In my sweep truck I have a large tool chest with
heavy duty steel drawers like what you would find
in a auto shop. Inside this tool chest is an 8
pole band rejection filter for every single TV
station in the United State and Canada, plus
rejection filters for various chucks of the FM
and, pager band, band pass filters for various
bands, etc, etc. I also have K&L Microwave
tunable 5 pole band pass and band reject filters
that cover up to 3 GHz as well.
All told I have many hundreds of pounds of copper
brass and silver in the "filter chest" so that I
can go to pretty where is the US or Canada and
knock down virtually any signal that might be
over powering my equipment. If a spy has parked
his sub-milli watt NFM bug at 97.45 MHz, and
there is a thunder lizard at 97.30 MHz that is
located at 800 feet away I can still kill the
offending lizard and hone in on the bug without saturating my sweep gear.
-jma
At 04:36 PM 2/19/2007, kondrak wrote:
>Proving once again, theres no such thing as a free lunch :-D.
>
>At 15:56 2/19/2007, you wrote:
>
>>Check out: http://www.tscm.com/TSCM101noise.html
>>
>>Response as follows:
>>
>>
>>
>>At 09:52 AM 2/15/2007, cont..._at_yahoo.co.uk wrote:
>>
>>
>>>.
>>>
>>>
>>>Wideband (AM) detectors are very popular...because they are easy to
>>>use
>>>and relatively cheap.
>>>
>>>...the problem is that they are not very sensitive.
>>>...another problem is that they cant separate signals at different
>>>frequencies.
>>>
>>>
>>>Question
>>>--------------
>>>
>>>
>>>-/////////////////////////-
>>>
>>>How many times more sensitive would a wideband detector become
>>>if it had additional filters in the frontend ?
>>>
>>>-/////////////////////////-
>>
>>
>>It can be hundreds of thousands, or even millions of times more sensitive.
>>
>>
>>Fow example, let say you want to build a simple
>>diode detector that monitors 398.5-400 MHz (1.5
>>MHz wide), you build a simple 8 pole bandpass
>>filter that contains 4 high pass, and then 4
>>low pass filters, or better yet, 8 high pass
>>cavities, and 8 low pass cavities. This will
>>knock down even the most powerful FM and TV
>>broadcast signals so you can pass the signal
>>to a LNA and then into a diode, and then sum
>>the voltage that comes out of this diode with a
>>output of a matching diode (reference
>>diode/amp), and apply the output of the summing
>>circuit to another amplifier that drives a
>>simple 30 dB or larger column of LED's.
>>
>>The goal here is to take a hypothetical FM
>>radio station that is presenting -20 dBm on
>>site, and to knock it down below -174 dB. This
>>means that we want to kill everything outside
>>of the band by 154 dB, but I know some
>>engineers who use only 40 db, others use 120
>>dB, and some even use 400 dB as their design
>>goals for TSCM and SIGINT bandpass filters. An
>>example is the 60 cycle high pass filters that
>>I make, they knock down 60 Hz by 400 dB, so you
>>can plug one end into a 480 volt circuit, and
>>the other end into the RF input of your
>>spectrum analyzer or oscilloscope. We als comb
>>out all the harmonics of the line voltage and
>>knock down any nastiness that might cause blue smoke to leak out of the SA.
>>
>>
>>
>>>For example the detector does 1 Mhz to 3000 Mhz
>>>
>>>Now i will devide that into 5 bands...using 5 separate filters :
>>>
>>>a) 1-80 Mhz
>>>b) 80-200 Mhz
>>>c) 200-520 Mhz
>>>d) 520-1000 Mhz
>>>e) 1000-3000 Mhz
>>>
>>>
>>>Ofcourse when using one of above filters... it seems very logical
>>>that
>>>the maximal detection range becomes much better then without a filter.
>>>
>>>I suppose that is caused by below factors :
>>
>>
>>When not use the wide band detector (3 GHz) to
>>gate the sampling side of the post filter
>>detectors. Simply put, when the 3 GHz diode
>>captures energy on the log scale that exceeds a
>>certain level (say -50 dB) that it uses to gate
>>all of the output of the diodes assigned to each of the five bands of interest.
