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From: Roger willey <kc4jnn@...> Date: March 26, 2025 at 2:45:40?PM EDT To: [email protected]Subject: 6 m repeater antenna
?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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Got a picture? Is it a DB212-2 or home brew or what???
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
|
?
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
?
?
?
?
?
?
?
?
?
?
?
if the?
On 03/27/2025 12:32 PM EDT Roger willey via groups.io <kc4jnn@...> wrote:
?
?
?
Begin forwarded message:
From: Roger willey <kc4jnn@...>
Date: March 26, 2025 at 2:45:40?PM EDT
To: [email protected]
Subject: 6 m repeater antenna
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
|
I think they should be on the same side of the tower 12 feet apart. My frequency is ?53.050 input is 52.050?
toggle quoted message
Show quoted text
On Mar 27, 2025, at 2:56?PM, John via groups.io <jhaserick84@...> wrote:
?
?
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
?
?
?
?
?
?
?
?
?
?
?
if the?
On 03/27/2025 12:32 PM EDT Roger willey via groups.io <kc4jnn@...> wrote:
?
?
?
Begin forwarded message:
From: Roger willey <kc4jnn@...>
Date: March 26, 2025 at 2:45:40?PM EDT
To: [email protected]
Subject: 6 m repeater antenna
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
|
?
Yep, that will work fine as a minimum center to center distance on 6M. Just no guy wires between or within 5 ft of the antenna elements, especially above the top element. (We were forced to have guys between a pair of DB212 side mount dipoles, and that lowered the frequency of the array after the two antennas were combined, so SWR went up on the high frequency TX side to 1.5 from 1.1SWR with the antenna elements originally individually set for resonance at 20% of the 1 MHz TX to RX frequency spread below the TX freq, 80% above the RX freq. in your case, 52.8 MHz.)
?
John
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
9.
On 03/27/2025 4:28 PM EDT Roger willey via groups.io <kc4jnn@...> wrote:
?
?
I think they should be on the same side of the tower 12 feet apart. My frequency is ?53.050 input is 52.050?
On Mar 27, 2025, at 2:56?PM, John via groups.io <jhaserick84@...> wrote:
?
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
?
?
?
?
?
?
?
?
?
?
?
if the?
On 03/27/2025 12:32 PM EDT Roger willey via groups.io <kc4jnn@...> wrote:
?
?
?
Begin forwarded message:
From: Roger willey <kc4jnn@...>
Date: March 26, 2025 at 2:45:40?PM EDT
To: [email protected]
Subject: 6 m repeater antenna
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
|
toggle quoted message
Show quoted text
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.
I think they should be on the same side of the tower 12 feet apart. My frequency is ?53.050 input is 52.050?
On Mar 27, 2025, at 2:56?PM, John via groups.io <jhaserick84@...> wrote:
?
?
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
?
?
?
?
?
?
?
?
?
?
?
if the?
On 03/27/2025 12:32 PM EDT Roger willey via groups.io <kc4jnn@...> wrote:
?
?
?
Begin forwarded message:
From: Roger willey <kc4jnn@...>
Date: March 26, 2025 at 2:45:40?PM EDT
To: [email protected]
Subject: 6 m repeater antenna
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
WARNING: Do not click links or attachments unless you recognize
the sender and know the email is safe.
|
Interesting, is that a 2 element Yagi with the driven element that gets snuggled up close to the mast then a director out front? If so they are not relying on the mast as a reflector as it looks like the mounting bracket goes on top of a mast leaving the hot side of the driven element above the mast.?
|
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:
?
This Message is From an External Sender
This message came from outside your organization.
I think they should be on the same side of the tower 12 feet apart. My frequency is ?53.050 input is 52.050?
?
?
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
?
?
?
?
?
?
?
?
?
?
?
if the?
?
?
?
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
WARNING: Do not click links or attachments unless you recognize
the sender and know the email is safe.
|
Looks like a homemade clone of a DB-225
antenna. It would be mounted to a metal mast or tower that must
extend beyond the top of the folded dipole. The DB-225 is a 50-ohm
antenna. Since this one is homemade, hard to tell what impedance
it is, and I agree, the photo is poor. Can't see how the feedline
attaches. The DB-225 had pigtails long enough to bring it to a tee
connector at the proper spacing. The center of the tee went to an
electrical 1/4 wave section of 35-ohm coax which then attached to
the 50-ohm heliax transmission line.
Chuck
WB2EDV.
On 3/28/2025 1:13 AM, Mike via
groups.io wrote:
toggle quoted message
Show quoted text
Interesting, is that a 2 element Yagi with the driven element
that gets snuggled up close to the mast then a director out
front? If so they are not relying on the mast as a reflector as
it looks like the mounting bracket goes on top of a mast leaving
the hot side of the driven element above the mast.?
|
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
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Show quoted text
On Mar 28, 2025, at 06:17, Chris Boone WB5ITT via groups.io <setxtelecom@...> 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:
?
This Message is From an External Sender
This message came from outside your organization.
I think they should be on the same side of the tower 12 feet apart. My frequency is ?53.050 input is 52.050?
?
?
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
?
?
?
?
?
?
?
?
?
?
?
if the?
?
?
?
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
WARNING: Do not click links or attachments unless you recognize
the sender and know the email is safe.
Attachments:
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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:
![image2.jpeg]()
?
This Message is From an External Sender
This message came from outside your organization.
I think they should be on the same side of the tower 12 feet apart. My frequency is ?53.050 input is 52.050?
?
?
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
?
?
?
?
?
?
?
?
?
?
?
if the?
?
?
?
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
WARNING: Do not click links or attachments unless you recognize
the sender and know the email is safe.
Attachments:
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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.?
?
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
?
?
?
? ?
