[Elecraft] K4 Question

[Eric Norris]

Hi Wayne,

How far apart in frequency were the TX and RX signals into the respective
radios?  My guess is my neighbor is about 500ft away, but I will measure it
with a gps.  He has never tripped my K3 or K3S COR when we are on the same
qrg.  Thanks!

73 Eric WD6DBM

On Tue, Jun 23, 2020, 8:16 PM Wayne Burdick <n6kr at elecraft.com> wrote:

> Hi Eric,
>
> I did a quick test using my home lab to simulate a possible FD scenario.
>
> For this test I set up a K4D and a K3S with their antenna jacks connected
> directly together through a high-power attenuator. Receiver preamps were
> off. With this arrangement, the RX noise floor is minimized since there's
> no actual antenna involved.
>
> I set mutual attenuation to 30 dB, a rough estimate of the path loss using
> dipoles 500' apart at 7 MHz. This is a pretty wild guess, though. Loss
> could be much higher if the antennas were oriented to avoid coupling, and
> it'll vary with frequency, terrain, actual distance, etc. Of course path
> loss could be lower with gain antennas at either or both ends, aimed at the
> other. (A situation generally avoided at FD.)
>
> While transmitting with the K4D at 100 W and receiving with the K3S, I
> found I was engaging the K3S's carrier-operated relay. This is evidence
> that the path loss probably is higher than 30 dB in real-world scenarios. I
> dropped to 10 W on both rigs (10 dB down from 100 W) to avoid the confound.
>
> I then coupled in a weak signal at the equivalent of about S2 (-113 dBm)
> as indicated on both receivers. When keying one rig, there was no evidence
> of desensing of this signal at the other, and only a very slight observed
> increase in the noise floor (as indicated by the respective panadapters).
>
> Yes, the two radios have entirely different architectures. Each has pros
> and cons.
>
> With an SDR like the K4, the fundamental limit on narrowband TX noise
> performance is the DAC. The K3S, on the other hand, has to shoehorn its 8
> MHz IF transmit signal through a narrow crystal filter, adding ripple and
> group delay to complex signals (like voice and data). It also exhibits a
> characteristic "pedestal" of 15 kHz DAC noise that sits maybe 15 to 20 dB
> above the wideband noise floor.
>
> When it comes to CW keying bandwidth, both the K3S and K4 have essentially
> identical (and excellent) performance due to an optimally shaped keying
> envelope.
>
> 73,
> Wayne
> N6KR
>
>
>
> > On Jun 23, 2020, at 3:46 PM, Wayne Burdick <n6kr at elecraft.com> wrote:
> >
> > Hi Eric,
> >
> > S9+65 dB is about -8 dBm. Off the top of my head, this is far, far below
> what a basic K4 or K4D can handle, artifact-free, in-band, without the need
> for attenuation or additional filtering. When I get back to the lab I'm
> going to set up exactly this condition and get back to you.
> >
> > Of course the out-of-band rejection is even higher.
> >
> > A number of K4s will be used extensively during FD this year, including
> mine. I'll be taking advantage of the K4's low current drain (for its
> class) by running mine from a KX2 11 volt battery pack (3x 18650 cells).
> For at least an hour or so :)
> >
> > 73,
> > Wayne
> > N6KR
> >
> >
> >> From: "Eric Norris" <norrislawfirm2 at gmail.com>
> >> To: "elecraft at mailman qth. net" <elecraft at mailman.qth.net>
> >> Sent: Tuesday, June 23, 2020 9:32:04 PM
> >> Subject: [Elecraft] K4 Question
> >>
> >> My foaming at the mouth over the K4 has been tempered by it having less
> >> adjacent channel rejection than the K3 due to the different
> >> architecture--at least until the K4HD comes out. I understand this, and
> >> the reasons why. Thanks for your answers
> >>
> >> I know I have asked this question before, but I want to be more
> specific.
> >> My QRM neighbor is S9+65 db on my K3S S-meter. If he is blasting away
> on
> >> ft8 at 7074 kHz at that signal level, how would the plain K4 receiver
> >> perform at 7034 kHz on CW? Would there be AGC pumping, RX desense, or
> >> other degradation, or would I be able to carry on a CW qso unmolested
> like
> >> I can with my K3? What about an adjacent band like 3534 kHz or 10114
> kHz?
> >> Or is the answer I have to wait for the K4HD?
> >>
> >> No speculation, please, I'm looking for a real-world or lab-world
> answer.
> >>
> >> Thanks and,
> >>
> >> 73 Eric WD6DBM
> >
> >
> >
> >
>
>