Art Bell's (WB6OBB) really big loop antenna

Discussion in 'Ham Radio Discussions' started by KC0BUS, Mar 23, 2009.

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  1. W6PU

    W6PU Ham Member QRZ Page

    I probably worked you John! Maybe I'm getting the call mixed up, but I thought that HZ1AB (American Boy) was quite active around then, and the front to back on his terminated Rhombic was amazing. When he was running Europe, we just couldn,t get his attention even though he was still S7.

    For those who may not be familiar with high gain antenna arrays,the thing about a big Rhombic isn't so much about the forward gain that it produces!

    A large vertically stacked four or six bay Curtain

    ( refer to the photo of Duga-3 that my previous link will take you to)

    such as was used by the VOA and Radio Moscow has much greater forward gain, is steerable, and with even a non resonant grid wire reflector,produces an excellent F/B and front to side ratio.

    Also, it takes up a whole lot less real estate then does a rhombic which at 3Mhz or so, (commercial band) could easily be two miles long between the back tower and the front tower!

    To put it another way, for the new comers, each of the four wires joined together to create this big diamond loop, are often five thousand or more feet in length!

    At these low frequencies (as compared to 14Mhz) , towers in excess of two hundred feet are often used for long range International broadcast.. Figure at 3.5Mhz, a 130 foot tower is only one half wave high.

    Even some multi element Yagis, Quads, and Quagis will develope equal or rven greater forward gain , depending on their size and how low an angle of radiation they are set to deliver, which for horizontally mounted set ups is determined by their height.

    The primary advantage of the big Rhombics is their abilitiy to cover Octaves of frequency rather than Khz! There just super broad banded!
    Another plus is the inherent nature of wires of "one wave length and longer" to develope low angle radiation.

    The longer the single wire, the closer to the wire axis (think cone shape...like two ice cream cones back to back) the four major lobes are!

    For the new comers reading this: the ARRL antenna hand book has some great diagrams of the patterns developed by long ( a wave length or better) single end fed wires!

    For years I used to work ZL1AQ who used a big horizontal loop( not a rhombic), and he always had an excellent signal on all bands. It wasn't equal to the guys over in that area (VK-ZL) who were running the big long boom multi element rotaries, but it was always a respectable signal!

    Of course, the big diamond shaped loop that is the modern Rhombic, was merely an off shoot of the very long wire horizontal antenna.

    First they realized that you could reinforce the single lonw wire lobes by using two long wire in the shape of a V, the included angle was dependent on how long the wires were on the lowest intend frequency. Thus was born the Vee Beam.

    Not long after wards, they tried two vee beams, one being in front of the other, and got more foward gain. Next, some one thought of combining the lobes of Four seperate long wires into the shape of a elongated (rhombus) diamond, and the Rhombic was born.

    Hams in the Communications industry were at the cutting edge of these developments, and it must have been very exciting times to live in for a Ham radio operator and antenna experimentor!

    Take care, and 73

    Bob W6PU
     
  2. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page


    It's quite possible we did work Bob. Our call, HZ1JB was courtesy of Jaqcues Bernier (JB) who bribed a Saudi official at the post office. That cut through a lot of red tape and we got the call sign within a week. There was a guy named Jeff over in Jiddah with Aramco. I knew he was a ham and he may have been AB. I spent most of my time in Abha, Riyadh, Jizan, and Taif.

    We were a group of satellite system engineers working for Harris Corp at that time. We were contracted by the Saudi government to install a satellite and microwave switched telecommunication system that linked with the existing plant (land line system). Interestingly some of the exchanges were built by the Germans in WWII and were still in use. Anyway we had a lot more real estate and some very large towers to play with in Africa. Surprisingly, we were fairly restricted in Saudi in terms of space for antennas so a decent rhombic was out of the question.
     
