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From: kondrak <kon..._at_phreaker.net>
Subject: Re: [TSCM-L] Re: Wideband (AM) detectors improvement using
filters ?
In-Reply-To: <7.0.1.0.2.20070219142659.08256510_at_tscm.com>
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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=20
>diode detector that monitors 398.5-400 MHz (1.5=20
>MHz wide), you build a simple 8 pole bandpass=20
>filter that contains 4 high pass, and then 4 low=20
>pass filters, or better yet, 8 high pass=20
>cavities, and 8 low pass cavities. This will=20
>knock down even the most powerful FM and TV=20
>broadcast signals so you can pass the signal to=20
>a LNA and then into a diode, and then sum the=20
>voltage that comes out of this diode with a=20
>output of a matching diode (reference=20
>diode/amp), and apply the output of the summing=20
>circuit to another amplifier that drives a=20
>simple 30 dB or larger column of LED's.
>
>The goal here is to take a hypothetical FM radio=20
>station that is presenting -20 dBm on site, and=20
>to knock it down below -174 dB. This means that=20
>we want to kill everything outside of the band=20
>by 154 dB, but I know some engineers who use=20
>only 40 db, others use 120 dB, and some even use=20
>400 dB as their design goals for TSCM and SIGINT=20
>bandpass filters. An example is the 60 cycle=20
>high pass filters that I make, they knock down=20
>60 Hz by 400 dB, so you can plug one end into a=20
>480 volt circuit, and the other end into the RF=20
>input of your spectrum analyzer or oscilloscope.=20
>We als comb out all the harmonics of the line=20
>voltage and knock down any nastiness that might=20
>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=20
>gate the sampling side of the post filter=20
>detectors. Simply put, when the 3 GHz diode=20
>captures energy on the log scale that exceeds a=20
>certain level (say -50 dB) that it uses to gate=20
>all of the output of the diodes assigned to each of the five bands of inte=
rest.
>
>Lets assume (grin) that I have a stack of=20
>Astro-Med Everest analog chart recorders in a=20
>rack. Each chart recorder is capable of 32=20
>analog channels each, and I gang or slave 4 of=20
>them together so that I have 128 virtual=20
>channels. I built a trigger circuit for each=20
>chart recorder that monitors a wide swath of RF=20
>spectrum, so we have the first recorder=20
>listening and reacting to 100 Hz to 1.8 GHz, the=20
>second 1 .5 to 18 GHz, the third from 12 GHz to=20
>30 GHz, and so on. When the broadband energy at=20
>say 500 MHz goes over -50 dB it triggers the=20
>chart recorder to start moving the paper for 5=20
>seconds, but looking at the chart you can see=20
>which band of the 32 the energy appears in. The=20
>tricky part is that each of the 32 channels have=20
>to have thier own filter and LNA, then diode,=20
>and interface for the chart recorder.
>
>Maximum range requires first maximum filtration,=20
>folwed by maximim amplification, folwed by the=20
>most sensitive detection diodes you can find,=20
>then further amplification to drive whatever is=20
>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=20
>the bugs appear, and this is a tricky=20
>proposition. You have to break the bands into=20
>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=20
>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=20
>should see in the area you will be sweeping, and=20
>then to bring along filters to knock down things=20
>that may be making your measurements "dirty".=20
>Personally, I carry a fixed 8 pole band reject=20
>filter for every TV station allocation, plus a=20
>FM band reject filters (more then one), and=20
>filters to knock out the paging bands.
>
>You know what your going to need by looking up=20
>FCC allocations for everything within five=20
>miles, but 75 miles for any broadcast (AM, FM,=20
>TV) channels. If I am performing a sweep in=20
>Needham, MA there are huge antenna farms for FM=20
>and TV broadcasting, so every inch of the office=20
>that I am sweep in getting hammered with high=20
>levels of RF. Not only do I have to know down=20
>the main carrier, but even the 15th harmonic of=20
>the main carrier is radiating off of structural=20
>steel and causing massive headaches. This means=20
>that I have to use a filter that kills not only=20
>the main carrier, but also filters that kill=20
>every harmonic out to the 20th or so carriers=20
>that is going to tilt or saturate the sweep gear.
>
>Once you get above 2 GHz you can use one of more=20
>YIG filters to help you do this, but the low=20
>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=20
>with a control circuit. It has been done before=20
>with good results. Basically, you take a six=20
>pole switch, and hand a dedicated filter,=20
>amplifier, and antenna off each of the six input connectors.
