Paul,
I too have looked at consumer grade equipment with an eye towards EMI
measurement. I have the ICOM R7000 (modified) and R7100, as well as Yupiteru
7100 and AOR AR8000 handheld scanners, plus the usual amateur radio handheld
transceivers, and I have made some use of all of these one way or another. Each
has its shortcomings. None of these receivers meet the bandwidth and amplitude
accuracy requirements for EMI test equipment, but this is not a concern if
results are only used for engineering decisions.
Frequency coverage on the ICOM 7000 and 7100 is normally 25 MHz to 1999.99 MHz.
The R7000 has a gap from 999.99 to 1025 MHz. Coverage on the Yupiteru scanner is
nominally 500 KHz through 1.65 GHz, while the AR8000 has a nominal coverage of
500 KHz through 1.9 GHz. However, the AOR's sensitivity drops dramatically past
about 1.4 GHz. I have not measured the Yupiteru's sensitivity above 1 GHz.
Filter performance varies. The Yupiteru 7100 (mine, anyway) has poor ultimate
rejection, which means strong nearby signals will affect the reading where a
better filter would eliminate them. The AOR AR8000 seems much better in this
respect. Casual operation convinces me the ICOM R7100 has the best filters of
the lot. By the way, one must use WFM mode in all of these receivers to get
that bandwidth. AM mode gives about 16 KHz in the Yupiteru, about 6 KHz in the
AR8000 and 6 or 16 KHz (wide AM or AM) in the ICOM R7000 and 6 or 3 KHz in the
ICOM R7100 (AM or narrow AM).
None of these receivers are ready for conducted tests (0.15 - 30 MHz). The two
handheld scanners may be programmed lower than the 500 KHz service rating, but
sensitivity and internal synthesizer noise become issues. An up-converter may
be used with the ICOM receivers; for a couple of years an internal converter for
the R7000 was marketed by a British firm, and I have installed one in my R7000.
This converter -- and most others you can buy -- requires modifications to
reduce low-frequency roll-off. I increased coupling capacitor value, and
interchanged DBM IF and RF port connections to extend low frequency input
sensitivity.
S-meter calibration is relatively good on the ICOM receivers, for a
communications receiver. I find it varies about +/- 4 dB across the rated
frequency coverage. My up-converter introduces about 6 dB of loss. It is
possible to prepare a calibration table which allows turning S-meter readings
into more conventional units, but the meters themselves are hard to read. I
have not evaluated the receiver digital amplitude output on the R7100, but I
have seen an example posted as a graphics file on CompuServe and it would appear
linearity is not bad. Calibration accuracy will still vary depending on which
tuner is used.
The handheld scanners offer a bar-graph signal strength display which seems of
limited use. I have noted scales of from 2 to 8 dB per division depending on
the scanner. A unit such as the AOR AR8000 may offer a digital signal strength
readout which will probably be more accurate than that.
However, none of these receivers are designed with the amplitude headroom needed
for a precision measuring system. Since they do not use tuned preselectors, I
would expect strong ambients to be a factor, especially if the AGC were
disabled. In this case, I'd expect RF or IF saturation, self-bias (with desense)
and IM products due to high gain before the detector. Under these circumstances
it would probably not be useful to add a quasi-peak detector, as with the AGC
engaged, IF amplitude will be more logarithmic than linear, which makes QP
detection almost a time-weighted geometric mean than an average.
If I had a choice, I'd want an AOR AR5000. This receiver not only has computer
controlled everything at a reasonable price -- about $2000 US __ but offers
independent filter selection and at least the possibility that a custom filter
could (if needed) be installed. Its frequency coverage is also excellent, going
well past 2 GHz.
These radios also have something lacking on spectrum analyzers, a BFO. This is
surprisingly useful for probing and identifying sources of emissions.
Perhaps others can chime in here with their own experiences, good or bad, with
using consumer grade radio receivers as test adjuncts. I will say that so far I
have not seen any such radio suitable to be relied upon as a sole means of
measurement even for engineering purposes
Regards,
Cortland
______________________________ Reply Separator _________________________________
Subject: LOW COST mesurement equipment. (Was Shiep rules)
Author: Paul Rampelbergh <[email protected]> at internet
List-Post: [email protected]
Date: 1/1/97 23:58
Hello everybody in this new year.
The most difficilt part for me to this situation is to remind me I have
to type 1997 and not 1996 (no, not all is automated)!
Let me open a new subject item concentrating on the CHEAP equipment
question for ROUGH pre-compliance limit testing before approved lab tests.
If you agree, I like to concentrate the whole subject on the ECONOMICAL
aspect.
I'll quit on the Cenelec/BITP constrains in this NEW subject, I think my
opignion and bad experiances where clear enough.
I'll still "work" on it, you bet, and will comme back on it when new
items appear under the old subject name.
SUBJECT:
Just to state a few of the general LOW COST items:
- can anybody sugest cheap data, test and calibration equipment (other
than the standard ones used in general complying with the more strict
EMC regulations like for instance the CISP 16)
- has anybody have experience with that "other than the standard"
test equipment
- what are the recomendations when using this type of equipment
- what has to be modified (eventually) to make it a reasonable equipment
- what has to be added to the equipment to ensure personel and
equipment protection (I'm thiking of a LISN for instance)
- how can I build equipment like antenna's
- how can I calibrate (?) rougly all those devices?
- How mutch due to the deviations from standard and special purpose
equipment do I have to take in account (approx.)
- ...... OPEN ......
Let me start the subject:
1. I use a NEAR field probe during the design phase of the project sold
by Credence Technologies, Inc Santa Cruz, CA (free advertising!),
Greenwood Electronic (UK) and somebody in the Netherlands (but more
expensive at the first glance).
I have very good experiance with this probe, efficient pinpointing
the problem areas.
It allows at least to:
- detect the radiation area's on the Circuit board and other parts
- gives valuable indications of improvements to the design
- cost +/- $US 200 if I recall correctly
- higly recommended (remark: I have NO financial or other interests).
2. I heard somebody using an electrostatic gas lichter to simulate
"some" static discharges.
Its modified with a ground wire and front protection cap removed.
I'll find it a geneous idee ( a few $$). Who has experiance with it?
3. A scanner as a test receiver.
The subject is open.
I have a AOR AR 8000 scanner ranging for 100kHz to 1950 MHz, can be
fully controlled by a external PC: scan freq., mode, bandwith,
attenuator and a lot more.
Maintenance manual with drawing can be obtained.
Initil modifications required:
- remove internal antenna used for braodcast (remove diode)
- plastic outside box has to be shielded with conducting paint or by
putting the whole in a metalic enclosure. Is currently under test.
Anybody some more inputs on this subject?
4. It seems there is'nt a problem to construct Log-periodic antenna's.
Construction data is available.
Do not require special items as ballun's, etc.
It seems more difficult to have data and to build Bi-conical or
simular antenna's. Anybody can help?
How good can avail calibrations data be used when the antenna is copied?
Who can provide this data and info?
Best regards
--
Paul Rampelbergh
Wezembeek-Oppem (Belgium)
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