THE LOOP PAGE - Bow Tie for 75/80 and The BEAST on
40/20... The
BOW TIE LOOP is not new, it was
first used years ago, commercially as a UHF TV antenna and was sold as
an accessory with Zenith, Maganavox and many other television sets (see
picture below).The design was simple, cheap, and it receives better than those little circular loops that most Japanese sets provided. Ham Radio Operators caught on the the 60's using the Bow Tie with many VHF/UHF arrays. Sometimes placing several elements along one boom. HF use was limited to experiments, however many did find their way onto 10 Meters. Eventually, there were a few CB antennas designed around the BOW TIE but the Quad (in a vertical configuration) became the 11 METER antenna of choice. The BOW TIE is indeed a loop, but unlike the four sided loop, the BOW TIE has a 200-225 OHM impedance that incorporates a 4:1 current balun for the un-balanced (50 OHM coax) feedline. We will get into the actual impedance values later on in this article. First I must spell off the myth that LOOPS are big and require a large lot with four supports or towers to suspend these monsters in the blue. Nothing can be farther from the truth. In fact the BOW TIE can be made to function very well (1.9 DB gain over the Inverted Vee) in the same space, or less than the Inverted Vee. The trick is to imagine the bow tie as a shortened Inverted Vee with a second horizontal  compliment,
the same length in the same plane directly below. The vertical component
is two legs of the loop that are equal in length and can range (for 75
Meters) from 6 Meters to 12 Meters depending on the height of the A
and B supports.
The actual numbers are simple. The distance between the supports becomes the factor for D1/D2 and C1/C2. So in reality, if you have 90 feet in the back yard between two trees or one tree and a fiberglass pole or two fiberglass poles, you can put my BOW TIE LOOP in the air. How can this be ?? Well 2 x 90 = 180, now add 2 - 10 meter vertical legs (64 feet total) and you have 244 Feet in the air; and yes it will operate very well, even if the supports are only 30 feet in height. The current is spread over the entire antenna along the horizontal and vertical segments. If you have ever used or contemplated using a CUBICAL QUAD, you can understand the LOOP. It is basically one leg of a two element Quad. Now if the four sides are equal (75 meters each leg would have to be 62 feet) the impedance will be 120 - 130 OHMS. If two opposing sides are longer (75 meters, 2 segments at 100 feet and 2 at 23 feet) the impedance would be 50 - 60 ohms. However, either arrangement would be a nightmare to install. By design, these loops would require four supports and the antenna would be in a HORIZONTAL plane. The supports would have to be 40 feet high on 75 meters. In a VERTICAL plane, the supports would have to be 110 feet high...just to keep the bottom of the loop from touching the ground. Now look at the comparison chart below: |
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| ANTENNA | SUPPORTS | IMPEDANCE | GAIN | DESCRIPTION and COST to OWN |
| BOE TIE LOOP | 2 or 3 | 130 nominal | 1.9 DB | Built like a BOW TIE - $100.00 avg. |
| DIPOLE | 2 | 75 nominal | 0 | Simple Flat Top - $35.00 avg. |
| INVERTED VEE | 1 | 50 nominal | .6 DB | Dipole in Vee shape - $35.00 avg. |
| G5RV DIPOLE | 2 | 50 nominal | .8 DB | Dipole multi band - $65.00 avg. |
| FOLDED DIPOLE | 2 or 3 | 300 nominal | 1.2 DB | Dipole multi band - $40.00 avg. |
| SQUARE LOOP | 4 | 125 nominal | 1.7 DB | Basic Quad Loop - $85.00 avg. |
| RECTANGLE LOOP | 2 or 4 | 60 nominal | 1.9 DB | Vert. or Horiz. - 125.00 avg. |
| DELTA LOOP | 3 | 75 nominal | .8 DB | Triangle - Horiz. - $55.00 ang. |
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The chart shows you my findings after building and
experimenting with these antennas. However there is more to the eye than
what you see here. I use the MFJ 259B analyzer and I try to tune the
antenna as close to resonance as possible, and where the SWR is the
lowest. I also use COAX, because un-balanced line is easier for the
Novice builder and takes less of a tuner in the shack. Please
understand, I have worked on all these different types of designs. They
all work well, for one exception...NOISE !!! Any of the above
antennas that have open ended radials (DIPOLE by DESIGN) will be noisy.
