• Effective immediately we will be deleting, without notice, any negative threads or posts that deal with the use of encryption and streaming of scanner audio.

    We've noticed a huge increase in rants and negative posts that revolve around agencies going to encryption due to the broadcasting of scanner audio on the internet. It's now worn out and continues to be the same recycled rants. These rants hijack the threads and derail the conversation. They no longer have a place anywhere on this forum other than in the designated threads in the Rants forum in the Tavern.

    If you violate these guidelines your post will be deleted without notice and an infraction will be issued. We are not against discussion of this issue. You just need to do it in the right place. For example:
    https://forums.radioreference.com/rants/224104-official-thread-live-audio-feeds-scanners-wait-encryption.html

LTRDump & Data Dicer Questions & Help

Status
Not open for further replies.
Joined
May 3, 2007
Messages
2
Location
Oakland, NJ
#1
I have built the "data dicer" designed by Eric Cottrell and I am running it with LTRdump.

It seems to be decoding intermittantly, everyonce and a while I will get a good LTR decode LCN and TGID. I am also getting some messages decoded with the neighbor frequency (passport ?). But most of the time when I am hearing activity on the channel there is either "unknow" messages with all zeros in the fields or nothing.

I have scoped thur the circuit and most of the time when there is no activity on the channel (I see discriminator "white noise" at the input to the data dicer) there is a constant square wave at the output (pin 14) of the comparator/rs-232 driver. The wave form seems to change when there is activity on the channel. The output level is just less then 5v (4.5) on the positive or negivite peaks (about 9 v pp). Is this enough output level? I am feeding the output of the slicer into the CTS input even though the diagram says "rs-232 data output" which I take to mean RD input.

I am thinking that I might need a level shifter to increase the level going into the com port.

I have tried the normal/invert and it seems to work best on the invert position. I think that I have good RF signal it is very clean at the input, when there is activity on the channel.

Thanks for any help or ideas.

Nickde
 

Forts

Mentor
Database Admin
Joined
Dec 19, 2002
Messages
5,510
Location
Ontario, Canada
#2
Maybe it's because you built a dicer instead of a slicer? Or maybe yours dices and slices? Sorry, just being a smartass... it's actually called a data slicer, not a dicer. Have you tried it with any other programs like DOS Trunker or ETrunker? (Not Unitrunker as I believe the serial inputs are no longer an option). If you have any trunked Motorola or EDACS systems in your area, try your slicer on them and see what kind of performance you get. LTR is a bit of an odd duck to deal with, and decoding can be tricky.
 
Joined
May 3, 2007
Messages
2
Location
Oakland, NJ
#3
Oh yah, didn't mention that I am using a LM324 Quad Op amp instead of the MC33174 that the diagram wanted. It has a potentional defferance of 14 vdc across V+ and V-.
 

wa8pyr

Technischer Guru
Moderator
Joined
Sep 22, 2002
Messages
4,244
Location
Ohio
#4
nickde said:
Oh yah, didn't mention that I am using a LM324 Quad Op amp instead of the MC33174 that the diagram wanted..
That's likely part of your problem. Don't have the specs in front of me, but IIRC the LM324 has a higher noise figure than the MC33174. With complex subaudible data like that you want as little noise as possible.
 
Joined
May 3, 2007
Messages
2
Location
Oakland, NJ
#5
Trying other op amps

I had a MC3403 in my parts bag, so I tried it, no differance. Let me know about the noise figures, if I need to I will get one ordered up.

Thanks

Nickde
 

EricCottrell

Member
Database Admin
Joined
Nov 8, 2002
Messages
2,268
Location
Boston, Ma
#6
nickde said:
I have built the "data dicer" designed by Eric Cottrell and I am running it with LTRdump.

It seems to be decoding intermittantly, everyonce and a while I will get a good LTR decode LCN and TGID. I am also getting some messages decoded with the neighbor frequency (passport ?). But most of the time when I am hearing activity on the channel there is either "unknow" messages with all zeros in the fields or nothing.

I have scoped thur the circuit and most of the time when there is no activity on the channel (I see discriminator "white noise" at the input to the data dicer) there is a constant square wave at the output (pin 14) of the comparator/rs-232 driver. The wave form seems to change when there is activity on the channel. The output level is just less then 5v (4.5) on the positive or negivite peaks (about 9 v pp). Is this enough output level? I am feeding the output of the slicer into the CTS input even though the diagram says "rs-232 data output" which I take to mean RD input.

I am thinking that I might need a level shifter to increase the level going into the com port.

I have tried the normal/invert and it seems to work best on the invert position. I think that I have good RF signal it is very clean at the input, when there is activity on the channel.

Thanks for any help or ideas.

Nickde
Hello,

The Dicer part is my attempt at humor. A Dicer is a Slicer with a low pass filter.

The "rs-232 data output" can be used for CTS or DCD or whatever input pin is supported. I prefer DCD because it gets away from the handshaking on the port.

The reason for the M33174 is from information I read about data slicers. The author said the M33174 has enough high-frequency response to do 9600 baud but not enough to cause problems.

I found on some receivers that a DC level built up on the input to the dicer so I put a 1 megohm resistor between the input and ground. If you measure the voltage at the input and it suddenly works again then this is the problem.

It is also important to have both positive and negative voltages connected to the "power supply". Trunker and LTRTrunk will set the signal lines mentioned to provide the positive and negative voltages.

Also if you are in Filter Bypass Mode (Motorola/EDACS), you can decode LTR but any voice will kill the decoding.

73 Eric
 
Status
Not open for further replies.
Top