John,
As an aside, although I have never experimented with it, the
spacing between the D.E. and the director would likely need to be
altered if using in the original configuration.
Yes, as I recall the front end of the antenna can be detached. It
may already be the correct length to reverse the direction.
Actually, from a manufacturing standpoint it would make sense.
Chuck
WB2EDV
On 3/28/2025 7:29 PM, John via
groups.io wrote:
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Yes
Chuck, I noticed that also. The only way to find out is to
actually try it both ways, as it appears from the pictures
that the boom disassembles, and it probably will be possible
attach the pipe mount to that shorter outside section of the
2"x3" boom. The DB212 is designed to couple RF into the tower
to reduce the? back side null range? loss, and it may be just
the reverse with the beam????
?
I have
not yet been able to get my paws on a DB225.
?
John
On 03/28/2025 5:35 PM EDT Chuck Kelsey via groups.io
<wb2edv@...> wrote:
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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:
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.?
?
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.)
?
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:
This
Message is From an External Sender
This
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.
?
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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