On 03/28/2025 12:55 AM EDT Hudson, John@CalOES via groups.io <john.hudson@...> wrote:
?
?
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.
?
I think they should be on the same side of the tower 12 feet apart. My frequency is ?53.050 input is 52.050?
On Mar 27, 2025, at 2:56?PM, John via groups.io <jhaserick84@...> wrote:
?
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
?
?
?
?
?
?
?
?
?
?
?
if the?
On 03/27/2025 12:32 PM EDT Roger willey via groups.io <kc4jnn@...> wrote:
?
?
?
Begin forwarded message:
From: Roger willey <kc4jnn@...>
Date: March 26, 2025 at 2:45:40?PM EDT
To: [email protected]
Subject: 6 m repeater antenna
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
WARNING: Do not click links or attachments unless you recognize the sender and know the email is safe.
?
|
Its not related to a J-pole, the DB Products dipoles are simply a center fed dipole with a fat grounded element and the driven element is a folded monopole. Probably much lower impedance than a typical dipole of 72 ohms in free space due to its girth but when placed really close to a tower leg the impedance gets pulled way down.?
?
I recently picked one up at a swap meet and used some excellent info from this group and tuned it for 6m.?
?
|
Already covered above, but here are a number of ways to feed multiple antennas with 50 ohm feed-points.
?
2 x 50 ohm antennas:
?
?
Stacking distances also affect the compression of the elevation beam-width and the resulting peak gain figure, that matters for horizontal VHF DX work where we trade some gain away (under-stacking them at lower heights above ground) for a wider elevation beam-width to better hear signals arriving at different angles.
?
:-)
?
--
Lonney, K1LH
North Pole, AK.
?
?
|
Just for you Chuck Kelsey
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Show quoted text
On Mar 28, 2025, at 08:43, Lonney K1LH via groups.io <lonney9@...> wrote:
?
This Message is From an External Sender
This message came from outside your organization.
Already covered above, but here are a number of ways to feed multiple antennas with 50 ohm feed-points.
?
2 x 50 ohm antennas:
?
?
Stacking distances also affect the compression of the elevation beam-width and the resulting peak gain figure, that matters for horizontal VHF DX work where we trade some gain away (under-stacking them at lower heights above ground) for a wider elevation
beam-width to better hear signals arriving at different angles.
?
:-)
?
--
Lonney, K1LH
North Pole, AK.
?
?
WARNING: Do not click links or attachments unless you recognize
the sender and know the email is safe.
|
Nice work, Mike!? You really don't need the grey element spacers for 6M, as I see you left them off, possibly to reduce wind load.. Sometimes the end braces are needed in their place, if icing or high winds. Also a good idea to invert so the fed half is on the bottom, so the stronger half is on the top to better resist falling ice, or someone climbing the tower stepping on the coax! . Then be certain to place a drain hole just above where the insulator begins.That will be inside the center brace, if you angle the hole upwards. When you have the end piece off, is the time to measure where the top of the insulator is located.
?
King Starboard (ultra high density, UV protected polyethylene) from a marine supply company is a good source for the element brace.
?
Really great 6M repeat antenna, especially two on the same leg. Had a pair last over 35 yrs at 3500 ft, high winds, multiple lightning strikes, feet of rime ice, etc.No precip static if wrapped with vinyl tape, and because side mounted close in, no? coronal discharge noise
?
John
On 03/28/2025 10:32 AM EDT Mike via groups.io <prcradio@...> wrote:
?
?
Its not related to a J-pole, the DB Products dipoles are simply a center fed dipole with a fat grounded element and the driven element is a folded monopole. Probably much lower impedance than a typical dipole of 72 ohms in free space due to its girth but when placed really close to a tower leg the impedance gets pulled way down.?
?
I recently picked one up at a swap meet and used some excellent info from this group and tuned it for 6m.?
?
|
Yes, this is the real deal, not a
clone. What a difference a good picture can make.
Chuck
WB2EDV
On 3/28/2025 1:26 PM, Hudson,
John@CalOES via groups.io wrote:
toggle quoted message
Show quoted text
Just for you Chuck Kelsey
On Mar 28, 2025, at 08:43, Lonney K1LH
via groups.io <lonney9@...> wrote:
?
This
Message is From an External Sender
This
message came from outside your organization.
Already covered above, but here are a number of ways to
feed multiple antennas with 50 ohm feed-points.
?
2 x 50 ohm antennas:
?
?
Stacking distances also affect the compression of the
elevation beam-width and the resulting peak gain figure,
that matters for horizontal VHF DX work where we trade
some gain away (under-stacking them at lower heights above
ground) for a wider elevation beam-width to better hear
signals arriving at different angles.
?
:-)
?
--
Lonney, K1LH
North Pole, AK.
?
?
WARNING:
Do not click links or attachments unless you recognize the
sender and know the email is safe.
|
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:
toggle quoted message
Show quoted text
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
?
?
?
? ?
On 03/28/2025 12:55 AM EDT Hudson, John@CalOES via
groups.io <john.hudson@...> wrote: ?
?
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.
?
I think they should be on the same side of
the tower 12 feet apart. My frequency is ?53.050 input
is 52.050?
?
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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On 03/27/2025 12:32 PM EDT Roger willey via
groups.io <kc4jnn@...>
wrote: ?
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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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Wonder why they didn't make it a driven element with reflector, either space the driven element out from a tower leg for the reflector or include a reflector. That seems like it could be factory tuned and used with different mounting schemes with less affect on the tuning.?
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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????
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I have not yet been able to get my paws on a DB225.
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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.?
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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)
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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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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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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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On 03/27/2025 12:32 PM EDT Roger willey via groups.io <kc4jnn@...> wrote:
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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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Chris Boone WB5ITT
Hudson, John@CalOES