That is a fact of life. Like the LONG WIRE, noise is generated at the
ends and will eventually end up in the receiver front end, even in the
form of STATIC DISCHARGE !!! Most all antennas pick up static charge and
noise but the LOOPS are tuned circuits and tend to be less affected
by noise. They in turn are better for reducing HARMONICS. Again, please
understand that LOOPS are tuned circuits, DIPOLES are not. Dipoles
require height and the supports must be equal in height for the antenna
to perform well. This is the same for the G5RV and the Inverted Vee. The
Bazooka, on the other hand can be a great antenna, but it has it's own
set of problems. This is a difficult antenna to tune. The so-called
Carolina version that can be Off-Center-Fed has impedance problems and
none that I built ever worked well with coax. Sorry about that, but the
CHOKE hanging from the feed-line required a center support. These may
work for some, but all of the above "fancy dan" antennas are too
complicated and require too many considerations. Not to mention that
they are not very broad banded, no matter what the designer tells you,
or how much of a "Mystery" it is to you... I have not mentioned antennas like FOLDED DIPOLES or CAGE DIPOLES because these are very often fed with BALANCED (twin lead) line. These antennas are extremely good for HF bands, they do tend to be broader by design and are not hard to build. However, the FOLDED DIPOLE is a 300 ohm antenna and it still requires height. It is far less noisy than it's counterpart and it can be expensive or inexpensive to build, depending on the design. Not so for the CAGE DIPOLE. This antenna requires height and strong supports. It can be fed with BALANCED or UNBALANCED line. A good CAGE should no less than four elements and eight would be better. For 75 Meters, that would mean more than 1000 feet of wire in the air. No wonder the supports must be strong. The cost to build and raise an eight leg CAGE would be no less than $200 dollars not including the supports...Here you must understand that FOLDED DIPOLES are LOOPS...LOOPS are FOLDED DIPOLES (tuned circuits) but they are stretched closer to 4 equal sides (like the QUAD). They both use the same amount of wire and the same formula 1005/FMHz. So what makes the BOW TIE different ?? Actually nothing, but there are a few factors to consider. First, my BOW TIE is cheap to install. It requires LESS space than a DIPOLE, but it puts two times the wire in the air. It has a VERTICAL/HORIZONTAL compliment and is more OMNI-DIRECTIONAL than the DIPOLE. It has greater low-angle radiation at LOWER height than the DIPOLE. It can be used for both 500 mile rag chewing and 3000 mile DX contacts. It hears better, because it is quiet with respect to the DIPOLE. It can be fed with BALANCED line, but a 4:1 Balun and 50 Ohm coax is the normal installation. It is easier to tune and is far more broad banded than the DIPOLE. Best of all...it don't take rocket science to build !!  In
the picture here you can easily see that the TV LOOP is rather small,
but it has 32 inches of wire and is fed with 300 ohm twin lead. It is a
FOLDED DIPOLE. The BOW TIE is not folded it is a complete loop which has
two equal length legs 123 - 126 foot long, depending. The TV LOOP was used for UHF reception from CH 14 through CH 83. Rather broad banded and it worked very well with less variation and signal shift than the HOOP type antenna design, Two of these on a 3/4 inch wood dowl "boom" about 9 inches long with the feed line twisted and fed to the TV was like a ZL-SPECIAL for UHF TV. Many of these little antennas were used in city apartments for years before CABLE. So now it comes to life on 160 through 40 meters. Let me take a minute to explain why MULTI-BAND antennas like the G5RV and TRAP DIPOLES are a waste of time. First and foremost they are a compromise. If you are running a "KILLER WHAT" amplifier at 1500 watts, who cares what antenna you run, you are going to be heard. But if you are only running 100 watts from a transceiver, you will want some gain too. You also may want to hear better, but that is just my opinion. What I am driving at is this, you are not going to get an all band DIPOLE to function well on 160 - 75/80 - 60 - 40 - 30 - 20 and so on...It is not going to happen. You will need a tuner and some luck. A resonant antenna on 160 meters will not play very well on 75 meters. Compromise !!! The BOW TIE is no better. The 75/80 version can be used on 40 meters, but it will be a compromise. However, it really works great on 60 Meters with no compromise!! Your 75 meter Dipole will not out perform my BOW TIE on 60 (period). As for 40, you can hang a smaller BOW TIE in the same plane and in between the 75/80 version with no loss or interference with the either/or array. If you have read this far, you are probably considering the BOW TIE...so lets get started. First, find the distance between two supports. If you can measure 90 - 125 feet, you can build the BOW TIE for 75/80 meters. It will require at least 185 feet and no less than 3 supports at 45 feet for 160. The third support is for the middle. If you plan to use FIBERGLASS poles like I did, you will need a CENTER support to take weight off the end supports. I will supply addresses for FIBER GLASS pole supports. You will need a 4:1 BALUN. For 100 watt stations, you can use the W2AU Balun and it will work fine. For additional power I suggest the Balun Designs 4:1 model 4113E+. I will show details and offer contact information further on. It must be understood that the BOW TIE uses a little different formula than the QUAD LOOP. Take 995/FMHz and you have the total length. Divide by two for the resulting length for the each leg. EXAMPLE: 995/3.820 = 260' 3". That leaves you with 130' 1.5 inch for each leg. That figure is LONG. That is to say, there is a tuning percentage in the formula and that is because the antenna will be strung between varying measurements and have varying vertical segments. That is why we use the TUNING GIMMICK. The basic