The Hidden Radio

Every Bond villain has a lair and a master plan for global domination.

Every radio enthusiast has a man cave or shack… you see where this going? I also have a cat, but unfortunately she’s a black short hair Heinz 57 variety rather than Blofeld’s white one!

It’s all well and good building kits and homebrew but without an overall objective they just become a pile of boxes or boards that were great fun to build and tinker with, but now sit in the corner or under the bed gathering dust.

In an ideal world, where I’ve won the lottery, I live in a rambling pile in the middle of the country side where my shack is a large log cabin at the bottom of the garden and I can throw up antennas to my hearts content and play.

Unfortunately, the reality is that I live in a modern modest house on an estate in a city where erecting antenna’s are a problem as there just isn’t the space and the population density is such that you can guarantee that there will be EMC issues with a neighbour despite your best efforts! Also, I just haven’t got the space to give over an entire room to playing so there needs to be a cunning plan.

With all that in mind I’m looking to be modest with my kit and what I want to achieve. The whole realm of QRP and digimode is what I want to play with at the moment. I can achieve that with SDR and some modest antennas that can be salted away in the loft. So let’s go one step further and put everything in that last remaining space in the house.

Loft PC

As my house is a prime customer of the National Grid I want to utilise a low power PC and using wake on LAN to mange the machine seems an even better approach.

Future proofing the setup by buying something with a serious amount of grunt, processor, storage and memory wise is also high on the list. I’ve several servers dotted around the house but nothing that I could re-deploy immediately or would be powerful enough to make it worth while.

Current considerations are –

npi04_extra3

Novatech Pockit NPI04

http://www.novatech.co.uk/pc/range/novatechpockitnpi04.html

 

613680-613290-800

Same thing but without the branding or hard disk and half the price

http://www.ebuyer.com/613290-intel-boxd54250wykh3-intel-core-i5-4250u-nuc-barebone-boxd54250wykh3

It’s almost a shame to hide it in the loft as it’s pretty cool but that said if it needed to live on the desk for any length of time it wouldn’t get in the way.

There’s a reasonable number of USB connections as well. Networking wise it’s 1Gb LAN which would help as I want to be able to remote into it via VNC at home or over a VPN from outside and bandwidth consumption may well slow things down.

SDR Receiver / Transceiver

I’m sold on the idea of a Softrock

http://fivedash.com/

rx-ensemble-ii_LRG softrock-qrp-sdr-transceiver-rxtx-ensemble-kit-large

but am undecided over the RX or RXTX version

Sound Card

My trusty Sound Blaster Live 24 USB would get me going but in reality it’s going to need something like this –

index_completed_top

The USB2SDR from Christos Nickolaou, SV1EIA

Equally, I’ve got other receivers that I could plug into this which all require higher quality sound cards so running multiple devices would potentially expand the ability of the loft rig.

It’ll soon be Christmas and I’ve got an empty list so far, so you never know!

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Sound card considerations

WSPR signals are decoded by the PC which is running WSPR software. As such, as the old adage goes “rubbish in, rubbish out” is very pertinent when you get to this stage.

It was quite evident that my poor little receiver wasn’t getting anywhere near to what it was capable of. USB ports can be very noisy places and I had a sneaky suspicion that wasn’t helping matters in the slightest. By attaching a couple of ferrites to both ends of the 5V USB power cable and the audio cable, the dB indicator within WSPR was reduced slightly but the volume and quality of the spots didn’t increase dramatically. Stellar advise to get the Rx Noise dB level as close to 20 as possible.

Once again the set of cans and audio pass through we’re broken out and it wasn’t that impressive. To reduce the Rx Noise sufficiently so WSPR was happy meant having an input level just above zero. You don’t have to be very knowledgeable at all to work out that that isn’t optimal by any stretch.

Wise advice from Andy (G7UHN) was that PC sound cards utilising mic inputs will never produce anywhere near as good quality signal as a line-in input, but that’s where a lot of laptops fall down.

Firstly you don’t get a whole host of connectors, unlike a full size PC and secondly the embedded chipset of your laptop sound card is unlikely to give a sampling rate anywhere near what you need.

After a lot of googling, if you want to do this properly, you need to be spending serious money on a sound card that will give you good quality audio into the PC to allow it to do what’s needed and decode the spots.

If you’re running on a desktop PC and can accommodate a PCI card this comes highly recommended –

ASUS Xonar D1 7.1 Sound Card

http://www.asus.com/Sound_Cards_and_DigitaltoAnalog_Converters/Xonar_D1/

as does this

ESI Juli@

http://www.esi-audio.com/products/julia/

If you’re going to do it on a laptop or can’t accomodate a PCi card then this is where you need to be going

USB2SDR

http://www.wb5rvz.com/usb2sdr/

I’m looking towards using a Softrock SDR transceiver eventually and if you believe everything you read, you need to invest serious money to reap the benefits.

