Category Archives: Kits

Win an MFJ-8100K shortwave receiver kit!

After posting Ron’s note about the MFK-8100K receiver kit, I touched base with MFJ and they have kindly donated a new 8100K kit to us for an SWLing Post giveaway. Thanks, MFJ!

This giveaway is open to anyone, anywhere. MFJ will ship it directly to you if there are no Covid-19 shipping restrictions to your country.

Here’s how to enter the giveaway…

Simply comment on this post and tell us about your favorite kit that you’ve built. This can be your first kit, your last kit, or anything in between. Don’t just give us a model name, tell us what made it a fun or special project.

If you’ve never built a kit, but are eager to do so, tell us why you would like to build the MFJ-8100K! Do you have a soldering iron?

We simply want to make sure a kit builder or want-to-be kit builder gets this prize! We’d even invite you to share a short post about building the MFJ-8100 (no obligation–only if you wish).


We will pick a winner at random from the valid comments in this post on Wednesday, September 23, 2020 at 16:00 UTC.

This means you must enter a valid email address in the appropriate comments field (not within the comment text itself) so that we can contact you.

Of course, the SWLing Post doesn’t sell or share emails–never have, never will–this is only so we can contact you to obtain your shipping address if you win. Feel free to use a throw-away email address if you wish.

This is all about taking us on a great kit-building nostalgia trip, so have fun!

Click here to comment with your kit story and enter the giveaway.

Many thanks again to MFJ Enterprises for sponsoring this contest!

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Ron reminds us that MFJ still offers a shortwave radio kit

Following up on our recent MFJ post, SWLing Post contributor, Ron, writes:

Another thing about MFJ is they still offer the MFJ-8100 as a kit or built. This is the only regenerative receiver available as far as I know.

Mr. Jue and his guys did a couple of tweaks like limiting band coverage to insure stability, using 1/8 inch 3.5mm stereo phone jacks and use an LM386 audio IC to drive headphones or speaker.

The whole thing is in a metal enclosure to minimize hand capacitance found in most regens.

The QRP crowd likes to use the 8100 with flea power CW rigs, it’s that good.

And it’s been in production far longer than the Heathkit GR-81 or any of the Knight Kit regens, too.

Thank you for sharing that, Ron! I had completely forgotten about this little kit when someone recently asked about the availability of Ten-Tec regen receiver kits (that are, sadly, no longer on the market to my knowledge)! I might have to grab one of these kits–looks like a fun one to build.

Click here to check out the MFJ-8100K.

By the way, I also believe the NM0S Ozark Patrol regen kit is still available from the Four State QRP Group. Click here to check out the product page. It doesn’t have a metal enclosure like the MFJ, but it’s also a fun kit to build.

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List of electronics and radio surplus outlets

Many thanks to SWLing Post contributor, Neil Goldstein, who writes:

I added a sub-page to with a list of the remaining electronics and radio surplus outlets I was able to find and verify. The list is evolving, but is complete enough to publish at this point. Enjoy!

Many thanks for sharing, Neil!

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Adding CW mode to the EA3GCY DB4020 Dual-band 40 and 20M QRP Transceiver Kit (Part 2)

Many thanks to SWLing Post contributor, Frank (ON6UU), who shares the following guest post which expands upon his previous DB4020 article:

The EA3GCY DB4020 transceiver now has CW mode

by Frank Lagaet (ON6UU)

After telling you all about the DB4020 SSB build I’m here with the CW part of the kit,  let’s say this is part 2.  At a certain moment Javier let me know the CW interface kit was ready for shipment and some week later it was delivered to my QTH.

Again, a well packed kit arrived in a brown envelope, components and boards well packed in bubblewrap.  I found even a board I did not expect which can hold a push button,  a switch and the connector for your morse key.  Javier thinks of everything it seems!

Unpacking the bubblewrap gave me this result,  all components in 2 bags.  In the bigger bag another 2 bags with 2 printboards,  one for the CW interface,  one for the CW filter.  Great !!  Checking the material bill resulted in all components there,  another thumbs up.

I started, of course, immediately building it because I wanted CW in the transceiver as soon as possible.  I don’t do much in SSB mode anymore and I already started missing CW on the DB4020,  so I started my KX3 to listen to while I was populating the boards.  I never thought CW was going to have this impact on me! …. ..

I started building the CW interface,  again starting with all small items.  I soon saw that the 2 relays which need to be soldered in were ideal to protect all components when the board is upside down, so I soldered them in very quickly.  I then soldered in all other components ending with the elco’s.