>>
>>Lets assume (grin) that I have a stack of
>>Astro-Med Everest analog chart recorders in a
>>rack. Each chart recorder is capable of 32
>>analog channels each, and I gang or slave 4 of
>>them together so that I have 128 virtual
>>channels. I built a trigger circuit for each
>>chart recorder that monitors a wide swath of RF
>>spectrum, so we have the first recorder
>>listening and reacting to 100 Hz to 1.8 GHz,
>>the second 1 .5 to 18 GHz, the third from 12
>>GHz to 30 GHz, and so on. When the broadband
>>energy at say 500 MHz goes over -50 dB it
>>triggers the chart recorder to start moving the
>>paper for 5 seconds, but looking at the chart
>>you can see which band of the 32 the energy
>>appears in. The tricky part is that each of the
>>32 channels have to have thier own filter and
>>LNA, then diode, and interface for the chart recorder.
>>
>>Maximum range requires first maximum
>>filtration, folwed by maximim amplification,
>>folwed by the most sensitive detection diodes
>>you can find, then further amplification to
>>drive whatever is giong to be your indicator
>>(LED column, speaker, chart recorder, etc)
>>
>>
>>
>>>1) The environmental noisefloor is much lower so a signal would stick
>>>out much easier.
>>
>>
>>Yes, but you have to know the frequency on
>>which the bugs appear, and this is a tricky
>>proposition. You have to break the bands into
>>things like 135-150 MHz, then 150 to 174, 174 to 200 MHz, and so forth.
>>
>>
>>
>>>2) Bandwidth in the receiver is directly related to noise.
>>
>>Yes, it is all part of the KTB formula, with B
>>being that which we can control the most.
>>
>>
>>
>>>Offcourse the adantage of filtering would also be that :
>>>
>>>1) The wanted signal is not masked (overpowered) by other out of band
>>>signals
>>
>>
>>Big rule of TSCM is to estimate that which you
>>should see in the area you will be sweeping,
>>and then to bring along filters to knock down
>>things that may be making your measurements
>>"dirty". Personally, I carry a fixed 8 pole
>>band reject filter for every TV station
>>allocation, plus a FM band reject filters (more
>>then one), and filters to knock out the paging bands.
>>
>>You know what your going to need by looking up
>>FCC allocations for everything within five
>>miles, but 75 miles for any broadcast (AM, FM,
>>TV) channels. If I am performing a sweep in
>>Needham, MA there are huge antenna farms for FM
>>and TV broadcasting, so every inch of the
>>office that I am sweep in getting hammered with
>>high levels of RF. Not only do I have to know
>>down the main carrier, but even the 15th
>>harmonic of the main carrier is radiating off
>>of structural steel and causing massive
>>headaches. This means that I have to use a
>>filter that kills not only the main carrier,
>>but also filters that kill every harmonic out
>>to the 20th or so carriers that is going to tilt or saturate the sweep gear.
>>
>>Once you get above 2 GHz you can use one of
>>more YIG filters to help you do this, but the
>>low frequencies (below 1 GHz) are going to be quite troublesome.
>>
>>
>>
>>>2) You have an indication of the frequency-band of the found signal
>>>
>>>...etc
>>
>>
>>Simple sample and hold circuit that triggers a flip-flop circuit.
>>
>>
>>
>>>The mentioned unit lets you either switch to each filter by hand...but
>>>it can also go into a so called "Scanning-Filter mode"
>>>
>>>Filter-scanning mode will switch between filters like this :
>>>
>>>Filter 1 >> Filter 2 >> Filter 3 >> Filter 4 >> Filter 5 >> NO-
>>>Filter ......and over again.
>>
>>
>>Simple six pole mechanical coax switch/relay
>>with a control circuit. It has been done before
>>with good results. Basically, you take a six
>>pole switch, and hand a dedicated filter,
>>amplifier, and antenna off each of the six input connectors.
>>
>>One key is not to apply power to any of the six
>>amplifiers other then the one you are using at the time.
>>
>>
>>>That NO/filter seems to be a good idea in practice...to also receive
>>>out of band signals
>>>not covered by the filters (in this case below 1 mhz and above 3000
>>>mhz)
>>>
>>>The scanning-speed has still to be determined...it depends on the
>>>shortest duration
>>>of possible digital signals (pulses) that you want to detect :
>>>
>>>...if it is to slow you might miss a short on-time signal (non
>>>continious bursts)
>>>...if it is to fast to fast there is no time to validate the signal
>>>(continious but very-short pulses)
>>
>>
>>
>>A very effective method of detecting tracking
>>devices in a vehicle is to use a gang of
>>generic diode detector such as the CPM-700, add
>>your own bandpass filters for each of the
>>"phone to tower" frequencies, and follow it by
>>a small 20 dB preamplier, or "convert" the RF probes.
