Received: by 10.11.53.59 with SMTP id b59mr2620262cwa; Thu, 13 Apr 2006 21:42:03 -0700 (PDT) Return-Path: Received: from ams006.ftl.affinity.com (lvs00-fl-n06.valueweb.net [216.219.253.152]) by mx.googlegroups.com with ESMTP id v11si5509406cwb.2006.04.13.21.42.02; Thu, 13 Apr 2006 21:42:03 -0700 (PDT) Received-SPF: neutral (googlegroups.com: 216.219.253.152 is neither permitted nor denied by best guess record for domain of jm...@tscm.com) Received: from [151.199.42.134] ([151.199.42.134]:12298 "EHLO nikola.tscm.com") by ams006.ftl.affinity.com with ESMTP id S360577AbWDNEmB (ORCPT ); Fri, 14 Apr 2006 00:42:01 -0400 Message-Id: <6.2.3.4.2.20060405185606.0dfa87d0@pop.tscm.com> X-Mailer: QUALCOMM Windows Eudora Version 6.2.3.4 Date: Fri, 14 Apr 2006 00:35:07 -0400 To: "TSCM-L Professionals List" From: "James M. Atkinson" Subject: Re: [TSCM-L] Re: NLJD and cell phones In-Reply-To: <1144272252.447029.307130@j33g2000cwa.googlegroups.com> References: <000c01c655e7$49485000$6601a8c0@jp> <1144272252.447029.307130@j33g2000cwa.googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; format=flowed This is why it is important to have more than one instrument to perform non-linear junction detection. If you know the frequency of some part of the eavesdropping device, such as the control frequency of 433.92 MHz it is a simple matter of pulsing that signal out to the suspect area and then listen on the harmonics for it bouncing back. The 433.92 MHz signal will get though the filters and be reflected back at you, if the filtering on the final stages of the device is poor then you will get a non-linear response on the harmonics of interest (866, 1301, 1735 MHz, etc). However, if the filters in the bug are good, and the circuit is well designed you will not get a detectable signal on the harmonics, but will a good reflection on at 433.92 MHz. A fixed band NLJD does a pretty good job of detecting imbedded devices when you are no more than a few inches away, and a fixed band NLJD is an extremely critical part of any TSCM project. But a fixed band NLJD is different that a fixed FREQUENCY NLJD. A fixed tuned unit will give you superior results on poor quality spyshop devices, raw circuit boards common with hobbyists, and devices that lack the extensive filtering and isolation present in more expensive bugs. An example of fixed tune NLJD is the original SuperScout that consisted of a transmitter on a single frequency that required that you open the case (which took an hour), then the tweaking of multiple pots, caps, and filters to just nudge the illumination frequency just a little. It then took 3 more hours of sacrificing small animals to the deity of your choice, and wave a chicken foot over the control box to coax the 'Scout to behave itself. One of the painful problems with a fixed tune NLJD is that a spy can very easily detect their use, and can develop some method to get the bug out before the sweep team finds the device. There is also the problem of a fixed tuned NLJD choking on interference on a congested frequency. Since many of the older NLJD's where fixed dead in the middle of the 902-928 band there was massive problems with other electronics operating dead on the same frequency. To counter this you had to re-tune your 'Scout a little above or a little below this %+**&^ point. A tunable NLJD is much more desirable instrument, but you do take a minor performance hit. On the other hand, with modern electronics a tunable NLJD can be made extremely inexpensively for one of the ISM bands like 902-928, although there will be a huge expense in the mechanical parts of the NLJD. If someone was so interested they could actually build a fairly effective NLJD for less than $200 in electronic parts by using the circuits from a 900 MHz/2.4 GHz cordless phone, but the milling of the enclosure and mechanical parts would cost much more. A swept tuned NLJD is the ideal solution, but most TSCM folks lack the capability of obtaining the equipment to do this, and even if they did assemble the equipment it would only be practical to use for short durations, and small areas due to potential interference issues. A swept tuned unit is best used where the thing being tested is placed inside a shielded enclosure, or where the testing environment is highly controlled such as in an underground or shielded SCIF. A pulsed NLJD illumination circuit is desirable because the receiver circuit can be blanked out only at the exact moment the transmitter is lighting up the target. In this manner the receivers can be made to be much more sensitive, or at least create the illusion of increased sensitivity. A mutli-band NLJD is more desirable than a switched band NLJD. In a multi-band unit you have three separate receivers that are phase locked to each other, which are phase locked to the illumination transmitter. In a switched or multi-band NLJD you transmit the illumination signal, listen with one receiver, then re-tune the receiver, transmit another signal, then tune back to the original signal. -jma At 05:24 PM 4/5/2006, contr...@yahoo.co.uk wrote: >A releted general question >what happens with NLJD's if there's a circuit very close that is > >A) exactly in resonance at the working-frequency of that NLJD >B) almost/tending to resonance of the working-frequency of that NLJD > >I assume absorption or attenuation or similar takes place ? > >contranl ---------------------------------------------------------------------------------------------------- We Expertly Hunt Real Spies, Real Eavesdroppers, and Real Wiretappers. ---------------------------------------------------------------------------------------------------- James M. Atkinson Phone: (978) 546-3803 Granite Island Group Fax: (978) 546-9467 127 Eastern Avenue #291 Web: http://www.tscm.com/ Gloucester, MA 01931-8008 Email: mailto:jm...@tscm.com ---------------------------------------------------------------------------------------------------- World Class, Professional, Ethical, and Competent Bug Sweeps, and Wiretap Detection using Sophisticated Laboratory Grade Test Equipment. ----------------------------------------------------------------------------------------------------