Thanks for all your replies, am still processing.. Great brain
food..
After 70 years of hamming, this subject has been one of the most interesting fer sure..
Here is latest 630m report showing some relative proof of
performance..
VK4YFB
5720 km DC0DX > W1FRV -26 WSPR
Fessenden noticed a lot of signal loss working Scotland from here
in the summer months. His Elmer was Kennally ( of
Kennally-Heavyside ) who told him what happens and to maintain a
salt water connection between here and Scotland..
www.radiocom.net/Fessenden
He also used and researched RF loops.. Had hundreds of inventions
during his run here in town..
1/4 db ( watching long fft ) of noise trimmed here, another one
there, pretty soon adds up to real DX..
Today added a separate local earth ground rod for the the SDR play
receiver which now shows 2 db less noise or 2db of more signal
above noise on 160m..
Tonight the R75 is running off battery.. Will see..
I have no such thing as a calibrated noise source on hand, just comparisons..
Cushman CE24, HP 3586c level receiver, Icom R75, ic718 and two
SDR rsps all show different noise floors.. Or MDS...
So I take approx 200 nV of RF and a step attenuator, send it to
each of the receivers one at a time and the one RX that shows the
most RF up and out of the noise wins...
Don't have up to date cals with the above.. Probably are in the
ball park..
All is done relative here.. Today the 2 turn coax loop on 160
shows 4 db between the loop and a 50 ohm load.. W1NMF
Too much fun... 73s from Dave @ W1FRV 'first radio voice'
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