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   Home   Help Search  
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Author Topic: Small Wonders QRP CW Transceiver - Help with Band Identification  (Read 794 times)

Posts: 2

« on: July 07, 2019, 12:47:11 PM »


Over the years I have managed to collect quite a bit of Amateur Radio gear.  I’ve been inactive for some time and now have downsized to a condo.  Given my recent changes, I have lots of gear that I’m now selling.

QRP and building kits were a couple of things I really enjoy doing.  Two of the pieces of equipment I am going to be selling are CW transceivers.  When I list them on eBay, I want to be accurate, but cannot remember which bands they are for. I’m pretty confident one is for 40 Meters.  The other may be 20 Meters, but I’m not sure.  Both of these radios are from Small Wonders Labs.  I believe they are the DSW series radios are in the beautiful blue anodized  aluminum cases that came with the kits.

Can you help me identify the band of the transceiver by the crystals installed in the radio which came with the kit?

One radio has crystals marked “Nymph 4.0320”, I’m pretty sure is a 40 Meter transceiver.  The second transceiver has crystals that are marked “5.0688 ITT”.

If you can help me with this information, I would appreciate it. I’m hoping to list these transceivers on eBay today.

Thank you & 73,


Posts: 702


« Reply #1 on: July 07, 2019, 02:48:25 PM »

The unit with the crystal marked "5.0688", is probably the 20 meter. These units had two local oscillators (LO) because they had 9 MHz crystal filters. So one of the LOs was at "5068.5 KHZ" and the other at "9004.5 KHz". That may be the unit that was intended for operating PSK.

14073.0 KHz - 5068.5 KHZ = 9004.5 KHz

The other unit may be the 40 Meter version, but I can't be sure. It may be for a different band. I think they use to make 80 meter and 30 meter versions.

Don't you have the original manuals? The manuals should describe the differences between the units. Those are nice transceivers, but you are going to have a hard time getting what they are worth, if you don't include a manual.

You might try Midway Electronics. One of their kits is an updated version of the "SW-20+ from Small Wonder Labs and Dave Benson". They may have some information on the original SW units.

Martin - K7MEM

Posts: 2

« Reply #2 on: July 07, 2019, 07:23:31 PM »

Hi Martin,

Thank you for taking the time to try to help me out.  I should have the manuals/build instruction for these rigs, guess I need to dig through my storage unit to find my paperwork.

Thanks again for the reply,


Posts: 1044

« Reply #3 on: July 09, 2019, 06:18:42 PM »


The DSW series used encoder tuning and had audio frequency annunciator (push the tuning button and the frequency will be given in morse code through the headphones).

For most radios, you can look at the first and last capacitor that goes to ground from the LPF series inductor.  It's reactance should calculate out to about 50 ohms near the cutoff frequency (~7.2 MHz for a CW 40m rig and ~14.2 MHz for 20m).

Take one of the radios and listen around 10pm with a piece of wire on the antenna socket.  If it's a 40m rig you should be able to find stout CW signals; a 20m rig should receive nothing at this time of day.



Mark -- N7EKU/VE3

Posts: 1450

« Reply #4 on: July 10, 2019, 04:36:07 AM »

The DSW series used encoder tuning and had audio frequency annunciator (push the tuning button and the frequency will be given in morse code through the headphones).

Only the last 3 digits are annunciated, not the MHz. Just email the designer Dave Benson K1SWL and ask him how best to ID the band.


Posts: 576

« Reply #5 on: July 11, 2019, 12:27:06 PM »

Why not just fire up a rig into a dummy load.  Place a wire near the dummy load and connect to your receiver.  If it is a 7 MHz rig the signal in the RX should be MUCH stronger on 7 MHz than on say 3.5, 14.0, 21.0, etc.  You should really see if a rig is working before you list it for sale anyway.  Once you identify a rig as 7 MHz, run it into a dummy load and use it to check 7, 14, 21 MHz receivers.  The harmonics of a 7 MHz rig (14, 21, etc) should still be readable on a RX, but much weaker than the 7 MHz.  This is a crude way to at least see which bands a unit transmits on and on which band it receives on.
    A RX or TX may still be poor, so other tests may be needed to see if they are OK.  For example most afternoon or evenings you should be able to hear many signals on 40 meters, even with just something like a 30 foot piece of wire.  On 20 meters signals will be present on some, but not all days, but not too often into the hours after sunset.  A very rough check of a RX is that when you hook up an antenna, the noise level should increase, if not the sensitivity of the RX may be poor, depending upon the antenna used.   
                   Good Luck    Rick  KL7CW 
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