At 12:45 10-01-99 -0500, W8JI wrote:
>1.) Add attenuation, and watch signal levels for a linear progressive drop.
>Receiver IMD falls out faster than the amount of attenuation added. Just
>remember virtually ALL S meters are not 6 dB per S unit, and those that
>are generally only behave properly near mid-scale. (My FT1000 is about 2 dB
>per S unit below S6 or so but pretty good at S-9 plus or minus)
After calibrating the S-meter in my FT1000D per the Yaesu tech manual, I
ran the signal generator past it. Here's what I got using the 500 Hz filter
in CW mode:
S1 = -103.5 dBm
S2 = -101.5 dBm
S3 = -98 dBm
S4 = -94 dBm
S5 = -90 dBm
S6 = -85 dBm
S7 = -80 dBm
S8 = -75 dBm
S9 = -70 dBm
+10 = -60 dBm
+20 = -51 dBm
+30 = -42 dBm
+40 = -33 dBm
+50 = -24 dBm
As you can see, it follows what Tom described fairly closely. Why do I
care? Well, I hope that I can use this info to help find a possible noise
problem I may or may not have.
I don't seem to hear as well as most of the other topbanders in the
vicinity. I thought I'd fixed the problem when I had the local power
company repair all the noisy 69kv poles in the neighborhood. Although I
can't locate anymore noisy poles the noise level still seems very high.
Even with my rotatable Flag RX antenna, I'm still the last man on the
receiving totem pole. The Flag has a demonstrably deep null off the back
that I can use for locating local signals, but I can not find a noise
source with it.
The noise doesn't seem raspy enough to be power poles, instead it sounds
almost white like galactic noise. (Bandwidth limited by the RX filters, of
course) It's as if the sun were directly overhead sending a nice little
flare to me personally!
The noise level during the day on my TX antenna is usually S5, which as we
now know is -90 dBm in a 500 Hz filter.
I wonder how this compares with the daytime noise level at others QTH's. If
you have a method of semi-accurately measuring the noise power at the RX
antenna terminals when using an omni TX antenna, please let me know what
that level is. Maybe I only think my noise is high and I really live in the
bottom of a "black RF hole".
If I really do have a high noise level for some reason, I don't know what
more I can do about it. Traditional methods I've used for locating noise in
the past have so far failed me. Since it seems to come from every direction
equally, ( or up?, or down? ) noise cancellers like the MFJ won't help.
Suggestions anyone?
73,
Larry - W7IUV
w7iuv@axtek.com
http://www.axtek.com/w7iuv
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