Category: free content


Have your own HAM SWL radio station!

Follow Quadrus SDR

Gadget of the past? HAM SWL radio station!

In most cases we write posts about unique designs and ides, which are useful for advanced level HAM SWL radios, e.g., this or that posts on software defined radio (SDR) technology. But what about the beginners? Well this post is for them! Ready, steady, HAM SWL Radio!

Some weeks ago I was surfing the internet looking for some new ideas for a special issue of Quadrus SDR. It was easy to find a creative idea for my problem, and to prove to my family that HF broadcasting is alive. We can access high quality radio service there based on new, digital operation mode (i.e., DRM), which has a very useful community for SDR fans. When I started to deal with HAM SWL radio, there were no opportunities such as the internet. It was ooch… 35+ years ago. We – the members of the community – talked to each other only using the radio at the club station or using our self-made radios at home, but it was an amazing experience that I never forget. I had my own HAM radio station at home – built with my own hands from scratch – with CW capability for the 80m ham radio band. Lovely, isn’t it? (and I was 17 years old when I made this…)

front internal top front

I have two sons. They are not interested in making, but they are professional in using gadgets. Like every teenager nowadays. Maybe my father said the same thing about my HAM radio equipment. Gadget.

Do or do not, there is no try

So, what about beginners? I found a very good post about how to start this kind of a hobby. Hobby? No! This is a way of life. I could not summarize this better then Gregory L. Charvat:

“The only way to get started is to build something. Start small, check out the QRP community, try making a single-conversion receiver, and move up to something with a crystal IF filter. Borrow and scale circuits from books such as these:

Or leverage complete ICs and modules like those from Mini-Circuits.  There is nothing like making that first long distance contact (DX) on radio gear you created from scratch.”

You can read the whole article on Hackaday.

But if you are more of a computer geek, you can switch to software implemented radio and start with less complex and less expensive SDRs or a professional one like Quadrus SDR from our webshop. Even I experienced that old fashioned radio moment Gregory mentioned above, when I first received a DRM station from Mubay, which was a very nice feeling for my radio infected heart. You can see the report on this reception here in the Quadrus SDR blog:

Further reading on DRM, the new digital HF broadcast technology:

And don’t forget to share your success stories or questions regarding SDR issues with us on our Facebook pageTwitter page, or G+ community page. Be social; whatever is your preferred platform, we are there !

Bertalan, HA6QU

Share Quadrus SDR

HF preselector filter

Follow Quadrus SDR

Direct digital HF receiver

Earlier we’ve introduced the concept of direct digital receivers in this blog.

Furthermore, VHF/UHF direct digital filters discussed:

In this operation mode the ADC input has to be kept clean from various spectrum components in other Nyquist bands. The input preselector filter helps in selecting the right part of the given Nyquist band.

The HF preselector filter

In case of high performance reception of HF signals, the main challenge is to prevent interference from higher frequency VHF/UHF signals. This may be achieved with a Low-Pass Filter (LPF) cutting the components above say 30-32 MHz, but that depends on the reception requirements. We have to carefully construct the filter such that it provides sufficient attenuation in the 88-108 MHz FM band, where the highest level signals may be found usually. The input bandwidth of the DRU-244A hardware is up to 440 MHz, thus the input filter should attenuation in the upper VHF/UHF band as well. This can be ensured with careful design and implementation using small, surface-mounted components. If we are concentrating on real HF signals, and are not interested in lower band mid- or long-wave reception, the input should be clean from high level AM broadcast signals as well, usually present in the spectrum below 1.6 MHz. For this purpose, a High-Pass Filter (HPF) should be inserted in the signal path with a 1.6 MHz corner frequency.

HF preselector filter design and realization

To satisfy the requirements of the HF input preselector filter described above, we’ve designed an input filter block with a cascaded HPF and LPF using a professional filter design software. The approximation is elliptic, ensuring a cutoff at 40 MHz. The implementation is a small PCB containing the HPF and LPF sections with SMA connectors at the ends and a place for an optional choke for remote powering capabilities of an active receiver antenna.

The photo of the finished HF preselector filters:
The measurement results up to 500MHz:


The full design package of the HF preselector filter, including the schematic and layout design in Protel (Altium Designer) file format, are available for download.

Share Quadrus SDR
software radio presentation

Free presentation on Software-Defined Radios

Follow Quadrus SDR

Software radio presentation

Free presentation on Software-Defined Radio (SDR) technology is available on the QUADRUS SDR platform site. This presentation was given at an advanced communication seminar by NATO Research and Technology Organization (NATO RTO). NATO RTO is now operating as NATO Science and Technology Organization under the NATO Collaboration Support Office. A high-speed, high-bandwidth converter family is shown with some example applications like wide-band SDR receiver and radar.

Share Quadrus SDR

Free introductory paper on Software-Defined Radio (SDR)

Follow Quadrus SDR

Our original paper on SDR development is now freely available on the QUADRUS SDR platform site. The paper introduces our high-speed, high-bandwidth domain converter solutions, and demonstrates their capability through practical examples, like our wideband SDR search-and-intercept receiver and our SDR radar. The paper was first published in the proceedings of the advanced communication seminar by the NATO Research and Technology Organization (NATO RTO) – now known as the NATO Science and Technology Organization under the NATO Collaboration Support Office.

Share Quadrus SDR