Uniden P25 Simlucast - Possible Solution to Ponder

[whsbuss]

The OP is 100% right on!! Why should we be quality control for this?. I just love all the posts on how to attempt to fix an issue that should not be ours to fix. I am not going to stand on my head holding an 800MHz yagi, sticking a paper clip into the antenna jack, or play with a 100 menu settings to try and get a decent result. Enough of this is new technology, new scanners, etc. The same design in the scanners has not been changed only new bells and whistles added. Just give me a scanner that works, not one that will make me breakfast.

Amen brother. Features should only enhance the function of a scanner - which is to receive transmissions.

 

[jdobbs2001]

So who is going to develop the retrofit board that will solve this???

Seems that for at least the base/mobile scanners a retrofit could be put together?

I think a number could be sold if it really solved the problem and was less than $150.

15 dollar software defined radios can do it.

With gnuradio and a 15 dollar sdr you can demodulate properly. The problem is it an easier sell to spend the money on the BOM to add things like bigger LCD and wifi features as it is easier to market than improving the radio by spending 15 dollars on a part.

Marketing drives engineering when it comes to budget.

 

[matthias_h]

Simple P25 improvement proposal

There appears to be too much useless "noise" at the discriminator level on the circuit board that should be filtered out with a ceramic capacitor of fitting capacity.

I discovered during the process of installing a discriminator tap in my Uniden BCD996XT that including some tap line filtering really helped with my computer's ability to decode digital trunking system signals.

I limited the max. audio frequency on the tap output to around 20kHz with a combination of a tap line resistor and a ceramic capacitor. In my experiments this markedly improved my computer software's ability to decode the P25 signals on the line. I have the impression that I could probably filter down more aggressively to cut out unneeded high audio frequencies that are not part of the signal of interest.

Of course, the Uniden BCD996XT decodes P25 phase 1 without the need of a computer, I just ran the above setup as a research project to see what effect cleaning up the discriminator level audio has on digital signal decoding. And it really helped. If I could figure out what the internal discriminator audio line impedance is on the Uniden scanner board then I could just do a quick filter calculation and pick the right capacitor to solder onto the discriminator test point against ground.

 

[JamesO]

There appears to be too much useless "noise" at the discriminator level on the circuit board that should be filtered out with a ceramic capacitor of fitting capacity.

I discovered during the process of installing a discriminator tap in my Uniden BCD996XT that including some tap line filtering really helped with my computer's ability to decode digital trunking system signals.

I limited the max. audio frequency on the tap output to around 20kHz with a combination of a tap line resistor and a ceramic capacitor. In my experiments this markedly improved my computer software's ability to decode the P25 signals on the line. I have the impression that I could probably filter down more aggressively to cut out unneeded high audio frequencies that are not part of the signal of interest.

Of course, the Uniden BCD996XT decodes P25 phase 1 without the need of a computer, I just ran the above setup as a research project to see what effect cleaning up the discriminator level audio has on digital signal decoding. And it really helped. If I could figure out what the internal discriminator audio line impedance is on the Uniden scanner board then I could just do a quick filter calculation and pick the right capacitor to solder onto the discriminator test point against ground.

I have not had time to do more research and play with my gear, but I am starting to think part of what I have been having issues with is front end overload/adjacent channel from a number of Land Mobile/Cell sites along with a AGC system that nobody appears to understand/use as it is questionable if it works.

I really think if the AGC worked and could be properly configured and enabled that this might help matters along with something the poster above mentioned about how the filtering is for the P25 decoder.

I also speculate that a more stable base clock might help as well, but I have been totally brow beaten, discounted and bullied for even mentioned that there could be anything that could or might improve matters short of a full receiver/decoder design from the ground up.

But all this discussion is useful, out of the box thinking and possible trial and error may actually yield an improvement/hack/mod that might make decoding just a slight bit better.

Kind of like the 536HP headphone issue, maybe it will turn out the wrong capacitor or resistor tube was installed in the component placement machine and swapping a few parts around could improve things?

You never know until you try.