That works out to a low frequency cutoff of ~50Hz. Not "near DC"...Those are P25 Phase I symbols. Each is 1/4800 sec. So the audio was in a negative state for about 0.007 sec. Aside the brief positive spikes, the signal is negative for about 0.02 sec. Any series capacitor in a discriminator tap has to "pass DC" on that sort of timescale or it will distort the signal.
DC carries no information. It's not a part of the signal needed to decode bits properly.
I'm not following what you guys are talkign about with all the DC stuff. What software is that in the screenshots?
I will try re-doing the whole mod from scratch and see what happen when I get some time.
Yep!Some hands on experience with taps:
While aware of safeguards and advantages with use of resistors/capacitors in discrim.tap applications, found them to be non-essential in a number of installations: RS2005/2006,Pro93,Pro95,Pro34,Unidenxxx - all passed raw audio to decode properly with no problems/damage for years, in the absence of... also utilized solderless taps with good results.
I have units that I added a discriminator tap to over decades ago that are still working. As I write this I am using a PRO-95 to feed UniTrunker.
I am not sure why people are trying to preserve the DC component of a discriminator output. The output is essentially audio. I feed that audio into an input on a PC (line/mic). All inputs are not created equal as some may have input DC blocking and some may not. I've always felt the discriminator output should have a capacitor to block DC, and as written above, it should be non-polarized. Don't under-spec the cap; I'm using caps with a voltage rating of at least 10V. Cheap caps (from China) have a shorter life than better quality components.
So the +/- 12VDC levels commonly used in RS232 signaling are superfluous? We can start adding series caps to RS323 data lines?DC carries no information. It's not a part of the signal needed to decode bits properly.
Y'all are too focused on two level signaling. Taps are commonly used for four level signaling like NXDN, DMR, P25 and so on. DC levels absolutely matter.You don't need to preserve the DC component but you do have to preserve a digital leading or trailing edge and that requires a frequency response near DC. It all depends on what your are going to feed from the discriminator.