[600MRG] Relative outside noise...

[jamie labadia]

Tom, you are absolutely correct on the propagated noise issue. The noise
from Boston was the biggest issue for me during our Trans-Atlantic
experiment in December 2021.
 Even with the 1200 ft Beverage, which of course is still short for
630,....I could see the slow uptick in noise as we moved into darkness.
 It took Roy G4CLO and I a good 2 years of staying up through all hours to
finally make a two-way.
 Additionally, I've noticed the noise gradually fades down around 0200
local. (Around the same time I lose some of the NDBs out around 200 miles.)
I think that's when some of the higher angle stuff begins losing coherent
refraction at the low E-layer, and the virtual height for that angle
increases.  Absorption and scattering due to deeper penetration,.....etc.
 However it might be due to less human activity in the cities at that hour
as well.
 I'm glad you're with us Tom. We need your background and experience to
help us "push the envelope" a little.


       Jamie

On Tue, Jul 25, 2023 at 7:58 AM Tom W8JI <w8ji at w8ji.com> wrote:

> On 7/24/2023 10:45 AM, Ed Cole wrote:
> > Dave,
> >
> > I have been inactive for a few years but I recall trying a single wire
> > BOG of 1/4 WL at 500-KHz and it was 20-dB quieter than my Inverted-L
> > (43x130 feet).
> >
> > But I found the BOG about 20-dB lower on signals (using NDB's as
> > testing sources out to 1000 miles).
> >
> >
>
> The above is good example of why absolute levels of noise on a receiver,
> or noise on an antenna compared to a dummy load, are useless except to
> establish the system is noise limiting on external noise.
>
> Receiving has a different requirement than transmitting.
>
> 630M I can use a 40dB or 50dB pad when receiving on my transmitting
> antenna with no ill effect. If I was listening on the TX antenna I could
> use a feedline with 40dB loss with no ill effect on receiving.   The
> 3100Hz bandwidth measured wintertime noise level on my full size
> Inverted L antenna is -74dBm daytime and -70dBm at night.  (My
> transmitting antenna is a full-size inverted L about 500 feet or so from
> any power lines and probably about 20% eff).
>
> The consistent ~4dB noise increase on a winter night tells me noise
> propagated via sky wave is the limiting factor at night, not local
> noise, so other than making it more directional there is nothing I can
> do on the TX antenna to make it receive better. (On 40M my daytime to
> nighttime noise changes about 30dB because 40M is a quiet local band)
>
> 630M is just very noisy locally, even way out in the country.
>
> 73 Tom
>
>
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