Next phase was the CW filter.  This board is small and came together in a blink of an eye, no problems there, the long legs of the 3 and 4 pin headers went in last.

The following day, I made all wire connections and soldered a 13pin connector,  leaving one pin out since I want to have the option to choose the width of the CW signal I’m listening to.  By cutting the FL CW + pin and adding an additional switch, I have now 500Hz or 2400Hz.  Great option, for very little effort and simple.  Another thumbs up here.

Now it was simply a matter of inserting the sub boards in the main board and all should be working.  And it did!  Hurray!  The 500Hz filter works perfectly,  filtering away all above or below stations nearby my operating frequency.

This is the result of the soldering work,  2 small boards which need to be inserted in the main board:

The CW interface still needs the 13pin header of which I cut one pin and mounted a switch to have the 2400Hz width.

The IC you see in the middle of the CW interface is the KB2 keyer which gives you several functions like 4 memories and beacon mode.  The 4 potmeters are used to set the level on 40 and 20 meters,  to set the delay between TX and RX switchover and to set side tone monitor level.   The keyer also provides functions as keyer mode A or B,  straight key function and can be set for speeds between 1 and 50WPM.   WPM speed can be set in 2 different ways.  Handy!

Here a picture of the CW filter inserted on the main DB4020 board.

The CW interface is inserted at the side of the main board,  notice the 2 wires which go to the switch to allow switch-over between 500 and 2400Hz.

(Wiring still needs to be cleaned up in this picture.)

Finally, the result:  a good working multimode QRP transceiver with 2 bands.  It should be possible to make close to medium range with it as well as DX,  even with QRP power.

And while I was building I also made a new key for this radio,  it is made out of a relay and cost nearly nothing,  looks good doesn’t it ?  hihi.

Homebrew key

The key, when in practiced hands (fingers hi), can do 50 WPM without a problem. My friend HA3HK does without blinking an eye at 40WPM with this kind of key and tells me that he can go faster if needed.  Me? I’m going it a bit slower.

Battery pack

As this radio is only using little power (0.4A in RX,  1 to 2A in TX depending the power you set it) I thought,  let’s make a battery pack for the radio.

The first plan was installing it in the box.  I did not do that because the batterypack is also powerful enough to feed my KX2 and other QRP transceivers. Since I can use it with all of them, a loose battery works out better for me.

I started with an old laptop which had a broken screen and some other malfunctions,  but still had a good battery,  although I needed the battery connector of course.  A piece of wood to mount the connector on was my next goal.  And since I still have another laptop using the same batteries, I can charge the battery without problems.  Simple, but good and it weighs much less than a gel cell battery.

The battery provides me with 12.5V and some 5Ah.  Enough to last for hours on RX and for sure good enough to activate 2 SOTA sites in one day.   It doesn’t look great but works great– that is what matters and to test it was more then good.  Next will be getting the battery pack in a nice box.  Better to re-use stuff than throwing it away I’m thinking.

I need to do something about the cover of the OLED display,  there is still some work there to make it look nicer.

Some video can be seen on YouTube :

Finallym I’d like to thank you all for reading my articles about the DB4020. I had big fun soldering, tinkering with the box, making the key, and batteryholder/batterypack.  My Hungarian friend HA3HK told me it looks a bit like a spy radio. …. ..

I also include one more time the link where you’ll find this kit :

73 TU ee



Thank you so much, Frank. No doubt, you had a lot of fun putting this excellent little kit together.

Implementing a filter switch was a fantastic idea and, obviously, not terribly difficult to do.

Based on the videos, the DB4020 has a low noise floor and very good receiver characteristics. I’m impressed that the CW portion of the radios has so many features as well, such as a memory keyer and beacon mode.

I also love how you reused that 5Ah laptop battery! I think that could almost give you a full day of SOTA activations at those consumption levels!

Thanks again for sharing this with us, Frank! We look forward to your future articles!

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Building the EA3GCY DB4020 Dual-band 40 and 20M QRP SSB Transceiver Kit (Part 1)

Many thanks to SWLing Post contributor, Frank (ON6UU), who shares the following guest post:

Building EA3GCY’s DB4020 QRP Transceiver kit

by Frank Lagaet (ON6UU)

In May, I discovered via a newsletter that a new kit was available from Javier EA3GCY in Spain.  I was immediately sold as this was a kit from my favourite kit producer and it has 2 bands–it will also be able to do CW and there also will be a CW filter.

