Thanks for the post, Paul. I'm not trying to mis-state your position, believe
me! It's interesting to see what you have to do in order to make your scanner
do the job for you.
Yes, I found the frequency accuracy of even handheld scanners superior to the HP
spectrum analyzers I was using. This is a concern only when dealing with
someone who doesn't know they can be expected to differ.
On antennas: Almost any antenna you can build will do the job for you. Those
concerned with predicting antenna factor from construction need precisely built
baluns and elements - but for ordinary measurement, all you need is to calibrate
whatever you've built -- assuming it's efficient enough to detect signals below
the limit, and that's not hard.
Have you seen the antennas now being marketed as 30-1000 MHz antennas? they
consist of multiple (three, I think) "bow-tie" antennas of sheet metal,
assembled onto a common feed point. The longest one is actually resonant about
70 MHz, the next appears to be resonant about 100, and the smallest perhaps at
200, but the shape of the plates insures a gently changing impedance versus
frequency.
As for calibration, I think the most elegant (and acceptable, BTW) way is the
three-antenna method, where one measures the site attenuation between three
antennas, one pair at a time. This produces a data set contacting all antenna
factors, which may be extracted from three simultaneous equations. This _does_
call for three antennas, but you can borrow two of them.
Cheers,
Cortland
====================== Original Message Follows ====================
>> Date: 12-Feb-97 01:19:09 MsgID: 1044-129130 ToID: 72146,373
From: Paul Rampelbergh >INTERNET:rampelberg...@infoboard.be
Subj: frequency scanners & low cost equipment
Chrg: $0.00 Imp: Norm Sens: Std Receipt: No Part 1 of 1
Hello,
Sorry Cortland, I do not allow you to state a position witch I
didn't mention subject purpose of utilization range of scanners.
The purpose of the use of a scanner was and is for PRE-COMPLIANCE
tests in order to find out where the problem areas are before an
expensive and complete compliance test.
I talk only about the AR8000 from AOR (non commercial advertising).
I don't want to open the discussion on the different point of views
we had before, but I like to state that the new scanners have good
performances as long as you don't want to measure the exact
amounts you are below the rule.
Linearity for instance has no importance as long as you know the
indication below which you have to stay.
Anyhow, I think the first step to do in order to find out if the
equipment is susceptible to reach compliance, is to have measurements
done in not ideal conditions (small shielded enclosure for instance).
NOTE: The people who can afford a anechoic chamber don't have to
bother about scanners. Its a poor mans solution anyhow!
1. So as you are not, for the first instance, in ideal conditions you
gather the disturbing signal frequencies.
For this application, the stability and accuracy of a scanner
SUPERIOR to older well know expensive equipment's like the Rohde
& Schwatz generator SMDA - BN 41314, due to the actual technology
(phase locked loops & crystal).
NOTE: Its also, in most of the cases, possible to deduct those freq.
from the design but its good to measure it with the scanner just to make
sure you get them programmed in for field tests.
Modern scanners can memorize the frequencies of interest manually
or automatically.
2. Now once you have those frequencies you have to calibrate your
receiver (scanner) and there there are some problems.
2.1. Shielding of the receiver is insufficient. Solution: metallic
shielding spray or other mechanical means.
2.2. the front end of the receiver do not need pre-tuning,
if you have a strong signal close to the frequency you need to measure,
you MAY need an external additional input filter to avoid
intermodulation.
2.3. You need calibration of the interesting frequencies, the other
ones are of NO interest.
This is the most difficult part, you need a tests generator, I have
the one mentioned above but it needs probably recalibration.
3. The antenna's.
Who can tell me how and where I can get the required data to build
a Bi-connical antenna for 30 - 200 Mhz frequencies.
How much can the calibration deviate from one design to another?
The log-periodical antenna is no problem to build, you can find
data in the ARRL handbook. Its low cost, use of copper water
pipes should do it.
Inputs for more data?
antenna
4. Now you are able to go to the free air, smell some good cold whether,
an measure the previously obtained disturbing frequencies.
