Most of this very interesting post is not-relevant to my ham radio
operating (eme on VHF+).
Comments preceded by asterisk * inserted below:
---------------------------------------------------------
Date: Tue, 25 Oct 2016 05:21:20 +0000 (UTC)
From: Al Lorona <[email protected]>
To: Elecraft Reflector <[email protected]>
Subject: [Elecraft] [K3] The Way We Rank Receivers (long)
Receivers are always ranked by the "2 kHz third order dynamic range",
such as at:
http://www.remeeus.eu/hamradio/pa1hr/productreview.pdf but do we
really grasp the meaning of these specs? For instance, the Elecraft
K3's (after synthesizer upgrade) number is 103 dB, good enough to be
in the top ten. In fact, this number is so strong that very few hams
will ever be affected by it. To the best of my knowledge, I have
*never* been close to running out of dynamic range. To understand
why, let's put "103 dB" into English.
===snip
I have assumed a noise floor or MDS of -130 dBm because it's a nice
round number. If your 20 meter noise floor is higher than this, then
the two signals would have to be *even stronger* to hear the intermod
come out of the noise.
*I wonder where in the world one sees a 20m noise floor that low when
antenna is connected? Only when I lived off the grid running on
battery power did I see S0 noise on my radio (3.9-KHz with TS180S
from a dipole). I doubt that radio had a noise floor that low, but
maybe. I see S3/5 noise on my K3 connected to triband yagi, preamp
off. That is probably about -110 to -100 dBm noise floor. My SDR-IQ
is very good at 28-MHz and displays -132 dBm without an antenna
connected (190-KHz bandwidth). But connecting an antenna raises that
instantly.
===snip
Perhaps it's time to rank receivers by a different measurement,
something that affects more of us. Looking through the table at the
link above we see another measurement called "2 kHz blocking gain
compression" and for the same K3 it is 143 dB. This is a measurement
not of two interfering signals, but a single interferer just 2 kHz away.
*I can only think of two instances seeing such a strong adjacent signal:
1) At 310-KHz a GPS-reference station is locate less than a mile
away and I measure it at -30 dBm on my inverted-L (tuned to 490-KHz)
with SDR-IQ.
2) I once measured a high power pager running 158.100 100-foot away
from my company's 161.325 repeater showing 1/4w on the Bird power
meter installed on the repeater antenna whenever the pager
transmitted (repeater was turned off). That would be +23
dBm. Amazingly the repeater Rx survived this (due to duplexer and
helicoil prefilter). IMD mixing of the 158.1+161.325 produced a
horrendous signal on 156.450 (which interfered marine ch.9).
Both examples extremely unlikely to occur for HF hams.
===snip
Finally, we notice a measurement called "2 kHz reciprocal mixing
dynamic range" -- probably the limiting spec nowadays for top tier
receivers. In our example of the single strong signal, way before
reducing the gain of the receiver, that signal will have another
effect: it will mix with the phase noise of the K3's own local
oscillator and deposit that phase noise right onto your desired
frequency of 14.050 MHz.
*this has application for me. The occurrence of a high power signal
off frequency mixing with the phase noise of my eme Rx. This is one
of the reasons driving a goal for extremely low LO phase noise in eme
systems. This is one of the major selling points for me to purchase
my K3 and upgrade synthesizers.
===snipped the rest (though very interesting proposal)
73, Ed - KL7UW
http://www.kl7uw.com
"Kits made by KL7UW"
Dubus Mag business:
[email protected]
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