A drmna.info exclusive! Stephan Schaa talks about himself and the Pappradio!
For the first time in English, Stephan talks about his interest in radio, his involvement at HCJB Germany and his legendary and innovative Pappradio. He also tells us where he thinks DRM and DRM portable receivers are going.
Q: Stephan, what got you interested in HCJB and DRM?
A: I've been listening to HCJB's programming in German and English from the end of the 80s on. In the Mid 90s I lost a little bit the connection to shortwave and I went more to Internet and satellite, but with the development of DRM and the combination of computer and shortwave (SDR) I got back.
I bought the first DRM Kit from Elektor Magazine which has been created by Burkhard Kainka. This worked very well even as a simple single hetrodyne receiver with 455 khz IF.
When my brother Marco decided to make the practical part of his University studies at the German department of HCJB in Quito about three years ago, his connection to HCJB got closer, and mine too. At that time there where some test transmissions in DRM from Pifo [HCJB transmitter site in Ecuador - Ed.] and I always tried to receive them in Europe even if they were directed to the U.S.
There was not much to receive here in Europe from Pifo with 4 kW only and out of direction reception, but I got a little bit of signal here in Germany which I always wrote into the DRMRX forum. And I always asked Doug Weber if the could make some tests to Europe, too. The guys at HCJB didn't expect that the 4 kW would make it to Europe and so first times they refused it. But after some reports they changed their mind and a 14 day test with target Europe was scheduled.
After some frequency changing and tweaking it turned out that the transmissions to Europe worked very well and so the tests were extended from 14 days to one month and then even longer to some more months and at the end the tests lasted 2 1/2 years till Pifo was closed down first with the big steerable antenna and later to the end with a simple rhombic antenna.
These good results were so unexpected that even DW put the transmissions into their monitoring system and measured the signal all through Europe (with great results). (I think HCJB was the first station that used 14 kBit AAC+ with Mode A over these big distances.)
Q: Tell us how the Pappradio came into existence.
A: This is the moment when the Name "Pappradio" came up: As I wrote, my brother Marco has been in Quito at that time and he wanted to try to listen to the DRM transmissions there, too. And he asked me how. And so I tried to solder some parts together to make a direct-down-conversion RX to connect to a computer.
This worked fairly good and I sent it to him through the mail in the center of a paper cardboard.
When it was shown to the people at HCJB one said "oh, a paper radio". This was when the name was born. Iris Rauscher from the German department put it into the German name "Pappradio". As the time went on the development went on, too. And even now as no cardboard-direct-conversion-RX is in the current Pappradio, the name stayed.
Q: Give us some technical specifications of the Pappradio.
Today the Pappradio is a I/Q - direct-down-conversion HF front-end RX with 4 bandpass-filters for the shortwave range (5th order) and 3 step attenuator. (An add-on board for medium wave and longwave filters will follow in a few weeks, I'm currently working on it.)
At the cost of a Pappradio it is not possible use a high-end DDS or so as VFO. But the PLL we use is very good in noise and jitter performance and so with this design I can easily receive "real world DRM transmissions" with SNR higher than 40 dB on a daily basis (in the "Lab" up to 50 dB and more with antenna about 1m away from the DRM exciter).
It's a lot of fun to look at the spectrumscope (up to 192 kHz bandwidth depending on the sample rate of the soundcard of the PC used) and the waterfalls to look what happens on shortwave - digital and analog!
The Pappradio is for sure not the best HF radio you can get on the market: the Perseus, Quicksilver, Excalibur, Net-SDR and company are surely much better. But they cost at least 10 times the price a Pappradio costs and a lot of people can't afford to buy them or don't want to spend that much money for their first steps into the digital world of "Software Defined Radio".
Q: There certainly is a dearth of affordable DRM receiver sets on the market!
A: This is the biggest problem of the DRM system: the development of radios has been neglected for a long time. There are or have been some few models on the market, but they are expensive and weren't that good as everyone wished they should be. So what to do?
The "Pappradio" and other PC-based SDRs can help the more technically interested people to be able to listen to DRM, but an affordable, good standalone radio would be very, very necessary to help DRM take off.
The problem is that it would take a lot of effort for a company to develop a DRM radio. The bigger corporations don't want to do that and the smaller ones aren't able to finance that.
So my question is: would it be possible to develop a "creative commons" hardware platform and a open source software kit to help eliminating this problem? I've some ideas how to build a cheap and good HF front-end and I would like to use Android as base system for processing the signal.
Q: I'm an advocate of the open source movement, and so is DRM Consortium. In your mind, what are the benefits of this approach?
A: 1. Android is Open Source and ready for multimedia use.
As an Open Source platform everyone that likes to can build applications or can do modifications for his hardware. Android has a good user interface and is capable of multimedia content, for example AAC+ is already included for the Multimedia Player.
2. Existing pads and phones could be upgraded with a "Radio Dongle" and a simple app to upgrade them to DRM-ready radios.
The analysts say that the Android phones and pads market will grow very much over the next few years. With a Radio Dongle for - lets say $30-40 they could be able to receive analog and digital radio very comfortably even with a color touchscreen and multimedia extensions.
3. Processing power is getting cheaper and smaller every day.
As more and more smartphones and (Internet) pads come on the market, the price for processing power drops and the devices getting more and more battery saving. A (very small) processor that runs Android starts at about $8-10, TFT screens start at maybe $3. Existing Android pads run more than 8 hours with one battery charge. So it should be possible to build a basic and a multimedia DRM radio for hardware costs < $50-60.
4. There are some very cheap development platforms available for Android.
Normally you have to pay a lot of bucks to get a development board with software from a manufacturer. But there are some very cheap development platforms available which are ready for Android use. The Beagleboard is one of them.
If companies can take a open source software DRM package and can use a creative commons hardware design, they can lower their engineering expenses by at least 60-80%. In my opinion then they might be able to produce a DRM radio and put it on the market at a reasonable price point. My question: are there people out there that would like to join a DRM Radio Project?
For the hardware part I've already some things in mind, but there are lots of things to do at the software part: OFDM libraries, User Interface for Android...
So what do you think? Wouldn't it be great if the community could develop a free platform to help shortwave radio to get ready for the future?
Vielen Dank Stephan for a great interview. Keep us appraised of your further developments and the North American availability of Pappradio. I’m certain that the DRMNA community will be glad to participate in an endeavor as exciting as this one!
