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Eskimo
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Interference problems with police band radios

Mon Apr 02, 2007 11:58 pm

We have an ~2mile point to point with good line of sight. We have great signal strength (-50db) and connectivity. The link itself is strong and stable. One point of the connection is on a 150 foot tower that is also used by the local Sheriff departments repeater for their car radio units. The Sheriff is experiencing some interference from our link.

We are in the 5ghz range, they are between 155-159mhz, so I don't think we are walking on their band. At one point we were sharing a power source but that has been changed.

The only thing left I can think of is that the tower climber used unshielded cable for the run up the tower. That will be changed very soon once the cable arrives and I can reschedule the tower climber.

What else have I not thought of? The connection it self is using RB532 boards with SR5 radios in 19dbi Rootennas.

parts list:
1 RB532-4 RB532 Level 4 Lic WISP-AP
2 POE-48 48v Input POE Injector
3 SR5-80211a SuperRange5 802.11a 400 mW mini-PCI
4 SP-POE-MJ8 POE Surge Sup (60V POE, 7.5V Data Clamp)
5 RJ45-ECS RJ45 Field Replaceable Ethernet
6 R2T58W-19-XXX 5GHz 19dBi Roo2, White
7 5210004-006UFL Cable Jumper Ufl to SMA Male 8" RG174
 
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ghmorris
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Tue Apr 03, 2007 2:14 am

Some 532s have a problem with generating interference in that frequency range. IIRC its a 48v POE issue.

We have had a couple of instances of the same problem.

Try changing to an 18V power supply and re-jumpering the 532 for the lower voltage range.

George
 
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ghmorris
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Tue Apr 03, 2007 2:41 am

Here is some more info on VHF interference issues.

http://forum.mikrotik.com//viewtopic.ph ... terference

Geoge
 
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Eskimo
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Tue Apr 03, 2007 6:44 pm

Thank you very much.

I'll give these ideas a shot and let you know if they work out.
 
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Eskimo
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Thu Apr 05, 2007 9:10 pm

We will be changing the power supply to an 18v instead of the 48v early next week, also got our shielded cable in so we will be replacing that run as well. Which should have been done in the first place.

We will be doing it in stages to see at what point the interference stops or significantly decreases. So to better understand the real problem.

If this doesn't get us to where we need to be, out next step is to use EMI Filters.
 
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ghmorris
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Thu Apr 05, 2007 11:43 pm

Please keep us up to date on your results.

I'm particularly interested in the difference between older 532s and the new Series 5.

Thanks
George
 
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Eskimo
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**FIXED**

Thu Apr 12, 2007 11:40 pm

We added shielded cat 5 and changed power supplies yesterday as well as ferrite beads.

First we changed the power supply from 48v to an 18v and ran a test. This resolved nearly all the noticeable interference. Very little (if any) change occurred from the extra shielding.

After all was set up we cranked over 20mb of active traffic over the connection for a few minutes with no interference caused.

Thank you very much for the assistance. I hope this post helps someone down the line.

We are using a RB532-4, so I don't know if its the same as the series 5. Are they planning on altering the POE implementation of that series?
 
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ghmorris
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Fri Apr 13, 2007 2:04 am

Thanks for the update!!

I think the PoE is slightly different on the new series 5 boards.

The new boards look enough different it may be worth trying on 48v next time we get a chance.

George
 
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Eskimo
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Fri Apr 13, 2007 6:37 pm

Not a bad idea. The new boards really do look different.

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