>>
>>
>>To convert a probe you unscrew the probe body,
>>unscrew the antenna, unsolder the screw that
>>the antenna attached to and install an SMA
>>female connector. Next visit your local
>>hardware store and purchase some one inch
>>tubing and fittings. Mount the SMA/probe
>>assembly into the end cap, and solder the
>>ground of the probe to the copper as well. Then
>>slide the whole thing into a length of copper
>>tubing that it roughly half the wavelength of
>>the frequency of interest. The other end of the
>>copper tube is a Male BNC connector so that you
>>can merely plug the tube into the BNC connector of the CPM-700
>>
>>Next fabricate an antenna out of a length of
>>copper clad welding wire and terminate it on a
>>female SMA connector so that you have a high performance dipole antenna.
>>
>>Inside the copper tubing you will want to add a
>>small 8 pole bandpass filter and kill off the
>>tower-to-base and trunking frequencies by at
>>least 80 dB befoe you go into the probes amplifer.
>>
>>The simplest this is to make a standalone box
>>the size of a carton of cigarettes into which
>>the phone-to-tower antenna where mounted, then
>>feed into separate filters for each band (8
>>poles each), and then take the output and apply
>>it to dedicated amps all built into the same case.
>>
>>The box would best be a brass block that you
>>drill out with cavities for each of the filter
>>poles, and then a large cavity for the
>>amplifiers. You could go with an interdigital
>>filters for each of the bands, but you really
>>do not need to displace much heat, and the
>>physical size of the 800 MHz band will be
>>unpleasantly large and heavy. I would (and
>>have) leaned toward a simple LC filters for a
>>project like this and simply add a lot of pole
>>to keep the skirts of the filter as sharp as possible.
>>
>>Companies that make filters for the cell phones
>>themselves also make very small duplexer
>>circuits that you can use in reverse, but they
>>tend not to knock down the signals by more then
>>20 ot 30 dB, but it may be a good place for you to start experimenting.
>>
>>
>>
>>>Forget the scanning speed...lets talk just about sensitivity-
>>>improvement when using filters.
>>
>>
>>I am a *** BIG *** fan of carefully designed
>>and built filters, and their use in TSCM.
>>
>>I am also an even bigger fan of using big-ass
>>(excuse my French) wide band antennas to suck in as much energy as possible.
>>
>>
>>>I know that its a difficult question...but lets say i have to write an
>>>article or propaganda
>>>for a unit with those 5 switchable filters...and i have to say how
>>>many times more sensitive
>>>a Wideband(AM)-detector with 5 filters like above is...compared to the
>>>same one without filters
>>>
>>>I suppose that the smaller the filter-bandwidth the more "sensitive"
>>>so lets simplefy the question
>>>and lets assume that the 5 used filters all have the same bandwidth so
>>>the whole range is equally
>>>devided
>>>
>>>------------------------------------------------------------------------------------
>>>How many times more sensitivity or range would you get ?
>>>------------------------------------------------------------------------------------
>>>
>>>
>>>Thanks !
>>>
>>>
>>>Contranl
>>>
>>>
>>>
>>>Remark...i dont understand why not one single manufacturer of (AM)
>>>wideband-detectors
>>> has not incorperated some filters...they are not
>>>difficult to produce
>>> and not expensive...but greatly improves them.
>>>
>>>
>>>Please do not respond (in private) to my (old) Yahoo-emailadress...i
>>>´ve lost the password
>>>and after weeks of correspondence they dont want to give it...Yahoo
>>>SUCKS !
>>
>>----------------------------------------------------------------------------------------------------
>> World Class, Professional, Ethical, and Competent Bug Sweeps, and
>>Wiretap Detection using Sophisticated Laboratory Grade Test Equipment.
>>----------------------------------------------------------------------------------------------------
>> 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 E-mail: mailto:jm..._at_tscm.com
>>----------------------------------------------------------------------------------------------------
>> We perform bug sweeps like it's a full contact sport, we take no prisoners,
>>and we give no quarter. Our goal is to simply, and completely stop the spy.
>>----------------------------------------------------------------------------------------------------
>>
>>
>
>----------------------------------------------------------------------------------------------------
> World Class, Professional, Ethical, and Competent Bug Sweeps, and
>Wiretap Detection using Sophisticated Laboratory Grade Test Equipment.
>----------------------------------------------------------------------------------------------------
> 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 E-mail: mailto:jm..._at_tscm.com
>----------------------------------------------------------------------------------------------------
> We perform bug sweeps like it's a full contact sport, we take no prisoners,
>and we give no quarter. Our goal is to simply, and completely stop the spy.
>----------------------------------------------------------------------------------------------------
>
Received on Sat Mar 02 2024 - 00:57:15 CST