Ethernet noise is not totally broadband in nature. There are pockets of
high BB emissions, pockets of very little noise with frequency, and then
more pockets of noise as you tune around. All changes with frequency, and
therefore, not "really" BB. It tends to sound a bit more like a switcher
without the 60 Hz modulation with peaks at multiples of the switching
frequency. Any kind of digitally derived noise will exhibit some sort of
detectable digital modulation. If your noise has no peaks and valleys with
changing frequencies or no modulation, it truly is broadbanded and likely
from the PAs of you close-by broadcasters.
Dave WØLEV
On Wed, Dec 22, 2021 at 9:39 PM <nlsa@nlsa.com> wrote:
> Dear Lloyd & others,
> I appreciate the several replies on and off-list. After building my EME
> system from scratch over the past seven years, I would prefer that the
> noise problem be something I can solve. Whether that's the case remains to
> be seen.
> In my online reading, I have seen plenty of reference to EMI from Ethernet
> cabling. What does Ethernet EMI look like? I wonder whether it resembles
> "my" noise. There are houses, including my own, in my line-of-sight to the
> TV tower.
> 73,
> W9IP
>
> -----Original Message-----
> From: RFI <rfi-bounces+nlsa=nlsa.com@contesting.com> On Behalf Of Lloyd -
> N9LB
> Sent: Wednesday, December 22, 2021 2:33 PM
> To: 'RFI' <rfi@contesting.com>
> Subject: Re: [RFI] Strong RFI on 2m
>
> We had a full-power 50 KW Channel 3 VHF TV station here in Madison WI
> since the 1950s.
> The transmitter was an all-tube RCA TT-50, worked well, reliable, and
> spectrally very clean.
> Then about 30 years ago, an All Solid State Harris Transmitter was
> installed.
> That solid state transmitter totally destroyed 6m use for miles around.
> ( The old RCA was used on Tuesdays only, the Solid State was run the other
> 6 days each week. ) The local ham community complained bitterly about it to
> the station and to the FCC.
> An FCC Field Engineer from Chicago came to Madison and made measurements.
> He found:
> 1. Wideband noise was being generated by the Solid State transmitter, not
> present with the tube rig.
> 2. The noise was "within spectral limits" so the TV station was operating
> legally. Too bad for the hams.
>
> Years later, with the transition to digital, a change from channel 3 to
> channel 50 was made and no more RFI.
>
> 73,
>
> Lloyd - N9LB
> ( Former Transmitter Supervisor for that channel 3 transmitter site back
> when it was still all vacuum tube. )
>
> -----Original Message-----
> From: RFI [mailto:rfi-bounces+lloydberg=tds.net@contesting.com] On Behalf
> Of David Eckhardt
> Sent: Wednesday, December 22, 2021 12:48 PM
> To: nlsa@nlsa.com
> Cc: RFI <rfi@contesting.com>
> Subject: Re: [RFI] Strong RFI on 2m
>
> I suspect what you are experiencing is broadband noise from solid state
> transmitter PAs. During the days of vacuum tube amplifiers for commercial
> broadcast this was much less of a problem. However, the newer solid state
> PAs produce *much* more broadband noise than their older vacuum tube
> counterparts. There likely isn't much you can do about it other than not
> point your antenna(s) at the source(s). The noise is there and all the
> filtering in the world is not going to eliminate it. Not what you want to
> read for an EME setup.
>
> With that many sources, both FM and TV, I doubt you would be able to
> convince all of them to install aggressive BPFs on their outputs. Best
> case might be only one or two of the broadcasters are responsible, but I
> doubt you should be so lucky.
>
> Dave - WØLEV
>
> On Wed, Dec 22, 2021 at 3:18 PM <nlsa@nlsa.com> wrote:
>
> > Dear friends,
> >
> > I have recently commissioned my 4-yagi 2m EME system. To my unhappy
> > surprise, I find strong RFI in the direction of a large commercial
> > broadcast tower 3.5 miles away. The noise is uniform across my 96-kHz
> > passband, as if the noise floor has been raised 20-30 dB. I don't
> > detect any modulation or other structure to the noise; it is wideband
> > and constant. It affects my RX in other directions via antenna
> > sidelobes.
> >
> > I have discounted fundamental overload to my system by placing a
> > 2-cavity bandpass filter in the RX line. It should attenuate
> > everything outside the 2m band by at least 40 dB and yet there is no
> > effect on the RFI noise. I conclude that the noise is "real," in
> > other words not an artifact of my RX chain.
> >
> > Questions:
> >
> > * Should I expect modulation of some sort on spurious emissions
> from
> > TV or FM broadcast stations? (I have five TV and five FM transmitters
> > within a 5-mile radius).
> > * Other than the usual direction-finding, what else might I try to
> > investigate in order to identify the source?
> >
> > Thanks for any suggestions -
> >
> > Mike, W9IP
> >
> >
> >
> > _______________________________________________
> > RFI mailing list
> > RFI@contesting.com
> > http://lists.contesting.com/mailman/listinfo/rfi
> >
>
>
> --
> *Dave - WØLEV*
> *Just Let Darwin Work*
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--
*Dave - WØLEV*
*Just Let Darwin Work*
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