After building 2 MFT’s from Javier which work without problems, I needed to have the DB4020.  The MFT’s are for 20 and 40 mtrs and do DSB (double side band).  I did put them in a not-so-graceful box but they do what they are intended for which is QRP phone (SSB).   They came together without problems so I expected the same for the DB4020–I knew for sure when I saw the board:  all through-hole components (except for some capacitors which are factory soldered) and a lot of space on the board.   The board has been silk-screened with clear indications on where all components have to come and the manual has very clear instructions where each component has to be soldered with referral to a quadrant.  The manual provides a 252 quadrant page so it is a piece of cake to find where each piece goes.

What do you get?

Javier provides you with all components which need to be installed on the board and, of course, the kit board.  The components come in small marked plastic bags and all is well-wrapped up in bubble wrap.  The board is wrapped separately and that is put together with the component wrap which is then again wrapped up in bubble plastic.  All goes into an envelope.  Very well packed I must say.

Here’s a picture of the bags with components:

The silk-screened board:

I started with the resistors since that’s the easiest way. After that, I did the capacitors.  I like to solder in all flat components first, so next were the diodes and IC sockets followed by the elco’s.  The transistors were next together with all relays.  As you solder in the transistors one also has to mount the cooling heatsinks,  these cooling sinks are high and are ideal to protect the coils one has to make,  they also protect the polystyrene caps (which I always find vulnerable) when the board is upside down.

Many kit builders are afraid of winding the toroids in kits–don’t be!  It is easy.  Just take your time and follow the instructions given by Javier in the construction manual.  In this kit the builder has to wind 8 toroids:  6 are a single wire which goes through the toroid body,  1 is a toroid with 2 different windings, and 1 has a twisted pair which goes through the final toroid.  Be sure to measure the wire you need per toroid as instructed in the manual.  Javier gives some spare, so you can be sure.  You will also see that on next picture where the legs of the toroids have not been trimmed yet.  Once done I still had some centimetres of wire leftover.

Picture of the toroids ready to be soldered in:

Finally all other parts and pin headers went in,  jumpers were immediately put on where needed.

As I’m using a military-grade plastic box, I have to break-out some components like the display,  tuning encoder,  volume and rx control from the board.  I also have put an on/off switch on the box and already have the CW KEY connector ready installed. I also installed a loudspeaker in the box.  The SI5351 board and the Ardiuno Nano are the final components which go into the board after installing all wires.

Picture of the board:

I intend to attach a CW paddle to the box made out of a relay.  A HWEF tuner (from EA3GCY) which I was planning to incorporate in the box is I think a bit overkill. That HWEF tuner is already in a nice little box and would be a pity to dismantle,  also I’m running out of space in the box…  Maybe I can fit in a 9-1unun which would then give me good results on both bands…?

Maybe I will install a battery pack in the same box.

The box with board installed:

The box completed front side:

Mind you,  it still needs some additional switches for the CW part of the transceiver.

Frank (ON6UU)


Brilliant, Frank! I really appreciate the video as well–sounds like the kit produces smooth audio and should serve you well. No doubt, that military box enclosure will survive even the roughest field conditions!

Click here to check out the DB4020 kit at EA3GCY’s store.

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Frank recommends the DB4020 QRP transceiver kit by EA3GCY

Many thanks to SWLing Post contributor, Frank (ON6UU), who writes:

As so many, I enjoy reading your posts on the SWLing Post, very clear and understandable written with eye for details. I just did a “read-again” of the QCX+ article and thought that maybe you also would be interested in another European kit, namely the DB4020 by Javier Solans of QRP HAMRADIO KITS in Spain.

The DB4020 is a 2 band kit enabling you to do 40 and 20 meters, SSB and CW. The SSB part of the kit can be obtained for 150€ (169$), Print is a beautiful doubled sided silkscreen with enough space to mount all parts without problems. Some SMD parts are factory installed by Javier, all other parts are normal parts that can be soldered by anyone who knows how to hold a soldering iron. The CW part is an additional module which needs to be plugged into the main board. There will also be a CW filter available soon.

For more information please see :

I’m building the kit at the moment and enjoy every minute of it. I’m not related or don’t have any benefit in sending you this mail, only want to draw some attention to a great kit and super friendly owner who goes the extra mile to have happy customers.

Have a great day

Thank you for the tip, Frank–and I’m glad you enjoy the SWLing Post! EA3GCY’s kit does look very nice indeed. We would love to see your photos once the kit is complete! It looks like a kit I’d certainly love building!

Click here to check out the DB4020 QRP Kit at

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