Search results for: Marty Wittrock

Videos showing the LimeSDR in Action on HF with GQRX

Over on YouTube LimeSDR beta tester Marty Wittrock has uploaded several videos showing the LimeSDR receiving HF frequencies. In the first video Marty shows it receiving the USB voice on the 20m band during the 2016 ARRL field day. The second video shows reception of PSK31 signals. More videos are available on his channel if you are interested.

In the videos he uses GQRX and his own KN0CK HF upconverter. The LimeSDR should be able to receive HF on its own without an upconverter, but at the moment the HF capabilities have not been programmed into the drivers yet, so during this beta testing period an upconverter is required.

Marty also wrote in to us to make some comments on his experiences with the LimeSDR. He believes that the LimeSDR is amazing and writes:

The quality of the receive and audio [of the LimeSDR] is incredible against other SDRs I have in the house (Flex 5000A, RTL-SDR, HackRF, Red Pitaya – and soon SDRPlay).

Marty also writes that he will soon have more videos of the LimeSDR operating in Windows with SDRConsole in the near future, and we will post those videos too when they are ready.

LimeSDR Receiving 20m Voice on USB

LimeSDR Receiving PSK31 on the 20m Band

Testing the RTL-SDR on Windows 10 reader Marty Wittrock has written in to let us know that he has been successful in getting his HF modified “KN0CK” RTL-SDRs (and by extension standard RTL-SDRs) to work with Zadig and HDSDR on a PC running the Windows 10 technical preview on a VMWare image.

We decided to also test RTL-SDR compatibility with other common software on our own Windows 10 system. We tested SDR#, SDR-Radio, CubicSDR and Unitrunker and found them all to work fine with no problems either. Finally, we also tested the Airpsy and SDRPlay on Windows 10 and found no problems with those devices either.

HDSDR Running on Windows 10
HDSDR Running on Windows 10

An interesting RTL-SDR direct sampling modification

Over on the Reddit RTL-SDR discussion board user pksato has posted an image of his direct sampling modified RTL-SDR dongle. His mod includes a simple common base amplifier with 9dB gain, an impedance transformer with calculated output impedance of 50 Ohms and a 5V power filter.

The direct sampling mod allows you to modify your RTL-SDR to receive HF frequencies, without the need for an upconverter. It requires a hardware mod that can be as simple as soldering a wire to one of the RTL2832U pins, but for improved results you will need filters, impedance transformers and amplifiers. There is more information about direct sampling here.

More information and images about pskato’s mod can be found on the Reddit thread.

We also note that amateur radio hobbyist KN0CK (aka Marty Wittrock) sells direct sampling modified dongles that are modified in a similar way to pskato’s mod (circuit placed on top of the RTL-SDR PCB). His products can be found at

Direct Sampling Modified RTL-SDR.
Direct Sampling Modified RTL-SDR.
Direct sampling mod with amplifier circuit schematic by pskato.
Direct sampling mod with amplifier circuit schematic by pskato.

“Worlds Smallest HF Receiver” (KN0CK Integrated RTL-SDR + Upconverter)

Update: KN0CKs products are now available at

Yesterday Marty (KN0CK), developer of the miniature integrated HF upconverter for the RTL-SDR that was recently posted wrote into us with some updates.

Worlds Smallest HF Receiver

The version we posted about recently was his “Production 3” version. He writes to tell us that along with his “Production 3” release he created a 15mm x 15mm “Small Form Factor” radio enclosed in one of the smaller RTL2832 tuner dongles, which is the “Worlds Smallest HF Receiver”. Marty writes

This is a non-preamplified model receiver but has EXCELLENT performance for what you get.  It has become my most favorite receiver to use here in the shack because of its size and performance – not that I don’t like the preamplified models of my receiver line.  I just like how well it performs for such a small receiver – it’s truly unique.

This Small Form Factor Radio has an operating frequency of 100kHz to 54 MHz allowing the 6m band coverage that everyone was so rabid about.  The entire design is predicated on using 0402 SMT parts except for what can’t be squeezed down (the crystal oscillator and the SA612 mixer).  I have built 6 of these radios and have 3 on hand now for sale now.  They retail out at $70.00 because they are HARD to manufacture and are hand-assembled and tested.

If you are interested you can contact Marty at martywittrock_AT_gmail_DOT_com.

Below are some images. The first image shows the size of the worlds smallest HF receiver, the second shows an example of expected HF performance in HDSDR, and the third image shows the upconverter circuit layout.

Worlds Smallest HF Receiver

AM Band Reception from Smallest HF Radio

Smallest HF Radio 15mm x 15mm Circuit Plot

Production 4 Model

In addition to creating the worlds smallest HF receiver, KN0CK has also been working on his “Production 4” model, which has the same performance as his “Production 3” model posted earlier, but is capable of being installed into any RTL2832 DVB-T radio.

This model is now released and will be available for sale at when “Production 3” is sold out.

Marty writes

The latest production I have is termed as ‘Production 4’ and became a hybrid of my ‘Small Form Factor Radio’ and the existing ‘Production 3’ design.  I took the best of both worlds and then modified the low pass filter to operate into 6m like I did on the Small Form Factor Radio, too.

[The ability to install into any RTL2832 DVB-T radio] was the reason for this final [Production 4] spin – so it could go into the DVB-T radios that incorporated the goofy through-hole capacitors they used in their power supply design (and also cheaper to sell).

I’ve incorporated this new HF upconverter design into the RTL2832/820T model radios, too, and while the performance of the DVB-T stick is not wonderful, it works pretty well with the HF Upconverter I have designed and installed in it.

I must tell you that the RTL2832/820T model radios are the cheapest out there and have 3 goofy through-hole caps in there that made it impossible to install my ‘Production 3’ model HF Upconverter into that radio….Until Production 4 came along… 🙂

The three images below show the circuit layout, upconverter and RTL-SDR dongle together, and upconverter circuit by itself.

Production 4 Board Plot

Receiver Opened Up

Upconverter Board by Itself View1

Future Models from KN0CK and Transmit Capabilities

For the future plans of his worlds smallest HF receiver Marty writes

At this time, I’m going to respin my ‘Small Form Factor’ board to solder the crystal oscillator directly on the board like the Production 4 models do (for awhile, I didn’t have a circuit pads for that oscillator and had to hand wire those on the back of the ‘Production 3’ boards.  Production 4 cleared that issue and now I’ll clean up the Small Form Factor radio the same way.

Finally, Marty talks about his plans to create a transmit (TX) modification to the dongle. He writes

[I] am working toward a transmit side app for this stick – – target is December to make that happen.  I would keep the ‘Production 3’ form factor and then put the TX stuff on the back side of the board.

We look forward to Marty KN0CKs future work, which is likely to be posted about first by KF7LZE, a friend of Marty’s on KF7LZE’s popular blog.