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K2 Panadapter

This page is work in progress and will be updated frequently. 

Introduction

For years I'm onto Instagram and one of the accounts I follow is the account of OM Luca Facchinetti IW2NDH because he makes a very nice audio DSP for hamradio rigs (one still on my whish list).

But recently he is teasing us with a standalone Panadapter, and 9 June 2023, he made a post announcing it could be ordered and published a page on his website about it. So I contacted OM Luca, we exchanged a few e-mails and I bought one of his Panadapter PCB's and one of the IF PCB's. The last one I didn't need for my K2, but maybe I'm going to upgrade my FT817 or my 818 with it ;-)

OM Luca doesn't sell the TFT displays (you need one with a a ILI9341 SPI controller), so I ordered one at Amazon.nl (link) but they are very common available. 

The package from Italy 

On monday 19 June 2023, a small package was dropped in my letterbox and in it, very well packed I found the 2 PCB's i ordered from OM Luca.  

The Panadapter PCB, not that there is no header installed for the display because the display can be installed directly to the PCB (although I prefer headers).

The very tiny IF buffer PCB, excellent work as I may say. But we put that aside for later. 

Hooking up the display 

As mentioned before I don't want to solder the TFT display directly to the Panadapter PCB. So I soldered a female header to the Panadapter PCB, allowing me to seperate the display when I want to because I'm not sure which case I'm going to use for the display. Check out OM Luca's page for a very fine 3D printed case (including buttons etc). 

The proof of pudding . . . oh wait . . . 

With the display installed of course I wanted to give it a try, but first the IF frequency has to be set. OM Luca send me a first draft version of the manual, explaining how to setup the Panadapter. 

The first setup is done by connecting the Panadapter PCB to your computer and you computer will find a serial port which you can connect to. Once you start up your terminal program (for example Putty, minicom etc) you open that port and you can configure the Panadapter with some simple commands (and there is a simple help command).

The commands are : 

• corr = to adjust the frequency of local oscillator
• freq = to set the IF frequency (in Hz, so 4914KHz should be entered like 4914000)
• gain = to set the hardware programmable amplifier with gain between 0 and 47.5 dB, in steps of 0.5 dB
• help = show the commands availble. 
• mirr = to set the direction of the IF (some rigs have a mirrored IF)
• save = save the current settings in flash

But for now I will limit it to : help, freq, and save.

On my Linux computer I have minicom installed (Windows users can use Putty) and I could connect to the Panadapter with the command : 

$ minicom -b 9600 -D /dev/ttyACM0

ch> help
Commands: corr freq gain help mirr stat save
ch> freq
usage: freq (frequency(Hz))
ch>

After entering the IF frequency (4914KHz) and saving it : 

ch> freq 4914000
ch> save

I was ready to give it a try . . . . . 

The proof of pudding . . . Take 2

Eager I hooked the Panadapter to my K2 in which I already had installed IF adapter with output a few months ago. Using a USB powerbank as power supply, I powered up my K2 and . . . . Almost no signals on the display even after I switch in the gain up to 30dB . . . well that was disappointing. 

But I remembered that I installed the IF adapter in my K2 including a 30dB attenuator to prevent overdrive of the RTL-SDR stick.

So I removed the attenuator and bingo . . . we have some serious signals on the display :-) 

Even with 0 dB signals a coming through nicely and with the gain steps of 10, 20 and 30, I can pull signals out of the noise to get a better look.  

Here's a small video of the Panadapter in action (switching between the 3 gain settings) :  

 

 

Boxing it all up

Although I have plans to make one for my own in the style of the Elecraft K2, I fired up the printer to make print a enclosure a which OM Luca has on his website (safer to have the Panadapter boxed-up until I have the final enclosure ready).

So after almost 11 hours of printing, the parts where ready.

 

When I placed the TFT screen into the enclosure I wasn't that happy that it was mounted only on one side. So based on the 3.2" front I designed a holder in which I could slide the TFT display and I could glue to the front (for those who want it, please contact me and I send you the STL file). The holder also has 2 holes in it to drill 2 holes in the front, so 4 bolts are visible (2 are dummies and pure for my OCD ;-) 

Holder glued  into place . . . 

 

. . . and the holes for the dummy bolts are drilled. 

 

The dummy bolts are normal bolts as used to mount the display but cut of and glued into place.

 

The TFT display fits in perfectly and can be positions as needed. 

 

2 M3 bolts and 2 M3 black nylon stands keep the display in place. 

 

The Panadapter PCB is placed and a M3 nut fixates everything. 

 

 

The 2 dummy bolts are glued in place and also the buttons are on there correct spot.

 

USB power applied and everything seems to work as designed.

 

I'm very happy with the result 

Testing in real life

When I received the brass insert nuts, I put everything together so I could use it in real life. On the next morning, I monitored the bands and found Etienne OS8D/P who was activating a castle. 

I made a short clip showing a few of the possibilities of the Panadapter (different gains and display layouts). 

The Panadapter allows to see a different spectrum widths (16, 32, 48, 64, 128 and 192 KHz). The image below shows the 48KHz spectrum width on the 40m band (center 7125KHz).

But this project isn't far from ready so stay tuned.

 

Calibrating the freq reference.

OM Luca pointed out that the you can calibrate the freq reference of the Panadapter. To do this I used my Rigol DG1022Z to generate a 10MHz 0dBm signal with a unshielded QRP-Labs dummy load connected to the output. 

I switched the Panadapter to a 16KHz spectrum view, and used a small pickup coil connected to the input of the Panadapter to pickup the signal. As shown below it was off by aprx 3KHz. 

Initially the corr value was 7930, but after some changes tweaking I managed to pull it close to zero. 

And by incrementing the frequency of the generator with 1KHz the waterfall shows them almost exact where to expect them. 

 

Now connecting the Panadapter to my K2, and using a pickup coil on the K2 antenna input, I could zero beat the signal. There is a  aprx S5 signal (it's measures RF), but no sound, so zero beat accomplished. 

And when you have the generator all powered up, then why don't we give it a try generating a nice AM signal with a 1KHz modulation with a depth of 50%? 

Look at this beauty. 

 

To be continued . . . . . 

It seems that LSB and USB are swapped and my guess is that it comes to the fact that the Elecraft K2 is a single conversion with a low IF frequency (4915KHz down conversion results in swapping the orientation of the sidebands aka sideband inversion see page 111 from the K2 manual). Then I remembered that when I tested my K2 IF I used a SDR dongle with a upconverter and had the same problem in gqrx sdr software. I had to swap the I & Q to fix the USB/LSB swap.  So I expect that the software for the Panadapter was designed for a up conversion rig (like the Kenwood TS-570) in which there is no sideband inversion. 
For reference I took out my uBitx V3 (it's uses upconversion), hooked it up, set IF to 45MHz and there everything was normal thinking that it might prove my theory about sideband inversion.  

But overall the Panadapter is working like a charm and it's a nice addition to my rigs. 

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