Since I am trying to decide whether to buy another K3 for the 2m
station, this is all very timely.
Probing around using a very small insulated pickup loop and a completely
separate 2m receiver, the 144.416MHz signal is definitely not a spurious
response of the K3's receiver. It is a real carrier and it's coming from
the region of the DSP board(s) behind the front panel.
The frequency seems to be completely independent of the K3's main
tuning, band or mode, and on my particular K3 the frequency is
144.4162MHz (zero-beating on a GPS-locked receiver).
The signal is quite loud with the probe loop held anywhere close to the
DSP board along its whole length and on either side. The signal is
louder when the loop is anywhere close to the main voltage regulator,
the board interconnects or one of the mounting pillars; and when the
probe is directly above or below U17 (EPM240TQFP100) it's S9+. All this
suggests quite a strong discrete signal source that doesn't have
sufficient local decoupling, so it is escaping via the supply rails and
probably creating circulating currents in the groundplane and metalwork.
The frequency is somehow being generated from the 14.7456MHz DSP clock
crystal Y1 (as can be heard by probing very close to the board, which
detunes the frequency). That isn't a precision oscillator, which
probably accounts for any small differences in the reported frequency.
However, there is no obvious harmonic relationship between 14.7456 and
144.416 (the factor between them is 9.79).
That's as much probing between expensive circuit boards as I'm willing
to risk! Over to Wayne... sorry, this is a fine way to begin the Monday
morning after Visalia.
73 from Ian GM3SEK
-Original Message-
From: Elecraft [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of
Dave
Sent: 20 April 2015 16:13
To: elecraft@mailman.qth.net
Subject: [Elecraft] Elecraft] K3 K144XV spurious signal on 144,414.1
Its also by far the loudest sprog I can hear on the 3 K3/K144XV combos
I
have tested. Unfortunately for me it stops me hearing the PI7RTD and
ON0VHF
beacons 400km away unless they drift to a frequency that I can use my
250Hz
filter to dig them out
Dave
G4FRE
From: Sverre Holm (LA3ZA) la...@nrrl.no
To: elecraft@mailman.qth.net
Subject: [Elecraft] K3 K144XV spurious signal on 144,414.1
Message-ID: 1429428332185-7601496.p...@n2.nabble.com
Content-Type: text/plain; charset=us-ascii
I would appreciate it if other owners of the K3-K144XV would check for
this
signal.
It appears as if it is a regular input signal, i. e. it tunes normally.
But
it is still there even if the 2m antenna is disconnected or the input
is
shorted, so it seems to be internally generated.
I have tried all the tricks I know such as moving of internal cables in
the
K3. I also updated the K144XV firmware and that got rid of the spur at
the
36th harmonic of the 4 MHZ K144XV processor crystal at 144,005.
But the 144,414.1 spur remains, close to the SK4MPI beacon at 144,412
which
is one of the main indicators of propagation here.
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