Sunday, January 31, 2016

QSL card for 100mW contact 16,194 km hand delivered

Yesterday I was emailed by Marek Petko, OK1BIL, of the Czeck Republic, who is visiting Australia for work. He noted that I had received his club's 100mW U3 WSPR beacon on 20m. Today at the ARNSW trash and treasure meeting, we met up and he handed me a QSL card.

Here's the report in the WSPRnet database:

The club is running a multi-band vertical antenna at their end and on my side it's a half size G5RV. The transceiver is an FT-817 and WSJT-X is running on MacOS.

Marek alerted me to the WSPR Challenge site which ranks wspr reporters on their relative 'receiving power'. I note that I'm the winner of the total of the distance to transmitting stations that I receive, presumably being in Australia and very far from everyone else helps us VKs:

I'm happy with my overall world ranking on 20m, the highest I've seen is 8.

Sunday, January 24, 2016

Cheap Windows 10 tablet running SDR# with SDRPlay

Wanting to get some hands on experience of Windows 10 in tablet mode led me to pick up a very reasonably priced Teclast tablet via Banggood. It's a "Teclast X98 Plus 64GB Intel Cherry Trail Z8300 Quad Core 1.84GHz 9.7 Inch Windows 10 Tablet PC".

The feature that attracted me is the screen resolution of 2048*1536, most of the cheap ones are much less.

I paid AU$276 including postage but the price seems to have crept up a little since then.

One thing I wanted to try was to see how well it would run SDR software so here it is running SDR# with an SDRPlay (which is powered by USB from the tablet).

As you see it's pretty usable although a bit more CPU performance would make the drag tuning smoother. This really has to be the future of radio receivers and possibly transceivers. A big responsive touch screen showing the spectrum is a great way to see what's on the band. The SDRPlay has a particularly wide band so you can zoom out to find activity.

Friday, January 22, 2016

Digital QST - does anyone like this reader?

I recently re-joined the ARRL so that I can get QST magazine. These days I prefer to read books on tablets or a Kindle. I was hoping that in the years since I last subscribed it might have improved but alas it's as bad as before.

The publishing and reading system is the proprietary nxtbook system. I'm an iOS user, it might be different on Android, but I find the reading experience:

  • Slow
  • Ugly
  • Extremely annoying to use
Judging by the "Digital QST FAQ" I'm not alone in having a bad experience.

Why is QST in digital format instead of PDF format?

"Research has shown that those who read magazines on electronic devices prefer this type of format. The digital format also allows us to use multimedia content and other features that are not available with "raw" PDF files. In addition, the Nxtbook digital format allows us to use digital rights management so that the digital edition of QST  cannot be viewed or downloaded unless you are an ARRL member."

Really ARRL? What research is this?

My QST app is slow and/or crashes. What can I do?

"We are sorry to hear that you are experiencing crashing and download problems. For best performance, shut down any other apps running in the background, force quit the app, then re-open it, or turn your device off and then turn it back on. Finally, you can try deleting and re-installing the app."

Hmm, or fix the app.

I suspect that the reason the ARRL has gone with the horrible nxtbook technology is that it appeared to offer some sort of DRM (digital rights management). Aside from a tiny bit of security through obscurity, this is certainly not the case at the moment.

I'll refrain from revealing the details but it seems that after a bit of logging in and reading JSON, pages of the magazine are downloaded by the app as simple JPEG image files with guessable urls like this. Click and you'll find that the image urls are not protected at all.

Others, like MikeW have proposed schemes to print to pdf from the app, but that is not a good solution (but again illustrates that the ARRL are being ripped off if they think they are buying DRM).

What I want, as a digital reader

First, what I don't want... tablet screens are mostly too small to show a full printed page with three or more columns of text. Zooming in and out is painful. Don't give me an image or even a PDF of the printed magazine.

The native reading experience on iOS iBooks, Android's reader and the Kindle reader are all excellent. They each have DRM that pretty much works.

I recommend selling QST (and that goes for you too WIA Amateur Radio Magazine), through each platform's native publication system. Arrange the content as a stream of single column text (with images) and give up the page layout.

This means that users can choose how they view, can increase or decrease the font size and pay you for your good work.

Monday, January 18, 2016

Radio gear as used at Mawson's hut in the antarctic

We visited the replica of Mawson's hut in Hobart this week and it has an interesting reproduction of the radio gear that would have been used.

One thing that immediately struck me was the spiral inductors used in the antenna tuner.

The capacitors are also novel.

I assume this gear generated very high voltages.

Saturday, January 09, 2016

VFO with Si5351 and rotary encoder

Playing around with the Si5351 clock generator to make a VFO for a 7MHz direct conversion receiver that will be tuned with a rotary encoder. Here's the simplest Arduino sketch:

#include "si5351.h"
#include "Wire.h"

Si5351 si5351;

Encoder myEnc(5, 6);

void setup()
  // Start serial and initialize the Si5351

  // Set CLK0 to output 14 MHz with a fixed PLL frequency
  si5351.set_pll(SI5351_PLL_FIXED, SI5351_PLLA);
  si5351.set_freq(7000000ULL, SI5351_PLL_FIXED, SI5351_CLK0);

long oldPosition  = -999;
void loop()
  long newPosition =;
  if (newPosition != oldPosition) {
    oldPosition = newPosition;
    unsigned long int frequency = 7000000ULL + newPosition;
    si5351.set_freq(frequency, SI5351_PLL_FIXED, SI5351_CLK0);

And here's how it behaves (listen for the tone on the receiver in the background).

The flaw with this code is that if you turn the knob too fast it can't adjust the Si5351 fast enough to keep up. I have some vague ideas about how to deal with this, perhaps only updating a few times a second.