BTT SELECT-78 770/850 MHz Public Safety Filter

[kb5udf]

Per Freqseekers request, I tested today at my office (3rd floor/top floor) which has windows facing 2 cell towers nearby. With factory antenna’s my SDS100 and BCD436 are essentially unusable on any LWIN sites (a 700mhz p25 system, non-simulcast in my area).

With the filter, BOTH the SDS100 and BCD436 were usable in my office on the nearest/strongest site (LWIN Scott) and there wasn’t much need to find a sweet spot, I could generally move about. For the next strongest site (LWIN Lafayette), the BCD436 was not usable at all even with filter, but the SDS100 could be used with difficulty, if one found a sweet spot.

So to wrap up my experience with this filter across my P25rx, SDS100, BCD436 and airspy, is that there is a significant benefit in reducing problematic interference on 700mhz p25.

While this is very useful and I will buy it, it is not perfect (nor does it claim to be). It does not completely eliminate all of my problems, but renders my scanners as generally usable again. I suspect, a times, the Unidens and maybe the p25rx, could still get a little signal reduction and maybe brief garbling in reception, but it was far better. However, this would take more testing to narrow down, because I didn’t have the Motorola with me all the time to verify that the person transmitting was not the problem (sometimes they are).

In any even, this is a useful device and for someone like me, what limited attenuation it has is not very relevant compared to improvement in the noise floor and hence signal quality; on the site(s) I monitor, signal strength is not the issue. This product answers a need I have had for some time.

 

[btt]

Thanks for the honest review! Note that the 2nd filter (still in transit), the passive 770 band-only, will have much better stop-band attenuation, but will limit you to monitoring the 770 band only. The SELECT-78 filter has less stop-band attenuation due to the way that the dual band pass filters are combined with 90-degree hybrid couplers. It is a unique solution for systems where the decision was made to spread P25 systems across two unique bands right between cell phone systems. It will also be much less expensive than existing solutions. I'm very glad to see that we now have a real-world, case study showing that it does indeed solve real world issues.

To those who have mentioned that the SELECT-78 filter doesn't pass VHF, 900 MHz, 1200 MHz, etc, I want to say "Thank you for noticing!".

 

[btt]

 

[FreqNout]

So to wrap up my experience with this filter across my P25rx, SDS100, BCD436 and airspy, is that there is a significant benefit in reducing problematic interference on 700mhz p25.

@kb5udf nice job testing the SELECT 78 filter with all your radios. It sounds like a nice solution for the LTE problem impacting my listening on 770/850 P25.

 

[kb5udf]

Thanks FreqNout. Update: It was a brief and cursory test as I was pressed for time (work happens), but the filter also helped my
old Pro651. Without filter, I had stopped trying to use it in my shack for LWIN due to performing poorly, but sounded great with filter.

 

[kb5udf]

Another cursory test/update. I am in a top floor (15th) story condo in Orange Beach, and our building has recently "upgraded" cell antennas installed and you know what that means for the scanner listener, more hash.

Yet again the filter provides benefit. From my location on the p25rx with stock antenna, I could not decode any transmissions from the Escambia Florida 800 p25 system (my stock uniden never did either, but I haven't tested it with). With the filter, my p25rx seemed to be decoding quite happily at 800mhz, despite somewhat weak signal to work with (even though 150ft+ in the air) there is alot of concrete and steel in this building and between me and the site and I'm probably well outside of its intended footprint.

 

[btt]

Another cursory test/update. I am in a top floor (15th) story condo in Orange Beach, and our building has recently "upgraded" cell antennas installed and you know what that means for the scanner listener, more hash.

Yet again the filter provides benefit. From my location on the p25rx with stock antenna, I could not decode any transmissions from the Escambia Florida 800 p25 system (my stock uniden never did either, but I haven't tested it with). With the filter, my p25rx seemed to be decoding quite happily at 800mhz, despite somewhat weak signal to work with (even though 150ft+ in the air) there is alot of concrete and steel in this building and between me and the site and I'm probably well outside of its intended footprint.

Thanks for reporting your findings! Looks like USPS expects to deliver the passive 770 MHz filter today.