DPM144-5LVA ARRAYSThe basic antenna is the DPM144-5LVA, a six ft long rear mounted yagi, originally computer optimized by N1DPM. It is a nicely performing yagi with over 9 dBd forward gain, and a good pattern. It is equally well suited singly for roving applications on 144, or for combination with other similar antennas in a large broad beamwidth array for serious VHF contesting. The PDF formatted manual is here.
The project began with Fred Stefanik, N1DPM, trying to improve the contest score of NC1I, a limited multi-operator station that achieved top honors nationwide from Western Massachusetts over the last few years. Their original 144 MHz antenna consisted of one long 50 ft M2 antenna. While the antenna had great gain, the narrow beamwidth was not good for contesting. Long yagis tend to eat up rotators with gusto, and also require large amounts of time to be spent simply rotating to find stations in the first place. Fred dropped the long yagi idea quick, and eventually ended up with an array of two stacked 9 element yagis that improved the number of QSOS and grids. Fred thought this combination was too sharp as well, although their score went up markedly. He eventually ended up with a 5 element design that looked to be an optimum choice for contesting. It had a very wide horizontal main lobe and could cover large swaths of the country with no twiddling of the rotor control box! They never installed an LVA of these 5 element yagis at NC1I, but we did adopt the idea for use at K1WHS in Maine. See the picture below:
LVA at K1WHS Fall, 2003
This is the 144 MHz LVA as it appeared in 2003 at K1WHS. LVA is an acronym for Large Vertical Array. It started out as eight antennas with the ultimate goal of an increase to sixteen yagis: The top 5 element yagi is at 115 ft, while the bottom one is at 76 ft. With a 52 degree horizontal beamwidth, it covers much of the United States from this location in Maine. Imagine, useable beamwidth is around 90 degrees or more. Really, the real "hearing" problems occur when you get to the nulls in the pattern. The operating beamwidth is much wider than the listed -3 dB points of this array. With long yagi antennas, those nulls occur very close to the main lobe, a real disadvantage when compared to short boom yagis. As antennas are added vertically, the vertical lobe gets more and more flattened. 8 Yagis have a 6.5 degree vertical lobe. The main lobe remains at 52 degrees horizontal no matter how many yagis are added vertically. So we merely need to vertically stack a few LVA beams to produce more gain and over a wider beamwidth than a conventional long yagi.
A few things to consider in the LVA design seem counter-intuitive. In the past, gain was king. If brand X had 13.791 dBd forward gain, and Brand Y came out with a new model that had 13.992 dBd gain, the DXers would flock to the store and buy all of Brand Y's new offering. For contesting, the priority is to actually hear the station in the first place. Rather than thinking about how much gain you could muster in a particular direction, you should be thinking about how much area can I cover with my main lobe. If you can put all of your RF in a wide area, more people will hear you. It is that simple. You will not hear weak stations calling you in your beam nulls! The LVA has purposely been designed with a wide main lobe. It will never win a gain contest at your local VHF Conference. (Well maybe it might if there are few entries!) BUT, it will spew RF across a wide main lobe and have a great H plane pattern that is so necessary for proper stacking. The -10 dB beamwidth is 89.6 degrees. This is a good number to watch, as it covers the working part of the main lobe between the first nulls
LVA INSTALLATION, K1WHS, August, 2004
At our Contest station in 2004, an extra 8 yagis were added to the original eight LVA. Shown here is K1DY bolting on one of the last yagis in the array.Seen from a distance, this antenna system is starting to look rather large! The bottom antenna is at 32 ft, making the whole array occupy 83 ft vertically. This makes the vertical beamwidth about 3.25 degrees wide at the 1/2 powerpoints! Gain of the 16 yagi array is well over 20 dBd and compares favorably with the four 30 ft yagis on top of the tower. The best part is that no rotator is needed for the LVA to cover a wide range of azimuths. At K1WHS, we can work stations from Toronto (270 degrees) to Albany, NY to New York City, to Providence, RI. (185 degrees) without touching a rotator button. Even at the 90 degree -10 dB points of the main lobe, there is still almost 11 dBd of forward gain: the equivalent of a single 12 ft long yagi. This is more than enough to be heard.
Other interesting positive points when installing a large number of these short yagis includes the very sharp vertical pattern that will allow a large reduction of power line noise if your station is located on a hilltop, and the power lines are at the bottom of the hill. This was demonstrated at K1WHS, with the middle of the array at about 925 ft asl. The local power lines are at about 425 ft asl, and are about 2.5 to 4 miles away. A few calculations showed that each offending power pole was well outside of the main lobe and caused the power line noise to actually drop in level. Remember that the incoming signals are -3 dB at -1.6 degrees elevation!! This noise reduction only showed up when the array was enlarged to 16 antennas. Eight or four yagis will not have a sharp enough main lobe to reduce close in noise. Another positive feature of side mounted antennas involves rain static. The side mounted array is located below the rotatable 4- yagi array on the tower top. Interestingly, the LVA does not suffer from rain or snow static even while the top mounted four yagi array is experiencing 59 +30 dB noise levels. The higher metal will bleed off the static charges. This is a big improvement, and adds tremendous flexibility in contest situations.
An actual bandwidth plot of DPM144-5LVA is shown here: DPM144-5LVA Bandpass
Return Loss plot of the DPM144-5LVA is available here: DPM144-5 VSWR
Patterns? You want patterns? I'll show you patterns!!!
E & H plane single DPM144-5LVA polar patterns
4 X DPM144-5LVA stacked vertically
8 X and 16 X DPM144-5LVA stacked vertically
5 ELEMENT 144 MHz Yagi
|-3 dB BEAMWIDTH, E:||52||degrees|
|-3 Db BEAMWIDTH, H:||58||degrees|
|DRIVEN ELEMENT:||T Match, PTFE semi rigid UT-141Balun, brass element|
|CONNECTOR TYPE:||N (F) UG-58/U|
|MAST SIZE:||1 1/2 __________(2" on special order)||inches|
|MTG STYLE:||Rear or Center, V or H polarization. Mtg plate with 2 u-bolts|
|4 X DPM144-5|
|8 X DPM144-5||825.00|
|16 X DPM144-5||1620.00|
|BALUN & DE ASSEMBLY|
|BLACK DELRIN INSULATORS (100 PC BAG)||35.00/ 100 BAG|
|ELEMENT KEEPERS, stainless steel||$25.00/ 100 BAG|
* Stacking kits consist of all rf components required for installing your "array" of DPM144-5 yagis. This includes both power dividers and phase matched cable assemblies. Note that the 8 antenna array includes three power dividers, and the 16 antenna array includes five power dividers. All supplied cables are Times Microwave LMR-400 with type N male rf connectors.
The antenna bundles are supplied as a bulk pack. Antennas are not individually packaged. This allows significant cost savings for larger arrays.
With a large vertical array of this type, particular attention must be paid to the electrical lengths of all of the interconnecting cables or pattern degradation will result. When large numbers of antennas are involved, the lengths increase, and errors are more easily made. Our Directive Systems harnesses are made with minimum amounts of cable. The inner cables are actually shorter than the outer ones. This is possible by removing full wavelengths of cable and measuring the results for equal amounts of electrical degree delay. As they say on TV: "Don't try this at home kids!!" Precision network analyzers are needed to precisely match the delay numbers in the finished harness. Should you wish to make your own harness, You may use equal lengths of cable, but with more insertion loss, and more excess cable coiled on your tower.
For more LVA pictures, here are some more photos courtesy of Bruce Herrick, WW1M:
LVA looking up
LVA with top 144 array during September 2004 VHF QSO Party