[RFI] Why we badly need "party line" materials for all hams
w1rfi at arrl.org
Mon Jul 19 19:08:15 EDT 2004
I don't think it is as bad as you describe, Tom. While I agree that a step attenuator can do exactly what you say it can, I would bet that less than 5% of hams have one and know how to use it correctly. I will add your suggestion to the documentation I have describing how to make measurements and see if we can gather such data. But in the meantime, if all I can get is S meter data, I will use it. S9+ noise to a mobile whip is pretty clearly interference, so it still has value.
Oh, and there is one flaw in the test method; with many mobile antennas, the minimum signal is not enough to move the S meter, so the method may tend to under-estimate the relative field strength.
Ed Hare, W1RFI
ARRL Laboratory Manager
225 Main St
Newington, CT 06013
Internet: W1RFI at arrl.org
Member: ASC C63 EMC Committee
Chairman: Subcommittee 5, Immunity
Chairman: Ad hoc BPL Working Group
Member: IEEE SCC-28 RF Safety
Member: Society of Automotive Engineers EMC/EMR Committee
> -----Original Message-----
> From: Tom Rauch [mailto:w8ji at contesting.com]
> Sent: Monday, July 19, 2004 6:25 PM
> To: Hare,Ed, W1RFI; rfi at contesting.com
> Subject: Re: [RFI] Why we badly need "party line" materials
> for all hams
> Few hams have the resources to collect their data in any
> other terms, Tom. I am not sure what to do about that. >>>
> Almost any ham has the ability to provide useful data. All
> he has to do is:
> 1.) Use a step attenuator to calibrate the dB change in his
> particular S meter.
> 2.) Drive out away from poles, and record noise levels or
> weakest readable signal levels
> 3.) Go into the BPL area, and note the change and provide it
> in dB for a given receiver bandwidth.
> S-units are useless.
> <<One one hand, gathering some information about the level
> of pre- and post-BPL noise is important, and if all we can
> get is S meter readings, then that is better than no data at
> all. Although the S meter has not been adopted world-wide
> as a standard, IARU Region 1 has adopted an S meter standard
> that uses 50 uV for S9, 6 dB per S unit, so those readings
> to have some standards-based traceability.>>>>
> Because the IARU in region 1 says "all S-meters equal X at
> S-9, and are X dB per S unit it suddenly means S meters are
> useful? I don't think so. It's pretty well established most
> S meters are way out of whack for anything meaningful.
> Not only that, no one has any idea what the antenna loss is
> in the mobile.
> The problems would largely disappear and the data would be
> useful if people just followed a three simple steps. They
> can record the data in useless S-units, but give the
> results in meaningful terms like "the BPL system increased
> background noise 22dB at 9 meters from the line using a
> typical mobile station with XYZ for equipment and antennas".
> Presenting data in S-units using a system with unknown
> antenna efficiency, unknown absolute levels, and unknown
> change per S unit makes us look pretty foolish.
> Why don't we tell everyone how to do a calibration chart, or
> find people to offer those services for free for anyone
> wanting to present data?
> 73 Tom
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