Dave Richards AA7EE

January 11, 2010

Software Defined or Hardware Defined – Which Way to Go?

The main project going on in the AA7EE  “shack” (for which read “main room of my studio apartment”) has been, and will continue to be, the monumental task of committing my sizable collection of cassettes, CDs, DAT tapes and broadcast carts to backed up hard drives.  This is an ongoing project which I expect to take several years. Over the course of a 22 year career as a DJ, I amassed a lot of stuff that is becoming wieldy and expensive to lug around, so it’s time to start consolidating.

So whenever I’m listening to the radio or soldering something, I’m often also ripping a CD, scanning the artwork, or calling up my friend Antoinette and trying to give her as many of the CD’s that I just ripped as possible. I spent 22 years accumulating stuff (opens in a new browser window) and I now want a good portion of it gone (thanks Antoinette!)

All that aside, the amateur radio goings-on here have included building a neat little direct conversion receiver for 40M – the VRX-1 designed by NT7S and sold by the 4SQRP club. It’s a cool little DC receiver.  I’ve been having a bit of a problem with the input bandpass filter, so it’s on the back burner for a while, but it’s been a fun Manhattan building experience:

NT7S’ fun DC receiver got me all charged up.  The first successful TX/RX I ever built was an 80M DSB TX/RX designed by G4JST and G3WPO and published in the UK magazine “Ham Radio Today” in March 1983. It utilized a direct conversion receiver, to which I added an audio filter built from a 741 op-amp.  It was my first experience with DC receivers, and I remember being surprised that such a simple receiver could sound so good. Jason’s VRX-1 re-introduced me to the pleasures of DC receivers, as well as the technique of Manhattan construction (my first time), so by the time I’d finished construction, I was all primed up and ready to swoon at any direct conversion receiver that might flit it’s tail feathers at me.

John AE5X’s post couldn’t have come at a better time. Allow me to repost this picture of the 80M direct conversion TX/RX that the Arizona ScQRPions will be providing a kit for very soon:

The details are here. I was beyond excited when I found about this (thanks John).

I have a mental list of several different QRP rigs that I want to build, among them the Weber Dual Bander, and either the Elecraft K1 or K2. However……SDR has been on my mind too recently.  I built the SoftRock Lite II for 40M a few months ago and was impressed with the performance for such a simple piece of hardware, and low price too.  Of course, the simplicity of the hardware and the low price is a bit misleading because the signal processing is all done in software.  This is the beauty of SDR though – if a better demodulator or filter is available, you just download it.

I’ve been using the SoftRock to monitor the CW portion of 40M, and then once I see a signal, I can work him on the main rig, which is currently a Norcal 2N2/40.  Yesterday, I built a combined switch and dummy load into an Altoids-type tin so I can easily accomplish switching the antenna between the SoftRock and the 2N2/40.  The 2N2/40 is a cracking little rig – a sensitive low-noise receiver with a stable VFO (after the intial warm-up period).  It has a nice narrow crystal filter too which is great for working people, but not as convenient when you’re trying to find stations to work.

So….what I do is use the SoftRock to look at a wide portion of the band.  With my soundcard, I can look at a 96KHz-wide slice of the band on my screen, and the minute I see a station, flip over to the 2N2/40 and work him. It works well but it got me to thinking – why switch over to a traditional radio to work a station that I find with SDR? Why not just get an SDR transceiver and avoid having to switch over to a hardware defined radio?

Hardly original thinking.  I’m sure it’s the same thought process that has led many an amateur to adopt an SDR rig as their main station radio. FlexRadio are about to introduce their Flex-1500, which is a 5 watt all HF band SDR transceiver.

Mighty tempting and with my limited amateur radio budget, I’m now wondering whether to continue building all the QRP transceiver kits I’ve had my eye on, whether to build the SoftRock v6.3 HF TX/RX, or whether to go for broke and get the Flex-1500 when it comes out.

In the meantime, I have a KD1JV Digital dial on order, which will turn the Norcal 2N2/40 into an even more usable little radio.

Oh, and I have 1,000’s of CD’s to rip and perform hi-res artwork scans.  It’s not as if I’ll be sitting here twiddling my thumbs.



  1. If SDR is what you are thinking about, keep an eye on the Genesis Radio site http://www.genesisradio.com.au/ for news of their upcoming G59 multiband SDR kit.

    Comment by Julian, G4ILO — January 12, 2010 @ 9:09 am | Reply

  2. Thanks Julian. I’m aware of Genesis Radio but didn’t know that they have a multiband kit coming out.
    So many radios to build, buy, and play with – so little time (and limited cash)!

    Comment by aa7ee — January 12, 2010 @ 3:57 pm | Reply

  3. Just wanted to let you know that it’s not showing up properly on the BlackBerry Browser (I have a Pearl). Anyway, I’m now on the RSS feed on my laptop, so thanks!

    Comment by Tjene Penger — January 15, 2010 @ 10:57 am | Reply

  4. I prefer “real” radios to sw-defined radios. But then I listen to vinyl and shoot film, so I’m into analog hobbies. Computers are great, but they remind me too much of my job! I’ll probably get the Weber Dual-Bander myself. 73.

    Comment by alan — March 15, 2010 @ 3:41 am | Reply

  5. Nice blog – couldn’t agree more with whatever you said. Keep up the good work!


    CCNP Training

    Comment by David — May 1, 2010 @ 2:29 am | Reply

  6. Hello from France.
    J al very interesed by this qrp for starting radio activity, chiefly for local communications. Would you tell me where to find shematic ? many thanks
    all the best
    joseph Martin

    Comment by joseph Martin — October 27, 2012 @ 12:03 pm | Reply

    • If you’re referring to the schematic for the VRX-1 DC RX Joseph, the page is linked in the above post, and you can find a link to the schematic on that page. If you’re talking about the Fort Tuthill 80M DC TX/RX, QRPKits sell a kit version of it for 15M and 160M and schematic are available on their site at http://www.qrpkits.com/

      Comment by AA7EE — October 27, 2012 @ 3:22 pm | Reply

  7. Good evening Dave, and thanks for your reply. I saw the site qrpkits.com and the Fort Tuthill 80 M seems very interesting.
    I saw your description of the DSB80 and I should be pleased to find the schématic to be able to built this small rig and to use it here for local contacts.
    I was a radio Ham and I stopped it 15 ans ago. Now I am retired and I wish to built my rigs only with qrp stuffs.
    Could you please send me the schématic of this DSB80 with jpg file ? Your description is very nice and I am impressive by the work .
    I think its a good thing to built radio rigs to have many things to talk about.
    joseph Martin

    Comment by joseph Martin — October 28, 2012 @ 5:36 pm | Reply

    • I e-mailed you a copy of the original article for the DSB80 Joseph. Can you let me know when you’ve received it please? Thank you!

      Comment by AA7EE — October 28, 2012 @ 8:58 pm | Reply

      • Good morning Dave,
        I received your mail at 08 h 45 french hour. Thanks for your sending, and I ‘ll start this rig with a lot of pleasure. I ‘ll keep you in touch about it.
        all the best
        joseph Martin (France)

        Comment by joseph — October 29, 2012 @ 7:59 am

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