I was unable to do this due to the stubborn position of our
local authorities, not to mention the IBPT (=FCC).
--------------------------------------------------------
To come back on the position of our local authorities.
--------------------------------------------------------
The actual law in Belgium do not allow to have (even if not used)
a general converage receiver (a scanner is the sensible point).
By the way, the scanner I purchased in the Netherlands (no law
restriction) do have the FULL freq. range including cellular phone.
Surrounding country's do allow them!
In Belgium the concern is that you may be able to listen to the police.
I don't know, but I don't think outlaws really take care of the law!
The police (and other) equipment who has to be coded and protected,
that's the only way out.
Now since that discussion with the authorities they claim spectrum
analyzers, measurement receivers, test generators, etc..
fall in the OUTLAWED range, you have a speaker on them or you are
able listen and to transmit!
Good fellows of BIPT.
Do you think that other county's know what they are doing?
According to our superior BIPT people, NO.
How is it possible that for EMC you can, as a manufacturer or
as a European representative, do self certification?
For telecom equipment you are to stupid to do so, forget it.
You need to have a typical Belgium compliance sticking to Belgium
typical rules and performed by who?
Our magnificent BIPT authorities of course who give it to BELCOMLAB.
NOTE: The manager of the security division of the Ministry of
Economic affairs states for scanners used in EMC context:
According to the Belgium laws the general coverage equipment used as
a test equipment is not under control of the IBPT and may be used
as long as it is CE approved.
The CE approval is only required, as you know, for equipment you
sell and not for equipment under test.
This people are the once who accepted the EMC proposal without the
collaboration of our majesty the BIPT.
I hope he will survive the BIPT management autocratic, dictatorial,
monopolistic bureaucrats and irresponsible authority attacks.
I Quit on the subject for now.
The BIPT is proposing a modifications to Belgium laws for telecom, I'm
wondering how good they will recover on the EMC laws and try to
impose once again their monopolistic position.
==== STOP, STOP, STOP, STOP, STOP, STOP, STOP, STOP, STOP, STOP ====
Now once for ALL Cortland Richmond, STOP.
==== STOP, STOP, STOP, STOP, STOP, STOP, STOP, STOP, STOP, STOP ====
The dangerous people is not the expensive nor the low price test
equipment owners, but the outlaws as they do NOT respect any Law.
Using comments of telephone industry representatives concern is pure
intentional discrediting talk that doesn't make any sense.
You can use some expensive test equipment as well in outlaw conditions.
In fact, you are in a professional context of experienced people
who can design telephone decoders. So quit please and let other people
share their experience on EMC low cost equipment.
Cortland Richmond you never described your job function, are you
involved with similar authorities, rules making people or do you have
any financial advantage by discrediting possible competition low
cost equipment's?
re- Aaargh.
===================================================================
I like to continue the discussion on low cost equipment without ALL
the nothing to do with it considerations.
Lets find out how good, bad or limiting this kind of low cost equipment
is, lets look in which context it can be used or lets find out its
useful area.
I don't like to limit mail exchange to scanner type equipment,
but rather to ALL kinds of low cost devices.
I'm thinking for instance on a gas lighter for ESD, etc..
What are the results?
That would be at least a constructive input.
Lets look at home made antenna's, test cell's and other EMC test equipment.
For sure it will cost less than old equipment which anyhow will
require outside certification.
I don't say that we don't need outdoor certification with more
sophisticated equipment, but at least lets try to find a possible
way around or at least reduce cost due to a one time certification pass.
Don't mention publications, I purshased an promissing book "Handbook
of Antennas for EMC by Thereza Macnamara". Nice expensive and purelly
of no use. Its a theoritical consideration not covering the actual
used antennas.
So I sugest to remove book recomandations from those discutions and
have instead more practical designs and considerations.
I'm sure I'm not the only one who like to limit cost for EMC.
--
Paul Rampelbergh
Wezembeek-Oppem (Belgium)
-------------------------
**Primary Recipient:
ieee pstc list INTERNET:emc-p...@ieee.org
====================== End of Original Message =====================