    Last edited: Mar 27, 2009
  3. KQ6XA

    KQ6XA Ham Member QRZ Page

    W6OBB Big Loop - History

    Art W6OBB designed the big loop, mainly to be able to get a more substantial regional signal out on 75 meter band. Before that, he ran a fullwave inverted-V on 75 meters, with the apex at 100ft on his tower under the Log Periodic beam. The on-air comparison tests between the first big loop and the inverted-V were very impressive... the big loop won by 6 to 20dB in almost every direction and distance.

    The big loop went through several stages of evolution. I worked on Art's original big loop with him, and a couple of the upgrades. On one of them, I went out and did some field strength measurements at 8 radial points, 1 mile away, in my 4WD vehicle out in the desert. This was mainly to verify that the modelling of the pattern was similar to what the results were. It was pretty close to the model pattern.

    Several different feedpoint positions were tried, and they had slightly different effects on the pattern, elevation and azimuth. This also affected the impedance and stressed the antenna tuner capabilities due to very high impedance on certain frequencies.

    The first big loop was originally a single wire, then later a second wire was added to lower the total wire resistance, and make it more broadbanded. This is a similar technique used on multiband rhombics. It helped the impedance excursions and made tune-up easier for QSY.

    After that, the loop was expanded with more support poles, to cover more total area... effectively doubling the wire in the air, if I remember correctly. A ground screen was added under the whole thing... a huge project in itself. Keep in mind that the location is dry desert soil, and the natural RF ground is probably at least 30 to 80 feet below the surface. The pattern changed somewhat after that.

    It is quite impressive, not only how well the antenna radiates, but what you can hear on the big loop. On the higher frequency bands, it has some sharp lobes that have gain similar to a rhombic in certain directions. On the lower frequency bands, it has a broader pattern. On 75 and especially 160 meters, it probably puts out the biggest signal on the band in the southwestern US. It also can hear a 5 watt SSB backpack 75 meters... 1000 miles away.
     
    Last edited: Mar 27, 2009
  4. KE4YGS

    KE4YGS Ham Member QRZ Page

    Man what a small world.

    You Harris guys got it right. I was in both Nigeria and Saudi among a ton of other places. I was with the old SatCom Division and have done work in Kano Nigeria and all of the sites metioned in Saudi. We were installing then operating the 11M C-band systems. Analog half transponder video and then several transponders of analog SCPC. The dates seem about right too, I'd bet we have talked to eachother out there. To my knowledge the DAMA system never did work as it was advertised and the overall job was later passed to Bell Canada who replaced all the SatCom terminals with terrestrial microwave links. Spent MOST of my time in Sharourah, but made it to all the sites eventually.

    I was fortunate enough to go to every satcom site Harris had . We had some of the old RF-220 radios and later I think the RF-386 military looking units. Of course we only used the radios until we got the particular terminial on the air, then packed them up and sent them on to the next site being installed. We made plain old homebrew dipoles and were able to talk in country just fine. Several of us (not me) were hams at the time but I didn't think any of us operated in the Ham Bands over there.

    Scotty
     
    Last edited: Mar 27, 2009
  5. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    Wow it really is a small world Scotty. I was assigned to the HISCO Satellite division in Melbourne (not Palm Bay) at the time. We never installed any DAMA equipment in Nigeria but did in Saudi. There were a lot of problems with it but most were due to the fact that a lot of the exchanges in Saudi were still manual with switchboards.

    I wonder if we ever ran into one another? I worked with Rodger Tede, Jack Cox, Jeff Mann, and Bill Wilkerson in Nigeria. I spent the majority of my time in Kaduna but was also in Lagos, Jos, Calabar, Kano and Sokato. We also had a very large Puerto Rican guy named Carlos that ran the shop in Lagos.

    All of our sites had Harris HF equipment (RF 220s) and being hams we put up some killer antennas. I think the RF 220 would only go up to 18 or 20 MHZ as I recall.

    In Saudi I worked with Wayne Shambora, George Hilly, Jacques Bernier, and an old British guy who's name escapes me. Our primary digs were in Riyadh and that was where we operated HZ1JB.

    We also had people in Uganda at that time.

