Does anybody have any experience in using a DB-224 and adding elements
for other bands on the same mast?
I have seen a DB-224 with a 450 version's loops added... very full, but the
owner said it worked fine. (2 separate feed lines).
My specific question would be about the adding of a low-band loop - DB-212
to the center of the 224. The DB-224 would be in the omni directional
mode (all 4 rotated 90 deg to each other), so the 212 would not be
in the same plane as the middle loops.
I did a test on a 224 (mounted on a fence post), and the SWR did not change
with the addition of the 212, and the resonant frequency was about 500kHz
lower than when it was directly mounted on the Rohn 25G. Any clue how the
phasing of the 224 may change from omni?
I'm probably going to put the loop up on the tower in the next week or so,
but figured someone here may have tried it before with either good or horrible
results.
thanks,
Tim
Antenna Hybrids?
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Re: Antenna Hybrids?
You will get interaction of the added elements from proximity to the original elements.
Feed impedance may change, but I would suspect more error on the and edges than in mid-band.
Keep the feedlines out of all RF fields, if you have to run them opposite each other, that may help in cross talk issues.
Don't forget to use stainless hardware and make sure everything is tight, or you will have PIM issues to deal with once the weather changes.
If you have the actual, physical space to attach another set of dipoles for the other band, without distorting the pattern of the original antenna, super!
I've built hairpin loops for high band dipoles, and modified the feed stucture so the 150 band dipole elements are fed both in phase and out of phase (90 degrees).
I get a broader tuning range and although this is a RX only assy., the 4 dipoles operate adequately from 143 to 164 mHz, with a few dips along the band spread(acceptable)
This is why I love my 3 port SWR bridge..I can view the antire bandand and create points along the spectrum I need a better match for, and I can also broaden the antenna for use outside the intended original bandsplit as well, thanks to the matching devices used, and phase relationship of each dipole assembly.
You will always change the radiation pattern of any omni antenna when you modify the actual, physical relationship within the antenna structure, as metallic objects in the near field play a sizable role in the pattern.
Tower shadowing, location on a tower, relation on the tower to other antennas, as well as in band and out of band coupling to/from those antennas.
Feedlines and transitions on the feedlines will add loss, and can change the feed impedance of the entire system, and can detune your cavities as well.
Stay away from ANY PL-259 connectors!
Even @ 150, they are garbage, and are NOT a 50 Ohm impedance any longer.
You can sweep your system with a Wiltron, or any TDR and see the bumps in the display, indicating where the mismatch is.
A poor match equals unwanted noise in the system, and can introduce IMD products from nearby sites.
Feed impedance may change, but I would suspect more error on the and edges than in mid-band.
Keep the feedlines out of all RF fields, if you have to run them opposite each other, that may help in cross talk issues.
Don't forget to use stainless hardware and make sure everything is tight, or you will have PIM issues to deal with once the weather changes.
If you have the actual, physical space to attach another set of dipoles for the other band, without distorting the pattern of the original antenna, super!
I've built hairpin loops for high band dipoles, and modified the feed stucture so the 150 band dipole elements are fed both in phase and out of phase (90 degrees).
I get a broader tuning range and although this is a RX only assy., the 4 dipoles operate adequately from 143 to 164 mHz, with a few dips along the band spread(acceptable)
This is why I love my 3 port SWR bridge..I can view the antire bandand and create points along the spectrum I need a better match for, and I can also broaden the antenna for use outside the intended original bandsplit as well, thanks to the matching devices used, and phase relationship of each dipole assembly.
You will always change the radiation pattern of any omni antenna when you modify the actual, physical relationship within the antenna structure, as metallic objects in the near field play a sizable role in the pattern.
Tower shadowing, location on a tower, relation on the tower to other antennas, as well as in band and out of band coupling to/from those antennas.
Feedlines and transitions on the feedlines will add loss, and can change the feed impedance of the entire system, and can detune your cavities as well.
Stay away from ANY PL-259 connectors!
Even @ 150, they are garbage, and are NOT a 50 Ohm impedance any longer.
You can sweep your system with a Wiltron, or any TDR and see the bumps in the display, indicating where the mismatch is.
A poor match equals unwanted noise in the system, and can introduce IMD products from nearby sites.