Topband: Receivers, Noise Blankers and Key Clicks

[Michael Tope]

> I don't think they will. Anything more than about 80-90dB down is
virtually
> never a problem.

Tom,

For folks in rural areas like yourself that are fairly distant from
other amateurs, you are probably correct that 80-90dB is
sufficient. Try living on the side of mountain in a metropolitan
area and you might change your mind. On the higher bands,
every station in the eastern San Fernando Valley is really loud
here. And this is on the higher bands where the noise floor is
generally pretty low. I have one guy with an R7000 who is just
around the corner from me (he is probably about 500' away),
another guy who is down the street about 1/4 of a mile away
with a Force 12 tribander, and a fairly active HF dxer with a
nice little Christmas tree down the hill around 1/2 mile away
who just sends my S-meter needle smashing into the peg.
And when I lived in Pasadena, you should have heard
WA6CDR or N6LL when they were up on Mt. Wilson operating
on 160 meters (I could look out my living room window and see
their TX antenna on the top of the mountain 4000' above me).
I wouldn't want any of these guys to settle for -80 or -90 dBc/Hz
composite noise performance, nor do I want any manufacturer
getting the idea that -80 or -90 dBc/Hz is "good enough".
Even though its overkill in most cases, I prefer the Ten-Tec
Orion's -140dBc/Hz. That's the right paradigm. I still recall the
days when a very prominent east coast 160 meter DXer would
monopolize 1824 to 1826 in the 160 contests with endless
CQ's from his 2 KC wide phase noise machine. I wouldn't want
to go back to that.

By the way, I have been talking in dBc/Hz. Are you? -80 to -90dBc
in a 300 Hz bandwidth is actually fairly good (e.g. equivalent to
-105 to -115 dBc/Hz composite noise spectral density). On the
other hand -80 to -90dBc/Hz is equivalent to -55dBc to -65dBc
when listening on a receiver with a noise bandwidth of 300 Hz.
That would translate into audible noise sidebands from adjacent
signals that were only S9+10db - yuck!

>
> My own FT1000 only raises my own very quiet noise floor by about 25dB with
> 1/2 mile antenna separation, and I am pretty loud at my own house.

You are pretty loud here in California most mornings too,
but not so loud that I can hear your TX noise :):)

> By the way, the bulk of FT1000 transmitter composite noise comes from the
> dual-gate FET used in the transmitter's ALC gain control system. You have
to
> learn these things while trying to duplex on 160 in contests.

Interesting, thanks!

73 de Mike, W4EF...................