SDS200 SDS vs cell phone tower: Best filter to use?

Anderegg

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I have a dozen SDS200's in a newsroom, that are having a very hard time recieving a Phase 2 800MHz trunked site, that is hitting our 800MHz yagi with an indicated -50dBm. Full signal, but talkgroups will most of the time just flash for a fraction of a second on and off and never receive, or receive with massive error, like up to 120 error rate...at -50dBm. Trying lots of the filters, some, such as AUTO and NORM basically cause the scanner to receive nothing.

The cell phone tower we installed on top of the scanners is AT&T and Verizon, so we have 700MHz and 800MHz blasting 50 feet away from our receive antennas. What would the best filter be to use...I am assuming that 800MHz 3G/4G bands are causing the problem? See attached pic for the tower, and in the lower left of the pic, our tiny scanner antenna array. :(

Paul
 

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Ubbe

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If you monitor signals that are -50dBm from one site, then enable the 20dB attenuator in the scanner for that site. The scanner should work just as good down at a -90dBm signal as with -40dBm.
Are all scanners using their own telescope antenna or a common antenna with a multicoupler to distribute the signal to all scanners? In that case check if the multicoupler are being overloaded by putting a 20dB attenuator between antenna and multicoupler. If you only monitor signals that are -60dBm or stronger then that 20dB attenuator can be a permanent install.

Did you try the IFX setting as well?

/Ubbe
 
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Anderegg

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Tried the ATT, it made things slightly worse with -100 to 110dBm. The antenna is a yaggi on the roof and a multicoupler to the scanners.

Paul
 

AB5ID

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jonwienke

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Having the scanner antenna mounted to the cell tower is going to be problematic. Having the yagi in the newsroom farther from the TX antenna may work better.
 
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ka3jjz

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I would think that some sort of cavity would be needed here. Something that would be a bandstop to everything above 1
Ghz or so. Don't current cell frequencies work way higher than this? Mike
 

citiot

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Does the newspaper have any offices/facilities in another location?

Set them up there, get Proscan and stream them on the internal company network.
 
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Anderegg

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Maybe I was not completely clear...looking for the "proper" Uniden menu FILTER to apply to the 800 system...invert, wide etc...which one would work best to block AT&T and Verizon cellular from my selected 800MHz band?

Paul
 

jonwienke

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None of the above. That's not what they're designed for. You need a notch reject filter on the antenna to block cell frequencies, upstream of the distribution amp.

Or else relocate the antenna so the cell tower is farther away.
 
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Anderegg

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How much loss for 1 mile of RG6? :-\

What are the filters intended to filter then?

Paul
 
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jonwienke

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Zero, if you use ProScan and stream from a better location.

The filters are not designed for the level of RFI you'll get putting the RX antenna on the cell tower.
 

Anderegg

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Still, what are they meant to filter?

I have an SDS200 hooked up via LAN to ProScan...I can see it, and hear it, but I have no idea how to remotely control it...the on screen buttons do nothing.

Paul
 

ProScan

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Still, what are they meant to filter?

I have an SDS200 hooked up via LAN to ProScan...I can see it, and hear it, but I have no idea how to remotely control it...the on screen buttons do nothing.

Paul
Are you using the RSOIP Client or WebServer? If RSOIP Client then login as control mode. If Web Server then log in "Serve Scanner Control Mode" or "Super User"
 

Ubbe

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If you have a -50dBm signal and then enable the scanners 20dB attenuator you should receive a -70dBm signal, not a -100-110dBm. That's almost no signal at all. It's probably the multicoupler that gets overloaded so try and add an attenuator between it and the antenna. Stridsberg multicouplers doesn't take kindly to strong signals and gets easily overloaded. There are fixed 20dB attenuators to be had for $5 and adjustable ones for $20. You'll probably need to reduce the signal to a level just under where the multicoupler doesn't get into problems. It can be done by expensive filters that only take out the cell phone frequencies or you could try to attenuate all signals coming from the antenna to a level that works and probably still receive the systems you want to monitor.

As the scanner seems to partly receive and decode the control channel but then on the voice channel it looses reception, try and set IFX to the voice channels and try the filter settings again. Cellular frequencies can be either in 750, 800 or 850MHz band and the system you try to monitor are probably at 860 or 770MHz that are very close to those cellular frequencies.

The filter setting in the scanner are in the RF side of the receiver, at the first IF frequency, but could be too late in the receive chain as the receivers front end have already been hit by the full force from the whole frequency band, as also the multicoupler are exposed to.


/Ubbe
 

jonwienke

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The filter setting in the scanner are in the RF side of the receiver, at the first IF frequency
Are you sure about that? If they were physical filters, they would likely have been available when the SDS100 was first introduced, as opposed to a feature added months later via firmware upgrade.
 
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jonwienke

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Whatever you call the filter, it needs to be upstream of the amplified multicoupler, and block the frequencies used by the cell transmitters, or overloading and intermod are going to be intractable problems.
 

Anderegg

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I guess I am trying to apply the internal mitigation filters to whatever effect they can give me. I have some sort of hardware filter thing in a box I got from eBay, it's a bandpass/notch filter or similar, looks like a crayon with an SMA on each end. I forgot I was going to plug that inline and test if it did anything.

Paul
 
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