>
>One key is not to apply power to any of the six=20
>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=20
>devices in a vehicle is to use a gang of generic=20
>diode detector such as the CPM-700, add your own=20
>bandpass filters for each of the "phone to=20
>tower" frequencies, and follow it by a small 20=20
>dB preamplier, or "convert" the RF probes.
>
>
>To convert a probe you unscrew the probe body,=20
>unscrew the antenna, unsolder the screw that the=20
>antenna attached to and install an SMA female=20
>connector. Next visit your local hardware store=20
>and purchase some one inch tubing and fittings.=20
>Mount the SMA/probe assembly into the end cap,=20
>and solder the ground of the probe to the copper=20
>as well. Then slide the whole thing into a=20
>length of copper tubing that it roughly half the=20
>wavelength of the frequency of interest. The=20
>other end of the copper tube is a Male BNC=20
>connector so that you can merely plug the tube=20
>into the BNC connector of the CPM-700
>
>Next fabricate an antenna out of a length of=20
>copper clad welding wire and terminate it on a=20
>female SMA connector so that you have a high performance dipole antenna.
>
>Inside the copper tubing you will want to add a=20
>small 8 pole bandpass filter and kill off the=20
>tower-to-base and trunking frequencies by at=20
>least 80 dB befoe you go into the probes amplifer.
>
>The simplest this is to make a standalone box=20
>the size of a carton of cigarettes into which=20
>the phone-to-tower antenna where mounted, then=20
>feed into separate filters for each band (8=20
>poles each), and then take the output and apply=20
>it to dedicated amps all built into the same case.
>
>The box would best be a brass block that you=20
>drill out with cavities for each of the filter=20
>poles, and then a large cavity for the=20
>amplifiers. You could go with an interdigital=20
>filters for each of the bands, but you really do=20
>not need to displace much heat, and the physical=20
>size of the 800 MHz band will be unpleasantly=20
>large and heavy. I would (and have) leaned=20
>toward a simple LC filters for a project like=20
>this and simply add a lot of pole to keep the=20
>skirts of the filter as sharp as possible.
>
>Companies that make filters for the cell phones=20
>themselves also make very small duplexer=20
>circuits that you can use in reverse, but they=20
>tend not to knock down the signals by more then=20
>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=20
>built filters, and their use in TSCM.
>
>I am also an even bigger fan of using big-ass=20
>(excuse my French) wide band antennas to suck in as much energy as possibl=
e.
>
>
>>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
>>=B4ve 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 prisone=
rs,
>and we give no quarter. Our goal is to simply, and completely stop the spy=
.
>--------------------------------------------------------------------------=
--------------------------
>
>
>
--=====================_122727671==.ALT
Content-Type: text/html; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
<html>
<body>
<font size=3D3>Proving once again, theres no such thing as a free lunch
:-D.<br><br>
At 15:56 2/19/2007, you wrote:<br><br>
<blockquote type=3Dcite class=3Dcite cite=3D"">Check out:
<a href=3D"
http://www.tscm.com/TSCM101noise.html" eudora=3D"autourl">
http://www.tscm.com/TSCM101noise.html</a><br><br>
Response as follows:<br><br>
<br><br>
At 09:52 AM 2/15/2007, cont..._at_yahoo.co.uk wrote:<br><br>
<br>
<blockquote type=3Dcite class=3Dcite cite=3D"">.<br><br>
<br>
Wideband (AM) detectors are very popular...because they are easy to<br>
use<br>
and relatively cheap.<br><br>
...the problem is that they are not very sensitive.<br>
...another problem is that they cant separate signals at different<br>
frequencies.<br><br>
<br>
Question<br>
--------------<br><br>
<br>
-/////////////////////////-<br><br>
How many times more sensitive would a wideband detector become<br>
if it had additional filters in the frontend ?<br><br>
-/////////////////////////-<br>
</blockquote><br><br>
It can be hundreds of thousands, or even millions of times more
sensitive.<br><br>
<br>
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.<br><br>
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.<br><br>
<br><br>
<blockquote type=3Dcite class=3Dcite cite=3D"">For example the detector doe=
s 1
Mhz to 3000 Mhz<br><br>
Now i will devide that into 5 bands...using 5 separate filters :<br><br>
a) 1-80 Mhz<br>
b) 80-200 Mhz<br>
c) 200-520 Mhz<br>
d) 520-1000 Mhz<br>
e) 1000-3000 Mhz<br><br>
<br>
Ofcourse when using one of above filters... it seems very logical<br>
that<br>
the maximal detection range becomes much better then without a
