Saturday, 26 October 2013

Software Defined Radio- SDR




Software Defined Radio (SDR), mainly receivers are what really got me back into amateur radio earlier this year, after a 40 year absence.
 
I had a brief revisit to radio 10 years ago, when I was medically retired, but was disappointed that so little seemed to have changed.

So I went and played (when I was able) with computers, audio, video, home cinema and satellite TV (and sport cars) instead. But once I had done about all I could do there, I was after something new.

Then I re-discovered radio starting with the TV dongle software defined radio, rtlsdr.

While I am still annoyed that mainstream transceivers (that I could afford; or justify) are still little changed, SDRs really are a hoot; you can see what is out there- lots of really weird stuff and no dial twirling hoping to find anything of interest.

I started with the TV dongles; they are not to be dismissed lightly, a couple of MHz bandwidth, 60 MHz-1200GHz range, all for $20. I bought a discone antenna and put it up as high as I could with a piece of pipe ~5m. Still interesting looking at FM, TV and all manner of odd things on VHF/UHF; still much to be done there. See http://www.rtl-sdr.com/rtl-sdr-quick-start-guide/. It is an excellent blog now;. 

Added an up-converter and started using them on HF (I have a “Ham it up” and another simpler one. Silicon Chip magazine has been doing a series on SDRs over the past few months).

Minikits in SA do very sharp bandpass filter kits for the amateur bands, my first go at surface-mount components; not easy but it works. In Helensvale they do not seem to make a big difference. There does not seem to be much interference (other than what I generate with a couple of computers and wireless network).
 
I had bought a secondhand multiband vertical ten years earlier, so I put that up and could get onto the amateur bands; mainly 40 and 20m. That was a real buzz; finally being able to easily see what was on the band (all at once) and to quickly tune a signal, even if they paused, as they still showed up in the SDRs waterfall.

The SDR software is as important as the hardware. I tried everything I could find. Of all of them, SDR-Console is my favorite, although V2 is still in beta, with features being added all the time. http://v2.sdr-radio.com/. HDR# is a simple one, but fairly easy to get going. See http://www.rtl-sdr.com/rtl-sdr-quick-start-guide/ for lots more discussion. (The rtl-sdr dongles are cheap to get going, but the drivers can be a problem, first finding the ones you need. Second, if you are running Windows 8, it won’t let you use un-signed drivers. It can be done by restarting in a special mode, but it is a bit involved. That is not a criticism of W8, I recommend it.)

Another good one is HDSDR  http://www.hdsdr.de/. It is a more mature version and can do CAT control of transceivers.

I had an old Yaesu TRX but thought I would get a new “state of the art” one, eventually settling on an Icom IC-7410. I can control it using an SDR with HDSDR via USB CAT, which was pretty neat fun.

I decided I should get a better, but not too expensive, SDR than a TV dongle and bought an AFEDI-Net  US$250  http://www.afedri-sdr.com/. Network-based, nearly 2 MHz bandwidth, DC to 30Mhz. They are very good, especially with SDR-Console; which has just added CAT-control to V2, but I haven’t tried it yet.

I also have a  FUNcube Dongle Pro+ http://www.funcubedongle.com/  ~£150. DC – 1900 GHz, but only 192 kHz bandwidth (the original amateur SDRs were sound-card based with 192 kHz as a maximum). The bandwidth is not a limitation on HF, but annoying on VHF and up.

I have never been much of an operator, mainly tinkering, even when I had my first station (VK2ZXI) while at high school, 2m simplex at Echuca/Moama on the Murray River. But, eventually I wanted to transmit. Not so simple with a TRX and a separate receiver.

I bought a special antenna switch, ELAD ASW-1 ANTENNA SWITCHBOX RX-TX http://ecom.eladit.com/epages/990298944.sf/en_GB/?ObjectPath=/Shops/990298944/Products/%22ELAD%20ASW-1%22. The switch lets me use the TRX transmitter and the SDR, but not the TRX receiver. It works well, especially using CAT control.

But never being happy, I wanted to be able to use the Icom’s receiver as well, as it is supposed to be one of the best. I imported a special RTX/RX antenna switch from the UK, but have yet to set it up. One problem is that the SDRs must be protected (antenna input grounded) before the TX starts; not a simple problem, although I think I am a bit paranoid as the ICOM takes a while to switch from RX to TX. I have a sequencer from Minikits that will get around the problem, but again haven’t got it going yet.

Another way around the antenna sharing is to tap into the TRX’s first IF (64,455 kHz), above the roofing filters (the key to a good RX). I have made a start with that, ICOM even have a socketed test point to do it (some hesitation playing inside a new $2000 TRX! Much reading of circuit diagrams). With the plug (hard to get but only $1.50 and are used on all main brands of RTX), isolation amplifier  http://www.cliftonlaboratories.com/z10000_buffer_amp.htm (gives details of how it is done), preferably through a bandpass filter (obtained but not installed) then to Funcube. I have it running, but not permanently installed.

A SDR at the first IF is really neat. It can be used as a panadator for the RX, although the SDRs display gets a bit woozy as I tune. However, you can see a large section of the band with the SDR and all the little signals that are swamped just using audio. The SDR can be used indepentently as a rx and tune within the first IF; basically using all the good front end of the RTX that the SDR doesn’t have.
 
