----- Original Message -----
From: "Tom Rauch" <firstname.lastname@example.org>
To: "Jim P" <email@example.com>; <firstname.lastname@example.org>; "Fred Stevens K2FRD"
Sent: Thursday, August 10, 2006 5:16 AM
Subject: [BULK] Re: [RFI] Ambient Noise Levels
> > It was 'the sun'.
> The sun certainly can cause noise that we hear above 10-15
> MHz or so, as we can also hear accumulated noise from other
The noise I heard didn't occur but about three times that I recall
and that was weeks to months apart. (After the 1st - or was it the
2nd - time I noticed it I was primed to note the time and observe
the signal strength.)
It was an event that took some 5 to 10 seconds to ramp up,
seemingly waver a bit and decline. I do recall one event that
went on for longer than that then it too 'ramped' (versus
stepped or turned off abruptly) down iin strength.
That one event lasted long enough for me to get to the radio
and then I stood in awe as the signal strength rose and then
died back down, smoothly.
I haven't heard anyone else chime in with the same observation
so I would have to say that no one else either witnessed similar
events (recently?) or chalked it up to other sources and continued
to work DX.
> galactic sources. All it takes is a low terrestrial noise
> level and very low ionospheric attenuation of galactic
> > Fred, I don't but wonder if your noise is due to, by
> > chance, to "static build-up" on your antenna.
> Charge build-up does not cause noise. Charge movement does.
Your claims and assertions stand counter to the expereince
of others, Tom.
A simple GOOGLE search is enough to put this one to rest.
Here's one good write-up here:
Notice his list of references at the bottom of that page too.
> Corona discharge from an antenna in inclement weather gives
> rise to a hissing whining noise that increases in pitch,
Seen all that; been there, done that; got the tee shirt.
SAW it MOST pronounced while driving out west where I
was constantly monitoring an AM radio in the 10 M
> often abruptly disappearing for an instant when a distant
> lightning flash reduces cloud to earth potential. If that
> same charge difference is present without the corona, say
> the antenna has rounded points or does not protrude into the
> air, you hear no noise.
> > you have even a high-valued resistor to ground to
> > preclude any charge accumulation (provide a simple
> > leakage path to earth)?
> That only protects from a charge difference between the
> antenna and earth that might cause something to arc. It has
That was exactly the intention, Tom.
It is the same reason that Radio Shack has a 1 MegOhm
resistor from the chasis to (hopefully) the low side of
the AC line in some of their stuff that can be plumbed
up to an external antenna (provides a rudimentary
> no effect on corona noise as the element discharges into
Hmmm. Still think that is the case after reading the article
> space. The resistor will primarily cure, if there are no
> other dc paths, the "tic tic" or "snap snap" of something
> in the antenna arcing to ground. Nothing else.
Right, and that tic tic is noise as is the broadband hash
that is generated as 'leakage' currents bleed off as corona
into the air.
> It is a good idea to have a dc path of some form to prevent
> equipment damage as some dielectric might punch through. An
> example is antenna tuners. Charges can accumulate in a
> T-network antenna tuner's output capacitor to the point it
This can also cause noise, as surface 'creep' or surface
corona occurs esp. when that 'rate' varies with time (sudden
starts and stops).
> flashes over. That discharge "rings" the coil, and that
> energy can pass through and ruin the detector diodes in the
> directional coupler or even the receiver!
> > I take it you were able to 'kill' the noise by removing
> > the antenna from the radio at which time the the
> > noise level dropped back significantly. (I notice
> > today's rigs employ two levels of 'preamp' as well
> > as several levels of attenuator; I find the preamps
> > generally just contribute additional white noise
> > with little real improvement in S/N ratio
> The noise they "contribute" is very minor. You can test it
Depends of the rig; the little 'rushboxes' like the HTX-100
have so much gain I have to run with the RF gain knob
cranked about half way 'round.
> by terminating the receiver input and turning the preamp on
> and off. I think what you are trying to say is the preamp
> increases the level of signals and noise from the antenna.
Well, that's certainly true; I can get the current noise on
10 Meters to easily read S8 that way.
> At my location in winter using narrow selectivity, I have to
> use preamps. Otherwise I am limited by receiver noise floor.
So, what do the preamps really do besides push the signal
level to the point where the AGC system is always operating
and AGCing on that white noise?
