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DB224 refuses to duplex

kayn1n32008

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Also, understandable about the 1/4, 3/8 and 1/2 wave spacing. Most of the Comprods in my area are 1/4 wave spacing for offset use. Like you mentioned, I would be hesitant to mount one of these 22-foot antennas out the top of a tower unless I had a zero-torsion mount and then I would cringe every time we had a storm. That's a lot of antenna to be top mounted!
The local club I'm a member of has a Sinclair 310-C4 on top of a 210-C4 mounted at the top of their 60m freestanding tower. It's been up for 30-ish years with out issue.

Sinclair and Comprod are not even in the same class of antenna that db are. The trade off is they are not cheap. But they also just work, and will work, trouble free for many years.
 

KevinC

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Not sure of your budget but I've put up a ton of the below antennas. The oldest one being around 7 years old now and no issues.


It's a beast of an antenna, but it's broadband and seems to be pretty tough.

Oh yeah, my favorite part is the figure in the installation guide holding up the antenna in one hand. :p
 

KevinC

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Looks familiar.....

These are a good antenna. I wish I could find funds for them to replace all my SAR stuff with those.

View attachment 160562
Never forget the first ones I did. PM sent me to the shop to do pre-sweeps, I get there and the service manager pointed to all the huge crates. I spent all day uncrating, assembling, sweeping, disassembling and recrating antennas. Oh yeah, it was about 95 that day. UGH!!!
 

WRMD298

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That looks good. I'm looking at the specs now. We are using RFI Corporate Collinear antennas on all of our 700/800 MHz trunked sites and they are beastly!
 

wsp44

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Never forget the first ones I did. PM sent me to the shop to do pre-sweeps, I get there and the service manager pointed to all the huge crates. I spent all day uncrating, assembling, sweeping, disassembling and recrating antennas. Oh yeah, it was about 95 that day. UGH!!!
I have uncrated my fair share of these, We probably have 150+/- between UHF and VHF, with some being close to 10 years old at this point with zero problems. RFI has it figured out with these.
That looks good. I'm looking at the specs now. We are using RFI Corporate Collinear antennas on all of our 700/800 MHz trunked sites and they are beastly!
How do the 7/800 seem to perform? I bet they are beast.
 

freddaniel

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I agree the most likely cause is Rusty Bolt PIM as shown in the diagram below. This was taken from an PIM article which offers help in measuring the distance to the PIM.
Another possibility is an antenna near the top of the tower connected to a barefoot receiver or transciever, without proper filtering. The photo shows on the left, another VHF antenna below the victim antenna. As you know, barefoot receivers typically have little filtering ahead of the pre-amp or mixer, which looks like a mixing diode to any strong signals over 0 dBm. I suggest temporally disconnecting the radios, in the building, from any nearby antennas while performing your PIM test. I have identified this issue with remote base stations on towers 100 feet away from my tower causing problems.
 

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