K3 S-Meter and Noise

[Toni Lindén]

I found out similar behavior with K3 while testing it for the first
time in SAC contest.

I was sure that the noise was some kind of power line noise or
similar. After the contest I disconnected *all* electrical devices but
noise was still there. Changed to FT1000 Mark V and the band was quiet
while with K3 I had S3 to S5 noise.

It cleared out to be the problem with K3 preamp. Every time when
preamp's turned on, the band are really noisy but switching preamp off
make the noise go away. I guess it's not the "K3 has the best RX"
issue but problem with preamp.

73 de Toni, OH2UA


> All four are equally quiet without an antenna connected and with a dummy
> load connected.  When connected to an antenna the K3 has about 2 S units
> more noise indicated than the other radios connected to the same antenna
> (A/B switch) and the noise level sounds about that much louder.
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[Dave, G4AON]

I have a feeling something may have changed in later K3 firmware,
possibly as a result of calibrating the receiver gain via the K3
Utility. Previously I have been able to calibrate the S-Meter from
around S6 to S9 +60 and have it almost perfect, now it doesn't seem to
be possible to get it that good.

Anyway, these are actual measured results from my K3, which is using the
latest pre-release beta firmware (v3.41). These measurements seem OK to
me and the K3 doesn't seem any noisier than other radios on my 80m
dipole. The S-Meter has been calibrated without the pre-amp in use. It
is quite hard to set it correctly all the way from S1 to S9 +60... AGC
set to default values. SMTR OFF = 027, SMTR SC = 010, SMTR PK = OFF and
SMTR MD = ABS (the latter makes no difference to the S-Meter readings
below).

S1 is solid at -115 dBm, S2 is solid at -109 dBm and S3 is solid at -105
dBm. These are using CW with the pre-amp off on 80m, 2800 Hz filter.
There is about 1 S-point drop using either the 400 Hz or 250 Hz filter.

MDS (3 dB SINAD) is -135 dBm in a 400 Hz bandwidth with the 2800 Hz
filter, pre-amp off. An input of -126 dBm gives 10 dB SINAD for the same
settings. SINAD is signal to noise and distortion.

The K3 is sensitive enough on the lower bands to not need the pre-amp,
which of course would give rise to higher noise levels.

73 Dave, G4AON
K3/100 #80


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[Jan Erik Holm]

I have noticed this on my K3 also. Compared to my FT-1000D
it´s much noisier. As far as I understand the MDS of the
K3 is around 134 dBm, I have measured my FT-1000D to about
141 dBm I think it was. My feeling is that something isn´t
right with the K3 but I simply haven´t had time to persue
it.

/ Jim SM2EKM
----------------
Dave G4AON wrote:

> I have a feeling something may have changed in later K3 firmware,
> possibly as a result of calibrating the receiver gain via the K3
> Utility. Previously I have been able to calibrate the S-Meter from
> around S6 to S9 +60 and have it almost perfect, now it doesn't seem to
> be possible to get it that good.
>
> Anyway, these are actual measured results from my K3, which is using the
> latest pre-release beta firmware (v3.41). These measurements seem OK to
> me and the K3 doesn't seem any noisier than other radios on my 80m
> dipole. The S-Meter has been calibrated without the pre-amp in use. It
> is quite hard to set it correctly all the way from S1 to S9 +60... AGC
> set to default values. SMTR OFF = 027, SMTR SC = 010, SMTR PK = OFF and
> SMTR MD = ABS (the latter makes no difference to the S-Meter readings
> below).
>
> S1 is solid at -115 dBm, S2 is solid at -109 dBm and S3 is solid at -105
> dBm. These are using CW with the pre-amp off on 80m, 2800 Hz filter.
> There is about 1 S-point drop using either the 400 Hz or 250 Hz filter.
>
> MDS (3 dB SINAD) is -135 dBm in a 400 Hz bandwidth with the 2800 Hz
> filter, pre-amp off. An input of -126 dBm gives 10 dB SINAD for the same
> settings. SINAD is signal to noise and distortion.
>
> The K3 is sensitive enough on the lower bands to not need the pre-amp,
> which of course would give rise to higher noise levels.
>
> 73 Dave, G4AON
> K3/100 #80
>

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[Julian, G4ILO]

Dave G4AON wrote

The K3 is sensitive enough on the lower bands to not need the pre-amp,
which of course would give rise to higher noise levels.

But surely the preamp won't make the receiver noisier. It will only make the noise sound louder. But if you are listening to a signal then switching the preamp in should improve the signal to noise. If it doesn't, the preamp doesn't need to be on in the first place.

The only band I have found the K3 preamp useful on is 6 metres. But that probably has more to do with the noise level I have here than the K3's sensitivity.