    After I returned from Saudi I went over to the Government systems group in Palm Bay and my first job over there was the AJ modem. I worked there for another ten years and was on a bunch of different programs.

    John.
     
  6. KE4YGS

    KE4YGS Ham Member QRZ Page

    Im sure we did meet at some point. I remember Shambora and several of the other names you mentioned. The older Brit guy you were thinking of might have been John Weatherly. Did you know Al Fritz, Bill Salber, Nick Tamerof, Mike Joyce, Jack Acker,? I was in the flats in Riyahd for a short while. Later came back up and worked at the Riyadh site for a bit.

    A short anecdote, When I first came in country the PM asked me where I would like to go. Being young and ready to bolt, I said I want to go to your worst site. The site nobody else wants to go to or can handle, the one you have the most trouble with. Hence my primary job ended up being running the Sharourah site, in the Arub Al Khali. I learned from that, boy did I learn. Those were the days !

    I transfered to HISCO (the unbrella Corp.) from Composition Systems as the Phase One Nigeria was ending I was under Don Shingler's O&M staff. Worked in Sudan, Nigeria, Saudi, Uganda (Arua then Kampala). Saudi was a trial but I found it quite doable. We had a little Hitachi portable exchange in Sharourah. One of the few things I ever saw work well over there. I tried to stay away from the down town exchange in Riyadh. Place would have been better to bulldoze it and rewire a new one instead of patching everything there. Half or more of the cables and wires didnt go anywhere anymore anyway. What a mess, and no documentation. John Weatherly and Mike Joyce were hams at that time.

    I came back in plant and worked in Training as an instructor for a few years and then as they closed Sat Com Division, I went to Palm Bay and worked on the JRSC terminals instructing the Army and AF. One really good friend Sharon VonK worked on the AJ modems with yall. Think she was in Contract Management maybe.

    Lordy the memories !
     
    Last edited: Mar 29, 2009
  7. W8HDU

    W8HDU Ham Member QRZ Page

    KQ6XA,

    A post I read suggested that this is (2) turns of a wire connected to the feedpoint.

    From what you say above, you're hinting that it's parallel wires to improve bandwidth.

    Can you explain better which design was used, and perhaps make some detailed sketches with distances between towers?

    I would really like to know more about the practical results, as compared to the modeled version, as I'm thinking of putting something up after I retire at our new home.
     
  8. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    Oh Scotty. I worked with Al Fritz and Mike Joyce in Saudi. I also remember D D Don Shingler:D who could forget him. John Weatherly was at the main site downtown but I also saw him fairly often, he was a great guy. We were at the primary site, the one with the big 30 meter dish out on smash em up ally on the road to Medina.

    There was a story about a British guy who accidentally wound up in Medina and got out of his car to ask directions. Being an infidel who stepped on sacred soil he was arrested by the Saudis and they were going to cut off his feet. I got in trouble for sending telexes from Abha to Ryahd like " if you plan to go to Medina don't wear expensive shoes". Apparently the Saudis in the home office didn't see the humor in that. We also had John (Doc) Holiday and Mike Joyce with us at the main site.

    Like you I was assigned to, or visited every third world toilette in Africa and got caught in the middle of several pretty ugly tribal conflicts.

    I haven't been back to Melbourne in years since my good friend Tony Campagna (AB4VR) died. By the way, I was a member of the PCARS for about 7 years. Lot's of memories and stories to tell Scotty.

    Sure wish we could have an eyeball and beer. I'd really like to set up a sched but my station is packed away, we're moving to Las Vegas. I made a note of your call in my log and will try to contact you as soon as I get set up again.

    John..
     
  9. KE4YGS

    KE4YGS Ham Member QRZ Page

    Oh indeed ! Drop me an email at the one listed in the lookups. Love to set up a sked when you get relocated if you can stand the slow code LOL ! Anytime anyplace. Yes Mike Joyce is still a close friend and I always liked John Weatherly. First met John In Sudan out in Al Fasher. Later learned we werent supposed to get along and that would be their reason to get rid of both of us. We clicked from the first minute we met LOL ! I met Al in Ethiopia when he worked for Radiation before it was Harris, used to babysit his kids there when I was in the Navy. We got some turf to cover for sure.

