Re: [TSCM-L] Re: Wideband (AM) detectors improvement using filters ?

From: James Brown <epau..._at_yahoo.com>
Date: Mon, 19 Feb 2007 19:40:33 -0800 (PST)

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From: cont..._at_yahoo.co.uk
To: "TSCM-L Professionals List" <TSCM-..._at_googlegroups.com>
Subject: Wideband (AM) detectors improvement using filters ?
Date: Thu, 15 Feb 2007 06:52:34 -0800
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.


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 ?

-/////////////////////////-



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 :


1) The environmental noisefloor is much lower so a signal would stick
out much easier.

2) Bandwidth in the receiver is directly related to noise.


Offcourse the adantage of filtering would also be that :

1) The wanted signal is not masked (overpowered) by other out of band
signals

2) You have an indication of the frequency-band of the found signal

...etc


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.

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)

Forget the scanning speed...lets talk just about sensitivity-
improvement when using filters.

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

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How many times more sensitivity or range would you get ?
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---------


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 !

Received on Sat Mar 02 2024 - 00:57:15 CST