View Full Version : Urgent, -XR9 Interferance Problems
DieselPower
02-22-2009, 07:03 PM
I've been fighting bad connections all day on our XR9 network, and just found that there is a new system on the 500 ft tower we are leasing space on. It is a Motorola XPR 8300 running 45W at 453.3MHz. I'll have to see where their antenna is located in the daylight, but it must be pretty close to ours. I'm getting a noise floor in the -50s and CCQ of 6% to 18%. I do have the CF917 917MHz Cavity Filter installed. What can I do? I have 37 customers on this AP, Help!
The second harmonic of 453.3 is still with the CF917's low side passband. You may need the CF912 also.
DieselPower
02-22-2009, 09:16 PM
The second harmonic of 453.3 would be 906.6, and the CF917 cuts off around 903, and the CF912 at 895. I'm running channel 5, 912MHz, I don't see how a 912 would help?
It cuts off closer to 905. At 903, the filter will still pass significant signal. It will attenuate 903 it by only 10 dB. And keep in mind, 903 is only the center frequency of the second harmonic, it will still have power at 905.5 if its running 5 KC deviation.
DieselPower
02-22-2009, 09:42 PM
Something is still not making sense to me. Here is the 912 with the harmonic center in red, and my signal center in green. AFAIK there is no way to filter it out, and the 917 comes closer to it than the 912. Maybe I'm just missing something...
http://orbwireless.net/CF912.png
mike95826
02-22-2009, 09:56 PM
If your problem is in deed a second harmonic of the Motorola repeater then the signal at 906.6 is in the pass band of a stand alone (no external filter) XR9. Even if you were to put a tight filter on you equipment (one just wide enough for you particular frequency and bandwidth) there would probably still be enough energy present to cause an increase in the noise floor. A better solution is always to knock it out at the source. If you could talk to the owner of the repeater and their technician and ask if the repeater has a harmonic filter installed along with a circulator, then to be sure that they are also using a pass/reject type duplexer and not a notch type. In the worse case you may want to purchase a filter to notch out your frequency at the output of their repeater if they would agree to install it. From the frequency that you have noted it would appear that the system is use by a local government or public service entity.
DieselPower
02-22-2009, 09:57 PM
Here is a composite image of both the 912 and 917. The CF912 (green) lets more low band (around 906.6) pass than the CF917. This is NOT what we want. Anyway, back to the original topic, HELP! is there nothing I can do?
http://orbwireless.net/CF912-17.png
DieselPower
02-22-2009, 10:08 PM
Thanks Mike, I still have to talk to the radio station engineer tomorrow and find out who owns the blasted offender! We have TVA (Tennessee Valley Authority), NOAA weather, Tennessee Gas, Lobelville City com, and the original FM radio station here. It has worked great so far, and I hope we can continue that. I will definitely be asking about filtering their equipment, I know that it has no filtering now, I walked in there this evening and found a new piece of equip sitting there, and a new hardline running up the tower. One of those ahah! moments, with a sinking feeling afterwards!
mike95826
02-23-2009, 06:56 AM
Are you using the whole 20 Mhz? If you can't eliminate the interference then you may have to drop your channel bandwidth to 10 Mhz and move your center frequency up 5 Mhz. That would be the extreme because you would have to reconfigure all your clients but it is better than loosing them or having to find another tower for you AP.
From your list I would guess it is something from Lobelville City.
bobbyc
03-10-2009, 08:50 AM
Did you ever get this resolved? With that noise that close, I'd think the only solution is to get them to take their gear back down.
Bob C
DieselPower...
It would be nice if you could get a spectrum analyzer and see just what you're dealing with.
rmichael
03-19-2009, 07:57 AM
DP, perhaps you need one of this:
https://system.netsuite.com/core/media/media.nl?id=10110&c=283276&h=e655a7ee460879f3ca0c&_xt=.pdf &ck=Rl99USE1AYKRV5WF&vid=Rl99UVI1ASdFHnfp&cktime=79159&cart=1783728