    Now that we have hijacked a perfectly good thread, lets take it to email shall we?

    Scotty
     
  10. WB6BNQ

    WB6BNQ Ham Member QRZ Page

    #
    Fred,
    #
    I can back up what Bonnie, KQ6XA, has stated. She was definitely involved in the original planning of the antenna. Art put considerable effort and money into the construction; to say the least, this is not your average antenna project.
    #
    1. The loop is approximately 1600 feet in length made of #10 ga. Copper wire. Its lowest resonant point is around 600 KHz.
    #
    2. There are two loops of wire with the top loop being at approximately 70 feet, except for the feed point. The second loop of wire is approximately 7 feet below the top loop.
    #
    3. The start of these loops, and the feed point, is at the original crank-up tower at about 100 feet. Both loops converge to a common feed point, that is to say both loops are electrically tied together at the feed point and fed with open wire (ladder) line. It is * * NOT * * a transformer, i.e., two turn loop.
    #
    4. Each of the 12 supporting auxiliary poles are free standing very large diameter pipe. Each of these supports, for its total installation, cost approximately $3000. Yes, that is right, 12 poles at $3000 each !
    #
    5. Yes, Art had a ground screen (Chicken wire type fence material) laid under the antenna running between each support pole. It did appear to slightly affect the pattern (see discussion below).
    #
    6. Yes, Art did experience a voltage charge on the antenna. NO, it was not from a nearby AM radio station. This static voltage is atmospheric in nature and a natural build-up of charged particles collected over a large area due to the capacitance between the antenna as one capacitor plate and Earth as the other. The closest commercial radio station is Art’s own FM station, KNYE, at 13 miles distance. It only runs 6 KW at the transmitter output.
    #
    #
    Review the link in the first post carefully. You can plainly see the 7 foot separation of the two wires. You also can see portions of the pole construction and installation. As well, the pattern, antenna shape, and gain is presented in one of the slides. Yes, it would be nice if Patricia would have made the slide show go slower.
    #
    A vertical antenna is really one half of a dipole with its feed point sitting (isolated from) on the “ground.” The other half of the vertical’s dipole element is virtual and the virtual element’s current is displaced by 90 degrees along the path of the “ground” terrain. Thus the condition of the “ground” is highly important to the function of the vertical antenna. It is the 90 degree bend of current flow that causes the vertical antenna to have a very low angle of radiation.
    #
    This is not the case with balanced antennas. The loop, just like the dipole, inverted V, slopers, G5RV, off center fed Windom, and beam antennas, is a balanced antenna. These types of antennas do not need any reference to “ground” for any reason. The classic, in free space, antenna pattern is truly a “DONUT.” However, as you bring such antennas nearer and nearer to Earth, the reflections from the Earth plane mix, algebraically, with the classical free space “DONUT” pattern. The algebraic addition and subtraction of the “ground” reflected wave fronts with the initial antenna pattern cause distortion of the far field pattern. Close to the ground, i.e., 50 to 60 feet, these reflections cause the pattern to assume a hemispherical shape with the main gain primarily in the vertical (straight up) direction. In essence a NVIS antenna. It does not matter if the horizontal loop is round or square.
    #
    To obtain lower angle takeoff, a square loop needs to be NON-square in shape. An irregular shape causes the antenna’s current nodes and ground reflections to combine and cancel in an irregular pattern. This can be verified by distorting the shape of a square loop in Eznec. This is the advantage of a good modeling program like Eznec. The actual expected gain values are not the picture. What is important is to study the changes that occur with each change in shape and height. Such theoretical experimentation will give you insight as to what is happening.
    #
    Bill.....WB6BNQ
     
    Last edited: Mar 30, 2009
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