My SDR activities are on hold at the moment while I try and concentrate on getting decent antennas and tiltable mast (off a yacht) working.
 
Concrete has been poured and the mast is assembled and works. Initially had the end siting on a  saw horse while the concrete set, but my wife hit her head on it. So I put it on a step ladder; now I hit my head on it. I must tilt it up and out of the way.
 

 

Low-cost Amateur Digital Television- DVB-T ATV using UT-100C transmitter USB dongle




I am setting up a DVB-T tx on the atv channel on 70 cm. I am using a UT-100c USB dongle http://www.hides.com.tw/product_eng.html http://www.idealez.com/hides/product-detail/en_US/69859. It is only US$169 and produces 1 mW of DVB-T output. The software is at https://drive.google.com/folderview?id=0BzoVnSl8XNdQMmZPbDhEczA2RjA&usp=sharing. There are some pdfs of the device and how the software works.
 
To use the dongle, only the windows driver and PC2TV are needed. With PC2TV, only the video works at the moment. PC2TV takes a deal of setting up but will work with a PC/laptop webcam. 

Only the UT-100C dongle is needed to start. Some ordinary domestic DVB-T receivers can be used. The DVB-T channels in Australia are 7 MHz wide, the same as free to air TV.

As such, the standard Australian DVB-TV settings can be used. At 1 mW, it is possible to xmit on a free commercial channel and tune a TV to it, without causing any dramas. However, to work on the 70 cm channel, a TV dongle or set top box that can tune outside the normal free to air channels is needed. The cheapest and simplest way is to use a DVB-T receiver dongle (~$20)on the same PC as the xmitter; sounds bizarre but works. It is necessary to edit the channel parameters for the dongle, but that is relatively easy. 

The other person, I know of, using these TX dongles reports at http://www.oe7forum.at/viewtopic.php?f=7&t=410. It is German, but he has photos and web links. His work is also on the British ATV forum http://www.batc.org.uk/forum/viewtopic.php?f=15&t=3158 and http://forums.radioreference.com/amateur-radio-equipment/269047-dvb-t-70cm-23cm-2-3mhz-bw.html.

The Europeans are limited to a 2 MHz bandwidth, whereas we can use up to 7 MHz, hence their need for narrow bandwidth receivers (that are available from Hides). I bought the low bandwidth receiver ($80) but haven't used it.

In terms of other amateur DVB ATV activities:  

There is a long-running DVB ATV amateur project DATVexpress, a collaboration between amateurs in the USA and UK.  http://g4guo.blogspot.com.au/ http://datv-express.com/ (see technical articles for some of the background of DVB) http://www.w6ze.org/ (DTV section).

There are ATV groups in Brisbane  http://members.optusnet.com.au/~cardenrj/ and Melbourne http://www.vk3rtv.com/index.html. Both good for information.

Both have ATV repeaters. My aim is to access the Brisbane Repeater.

Currently I am trying to do (too many things at once):

1) Increase the power output, via a couple of Minikits amplifiers http://www.minikits.com.au/ . They are very good source of kits and bits. Also RF Shop   http://www.rfshop.com.au/. I have a Chinese generic 70 cm 50 W amplifier as the final. Although I was hooking them all up last night and found the Chinese amp has some weird thread on its UHF connectors. I pulled it to bits and can replace them with N connectors easily (I think). With TV, the amplifies can only run at about 10 % of their rated power. 

2) Setting up a better camera than a webam. I have changed from my laptop to my main station computer so I could install a HDMI camera input card (also does other analogue video inputs), an Avermedia DarkCrystal HD Capture Pro PCIE Card C027 ($100) from local Umart http://www.umart.com.au/newindex2.phtml?bid=4 .

I am using a cheap Canon camcorder HFR406 ($209) from JB Hi Fi. Somewhat surprisingly it worked quite easily, I think because I can use standard digital video ie 1080i or 720p in the PC2TV software. (Video formats drive me nuts).

3) Build a tilt-up mast, rotator and 2 m and 70 cm antenna. I am still setting up the basics of my station. Current status is mast is ready to tilt up, I have been waiting for concrete to set from a week ago. I have assembled all the bits to make the antenna (not simple to get). The design is per the ARRL Antenna book and uses insulated elements. It has been hard to source "top-hat" or stepped nylon washers and "push-nuts" for the insulated elements.

4) Playing around with studio software, to be able to have overlays (call sign) and switch between camera(s) and recordings. See http://www.vidblaster.com/. It has a virtual camera that can be the input to PC2TV. It is a commercial product but there are freeware ones around. They are mainly designed to stream to a network or record for YouTube, rather than direct to a TV xmitter.

5) Trying to get some basic test gear going. I have an interest in Software Defined Radio. I can use an RTL dongle SDR as a spectrum analyzer, but currently have limited bandwidth (3 MHz, whereas I need 8+). I am chasing some cheap Chinese gear that will give me spectrum and constellation plots. I need the test gear to monitor my amplifiers to start with, to avoid clipping/overload etc.