1. The "16 bit converter is not so clear to me. Does a "Fluke 97 multimeter" do the job too?For devices that draw power from the line, measure the open circuit voltage and short circuit current to high precision (16 bit converter).
2. Most of serial bugs do not use ringing protection (even the "pro" ones), the "automatic recording devices" parallel or serial neither. They both uses diode bridges, the parallel using 2 x 2.2M resistors, the serial without resistors (of course). Even the "infinity transmitter" (parallel) has not any protection.2. The tap probably has some form of protection against the ringing signal. This is a nonlinear network across the line which should change the harmonic content of the ringing signal. Use the 16 bit ADC to measure the ringing signal and do a FFT on it.
Making tests from the central office is the only way I know to find almost any bug, using a "Megger", a "wien bridge" or making a "Varley" or "Murray" measurement. Even a dB meter can be used, comparing 2 lines about loss. The best is of course a TDR...If you have the cooperation of the central office....
Nina said:Well, after trying to find at sollution at many places, I've still remained confused
The sollution flatulent gave me is very good, (if I'm understing it right...) but i'm looking for a more "practical" one, for example a comparator (maybe a Schmitt trigger comparator) that may sense a minor drop on the 48V line's voltage, or senses a current change (after mesuring the line end with a short, as flatulent suggested).
I need help designing such a comparator, and be very thankful if anyone may help
Tia,
Regards,
Nina
Take a look at the links I've attached. I really don't expect the devices mentioned to do a TDR's job. I'm working as manager of my national telecomm electronics lab and I have also a lab of my own, as electronics was an is one of my hobbies.You want a simple solution to detection complex measure problem in many dimensions.
Yes, unfotunately you are perfectly right !!!if parallell tap using low capacitance (lose coupling) and high resistance very close to wire (no long wire before high resistance) , is impossible to detect with TDR-methode or other methode using reflection on line (S11).
Nina said:Well, after trying to find at sollution at many places, I've still remained confused
The sollution flatulent gave me is very good, (if I'm understing it right...) but i'm looking for a more "practical" one, for example a comparator (maybe a Schmitt trigger comparator) that may sense a minor drop on the 48V line's voltage, or senses a current change (after mesuring the line end with a short, as flatulent suggested).
I need help designing such a comparator, and be very thankful if anyone may help
Tia,
Regards,
Nina
But, if tap mounting near know big impedance discontinue point like cross coupling board etc. seems hidden from TDR-measure (simular small submarine close to oil-tanker) and needs visual controll on every impedance discontiune point - you cannot measure on electrical way to find if discontinue is by nature of connectors or have extra small load of 2.2 MOhm from wire tap...
is also possible to listen on unused line in same cable, ie listen on capacitive leaking from intresting line, special if cable is not use twisted pairs.
Nina said:Yes, of course you are right !!! And the submarine example is very nice, expaining exactly some of the problems.
This is the reason my staff - if suspects there is a fault on a cable near a telephone, not a tap, as we are not looking for those devices - always disconnect the far end (the phone, fax or whatever) and do tests from both sides of line, including bridge, varley etc.
But, this still does not even gives me the clue how a device can detect a bug in the way they described, and more of that - to defeat it !!!
If you may think about any way, I'll be very glad to hear (see)
Regards,
hmm.
is possibly using oveload action as high frequency or high pass filtred very strong noise (needs lowpass filter on phone in both end), but need know how this tap are constructed and find out weakness on most common used models of tap.
if you can measure from both end - short other end, rising voltage slowly and measure current to detect non linjarity at diod-bridge from serial tap.
also using TDR-measure with normal line-current and none line current and see difference between measure (diod-brigdge give high impedance with no current) - but good constructed serial tap can using capacitance to bypass high frequency TDR-pulses....
Can also try using two-tone measure (ex. 1000 and 1500 Hz or possibly DTMF) and listing of intermodulation (best listing on other ends) from non linjarity component (diode....) human ear hear weak IM as disharmonic of two tones very well and if disharmonic exist and vary on adjustable line current (0-100 mA and more), you have non linjarity component on wire.
- Or burn out with very high current pulses simular stroke of ligthing (shorted other ends) with risk to break connection (inside serial tap) - but now easy to find with TDR-equipment after this... - but this moment give alway risk for starting fire on unwanted place under process of High-current 'cleaning'... ;-)
use 'megger' do overload and burn paralell-tap with very high voltage - but also possibly to break down insulation on weak spots on phone line or high voltage protector on wire take down voltage....
---
ie. not easy to defeat wire-tap/bugg.
Use voice scrambler (possible passing on computers soundcard ???) or
encrypted Voip-communication (like skype-phone, but using crypted datastream)
for sensitive phone speak.
---
[added couple of days later]
high speed modem-communication (28800 baud and higher) is near impossible to restruct from paralell-tap (voltage tap) or line tap (current tap) separatly, You need both value syncronized and know phase to restruct this (read telephone hybrid (bridge) of very good quality and indivudal tuning to actal line impedance, and more advanced than 99.999% percent of amature-spy can make it) - in first step
next step needs know how modems equlizer and calibrate paramterer to decode modem-modulation - even if listen on calibrate sequence in start, you cannot use this from tap-point view - calibrate parameters describe whole system responce between A-B point, wire tap in middle, seeing totaly different transmissions responce and cannot using calibration parameters directly listen from modem communictation....
if computer in both ends of modems, using compression ala GSM, mp3-code or simular from soundcard (using headset) and using DES-crypto or simular (for fast response) , you need more or less high tech military resources and knowhow to decode this talking, tapped from line...
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?