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Splitters, Filters and Multicouplers - For discussion of all inline devices used to split, combine or amplify a receive signal. This forum is not for any bi-directional (transmit) device. Use the Amateur or Commercial Radio forums for those.

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Old 11-07-2018, 5:19 AM
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Default filtering out 930 mhz pager systems

I was going to post this in my FM notch filter thread however I decided to separate it. I'm curious if anyone knows of similar band filters for 900 mhz without also wiping out public safety systems in the 800 mhz band?

Unfortunately I recently found out that I happen to live within a mile of a few high power 300-1000w pager systems that operate near 930 mhz which may be impacting my reception abilities to pick up a neighboring county's trunking system due to interference they likely cause.
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Old 11-07-2018, 8:30 AM
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Originally Posted by crucialcolin View Post
I was going to post this in my FM notch filter thread however I decided to separate it. I'm curious if anyone knows of similar band filters for 900 mhz without also wiping out public safety systems in the 800 mhz band?

Unfortunately I recently found out that I happen to live within a mile of a few high power 300-1000w pager systems that operate near 930 mhz which may be impacting my reception abilities to pick up a neighboring county's trunking system due to interference they likely cause.
I'm in the same boat with two high power 929 and 931 MHz paging transmitters about a half mile from me.
I asked Par Electronics if they would consider building a filter for that range. They did and it worked fantastic for attenuating the 929 to 932 paging band. The filter is in the same housing as their other popular filters for scanner problems and it's performance was also about the same as their VHF filters when I ran the 930 filter through some tests.

I think the cost was the same or only $10 dollars more for this custom filters over their normal designs.

Did it work or help? I must say this filter did indeed help with signals in the 800 and 900 MHz bands but only on my GRE designs which include the newer Whistler TRX1 and 2 models. All my Uniden's saw no noticeable benefit from placing this filter inline. If anything, they could have impacted very weak signals due to insertion loss but in my case, they did not seem to hurt anything with the Uniden's if I left the filter inline.
I later changed my antenna arrangement and now have all the GRE designs regardless if they say RadioShack, GRE or Whistler, on one Stridsberg 8-port multi-coupler and the Uniden's on another couple 8-port couplers. The 900 paging filter as well as VHF paging filters are inline before the 8-port for the GRE designs and just a single VHF filter for 152 MHz remains inline for the two multi-couplers that feed the Uniden models.
Uniden seems to have pretty decent front end filtering over the GRE designs. I rarely need the 152 MHz paging filter for the Uniden's as it also reduces the signal from two of our statewide VHF P25 sites that have voice and control channels in the same 152 MHz range as the paging signals. One must use filters here with caution but they do usually work to reduce the powerful paging signals to a level the GRE or Uniden's AGC circuits can handle and still leave enough signal to monitor systems in that range.
Luckily the FCC does not allow anything but paging in the 929 MHz area so filters will only help if you seem to be getting intermod or desense from nearby 929 to 932 MHz paging signals.

Probably the easiest test you can try needs two receivers (more if you have more than one 900 MHz paging source). One scanning the 8 or 900 MHz trunked or analog system you want to hear and another radio tuned to just the 900 MHz paging signal. If you notice bad or poor reception of the voice system you want to monitor only when the paging site is on the air, then a filter may indeed help.
Some of these paging sites have such a high duty cycle that makes catching them off the air a hard thing! Then when they do drop off the air, you have to hope the signals you do want are on the air! That one can be tricky.
That's probably the easiest and cheapest test you can try to do to determine if a 900 MHz paging filter is needed. If you don't hear any improvement when the paging signal is off the air, a filter may be a waste of money.

I also have an antenna feeding another pair of multicouplers that have no filters at all. These feed my communications receivers which are mostly Icom's like the R7000, R9000 and newest R8600 and almost all models in between including many of Icom's portables. I wish scanner makers could make bulletproof front ends like seem to be in higher quality comms receivers.

