Need help Universal Trunker Scope Display

[rkorchensky]

I "think" I have a problem with my Disc Tap and would appreciate any comments.

I have 2 radios that I use on 2 computers each running Unitrunker v1.0.0.9. One is a Radio Shack Pro-2040 and the other is a Radio Shack Pro-2004. Both are tapped as per the usual available directions, and both work to decode any given mode (but mostly EDACS and Motorola). I am just concerned that although they both work, both could work better!

Assume both radios are tuned to the same frequency at the same time and both are on EDACS (it doesn't make any difference if both are on a Motorola syatem).

Assume the scope window is about 3" x 3" on my screens.

If I look at the scope on the Pro-2040 the pattern is about 1/2" in height.

If I look at the scope on the Pro-2004 the pattern is higher than the window....about 3 1/4" in height. It is flattening at the top and bottom.

My question is this.....is either pattern correct or are both wrong. Is a small pattern ok? I am assuming the large pattern is too large.

Would some form of capacitor or resistor in series with the Disc Tap help? What type and size?

Anyone have any answers or suggestions?


Thanks in advance, Ralph VE3EUK

[Unitrunker]

Originally Posted by rkorchensky

If I look at the scope on the Pro-2040 the pattern is about 1/2" in height.

That's 1/6 or about 17% deflection - which is quite adequate. With 16 bit sampling, there is more than sufficient resolution.

If I look at the scope on the Pro-2004 the pattern is higher than the window....about 3 1/4" in height. It is flattening at the top and bottom.

That's not good - you'll want to adjust that down. Ideally you should keep the signal inside the sampling range of the audio input. Motorola and EDACS waveforms are such that some clipping is tolerated. This will however destroy P25 decoding.

My question is this.....is either pattern correct or are both wrong. Is a small pattern ok? I am assuming the large pattern is too large.

A small pattern is okay. If you want to decode P25 on the 2004, you'll need to reduce the signal level slightly.

Would some form of capacitor or resistor in series with the Disc Tap help? What type and size?

A capacitor is redundant - your computer's sound input already has one. A resistor may help. They're cheap so you can buy several to see which is best. Start with a 47k resistor and go up or down from there.

[rkorchensky]

Thanks Unitrunker. I appreciate your help.

Ralph, VE3EUK