That's actually called a DB225...single dipole with director.... I've been dealing with them for over 45 years.. This one looks to be homemade though.. a DB212 loop with a homemade director.. there's no wood in a Decibel antenna?
Chris WB5ITT? Chilled on Friday ??
Chill out Chris.
That is a DB antenna. It is a 212 folded dipole with a director.? Ran into one on a paging system around 35MHz, it was a monster but that’s low band.
In order to recycle it to 6 meters the length of the radiating element and the director need to be shortened as well as the spacing between the radiator and the director.? The piece that connects the radiator and the director is rectangular extruded aluminum tube.? The antenna must mount on a tower leg. ??
In the case of the 35MHz version that I encountered, the tower was square, a very old observation platform, and the desired direction of maximum radiation meant that the antenna was mounted in the middle of the one side of the tower, resulting in very high reflected power.? After a call to DB, the antenna was remounted using an aluminum mast that was 10 ft longer than the antenna, several side mount kits, and lots of crossover brackets to push the antenna 4 ft outward from the face of the square tower. This arrangement allowed the transmitter to be happy but the antenna was very good at catching wind and eventually had to be guyed in place. ?
Milt N3LTQ On Mar 28, 2025, at 06:17, Chris Boone WB5ITT via <setxtelecom=[email protected]> wrote:
? Number one that's a poor picture because it's doesn't show everything and I can't zoom in, number two that looks like a homebrew antenna because the wood support boom and it looks like PVC holding up the far end of the folded dipole (is it folded?)? That's not a DB212 ... I'm not even sure that's a 50 ohm antenna. DB products in their DB212 uses a special harness designed for both impedance and bandwidth. To connect two 50ohm antennas together,? you need a phasing harness of 75 ohm coax odd multiple of 1/4 wave length ..this raises the antenna Z to 100ohm at the end and a T with both antennas tied to it becomes a 50ohm feed.
Chris WB5ITT? On Thu, Mar 27, 2025, 11:58 PM Hudson, John@CalOES via <john.hudson= [email protected]> wrote:
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I think they should be on the same side of the tower 12 feet apart. My frequency is ?53.050 input is 52.050?
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If the coax to the T is 50ohms, then yes , an electrical 1/4 wavelength of 35 ohm coax from the T to the feedline. You could? less ideally alternatively do two? 1/4 wavelength 75 ohm coaxial cables in parallel
. Try to use polyethylene jacketed coax for longer life.. Both 50 coaxial cable antenna pigtails need to be the same length, but can be any length.? ?
I recommend mounting both antennas on the same tower leg.Those UHF T connectors are difficult to waterproof. without using butyl rubber under Scotch 88. First tape one layer of 88 , then squeeze and mold the butyl rubber, then 2 layers of 88 on the outside,
to make it easier to remove the butyl rubbber when it eventually gets disassembled. Messi and Paolini in Italy make great 75 ohm direct bury type coax, if you are forced to go that route.
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John
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Begin forwarded message:
I have a 6 m folded dipole antenna, two of them with coaxial lines going to a T what length of cable should I use out of the T to get The impedance and the length? I was thinking maybe 35 Ohm
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