3347LY Long Boom 16.5 wavelength Loop Yagi

The new and improved 3347LY out in the winter wind and weather, for some real time evaluation. It stayed in this spot all winter, while we checked for mechanical oscillation, wind and ice performance etc. etc., It then went up on top of the 120 ft tower on the hilltop in the Spring of 2006.

PDF File for the 3347LY .....................PDF File for the 3347LYK (Kit version)

The 3347LY is the largest 900 MHz antenna that we manufacture. It is built on a 1" diameter boom with an overall length of 18 ft. Needless to say, this antenna requires a good boom brace. The boom bracing structure first utilized on the long microwave antennas such as the 1376LY and the 9112LYK provided so much strength, that we have adopted the same concept to the 900 MHz long boom antenna with equally superb results. The old bracing system on the 3347LY has been replaced with a very much improved design. The new 3347LY design is available now. The new instruction manual has been posted for the 3347LY. We are still working on some fixtures, but the new mechanical design is working very well after one year exposed to the elements.

The basic 47 element design produces 20.5 dBi gain at 903 MHz. The bandpass of the antenna is such that it produces very close to maximum gain across the entire 902-928 MHz band. A sample bandpass plot of the antenna is included below. The return loss plot is also included.

The horizontal divisions are 10 MHz, and the gain is still within about 0.7 dB of maximum gain, up at 930 MHz. Note that the VSWR remains fair across the entire band. The 3347LY"A" version of this antenna is peaked higher in the band to favor the upper end of the 902-928 MHz band.

Some Specifications

Construction utilizes a 1.0" boom of 6063-T832 alloy with a sturdy sub boom made of 3/4" square x 1/8" wall aluminum . The sub boom is a two piece 106" long assembly with approximately 55-58" of the main boom un-suppported at each end of the boom. The main boom is supported in three places. This provides a sturdy support that will withstand very heavy ice loading, and high cross winds. It is similar to the support arrangement on the 2304 MHz Blowtorch, the 1376LY, which has proven to be an exemplary ice storm survivor. It is not a light antenna. It tips the scales at 10 pounds assembled weight.

3347LY, 3347LYK

The forward gain of the 18 ft loop yagi is considerably more than that of the standard 12 ft. 3333LY version. 20.5 vs. 18.5 dBi. The addition of a more robust bracing system on the 3347LY makes it a great choice, even in areas of severe icing. For additional gain, the 3347LY may be combined in arrays of two or four. Slightly more than 2.5 dB is achieved for each doubling of antenna size. A two bay array will produce 23 dBi, while a four bay array will achieve almost 26 dBi. The proper stacking method employs equal lengths of 50 ohm coax and a two or four way power divider. In either case feeder losses of under 1/2 dB are achieved with Times Microwave LMR-400 coaxial cable. In addition, the good VSWR bandwidth of the 3347LY remains the same no matter how many antennas are phased together. Halfpower beamwidths are halved when array size is doubled for each plane. A two bay or four bay array will have an E-plane -3 dB point of about 7.4 degrees.

We have included some plots of a four bay array of 3347LY loop yagis spaced at the recommended 38" H-plane and 41" E-plane stacking distance. You can compare these return loss and gain plots with those above of a single antenna.

This four loop yagi array provides great performance across the entire band, and with gain of about 26 dBi, will make your 900 MHz signal second to none. 26 dB is the equivalent of a 400 X increase in power. Put another way, your 100 watt power level will sound like 40,000 watts when transmitted into this array!

The last two plots are very interesting when compared to the first two plots of the single 3347LY antenna. When compared, you can see that the VSWR bandwidth truly does not degrade, or get any narrower. (In fact it gets slightly wider!) The basic curves remain quite similar. The gain bandwidth also stays quite consistent with that of a single antenna as well. All this is accomplished with a 33-4PD power divider and equal lengths of 50 ohm coax cable. The introduction of the power divider and equal lengths of 50 ohm coax does nothing to restrict the bandwidth. The same results would not have been obtained had odd multiples of 75 ohm coax (or 50 ohm for a 4X array) been used. 11 or 13 quarter waves would have severely restricted the bandwidth. There is a good chance that the resonant frequency would not have been anywhere near 902 or 903 MHz. Such results are why we always recommend the power divider approach to antenna stacking. The results are predictable and very repeatable!

A photo of the 4 X 3347LY array as it is being gain & pattern tested in January of 2006. Always a good time for antenna work!