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.
 

 

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