This is my experience with a notch filter for the common 929 to 932 MHz paging range. If you wish to pursue this, Google Par Electronics and give them a call. Tell them you need a filter for that range and they will build it. Mine even has a custom label on the filter so I can distinguish it from all the other Par filters I own as they all look identical!
Par gave the custom filter they made for me a Part number of UHFSYM(929-932)HT.
The outside of the housing looks identical to their other filters of this type but you can see that the two adjustment caps are of a different design over their VHF filters. It appears to still be a three cavity filter which is also their standard notch filter design. Who knows what the inside yields, I'm not going to bust it open to see!
Mine is fitted with the standard BNC fittings that are used on their regular VHF and UHF filters. They may offer N type connectors as well but for reception only, there is not that much of a difference between the two connector types and BNC does not really introduce much more loss over a good quality N connector.
If your coax needs to also feed higher frequencies, then filters with N connectors may be wise but for scanners, the BNC connectors should be just fine.
When I'm trying for weak signals above 1 GHz on the Icom's, I remove any multicouplers, filters etc and hook a feedline directly to the radio so there is no chance of anything causing loss.

Hope this helps.
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Old 11-07-2018, 5:24 PM
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Default 929-931

Thanks for your informative post kruser ! So I just plugged in a search limit to my PSR-500 of 929-931. Hearing all kinds of digital noises and beeps. I think that means I should consider a filter from Dale? At least to keep my GRE scanners happy? My 800 trunked systems are fine on Uniden 536HP and ok on the GRE PSR-500. Wow just typing this it's really noisy on the search limit. Emailing Dale now. Thanks again for the info!!
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Old 11-07-2018, 7:25 PM
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https://www.scannermaster.com/BPF_800W_p/24-531699.htm
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Old 11-07-2018, 8:00 PM
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Thanks for your informative post kruser !
Agreed! great post Kruser! I happen to have two scanners so that idea for testing was a great idea.

Im not 100% positive its the pager systems but a good place to start. They happen to be the closest to the frequencies I''m trying to monitor(850ish mhz ps system) and closest most powerful signals near me. Hence my suspicions after looking in the fcc database. They along with many other antennas like cell, microwave, etc happen to be located in the Union Pacific Rail Yard nearby and I have noticed the further I get away from the yard while mobile the more my 800 mhz band reception improves.

The other thing is I have noticed is signal strength doesn't seem to effect it. I can have full 5 bars on my uniden bcd325p2 and it wont sound any different then less bars. Lots of popping in the transmissions.

Examples of what it sounds like(at home):
control channel
https://www.youtube.com/watch?v=UKeMPXUiUQs
regular scan mode
https://www.youtube.com/watch?v=a_fCTZbMXmc
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Old 11-08-2018, 11:59 AM
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Originally Posted by crucialcolin View Post
The other thing is I have noticed is signal strength doesn't seem to effect it. I can have full 5 bars on my uniden bcd325p2 and it wont sound any different then less bars. Lots of popping in the transmissions.
This is typical for signal overload and you could use a variable attenuator to reduce the level to where the overload just stops or get a filter. I recommend to always have a variable attenuator to be able to test for overload. It's cheap and are a great help when monitoring with scanners either as a temporary test or used in a permanent installation. Add a FM trap filter and you have the two most basic tools needed for every scanner listener, that use external antennas.

/Ubbe
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Old 11-09-2018, 5:37 AM
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Originally Posted by Ubbe View Post
This is typical for signal overload and you could use a variable attenuator to reduce the level to where the overload just stops or get a filter. I recommend to always have a variable attenuator to be able to test for overload. It's cheap and are a great help when monitoring with scanners either as a temporary test or used in a permanent installation. Add a FM trap filter and you have the two most basic tools needed for every scanner listener, that use external antennas.