All of the above sample at 192kHz which gives you a much wider spectrum to play with. Think of it as a panoramic vista. You want frame-less sliding doors to enjoy the view from your living room, not a port hole!

That said I haven’t got that kind of cash to hand at the minute, plus I’m working in the here and now. After a week of dead ends and frustration I wanted this thing running now!

After a bit more googling I found that Creative Labs used to do a very nice USB sound card in the form of the Sound Blaster Live 24 USB.

http://www.amazon.com/70SB049000000-Creative-Technology-External-external/dp/B00030099O

It samples at 192kHz, just what’s needed. Now discontinued unfortunately, but eBay is everyone’s friend and for £20 I wasn’t complaining. It turned up yesterday.

And annoyingly it didn’t work

Stellar provide setup advice to fine tune the board and an introduction into the use of the WSPR software.

And this is where it all went wrong! When hooked up to WSPR http://physics.princeton.edu/pulsar/K1JT/wspr.html  and Spectrum Lab http://www.qsl.net/dl4yhf/spectra1.html  (the tweaking software Stellar recommend) I was seeing the square root of nothing.

After checking the component placements and solder joints at least half a dozen times I was sure the board was built correctly. Stellar’s tech support team provided some advice and trouble shooting via email but unfortunately that got me nowhere. By then the big guns in the form of Graham (M0CYX) and Andy (G7UHN) http://alloutput.com/amateur-radio/loft-receivers/  we’re brought into play along with other members of FPARC (Fort Purbrook Amateur Radio Club) http://www.fparc.org.uk  who all provided great advice and guidance.

The problem was eventually found in the RX side of the circuit where J3, the antenna connector sits. The PCB is double sided and the antenna connection feeds a track which runs along the top side of the board. There was no copper between the upper and lower sides of the board at that connection, so unless electrons were going to learn how to jump, nothing was ever going to be received by the circuit. A quick repair job with a short length of wire from a resistor leg between J3 and C15 and we were up an running.

If you need to fault find this board start by plugging a set of headphones into the board or pipe the audio of your mic/line in through your soundcard so you can hear what’s going on. WSPR tones are unique and you’ll hear them over the background noise. No tones means somethings wrong and it’s time to check for voltages and continuity on the board.

Anyway, with 5m of single core wire as an antenna and another length for the counterpoise we were up and running

Stellar WSPR 30m receiver build

My recent build has been the WSPR receiver kit from Stellar which can be found at their site, http://www.stellarwspr.com

My most recent build has been the WSPR receiver kit from Stellar which can be found at their site, http://www.stellarwspr.com

The kit contains everything you need to build a receiver on a pre-selected band, including cables for connection to the receiving PC. I plumped for the 30m variant after a crash course in WSPR and scouring the WSPR sites for the band with the most potential activity.
The provided instruction sheet is enough to walk you through the build. Just follow the sheet and you should have a working receiver in a few hours.

Unfortunately I didn’t but we’ll get to that in a bit!

Hind sight is a very exact science! If I was doing it again I’d leave the power and audio jack sockets off the board so I could mount panel them on the front of an enclosure. The way round this minor issue will be to mount the board as close as possible to the panel and drill large enough holes to allow the supplied jack plugs to connect to the PCB mounted sockets.

With a bit of care the on board LED will be removed and panel mounted, along with a SPDT toggle switch connected to a jumper connector to allow easy selection of the input source to your sound card be it mic or line in. A panel mount BNC connector will finish the job off to make things a little more ruggedised and portable.

Have you thought about putting up details of your growing setup on the web somewhere?

“Have you thought about putting up details of your growing setup on the web somewhere?” he said.

In a word, no but then having banged my head against a wall for over a week trying to get something to work it dawned on me that without people posting successes and failures on the internet, no one would ever learn and the cycle of frustration would continue.

So in response to that question and also as a way of a thank you to those who helped, this blog will contain, as much as I get time to publish, in relation to all things amateur radio.

Who am I? Yet another amateur radio dabbler,  BUT up until 5 months ago I didn’t have a clue what any of it was about. In that time I’ve had a crash course in a hobby/profession/community that has so much to offer for the inquisitive mind. I have no formal IT or electronics background. As such some people will probably role their eyes at the methodology and cock up which follows, but we all start somewhere.

If I publish one snippet that helps you, as much as others (and their websites) have helped me, job done!

Last Wednesday I received my Intermediate Licence exam results and M6ENO morphed into 2E0DFU. All the hard work was worth it as now I can play with all the fun stuff for a few months before I make headway towards my full licence.