BCD996P2 UHF receive design flaw ?

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AA1PL

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I have three BCD996P2 scanners, one at home and two in vehicles. The one at home recently replaced an older BCD785D and BC780 for my online audio feed through Broadcastify. I noticed that the UHF reception on the new 996P2 is much worse than the older scanners using the same Diamond Discone antenna. All UHF channels I'm trying to receive are analog conventional. Keep in mind that I am a two way radio tech with 34 years experience and have access to test equipment. So I did some testing today using the signal generator in my communications service monitor and an iso-tee. I comparedthe two 996P2's, the BCD785D, and the BC780. When the signal generator is directly connected to the BNC jack on each scanner the UHF receive sensitivity is approximately the same, around -120 dBm (0.2 microvolts) which is perfectly normal. Then I inserted the iso-tee between the scanner BNC and the antenna cable, and generated the signal into the decoupled port of the iso-tee. This is basically an Effective Receive Sensitivity measurement (ERS) which takes into account not only the receiver sensitivity but it also introduces the outside influences of all RF energy in the air around my location and tests the receiver filtering. The difference was astounding ! The BC785D provided the best performance with -76 dBm required to open the squelch, the BC780 provided good performance at -70 dBm, but both of my 996P2's were very disappointing, requiring a massive -50dBm signal to open the squelch. That's 26 dB worse than the BC785D !. THAT IS A HUGE DIFFERENCE ! Its no wonder THE 996P2 can barely receiving a UHF fire depart repeater about 15 miles away which comes in good on the old scanners. I then tested all of them on a 154 MHz VHF frequency. The 996P2 and the 785D were both good at around -70dBm. The old BC780 was very poor at -50dBm. Has anyone else noticed poor UHF receive on the 996P2 ? Keep in mind that I live in a rural environment. The nearest cell tower is about 0.6 miles away, and theres a 500 foot tower about 3.3 miles away with a UHF TV transmitter on it. The 996P2 may be overloaded by the TV signal while the older scanners didnt. I may have to try this test at another location. I'd love to get some feedback from others , especially from Uniden tech support engineers.
 

jonwienke

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Testing signal level needed to open squelch is not valid methodology. The test result will change dramatically depending on the squelch setting.

Retest with the squelch open, modulate your test signal with an audio tone, and look for the signal level needed to hear the tone.
 

Ubbe

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Did you calibrate your readings by using the insert T connection and replaced the coax to the antenna with a dummy load and noted the scanners sensitivity compared to a direct connection? It looks as if you used a 40dB or 50dB insert T as your results are at the -70dBm range.

My UBC780 are excellent at VHF as it has tracking filters in that band. It does poorly in 400Mhz and low-VHF but works good in 200-300Mhz range as it is not much there that can interfere. If you measure the 780 that bad in VHF it might be some broadband interference you haven't noted yet that will have an impact on scanners with not so good front ends.

Have you tried a FM broadcast trapfilter as those almost always will help increase performance, unless it's a radioshack type that sometimes noticable attenuate all frequencies. If you use some kind of active splitter or amplifier it might be the problem if not filtered or adjusted properly. Try using the "clean" signal directly from the antenna to the 996.

/Ubbe
 
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