[aprssig] Why is my AvMap G6 flaky?
dave at g8kbv.demon.co.uk
Fri Jan 4 05:23:51 EST 2013
On 2 Jan 2013 at 20:00, Ron Stordahl, AE5E wrote:
> Wouldn't this electrical noise make the AM broadcast band
> nearly useless? And if so how would this get by the
> Ron, AE5E
< big snip >
The EMC emission tests, are only designed to protect intended (local
area) broadcast signals, who's levels are several 10's of dB greater than
anything we might be interested in.
It's relatively easy too, to selectivly filter something, so it scrapes
through a test.
Then, there is the "Technical Construction File" route to passing a test.
Vehicle system susceptability/immunity (call it whatever, but EMC the
other way round) is rigerously designed for and tested, to *Very* high
levels (100's of V/m across the spectrum) so it is unlikely even a modern
Hybrid would falter or ever twitch at the sort of "normal" level RF we
might genereate in a vehicle with regular Off the Shelf commercial Ham
Much of this I've seen first hand, visiting Automotive EMC facilities,
commisioning and supporting their EMC test equipment, especialy the multi
kW amps they use. Unless you have a free 3-phase feed (63A/phase at
least) in the shack, you won't want one, as they tend to be under 20%
efficent, on a good day!.
The emissions test receivers/analyzers also are not as sensitive as a
"communications" grade RX, but they are stable accurate and calibrated.
That, and knowing the feder cable losses vs frequency, plus the measuring
antenna performance (from indipendant calibration) also how the chamber
or OATS behaves (Open Area Test Site) gives them a good confidence level
when measuring emission levels.
However, the nature of some emissions, beeing very wide band and very
short duration (narrow pulse trains) can "fool" the RX's into recording a
lower level, than is actualy being radiated. There are test procedures
to detect such phenominon, but they take time, and time is $ etc.
However, all that pales into insignificance, once a local mechanic has
had their hands on it, as there are as yet, no requirements to re-test a
vehicle after any service (or street modification) works are done. Yet?
It's dificult enough for Trafic Cops to measure tail pipe noise levels if
they suspect something is "too" loud, imagine them carting arround RF
analyzers/receivers and test antenna's? (plus exhaust gas analyzers and
Happy New Year All.
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