While amateur radio enthusiasts have been able to communicate with astronauts on the International Space Station since its inauguration in 2000, a new digital amateur television (DATV) transmitter installed in the Columbus laboratory will add a visual element to those conversations, the European Space Agency announced on Monday.
For the past 14 years, people on Earth have been able to communicate with the ISS crew using standard radio equipment, the ESA said. The DATV system was developed by Kayser Italia and arrived at the station last August on board Japan’s space freighter. It was then connected to an existing S-band antenna in the Columbus laboratory.
The video signal works like standard TV broadcasts in that the crew members will not be able to see their audience, but they will be able to hear their questions and comments over the regular amateur radio system. The sessions have to be brief, as the connection requires a direct line of sight. Since the ISS travels at speeds of more than 17,000 mph, it quickly passes through the field of view of Earth-based amateur stations, the agency said.
The crew finished commissioning the set-up for the device on April 12, and NASA astronaut Mike Hopkins was the first member to broadcast over what has been dubbed Ham TV. He took part in a video chat with ground stations in Livorno, Casale Monferrato and Matera, Italy.
The ESA explained that they have contributed five ground antennas and equipment to the Amateur Radio on the International Space Station (ARISS) organization, which can be easily transported and repositioned as needed in order to receive video from the ISS when it flies overhead. When linked together, the agency said that the station is capable of providing up to 20 minutes of contact at any given time.
According to ARISS, the Ham Video transmitted operates with a Canon XF-305 camera. It has download frequencies of 2.422 GHz and 2.437 GHz, contingency frequencies of 2.369 GHz and 2.395 GHz, and a DVB-S like signal. Other characteristics include a DVB-S like signal (without PMT tables), symbol rates of 1.3 Ms/s, 2.0 Ms/s, FEC of 1/2, video PID of 256, audio PID 257 and RF radiated power (approximately 10 W EIRP).
“Ham TV will add to ham radio for space educational purposes, offering schoolchildren the chance to talk and see astronauts in space with simple equipment,” the ESA said. “Anybody can still hail the Station via radio and, if an astronaut floats by the always-on receiver, they might just pick up and answer the call.”
While I’m finishing up the Puxing/Wouxun review I started a Google+ community to discuss Chinese ham-related products. These could be (but not limited to) radios, test equipment, accessories, kits, spare parts or components.
I also plan to invite manufacturers and sellers to join, which will give members the opportunity to give feedback and ask questions.
There’s a fine line between information and SPAM; this will defined in more detail later in time.
Normally I review radios separately, but this time I will make an exception. Both the Puxing PX-UV973 and the Wouxun KG-UV8D are a new breed of Chinese radios. Both have two independent VFOs, both are cross-band capable. In part one I will discuss some of the gory details, but focus a bit more on theory.
In order to be cross-band capable, you need two independent VFOs. The idea itself is far from new: the Standard C520/C528, manufactured from 1989 until 1993, could do it too. The concept of independent VFOs and cross-band repeat capability was abandoned in favor of models with only one oscillator, which were much cheaper to produce. Modern radios are still dual-band, but can’t listen to both bands simultaneously, nor do cross-band repeat. Instead we got dual watch radios, which switch between both bands on regular intervals to check for activity.
Not only are dual band / dual watch radios much cheaper to produce, you will also avoid a number of technical pitfalls. Cramming two transceivers into one package is the easy part, making sure these two transceivers won’t influence each other in some negative way is another thing. That’s hard, very hard, especially when you combine two amateur bands like 2 meters and 70 centimeters. Ever calculated the third harmonics of 145 MHz?
Cross-band capability makes sense in a number of situations, but in a hand held? A hand held is supposed to be just that – a portable transceiver. In the best of circumstances your little (negative gain) antenna will be about 2 meters above ground, in the worst case scenario (clipped to your belt) around 1 meter above ground. Cross-banding from such a low altitude is rather pointless.
In order to put the system to good use, you will need to connect the radio to an outdoor antenna, preferably as high above ground as possible. In that respect a cross-band system is no different from a normal repeater system: antenna height is everything. While this will ensure that range problems will be solved, it might introduce another problem: receiver overload. Whether this is a problem or not depends on a lot of factors (design, RF pollution in the area), but so far all hand helds I’ve seen can’t match the filtering of most mobile radios.
Problem 1: harmonic suppression
If there’s any situation in which you don’t want to see harmonics at all, it is in these cross-band capable radios. To my surprise both Puxing as well as Wouxun nailed this.
- Puxing PX-UV973: -76dBc on VHF, -65dBc on UHF
- Wouxun KG-UV8D: -65dBc on VHF, -64dBc on UHF
Third harmonics and above undetectable.
Problem 2: sensitivity
A cross-band capable radio needs much better RX filtering. Better RX filters however will also introduce a certain amount of insertion loss. Because of this – and assuming both manufacturers did it right – I expected these radios to be less sensitive than we got used to.
- Puxing PX-UV973: -120 dBm on VHF, -120 dBm on UHF
- Wouxun KG-UV8D: -122 dBm on VHF, -121 dBm on UHF
To put this in perspective: there have been a number of radios reviewed here what could pull of an astounding -129dBm. This means that both radios discussed here have sacrificed about 6dBm in order to get the filtering right. Before you look at these numbers in disgust: less sensitivity is far better than crappy filtering.
Problem 3: preventing both oscillators of interfering with each other
Here both radios fail miserably. For some reason both manufacturers weren’t able to to get this right, resulting in an awful lot of spurious emissions up and down the carrier.
The problem is most evident when you’re receiving around the third harmonics of your transmit frequency. Because my test frequencies are always 145 MHz and 435 MHz (mid-band for European hams), it was impossible to miss.
This is how 145 MHz signals looks like on the spectrum analyzer:
This image is valid for both radios. When you change the RX frequency, the distance between the peaks will change. When you lower the RX frequency enough the peaks will eventually disappear from the screen. Before you think that the problem is gone — nope. As soon as you adjust the frequency span of the analyzer, they’re back in town. The peaks got smaller and smaller eventually, but never disappeared completely.
This behavior is a problem, a really big problem. If you prefer clean signals under all conditions, these radios are not for you.
(to be continued)
Remember the various posts about Wouxun handhelds losing memory contents? Although the chance of encountering this problem seems to be remote, it does happen. A small component (a 24C64 serial memory IC) can give up in time.
The good news: it can be repaired/replaced at almost no cost (about 60 cents). The bad news: you need to be comfortable with working on small components and must have the tools to do it. If you don’t, have it done by someone with more experience.
The complete repair guide can be read in detail on Mike Mercury’s, which is the website of Tim N8NQH.
Link to a Chinese eBay seller (10 pieces for $2.38): http://www.ebay.nl/itm/290951221455