T4win Waveform comparison...

[funkytones]

i am at work so i cant post a screenshot of mine... but can people post screen shots of their waveform? so i can compair mine to others... i want to try and get it the best i can... mine has the boxy waves with the rounded edges but it looks like there is a little static in there... (edacs96)

or since t4win shows 100% on it, i should know that thats the best the wave can be?

 

[RolnCode3]

I've been wondering the same thing, especially since I only tapped my 785 yesterday. I get 100% decode with t4Win, but Trunker has problems sometimes. I think it might be poor signal (due to antenna issues), but Trunker will usually only run for about 15 minutes then freeze up (starts looking for the signal again). T4Win ran overnight no problem. Anyways, here's my waveform (BTW-/\/\ Type 2 800):

 

[funkytones]

Cool, my waveform is quite smaller... i dont know if its because of the different system (/\/\ / edacs) but mine is about 4 green boxes high and the lines arnt as straight... little more jagged... i'll have a screen shot up in about a hour...

 

[Jay911]

Here are my two. One is from a recently tapped 245, one is from a 245 I tapped a long while ago. Both are monitoring Motorola systems - and both are running 100%, interestingly enough.

This one was tapped recently.

This one was done a year or more ago - I'm pretty certain the difference showcases my inexperience and what I've learned in the meantime!

 

[BANDIT]

Jay, what did you use for the tap to get the clean waveforms. 100K, cap, or a combination?

Robert

 

[funkytones]

here is mine... edacs96

hmm... could be tweeked a little more i guess...

any techie people got any ideas? 1uf 35v cap to mono headphone style adapter to line in... i went that way becase i had all the pieces on hand... should i switch to a RCA tyle cord?

 

[Jay911]

Er... this is going to feel stupid considering I just talked about how much I've learned, but I didn't use anything. Am I allowed to plead ignorance this late in the game? I simply found a page on the web that listed the tap points for the 245 and soldered some wire to it, then soldered a cut-in-half mono audio patch cable to that, running it thru a drilled hole in the side of the scanner. I'm not using any resistors or capacitors.

What's the benefit to using such stuff? I may tap my 796 soon, and perhaps I should study this a bit more before I do that.

 

[RolnCode3]

My 785 is just a straight wire from data skip to jack. No capacitors, resistors, etc...the video from dataslicers does it this way as well, but I've seen others suggest using resistors,etc...mine works fine as is (or at least it seems to be)

 

[funkytones]

you you guys hook up the neg or ground of the cable to anything? and then the positive or the inside to the skip point... ?

somewhere i read that the neg has to be hooked up for the insulator... the cap i have is on the tap point... i guess i can remove it... maybe that will help my waveform out... i'll try... just dont want to short out on 796..lol

here is a apco p25 9600 waveform that i am getting... not getting decoded though ;(

 

[Jay911]

you you guys hook up the neg or ground of the cable to anything? and then the positive or the inside to the skip point... ?

Mine simply goes from the tap point on the scanner, and a suitable ground nearby. On the 245, I'm using the screw that holds the shield on that's right beside the tap point.

here is a apco p25 9600 waveform that i am getting... not getting decoded though

How sure are you on your cable quality?

My very first try was on a Maxtrac with the discriminator output already brought to the outside of the radio. I ran an RCA cable of old and questionable quality to the 16-pin accessory connector, and my waveforms and decode rates looked like crap.

I replaced the RCA cable with a new 1/8" mono cable (the other half of the one that went to one of the BC245s mentioned above) and got a perfectly square waveform and 100%.

 

[funkytones]

should be of good quals... its actually the cloning cable that came with a pro92 that i have... there is about a 6inch lead of single wire from the tap to the adapter where i hook in my mono adapter to get the signal out of the box... i'll start there and insulate that wire first and go from there...

why just got to figure out why the wave form is only 3-5 boxes tall...

 

[loumaag]

... just got to figure out why the wave form is only 3-5 boxes tall...

No thats not what you have to figure out. What you have to figure out is why your grid is different from everybody elses, including mine. You only have a total of six vertical grid squares while eveyone else has 10. :lol:

 

[RolnCode3]

Mine is tapped from data skip to jack. I am not using a ground at all. According to the dataslicers video, the metal chassis will ground the jack sufficiently to not need a ground wire. I'm done with the info, so if anyone wants to paypal me 5 bucks for shipping and the CD, I'll gladly send it along to anyone else (it cost me 10 just 3 days ago). Otherwise, I'll just hang on to it.

 

[Chris-M]

Here's mine from a tapped Pro-96, direct from TP4 with no resistor.
The cable shielding is grounded inside the scanner on a tin RF shield.

This is an EDACS96 waveform.

 

[funkytones]

re-tapped my 796... grounded the wire straight from the tap to a chassis screw with some mini coax... played with the audio properties a bit and made my waveform bigger by turning up some volume... i guess that is why my wave was small was because some volume property was low...

my new edacs wave: (more even and straighter than before)

new apco signal (doesnt decode):

and t4win was decoding this big mama jama aswell..ll edacs96

*edit* and i only cut and paste the wave... not hte empty green grid above and below the wave

 

[SCPD]

Thanks for posting these. One quick observation ...

These last two (Chris-M and FunkyTones) look clipped. Decoding software will tolerate some clipping on a two-level signal. Clipping of more complex signals (like APCO P25) will ruin any chance of decoding.

FunkyTones - the peaks on that P25 sample are clipped. Relative amplitudes on the four types of peaks or spikes in a P25 signal are +1, +3, -1, -3. Your signal looks more like +1, +1.5, -1, -1.5. The relative amplitudes are too close together. That P25 sample you posted earlier in this thread looks much better.

Try turning down the gain if at all possible. There may be an audio driver option for this. If not, add a resistor inline.

When I get a chance I'll post examples of the effect of impedance (mis-)match on the waveform.

-rick

 

[Jay911]

Try turning down the gain if at all possible. There may be an audio driver option for this. If not, add a resistor inline.

That's something I forgot to mention regarding my own successes or lack thereof: My audio levels on my sound card have to be near zero in order to receive a signal. Anything louder still shows up as a tall, square wave, but nothing at all gets decoded.

I presume you just gave us all the answer as to why that is.

 

[Chris-M]

Clipped..hmmm. This is from my tapped PRO-2053. I forget the resistor value. RFmobile does this look any better? I wonder if it's my screengrab image quality which is poor. I included some data in this one in case you see anything in there out of the ordinary.

 

[funkytones]

okey... got the apco back to the pic i posted earlier...

what type of resistor should i use?

and will unitrunker be able to decode 9600bd p25?

 

[SCPD]

what type of resistor should i use?

This is the experimental part ... try 10k, 47k, and 100k; 1/4 to 1/8th watt.

and will unitrunker be able to decode 9600bd p25?

Yes - but it requires a clean signal. Some of you may need to build a small buffer amplifier. Most electronic kit sellers offer a "hi-Z" microphone pre-amp - which should do the trick. Keep in mind that the issue isn't gain, it's matching the hi-Z impedance of the discriminator output vs. the relatively low-Z impedance of the microphone input.

In using a BC780XLT, I'm finding that I need a small JFET buffer amp to take the load off of the radio's weak discriminator output.

-rick