John,
I believe the 225 has the feed attached to the "outside" of the
top element while the 212 has it attached to the "inside" of it.
In other words the 225 has the attachment closest to the director,
the 212 attachment is closest to the tower. If one where to cut
off the boom to eliminate the director, this could be taken into
consideration accordingly. Do you agree?
Chuck
WB2EDV
On 3/28/2025 9:21 AM, John via
groups.io wrote:
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That is
indeed a DB-225 (see catalog pic). Notice the? 1.5 SWR
bandwidth at 50 MHz is only 0.5 MHz compared to the a DB212
which has a bandwidth slightly more than 1MHz on 6M.
Therefore, if duplexing with a? 1MHz split, in order to keep
the duplexer from detuning, if you can get it mounted to the
leg so the air space between the inner loop tubing and the
tower leg to be 6.5 inches like it is on a DB212, then I would
saw off the 3"x2" boom beyond the dipole loop, because the
director is limiting the bandwidth. . That air distance is
critical for a 50 ohm match.?
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Drill out
all of the dimples holding the 5/8'OD loops with a 1/4" drill
bit and tap them out. Saw off the needed amount off the 3/4"
OD or 7/8 " OD straight tubing, but exercise extreme care not
to break the element insulator in the process! (did it on one)
?
DB
factory lengths for your frequency was 50 7/8" from edge of 3"
boom to tip on each half, or 104 3/4" overall tip to tip,
however I found for 1.0 SWR, the upper loop ends up about 3/4"
shorter than the lower because of the coax center conductor
pig tail radiating and the top is a loop, the bottom just a
wide element. (basically a J pole antenna.)
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John
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On 03/28/2025 12:55 AM EDT Hudson, John@CalOES via
groups.io
<john.hudson@...> wrote:
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On Mar 27, 2025, at 13:29, Roger
willey via groups.io <kc4jnn@...>
wrote:
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Message is From an External Sender
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message came from outside your organization.
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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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if
the?
On 03/27/2025 12:32 PM EDT Roger willey via
groups.io
<kc4jnn@...>
wrote:
?
?
?
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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