As Bill wisely pointed out: 2) many rigs have considerable roll-off in receiver gain towards the bottom end of the expected receiver pass-band, the K3 is one of those BTW.
This seems not to be well understood or appreciated. My own KX-3 rolls off rather sharply starting at about 400 Hz when set for DATA-A mode, which is what most people set their Elecraft radios to for operating under WSJT-X. I know the same situation exists with the KX2, and may with the various K3 models. You can see this for yourself if you look at the WSJT-X waterfall display on a dead band with the gains turned up and the Flatten and Ref Spec buttons turned off. I think this was a deliberate choice by the radio designers, who are big RTTY fans. They must think that there is some performance advantage to doing this. The solution I take is to use USB mode while operating with WSJT-X. With the PBT control set to maximum bandwidth, the frequency response extends from below 200 Hz to about 3500 Hz. Of course, if you also operate SSB, you need to turn off the compressor, turn off the equalizers, and so on when switching to WSJT-X operation. A way around that is to place the radio in ESSB mode when using WSJT-X, which does all that for you. I added a Macro that allows me to switch between normal SSB and WSJT-X modes with a press of a Programmable Function switch. Other radios have the same issue. Not all, of course, but enough. This is really a problem for DXpeditions using F/H mode. The default start frequency for a single TX channel in F/H mode for a Fox is 300 Hz, as clearly stated in the documentation. But, if the Fox has a radio that cuts signals off below 400 Hz, even a loud Hound that gets a +10 report when calling above 1000 Hz may now be in the mud when s/he responds at 300 Hz. This inevitably leads to the “three strikes and you’re out” outcome for a Hound. The two solutions are to use a radio that receives down to at least 300 Hz, or to set the Fox TX frequency to above maybe 500 or 600 Hz. But, how many DXpeditions know this? Just this morning I was monitoring a moderately rare DX station operating as a Fox. His TX channel was set to the default of 300 Hz. He’d give Hounds reports of +00 and above, and then not complete the QSO. There were times when he was running five streams and not completing any QSOs for several decode periods in a row. Then, to his credit, he figured out his mistake and started at 700 Hz. Voila! The rate skyrocketed. For Hounds who have radios that roll off at low frequencies, if the Fox isn’t that loud and there’s QSB, the Fox might fall into the noise right when you’re trying to complete the QSO. How much fun is that? You can always offset your VFO setting by a few hundred Hz and be sure to transmit above 1000 plus that few hundred Hz, but that’s easy to forget or mess up. That’s why I researched this and made and use the Macro. I haven’t a clue how to popularize this message. I don’t think most DXpeditioners follow mails on SourceForge. Or, maybe I’m just all wet! Clarke K1JX
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