[Elecraft] Observation on new Synthesizers for K3

[Greg Troxel]

David Cole <dave at nk7z.net> writes:

> It occurs to me that the the the RX VFO phase noise would be less
> influencing, (on phase noise sidebands), than the transmit VFO phase
> noise...  Is that correct?
>
> If so, then that would explain why the largest change occurred when
> K7OLN got his new synthesizer, as opposed to me getting my new
> synthesizer, as shown in the difference between photos 2 and 3.  
>
> Is my understanding correct?

In an ideal system, the receiver sees the convolution of the transmit
signal, as conveyed by the antennas and progagation and the receiver's
LO.  So for the most part, I think TX and RX phase noise hurt equally
(when viewed in dBc/Hz at some separation).  Of course, RX phase noise
is under one's control, and TX is imposed on others, so from that
viewpoint TX phase noise is more like crossing the yellow line than
hitting a tree yourself.

>From the measurements I've seen, I don't think it's a fair assumption
that transmit and receive phase noise in a given rig is the same.  The
K3 (with original synth) has a transmitter which is relatively cleaner
than RX reciprocal mixing, according to:

  http://www.sm5bsz.com/dynrange/dubus313.pdf

But in many radios (including the KX3), that article says that the
transmitter is worse than the receiver.

Also see:

  http://k9yc.com/TXNoise.pdf

which focuses on lab measurements of transmitters, disconnected from
receiver issues.  Presumably the spectrum analyzers are good enough that
they're not an issue, but I wonder if that's really true given the
levels we're talking about.

I think QST reviews should give some measurement of joint TX/RX noise.
Perhaps the isolation required so that with one instance of a
transceiver at 100W, the 2nd instance receiving at 100 kHz separations
(perhaps for 2/10/50/100/200 kHz) ees some particular absolute level of
noise, picking some level that is about 10 dBo worse than typical MDS.
This is trying to capture "what happens when you have two of Rig X at
Field Day in the same band", or the 300m neighbor situation.

73 de n1dam