[Elecraft] K3 Power-hunting on FT8

[M Cresap]

 Hi Dave, Joe, and Jim
The GMSK to AM distortion across any 50 Hz bandwidth of a K3 filter would seem to be minor. With an FT8 symbol rate of 6.25 symbols per second, would that not create some relatively weak 6.25 Hz sidebands plus a bit of mush around those lines due to the pseudorandom nature of the bit patterns? That could increase the overall bandwidth by maybe 18 Hz above the nominal FT8 signal bandwidth. The narrowest resolution bandwidth I have been using is 10 Hz, which is too wide to pick up that level of detail. 

There is an equalization tool in WSJT-X that is supposed to equalize phase and amplitude filter distortions inside the radio for improved decoding. I haven't played with that feature, but it looks like it could provide degraded results if it collects data at one passband tuning setting, then tries to decode signals after the operator changes the PBT.

Bob has reminded me that ALC related measurements should be done with a fresh Tx Cal using the DC voltage/voltage drop that exists today in my shack. I recently changed the DC power wiring to 2 feet of #10 wire between the K4 and the power supply, just like what I did for my K3. I plan on doing that Tx cal tomorrow, will rerun the K4 measurements and let you know what I see.

73, Mike, W3IP

    On Sunday, July 23, 2023 at 11:59:58 AM EDT, Dave (NK7Z) <dave at nk7z.net> wrote:  
 
 Hello Mike,

Thanks for sharing your data!!  Help me understand something you said...

Are you saying that at 2 bars, (for your K4), all spurious signals, are 
at least 80 dB down from carrier, while at 5 bars, all spurious signals 
are running around 50 or 60 dB down from carrier?

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources

On 7/23/23 07:23, M Cresap via Elecraft wrote:
> For my K4, the FT8 signal is clean with no more than 2 bars of ALC.
> To be clear, the spurious responses I have seen with ALC set to 5 bars has NO measurable IMD responses. There is only the one strong signal present, the spurious signals being discussed here are all less than 50 or 60 dB below the intended carrier level. My goal is to reduce all the spurious responses to 80 dB below the intended carrier level.
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