[Elecraft] Spikes and noise on my K2 ...

[Geoffrey Mackenzie-Kennedy]

Hello Robin,

My K2 receiver behaves in the same way, and what we are hearing between 
14358 and 14363 kHz is one of the many K2 receiver's internal spurious 
signals or 'internal spurii', also called birdies.

In genral these internal spurii are created by one or more of the K2's 
oscillators producing a signal at either the frequency to which the receiver 
is tuned, or at a spurious response frequency of the receiver (the "Image" 
is one of these), or at the IF, which the receiver will 'hear'. If more than 
one oscillator is involved, the oscillators' signals will mix together 
*somewhere* to produce a family of signals (products) one or some of which 
might be heard by the receiver. In some cases an unwanted signal from these 
sources can get into the receiver's LO system and greatly increase the 
problem.

To get rid of this particular birdie and spikes I think that a fair amount 
of surgery would be required in the form of shielding as well as RFC - C 
filtering of DC supply and control lines as well as improved isolation 
between the Reference oscillator and the VCO varicaps via U4 and U6B, which 
I have not done. As far as the spikes are concerned it appears that a very 
strong birdie or a very strong 'real' antenna signal does affect the K2's LO 
system at some frequencies. I have not investigated this but my guess is 
that for some reason, probably unwanted coupling between the Reference 
oscillator, VCO (VFO) and BFO, the system either attempts to lock onto a 
very strong signal at some frequencies but fails or momentarily loses lock, 
producing the spike. I have noticed spikes around 7180 kHz when the BC 
stations in that part of 40m are S9++ but none when the BC station signals 
are weaker. Note that 2 x 7180 = 14360 kHz which suggests that the 20m 
birdie/ spikes and 40m spikes are related.

Sorry no simple fix yet.

73,
Geoff
GM4ESD


----- Original Message ----- 
From: "Robin Kiszka-Kanowitz" <oz6abm at qsl.net>
To: <elecraft at mailman.qth.net>
Sent: Sunday, December 17, 2006 1:55 PM
Subject: [Elecraft] Spikes and noise on my K2 ...


Hi,

I have noticed that when tuning my K2 up to 14358 I hit a spike and then 
hear a continuous tone all the way to to 14363 - yes it's out of band, but 
it is there.
I also have this spike at regular intervales, for example 14338, 14348, 
14358 and then 14363, 14368, 14373 etc. Fortunately it is nearly all out of 
band.

I have disconnected the K2 and tried it away from all sorts of noise 
sources - no antenna, no PSU (using the internal battey kit) etc., but it's 
still there.
I have the DSP, ATU, NB, SSB, 160M options installed, so it could be one or 
a combination of things. I'm just wondering if anyone else has this and if 
there are some ideas as to why it does this?

thanks and 73
Robin
OZ6ABM