Merlin,
Please define "noisy" so we can have a better understanding of what is
happening.
If you have a selective receiver available you can scan the spectrum on
each side of the signal for about 1 kHz and gain the same information as
with a narrow band spectrum analyzer. Another method is to use a DC
receiver and look at the audio output of that DC receiver with
Spectrogram to view up to 6 kHz of the spectrum at the signal frequency.
Are you certain it is not your receiver's response with a short antenna
attached?
Although the source could be anywhere in the transmit chain (or even
outside the K2 as you hinted (power supply maybe?) - there are 3 main
areas I would look first, BFO, VCO and transmit mixer.
73,
Don W3FPR
m0trx wrote:
Dear All,
I recently finished building K2 #6593 and have been thoroughly impressed
with the performance of the receiver. However, having done some initial
tests on transmit into a dummy load, whilst monitoring the signal on another
receiver, I have noticed that the the signal starts to sound noisy as the
frequency is increased (i.e. 40m sounds clean but 10m sounds far from
clean). I do not currently have access to a spectrum analyser in order to
check this quantitatively.
The K2 is located far from my linear power supply (at least 3-4 feet) so I
doubt this is due to modulation of the VCO from the 50Hz supply. If this
were the case then the problem would be prevalent on all bands anyway. I
wonder whether anyone could shed some light on the likely cause of this. I
am beginning to wonder whether the frequency components I am hearing are
actually on the transmitted signal or as a result of some mains coupling.
The reason I think this is because the level of said frequency components
relative to the carrier is higher on one receiver than on another (both in
same room, aerial etc).
Any commnets would be most welcome.
Regards,
Merlin Cooper
M0TRX
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