antenna I supply will be 12 GA. solid wire at the frequency you supply. It will be two equal lengths at that frequency. The kit will contain the GIMMICK and the GIMMICK JUMPER with stainless steel hardware. You also receive four insulators (non-egg) and 100 feet nylon poly rope. You will need the COAX and the BALUN of your choice. Assuming that you have 2 TREE supports, this project will be rather simple and take about 6 hours to complete. Now note that I show 3 design positions in the graphic above. The basic BOW TIE is the Monkey Suit. Just like the old fashioned BOW TIE it is designed for that presentation. The FLAT or DANGLING version is in grey above it. Note that the top horizontal plane is almost FLAT TOP and by design it can be placed in this position. The IMPEDANCE will rise slightly at this orientation, however the 4:1 BALUN will still match the antenna just fine. At the DROOPER or SLOPER orientation, in blue, the impedance is closed to 225 OHMS, but again there is no negative mismatch at this angle. You must be sure that the GIMMICK hangs directly below the feed point and at the distance listed in the chart below (E0). The INVERTED portion of the BOW TIE is the LOWER segment. This is slightly longer than the top, but you only design your installation for D! - D2 (equal) and A/B. The segments C1 and C2 simply come along for the ride, however these will change during TUNING. Ok you have 100 feet between your supports. If you allow 1 foot for the D1-A insulator then allow 1 foot for the D2-B insulator. That gives you 98 feet across the top VEE. In the normal orientation you can have 98 feet along the lower VEE, so 98 plus 98 = 196, in order to reach your tuned value you must drop the vertical legs about 32 feet on each side. That is a good place to start (10 meter vertical segments). The tuning begins with the antenna at near normal height. Check with an antenna analyzer, or use your SWR bridge and find the minimum SWR. It will most likely be BELOW the frequency you desire. Lower the antenna and at the GIMMICK cut and remove an equal amount of wire from each segment, about 6 inches from each side to start...Raise the antenna and check the SWR. Do this until the antenna begins to come into range. You will have to raise the insulator on the C1 and C2 segments to allow the lower VEE to reach the proper orientation under the upper VEE. Remember that the UPPER HORIZONTAL SEGMENTS should not be changed during tuning, only the LOWER SEGMENT. When you reach the point where your SWR satisfies your needs, the BOW TIE is tuned for you. I suggest that if you want to operate General portion , you set the antenna tuning at 3900 KHz, for the EXTRA segments, set the tuning SWR at 3800 and if you like CW and SSB Extra, start at 3700 KHz. You should be able to tune the entire band with any transceiver with an ATT built in. You will need a TUNER for your amp if you want to operate 3500 - 4000 KHz, but you will be surprised just how easy the antenna tunes from bottom to top... |
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A = see text B = see text C1/C2 = see text D1/D2 = see text E0 = (160 = 42in. - 75/80 =25in. - 60 = 22in. - 40/30 = 15in. - 20 thru 10 = 12in.) |
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In case this is your first visit, let me bring you up to snuff. The BOW TIE LOOP requires a BALUN. Don't operate it without one unless you have no fear about impedance miss-match. I have used a 4:1 BALUN on the BOW TIE for several months now and it works great. I will continue to use the 4:1 on my present BOW TIE, but I plane a 2:1 current type in the near future. It is simply a toss up. The 130 OHM impedance will work fine with 75 OHM COAX and 1:1 BALUN. Your SWR will be come in at 1.8:1 with either 1:1 or 4:1. I am not a huge fan of the 2:1 BALUN because it requires TAPS on the secondary, so I must design an actual RF transformer. If you attempt this it should be a CURRENT type transformer. I have a 50 OHM dummy load and a 75 OHM dummy load, I will tie these together in series to build my TEST JIG for the 2:1 RF transformer. More on this later... Remember that isolating the feed-line eliminates most of the 3rd order standing waves that travel down the OUTSIDE of the coax and return to the shack. Using a BALUN on a balanced antenna is highly recommended if you plan to use un-balanced feed-line. Remember, un-balanced means one side of the transmission line is at ground potential. Feeding the BOW TIE with LADDER line (450 OHM) will require a tuner with a minimum 6:1 transformer. Most all loops come in around 95 to 130 OHMS impedance. That includes the BOW TIE, QUAD LOOP, BOX CAR or the DELTA LOOP. Ok now that we have cleared that up...here is the latest formula for the BOW TIE...1005/FreqMhz. This will get you close to perfect on the frequency you desire as long as the vertical components are 18 feet or longer on the vertical components (A & B). I have tested the FULL WAVE formula and have come to one conclusion, It allows the center VEE portion of the loop to remain constant with height off ground. You can reverse engineer your antenna by determining the space you have available. If you can find 110 FEET in your yard, you can build a loop using 2 (36) foot fiberglass poles. Your antenna can be 262 feet overall. Now do the math, divide 1005 by the length you can find in the yard. This will equal to a resonant frequency of 3.865MHz before tuning. The same application can be applied to the BOX CAR as shown in t text below. THE BEAST or BOX CAR LOOP: The BEAST is a symmetrical loop that is hung between two
supports It is called the BOX CAR because the top and bottom arms are
equal in length and the vertical components are also equal in length.
This is a BALANCED ANTENNA. The BOW TIE may have unequal lengths on top
and bottom, but this will result in an antenna that is basically best on
one band only. Yes it will operate on other bands but the SWR will be
higher than desired. |
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