Re: K3 + HDSDR + RSP1A Help please
I acquired an RSP-DX a couple of days ago and have it working with my K3. Prior to that I've run a Softrock-IF into HDSDR from my IF port and it worked fine. There is an output level modification for older K3 models but I expect you should see something on the display even without it. The Softrock IF wasn't great with HDSDR because there was no tuning. I'd set the frequency to 0 and could it was useful for tuning, but not for rig control except with Omnirig, which worked well but got into a complex mix of virtual com ports when using other programs that didn't support it, like N1MM and DXLab.
Recently I found waterfallbandmap, and this worked nicely and was good for bidirectional control, although changing the filter settings moves the IF frequency slightly causing some inaccuracies in the frequency control. I doubt that can be fixed easily with either the RSP or the Softrock, although I guess the P3 knows how to do it - I've never used one. The IF frequency was about 8.215 MHz, I believe.
After reading about the RSP-DX, I decided to buy one before the prices went up. It will work with the IF, but also with the RX in/out which is on the same I/O board of the K3. Using the RX antenna in/out solves the IF-shift problem. The RX out is connected to a T adaptor which splits the signal between the RSP and the RX in. Enabling the RX antenna pushing the received signal through this cable so that both the K3 and the RSP can receive the signal. The ExtIO DLL tracks it (almost) perfectly. It will be perfect once I get around to calibrating the RSP or setting up a external frequency reference to both the K3 and the RSP. I'd go so far to recommend this setup instead of IF unless you have a specific reason for preferring the IF route (I'd like to know it, as maybe I'm missing something). I have an extra cable and antenna port on the RSP so I might try the IF route as well and get a good comparison.
There's no IF offset to worry about in this case, no issues with I/Q reversal when going to 6 metres, and back again when using the 2 metre transverter. It was simple and easy.
I haven't tried it with HDSDR yet. I've been using it with both N1MM and DXLab with Waterfallbandmap, but I will give it a try today if I have time, or over the next few days if I don't. With waterfallbandmap I needed to reduce the frequency range to the minimum (200kHz), increase the number of FFT buckets to the maximum, adjust the contrast and zoom in to get a good looking display with the skinny CW signals. With the default number of FFT buckets the signals showed up as blocks instead of dots & lines.
I'm looking forward to trying HDSDR. The RSP is a very capable unit. I'm sorry this is skirting around your question, but I'm hoping it might be helpful.