Category Archives: Guest Posts

Guest Post: Mark’s Micro Go-Box for the ICOM IC-7100

Many thanks to SWLing Post contributor, Mark Hirst, who shares the following guest post:

Micro Go-Box for the ICOM IC-7100

by Mark Hirst

You’ll be familiar I’m sure with the IC-7100 base unit and separate head unit design. It lends itself very nicely for vehicle installation.

Using it in any ‘portable’ situation however has always presented something of a challenge. A FT-857 or FT-891 can be carried as a single physical package with the head unit integrated into the body. The radios can sit and potentially operate on their tail in a backpack, with products like the Escort from Portable Zero making that process even easier.

I’ve had a few attempts at solving this portability conundrum, driven by a concern that there could be long term problems continually connecting and disconnecting the component parts for transport and operation, but knowing that a permanently assembled IC-7100 will always be an awkward dispersed structure.

My first solution was a Stanley 16 inch toolbox, which is fortuitously sized to accommodate the base unit and provides enough space to loop the original connecting cable and head unit. The box is not a bad fit, but certainly bulkier than necessary and leaves enough room for things to rattle around. When tilted vertically, the head unit can start moving.

Fast forward to this week when I discovered that the IC-7100 base unit will also fit inside a 5 litre XL storage box made by Really Useful Boxes:

The XL version of the 5 litre box has a taller lid, and as you can see from the accompanying photos, accommodates the base unit with the head unit sitting on top of it in a ready to use configuration. The tolerances for height are also exact, the VFO knob very lightly touches the lid, so don’t put something heavy on the box:

Once the lid has been removed, the radio can operate directly from the container:

To make the whole thing fit, I used a 25cm CAT 6 cable in place of the original connection cable and a significantly shortened power lead. As luck would have it, I created the shortened power lead a while ago because I often put the battery right next to the radio.

You can see that I removed a section between the power plug and the fuses, and now use the removed length as an extension should the battery be further away. Although it wasn’t my intention at the time, the main part is about 2 feet long, the secondary about 8 inches.

For transport, the power cable is coiled behind the head unit, ensuring the fuse holders sit in the void immediately behind it, while the microphone cable is coiled on top leaving the microphone resting inside its own coil. You can see the arrangement below:

In the next photo, you can see how the cabling emerges from the back of the base unit:

There’s just enough space for the power cable to leave the base and bend around without undue pressure, and likewise for the CAT 6 cable to curve round into the back of the head unit. Two angle connectors make the antenna ports accessible from above, while a short USB external drive cable provides access to the USB port for data modes and CAT control. A longer USB extension cable is attached to this short cable only when required, and the extension uses much more substantial ferrite chokes to mitigate noise from the computer.

To complete the transport package, I’ve cut out a kaizen style foam insert to make sure the base unit can’t move back into the cabling space, and another to make sure the head unit doesn’t slide towards the front.

The last problem of course is cooling. The fan is located in the front of the base unit, with slots along the sides and top to allow air flow. The box unfortunately is exactly the right size for the base, leaving no gaps for air to circulate. In the absence of a proper workshop or professional tools, I opted to use a hole cutter designed for putting pipes through wood panels. It turns out that plastic has a tendency to deform rather than cut under the blades due to friction heating. A sharp knife was essential in dealing with the effects of that deformation to produce the final smooth edges around the holes:

While I’m happy with the port exposing the front fan, the two holes on each side do not completely expose the side slots. Do I drill out the space between them knowing how tricky and flexible the plastic can be, and would a larger hole compromise the strength of the box? For now, I’m going to keep a careful eye for any temperature issues.

The current arrangement is to carry the box horizontally in a cheap travel bag:

Could the box be tilted vertically with the base unit nose down and carried in a back pack for longer excursions? Yes, but experience has told me that the lid latches on Really Useful Boxes have a tendency to pop open when you do that, so a luggage strap around the box may be required to prevent its very expensive cargo from spilling out. I’m also mindful that the box lid gently touches the VFO knob, so might put load on it in the vertical position.

The final result is something of a Swiss watch, and there isn’t much room for error. Things have to be arranged ‘just so’ to fit, but it does mean I can pack and pick the whole thing up in a handy container. The radio only needs a battery and antenna to be connected on site and then it’s ready to go.

There’s something oddly satisfying when unrelated objects come together like this. Who knew that this box was just the right size to fit the radio?

So, what do you think?

Thank you for sharing this project, Mark!

I love your Micro Go-Box: it’s practical, affordable and makes an otherwise awkward field radio easy to deploy and use. Looking at your photos, I realize that the IC-7100 does have one strong suit for field use. The IC-7100 front panel is tilted at a very comfortable 45 degree angle for use. 

Post Readers: What do you think?  Any other IC-7100 owners out there who take their rig to the field? Please comment!

Guest Post: SM0VPO’s 3D Printed 10KV Tuning Capacitor

The completed antenna.

Many thanks to SWLing Post contributor,Harry Lythall (SM0VPO), who shares the following update to his excellent homebrew 20 meter magnetic loop antenna post:

3D Printed 10KV Tuning Capacitor

by Harry Lythall (SM0VPO)


You may have seen my 20m (14MHz) loop, or frame, antenna, and the ease of construction with just a bit of wire and a bit of plastic tube. The tuning arrangement is a little primitive, using just a “gimmick capacitor”, comprising two bits of wire twisted together.