I mean, at the moment I don't believe the so-called 'preamps'
in these radios change the S/N ratio appreciably (as I would
expect a preamp to do) - rather I view preamps as switch-able
preconversion RF (as opposed to IF)) gain stages ... I would
be interested to know if they are really any value at all.
And remember, ANY loss in the feedline to the radio DIRECTLY
adds to the noise figure of the radio. For instance, If the front
end 'preamp' has a 1.0 dB NF amplifier and there is 2.0 dB
of feedline loss your effective NF is 3.0 dB ... so there goes
some of the S/N improvement a REALLY low NF preamp
might have provided.
> This is especially true on 20 meters and higher with
> directional transmit antennas used on receive, or on lower
> bands with dipoles or beverages.
> *2. I have
> > an old Yaesu FT-101EE that has no preamp
> > function and therefore never sounds like a 'rushbox'
> > quite like some of the later products do on the
> > bands.)
> If you can't clearly hear "antenna noise", you don't have
> the best S/N ratio you could have.
The rig doesn't sound like a 'rushbox'. The gain is JUST
sufficient such that front end and/or ambient noise in
the area isn't driving the AGC into operation and the 'noise'
level out of the speaker is reasonable (the FT-101EE
has no squelch control like later ICOMS).
(I have thought for some time that a lot of 'hams' have
to have literally tons of white noise pouring out of a
speaker in order to have some reassurance that
they are receiving something off the air!)
To this end, I think today's hams are 'gain crazy'.
> By the way, shielded loops can't filter noise by virtue of
> the shield. That is a popular but very wrong technical myth.
Why is that?
Its not B/C Tom asserts it?
> They also can't sort good signals from bad noise by virtue
> of "magnetic" or "electric" field response unless the noise
Yes you can; it depends on the mechanisms involved.
The right literature is ripe describing little shielded loops for
noise tracking and measuring purposes.
Here's one for instance:
> source is very close to the antenna and the conditions are
The 'source' doesn't have to be close to the antenna, if
the coupling involves, say, some length of AC distribution
system; the power wiring simply conveys the energy,
and the near/far effects apply when the energy begins
to become 'airborn' near the receiving antenna.
> just right. Time-varying fields behave the same whether we
> like to hear them or not. As a matter of fact at a distance
Time varying fields.
Tell me, can a magnetic field penetrate a copper sheet?
You know, just a regular old thin sheet of copper.
Or aluminum foil.
> of about 1/8th wave, a magnetic loop is electric field
> response dominant! It's only right next to the antenna it is
I've got proof to the contrary:
See "Figure 5, Electric Field Testing of Shielded Loops"
(The corollary to this is: "If the Electric Field impinging on
the shielded loop is uniform the E-field effects will cancel".)
I will ALSO have to defered to such practiced and experienced
engineers such as these:
NRSC AM bandwidth measurements with the loop antenna
Shielded loop antennas respond primarily to the
magnetic component of the RF field, and provide
good directionality in the form of a figure-eight
with nulls at right angles to the plane of the loop.
Compared to an amplified (E-field) whip. Empirical
tests prove the shielded loop to reject substantially
more electrical noise.
Until you can provide some measurements, Tom, I'm
going to have to side with the guys who have actually
used and seen the practical, useful, proven utility of the
loops for the reasons they cite.
> magnetic field dominant, and a noise source can have any
> field impedance.
> In reasonably quiet suburban or rural locations on low bands
> the noise we hear is indeed an accumulation of all the
> little drill motors, power line arcs, thunderstorms, and so
> on that propagate and accumulate to make what sounds like a
> "white noise". On upper HF galactic sources come into play.
Still no cite from one of you guys to support this, just
(Can't buy into it without proof and what little I've looked
into it I don't see even a plethora of small incidental radiators
having a MEASUREABLE effect contrasted with T-storm
produced static crashes (propagated by band conditions
to boot!) or crowded band conditions or foreign broadcasters;
and I still see LOCAL noise sources as being dominant with
local affectation being far more the case than not.)
> This is the real danger of BPL. The accumulated energy of
> hundreds or thousands of individual sources that by
> themselves are too weak to hear will add and raise the noise
> floor of everyone, even people thousands of miles from the
> sources. We have polluted the radio spectrum with noise from
> incidental radiators just like we are destroying every other
> resource we have.
> 73 Tom
(too lazy/forgot to put down my call previouisly: WB5WPA)
RFI mailing list