/Ubbe
Yeah I have a number of coax attenuators of varying levels for that reason. They come in handy. My FM notch filter is hopefully going to arrive tomorrow according to Amazon. I don't think its an issue of overload though as my city's local system also on the 800 mhz band has always been fine. Its the neighboring system further away(closest tower just under 7 miles) that suffers with the popping staticy transmissions from here.
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Old 11-09-2018, 8:09 AM
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Overload affects weaker stations. You loose sensitivity and get interference with that popping and crackle sound.

You could use fixed coax attenuators with values like 3-6-10dB and put them in series to dial in the correct value. If you didn't had those it would have been cheaper and easier with a variable 0-20dB attenuator and just sweep up and down the attenuation to find the middle where it receives best. Using fixed values you'll have to disconnect and insert attenuators in different mix and it's much harder to compare with the previous signal, especially if it slowly varies in signal strenght as it usually does.

/Ubbe
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Old 11-13-2018, 3:34 AM
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Quote:
Originally Posted by Ubbe View Post
Overload affects weaker stations. You loose sensitivity and get interference with that popping and crackle sound.

You could use fixed coax attenuators with values like 3-6-10dB and put them in series to dial in the correct value. If you didn't had those it would have been cheaper and easier with a variable 0-20dB attenuator and just sweep up and down the attenuation to find the middle where it receives best. Using fixed values you'll have to disconnect and insert attenuators in different mix and it's much harder to compare with the previous signal, especially if it slowly varies in signal strenght as it usually does.

/Ubbe
I gave it a try including attenuate a two way spliter building up 15.5 dB loss or where I just about lose the signal completely. Didn't really do anything for the popping static transmissions though as that persisted regardless of attenuation level.

So far I've only messed around with the pager systems for about 10 minutes or so, but my current observation has been that the beeps are intermentent whereas the static I hear on that 800 mhz trunking system is constant.
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Old 11-13-2018, 4:48 AM
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Seems the problem are before the point where you insert the attenuation. You don't have any active components before that? In that case it's in the air, could be local interference or perhaps the scanner isn't working as it should, it's off frequency or something.

You are listening to an analog 800MHz trunked system, right? And the popping can be heard regardless if they speak very loud or whisper and it is on every voice frequency in that system and you hear that crackling and popping regardless of how much you attenuate?

/Ubbe
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Old 11-13-2018, 8:01 PM
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Quote:
Originally Posted by Ubbe View Post
Seems the problem are before the point where you insert the attenuation. You don't have any active components before that? In that case it's in the air, could be local interference or perhaps the scanner isn't working as it should, it's off frequency or something.

You are listening to an analog 800MHz trunked system, right? And the popping can be heard regardless if they speak very loud or whisper and it is on every voice frequency in that system and you hear that crackling and popping regardless of how much you attenuate?

/Ubbe
Not really it happens regardless of which of my antenna I use and on both my Uniden Scanners. Again I have a ground plane(Centerfire), Larsen tri-band mobile mag mount, and RS 800 rubber ducky. It's always there.

Yeah it's a simulcast Motorola Type II SmartZone system with multiple towers. It does seem to affect every voice frequency as well and attenuation doesn't seem to affect it.

There's actually one other source of possible interferfance I can think of besides the pagers. My own city also has its own independent 800 MHz system. Both it and the bordering county systems use the same 850 MHZ frequency block.
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Old 11-14-2018, 5:40 AM
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Simulcast, ok, that probably explains it. Your only option then would be to use a directional antenna pointing to only one of the towers. There should be plenty of cheap cellular antennas for 800-900Mhz that you can use.
https://www.ebay.com/itm/Altelix-800...A/152671055295
https://www.ebay.com/itm/800-900MHz-...e/181650824017

/Ubbe
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Old 11-15-2018, 3:44 AM
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You read my mind haha. Seems like I can either spend money on filters or Yagi's. My suspicion is the issues I have receiving that system on the analog side are only going to get worse once they fully convert the current SmartZone type over to P25 (digital). Ironically, some of the agencies that make up the system just started broadcasting P25 from their console today. So Yagi it is
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