[Elecraft] SO2V mixed mode oddity

Thu Jul 21 18:31:06 EDT 2016

Reported by myself (Mike VE9AA) on the N1MM+ list but described much better
by VE3KI, Rich, below.

Has anyone found a work around to mixed mode SO2V operating when the sub rx
is on SSB?

(incidently, K8UT does not notice this on his K3S)

[Elecraft] [K3] Strange filter behaviour in the subRX
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%5C%5BElecraft%5C%5D+%5C%5BK3%5C%5D+Strange+filter+behaviour+in+the+subRX%22
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Richard Ferch Sat, 02 Jul 2016 15:43:22 -0700 

After a user reported problems with filter settings in N1MM+ in SO2V with

one VFO in CW and the other VFO in SSB, I did some investigating. I had

never tried mixed-mode dual receive before. After doing some experimenting,

first with N1MM+ and then with the radio on its own, I conclude that there

does appear to be a problem, but it seems to be in the K3 firmware, not in

N1MM+.

After some initial exploration, I ran audio spectrum analysis software on

the Line Out output of the K3 with band noise input on a dead band, default

filter settings and with no radio control software of any kind running.

With both VFOs in SSB, the noise spectrum display is similar for both VFOs

- reasonably flat (plus or minus a few dB) from 200 Hz to 2800 Hz, more or

less. If one VFO is in CW and the other VFO is in SSB (or DATA A, which

seems to behave the same way), the VFO A SSB plot looks the same as before,

but when I use the K3's A/B button to swap VFOs, the spectrum display for

VFO B in SSB looks quite different, with a more or less linear rolloff of

roughly 10 dB/kHz (not per octave, per kHz) from 700 Hz to 2700 Hz. That

is, at 1700 Hz the spectrum plot is down around 10 dB from the value at 700

Hz, and at 2700 Hz it is down around another 10 dB. The difference is

clearly audible. I can fix this by pressing the B-SET button on the K3,

which restores a flat response profile in VFO B, but when I press A/B twice

to swap the SSB and CW settings between the two VFOs twice, the rolloff

comes back when VFO B is in SSB mode.

Has anyone else seen anything like this? Is there a configuration setting

that can fix it?

73,

Rich VE3KI

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