DB224 refuses to duplex

[kayn1n32008]

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]

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.

VHF Binary Dipole Array, 6dBd, 136-174MHz

These high performance VHF dipole omnidirectional arrays are for use in highly populated radio sites requiring long haul omnidirectional coverage. The arrays feature high gain, low noise performance and enhanced null fill coverage with omnidirectional coverage characteristics.

www.rfiamericas.com

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.

 

[jeepsandradios]

Looks familiar.....

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

 

[KevinC]

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]

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]

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.

 

[kayn1n32008]

While these are great antennas they are a little different than the DB-224/264 series. None are plotted as true omni.

While not a true omni, I doubt anyone would really notice if its mounted above the top of a tower.

 

[freddaniel]

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.

 

[fontanei]

Why don't you apply full rf power on the transmit side of the duplexer and using a lab grade spectrum analyzer measure the spectrum characteristics on the receive port of the duplexer. Then you will have a clearer picture of whats happening at and near the receive frequency.

Check and see by how much does the noise level rise at the receive freq at different power levels.

 

[prcguy]

Why don't you apply full rf power on the transmit side of the duplexer and using a lab grade spectrum analyzer measure the spectrum characteristics on the receive port of the duplexer. Then you will have a clearer picture of whats happening at and near the receive frequency.

Check and see by how much does the noise level rise at the receive freq at different power levels.

If this is with the antenna connected and you detect noise on the receive port when transmitting I would also put a load on the duplexer to determine if the noise is from the antenna or bad duplexer tuning.

 

[rescue161]

How far down is the X50? If it is not in use, you could use it as the transmit at full power and use the 420 as the receive. It would be cheaper than antenna replacement.

 

[W8UU]

Side Note: That 6 Meter DB-201 is to die for. Best low band base station antenna ever made.

Carry on.

 

[mrweather]

My club has a DB-212 for its 6m repeater and it's awesome.

 

[prcguy]

Side Note: That 6 Meter DB-201 is to die for. Best low band base station antenna ever made.

Carry on.

Nope. The best would be a DB-212-4, 4 element dipole array. Second best might be an old PD/Celwave 5/8 over 5/8 colinear ground plane. A 1/2 wave coaxial with folded/grounded monopole and radials 1/4 wave down from the skirt is noticeably better than the DB-201 ground plane.

The DB-201 is just a 1/4 wave ground plane and about 1dB worse than a simple 1/2 wave dipole.

 

[mrweather]

We don't have the tower real estate for a 4-bay lowband antenna.

 

[buddrousa]

You should have seen an avanti Moonraker 6 100 feet above a single wide house trailer.

 

[W8UU]

Nope. The best would be a DB-212-4, 4 element dipole array. Second best might be an old PD/Celwave 5/8 over 5/8 colinear ground plane. A 1/2 wave coaxial with folded/grounded monopole and radials 1/4 wave down from the skirt is noticeably better than the DB-201 ground plane.

The DB-201 is just a 1/4 wave ground plane and about 1dB worse than a simple 1/2 wave dipole.

Hard to find the vertical real estate to hang a DB-212-4, although they're magnificent performers. Our sheriff's office had one on a 360 foot hilltop tower and you could hear that 250 watt GE MASTR II base station (39.62 MHz) a hundred miles away on any given day.

Not a fan of the colinear antennas like the DB-205s. They're lightning rods. We replaced several of them with DB-201s. Coverage was the same or better and almost no more lightning issues.

For simplicity and durability, you cannot beat a DB-201. There are DB-201 installations on telephone poles, rooftops, air raid siren platforms, and metal towers that are untouched and still working 40-50 years after they were installed. I wish you could still get them below 450 MHz.

I respect your position on the DB-212. Hell of a low band antenna.

 

[prcguy]

Hard to find the vertical real estate to hang a DB-212-4, although they're magnificent performers. Our sheriff's office had one on a 360 foot hilltop tower and you could hear that 250 watt GE MASTR II base station (39.62 MHz) a hundred miles away on any given day.

Not a fan of the colinear antennas like the DB-205s. They're lightning rods. We replaced several of them with DB-201s. Coverage was the same or better and almost no more lightning issues.

For simplicity and durability, you cannot beat a DB-201. There are DB-201 installations on telephone poles, rooftops, air raid siren platforms, and metal towers that are untouched and still working 40-50 years after they were installed. I wish you could still get them below 450 MHz.

I respect your position on the DB-212. Hell of a low band antenna.

KRECO still makes grounded folded 1/4 wave ground planes and they are mechanically more advanced than the DB Products.

 

[W8UU]

KRECO still makes grounded folded 1/4 wave ground planes and they are mechanically more advanced than the DB Products.

Hadn't heard of them ... but THANK YOU!