filter.<br><br>
I suppose that is caused by below factors :</blockquote><br><br>
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.<br><br>
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.<br><br>
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)<br><br>
<br><br>
<blockquote type=3Dcite class=3Dcite cite=3D"">1) The environmental noisefl=
oor
is much lower so a signal would stick<br>
out much easier.</blockquote><br><br>
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.<br><br>
<br><br>
<blockquote type=3Dcite class=3Dcite cite=3D"">2) Bandwidth in the receiver=
is
directly related to noise.<br>
</blockquote><br>
Yes, it is all part of the KTB formula, with B being that which we can
control the most.<br><br>
<br><br>
<blockquote type=3Dcite class=3Dcite cite=3D"">Offcourse the adantage of
filtering would also be that :<br><br>
1) The wanted signal is not masked (overpowered) by other out of
band<br>
signals</blockquote><br><br>
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.<br><br>
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.<br><br>
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.<br><br>
<br><br>
<blockquote type=3Dcite class=3Dcite cite=3D"">2) You have an indication of=
the
frequency-band of the found signal<br><br>
...etc</blockquote><br><br>
Simple sample and hold circuit that triggers a flip-flop
circuit.<br><br>
<br><br>
<blockquote type=3Dcite class=3Dcite cite=3D"">The mentioned unit lets you
either switch to each filter by hand...but<br>
it can also go into a so called "Scanning-Filter
mode"<br><br>
Filter-scanning mode will switch between filters like this :<br><br>
Filter 1 >> Filter 2 >> Filter 3
>> Filter 4 >> Filter 5 >> NO-<br>
Filter ......and over again.</blockquote><br><br>
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.<br><br>
One key is not to apply power to any of the six amplifiers other then the
one you are using at the time.<br><br>
<br>
<blockquote type=3Dcite class=3Dcite cite=3D"">That NO/filter seems to be a
good idea in practice...to also receive<br>
out of band signals<br>
not covered by the filters (in this case below 1 mhz and above 3000<br>
mhz)<br><br>
The scanning-speed has still to be determined...it depends on the<br>
shortest duration<br>
of possible digital signals (pulses) that you want to detect :<br><br>
...if it is to slow you might miss a short on-time signal (non<br>
continious bursts)<br>
...if it is to fast to fast there is no time to validate the signal<br>
(continious but very-short pulses)</blockquote><br><br>
<br>
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.<br><br>
<br>
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<br><br>
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.<br><br>
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.<br><br>
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.<br><br>
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.<br><br>
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.<br><br>
<br><br>
<blockquote type=3Dcite class=3Dcite cite=3D"">Forget the scanning speed...=
lets
talk just about sensitivity-<br>
improvement when using filters.</blockquote><br><br>
I am a *** BIG *** fan of carefully designed and built filters, and their
use in TSCM.<br><br>
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.<br><br>
<br>
<blockquote type=3Dcite class=3Dcite cite=3D"">I know that its a difficult
question...but lets say i have to write an<br>
article or propaganda<br>
for a unit with those 5 switchable filters...and i have to say how<br>
many times more sensitive<br>
a Wideband(AM)-detector with 5 filters like above is...compared to
the<br>
same one without filters<br><br>
I suppose that the smaller the filter-bandwidth the more
"sensitive"<br>
so lets simplefy the question<br>
and lets assume that the 5 used filters all have the same bandwidth
so<br>
the whole range is equally<br>
devided<br><br>
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How many times more sensitivity or range would you get ?<br>
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<br>
<br>
Thanks !<br><br>
<br>
Contranl<br><br>
<br><br>
Remark...i dont understand why not one single manufacturer of (AM)<br>
wideband-detectors<br>
&nb=
sp;
has not incorperated some filters...they are not<br>
difficult to produce<br>
&nb=
sp;
and not expensive...but greatly improves them.<br><br>
<br>
Please do not respond (in private) to my (old) Yahoo-emailadress...i<br>
=B4ve lost the password<br>
and after weeks of correspondence they dont want to give it...Yahoo<br>
SUCKS !</blockquote><br>
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Received on Sat Mar 02 2024 - 00:57:15 CST