my Racal RA17 and Eddystone receivers. Years later I was experimenting with a low band VHF vertical half Rhombic. I had to make up AMU's and my version of the "Monimatch" VSWR meters to feed into mil "C45" transceivers that we used there. With a remote station up on the Danish coast and the base in Hildesheim. N. W. Germany. The vertical half Rhombics worked a treat . The normal range for a pair of C45's using elevated ground-plain antennas was 15 to 30 miles tops. The next big test for the vertical half Rhombic was out in Malaya. I was with a light Infantry Battalion out in the jungle and our communication with Brigade HQ was via a Re-Broadcast station stuck out on a mountain range miles away. The Re-bro station broke down and no coms. Luckily I had the vertical half Rombic and matching unit stached away in my vehicle bins. I asked the units signal officer for permission to get the Assault Pioneer section involved to cut me a 30 ft bamboo pole down and clear a couple of hundred feet of jungle growth down in a straight line on the correct magnetic heading. We got the antenna up and fed into a Man pack A41 radio (1 watt o/p). This was setup on the Brigade frequency direct. I sent a "Slidex" encoded message requesting to use the frequency and explained what I was using. Got the answer back that the Brigade signals officer was on his way out to me in a chopper. I got a rollicking from him because I had not put a red light on the top. My excuse was we did not have the necessary girls there for that purpose. That was the vertical half Rhombic working to a elevated ground-plain antenna over a long distance. Not bad to say I was getting payed for my hobby.
  • @fredderf3207
    The Germans, at Stalingrad constructed a large Rhombic Antenna to establish a direct radio link with Berlin. It worked.
  • @handy335
    Thanks, Dave. As another "dated" ham operator, I always enjoy your presentations. Keep up the good work. It is greatly appreciated!
  • @thomthumbe
    I was manager of a large antenna field that included 13 rombic’s. About half were “nested”, or a low frequency outer antenna, with a high frequency, smaller antenna nested inside the low freq antenna. Several had both a balun and a terminating resistor at both ends. Of course only one balun and terminating resistor was used at any one given time. The dual feature allowed us to use the antenna in the opposite direction. All fed with 3”, pressurized Andrew coax. Fun times! Thanks!
  • @boulder89984
    A few years ago I could have built one. Have many friends in the utility trade and putting up poles was not a problem. Now the trucks have GPS and side trips for pet projects are now frowned upon. Your presentation was fascinating. THANKS!
  • @jonthebru
    The Maui Amateur Radio Club built a rhombic at Ho'okipa every field day for decades. Everything you spoke of; the size, the gain, it was beamed straight towards North America. Sorry, no pictures I know of.
  • @techguy9023
    The old AT&T long lines site in the Northeast had about 16 of them . I have a drawing showing them pointed to cities around the globe. Some were 700 feet long. This was over swampy ground. Can’t imagine the gain.
  • @sphexes
    Dave, it was great to see the joy in your face imparting this great information. I loved the historical back story. Thank you. 73 W8XDX
  • @ke4uyp
    A couple of things to consider when talking about rhombics. Even though they do produce beautiful unidirectional patterns with very high gain figures compared to say a dipole. Unfortunately compared to a multi-element cubicle quad or Yagi they actually are not that efficient. The reason is first you have the terminating resistor and in most cases that resistor consumes approximately 50% of your transmitting power and converts it into heat. Also because of the extreme length of the antenna the omnic loss through the wire are measurable and it also contributes at least a few percent of loss to heat. When you add these two losses together a typical four element yagi mono bander can actually outperform a large rhombo operating at the same height above ground that he mentions in the video that this rhombic was at.
  • @wramsey2656
    A conductor at that height reminded me of the transmission lines i would design as a utility engineer. We would install single or double conductors as static wires on davit arms as lightning protection (not as neutral carrying conductors). At that height needless to say in the Midwest and in Georgia (i moved around in my career), lightning would take its toll on those conductors; moreover, periodically burning the conductors in two falling on the phase conductors below. We used copperweld and even ACSR which are very strong conductors. So if you plan to put one of these up in the air and live in lightning prone areas don't go cheap on the conductors, grounds, arresters, and fittings, unless you like climbing poles or towers. Great video !!!!
  • @MrMmaretic
    I'm retired from FEMA we had a comm site in MI with 9 Rhombics the towers were 60' tall about an 1/8 of a mile apart with two 10 gauge steel wire on each hey were fed by no loss coax. I think five were for transmit four were for receiving, there was also two 100' tall spiral cone antennas. There was 100k Harris radios. Site on 210 acres.
  • @jonyzhu6531
    Excellent explanation! You have the best antenna series!
  • @craigszwed
    This year I put up, in my oak trees, a vertically mounted horizontally polarized quad that is about 102ft long and 50ft high, with the bottom element averaging 25ft over ground. That works out to about a 5/8 wave on 160m. I feed that with 40ft of 450 ohm ladderline from a 4:1 current balun at my outside junction/lightning/ground box. I used 65ft of RG8X between there and my TenTec 229 in the garage. I have tuned and worked 6 through 160, with 6m being under swr of 2 without the tuner. I'd send you a photo but it's hard to see in the oak trees. It's easier to watch my video about the system. Thanks for all your great videos!
  • The VOA Bethany station had a bunch of rhombics. They used a feedlne at the far end of the antenna to feed the power back in phase to the feed point so they didn't have the loss of a termnation resistor. They called these re-entrant rhombics. They were being fed initially by 200 kW rigs, so if they'd have used termination resistors they would have been huge. Another famous rhombic was erected on a hilltop and used to received TV channel 4 New York off-air at Schenectady for retransmission,
  • @KX4UL
    Wow! Really good video. And what an antenna!! Good info Dave. Thanks!
  • @dStruct619
    This video popped up on my YT feed some years after you made it here in 2021, but I found it informative and really enjoy the dive back in history. Enjoying the content, thank you and 73’s.
  • @dougtaylor7724
    A good friend of mine trained at a similar facility in the 50’s. He told me he still recalls the first day when the team was taken out to have a look at the horizontal antenna field. He was even more impressed when they used the antennas.