The original “Gimmick” capacitor that burns.

This arrangement works very well for QRP, where the average RF power is about 5 Watts or less. If you exceed this power level, then the twisted-wire capacitor tends to warm up and the tuning drifts a little. But if you use more than about 10 Watts of continuous RF power, then things start to burn. Cheap insulated wire also smokes. This is because the impedance at the ends of the coil is so high that you can get many 100s of volts and the insulation, normally intended for house wiring, breaks down.

In this page I will show you how to build a super-cheap tuning capacitor that will tolerate up to 10,000 Volts of RF and allow you to use up to about 100 Watts of RF into my 14MHz (20m) antenna. The capacitor is also tunable so that you can adjust it by hand (when the RF is removed, of course :-). The tuning range is about 8pf to well over 30pf when really compressed. The normal range for the antenna is about 12pf to 15pf.


My prototype does not look very pretty, and it is not supported on anything other than the connection wires from the antenna. Very few components are used:

  • two plastic foam pan scrubbers or one thick plastic bath sponge
  • two pieces of metal 4cm x 6cm. Copper-clad board works fine
  • one plastic nut and bolt – see text
  • one heavy-duty 3-pole block connector with centre-pole removed

Components for the 10KV tuning capacitor

The plastic nut and bolt need to be about 6cm long and totally non-conductive. If you want to make my bolt, then do NOT use black plastic because some black plastics use carbon as a colouring agent. You can use a nylon bolt, as used to secure IKEA toilet seats, but you will also need a washer to spread the stress, otherwise the copper-clad board tends to bend under the stress with time. I chose copper-clad board because it is easy to solder – no need for drilling or connection bolts. I made my plastic compression tuning bolt using my 3D printer. I have included the project files for you to download.

Ikea toilet-seat bolt

Note that the connector for the wires needs to be well spaced between the metal inserts, in order to tolerate up to 10KV, so I used a 3-pole connector and took out the centre pole. At 100-Watts continuous there is a very slight warming after a few minutes, but no sign of smoke, sparks or corona. 🙂

The connector with the centre-pole removed.

I tried a few different types of plastic dielectric and all worked well, providing they are 100% dry. The best ones those I stole from the kitchen cupboard (when Maj-Lis was not watching). I think it costs about $1.50 for a packet of 10 pieces. Perhaps I should have used a nicer colour? A pretty pink? Heart-shaped? No! maybe that would be going a bit too to far ;-). Here is my finished capacitor using my 3D printed tuning screw.

The assembled 10KV capacitor.

3D Files

Once more, this project is ridiculously easy to make with a 3D printer. The hardest part was to get the pitch of the threads right, then clone/connect the pieces to get a longer thread. They were printed with the bolt vertical, so the slope under each thread is a steeper angle than the upper slope. This makes the printout a lot easier to print. If the angle is too steep, then it may extrude PLA into mid-air. My nut and bolt heads are about 3cm Diameter, and the 10mm thread for the nut was cut using boolean subtraction. I then enlarged the nut by about 3% so it still fits but there is a little slack so that it does not bind. I may have overdone it a little, but not much.

Project rendered in 3D Studio Max

Here are the files:
3D studio MAX file – 3d-cap-01.max
ASCII STL file – 3d-cap-01.stl
ASCII OBJ file – 3d-cap-01.obj
the GCODE file for my Wanhao (Prusa) Duplicator i3 – 3d-cap-01.gcode

Just right-click on the file and select “save as”. Some web browsers try to open ASCII files instead of saving them. I usually export STL files, but on this occasion, I tried comparing OBJ files since CURA slicer will accept both. Although I use a WANHAO replica of the PRUSA Duplicator i3 printer, the GCODE files are rather generic and will probably work on most printers.

My printer settings in this GCODE are:

  • Nozzle temperature = 200°C
  • Bed temperature = 60°C
  • Support structure = brim
  • Layer height = 0.1mm
  • Print speed = 60mm/s
  • Fill density = 40%
  • Shell thickness = 1.2mm

The printer temperature is 200°C, which is 5°C hotter than recommended for PLA filament. I find that I get a better print at 200°C as it sticks to the bed a lot easier. When printing this screw thread, it may be advisable to start at 200°C and then turn down the nozzle temperature to 195°C after a few layers have been printed.

I hope that you find this project interesting. It is a bit small, but it gets me active on 14MHz from my car with this portable antenna. I have a new car and I don’t want to start throwing long aluminium tubes in it that scratch the interior to bits.

Don’t forget to visit my messageboard if you have any questions about this or any other project. I always look forward to receiving feedback, positive or negative ?

Very best regards from Harry Lythall
SM0VPO (QRA = JO89WO), Märsta, Sweden.
EA/SM0VPO (QRA = IM86BS), Nerja, Spain.

Thank you so much for sharing this, Harry! I love both the frugality and ingenuity in this unique capacitor design!

Post Readers: be sure to check out Harry’s website which is loaded with radio projects of all stripes. You’ll easily spend a few hours digging through his tutorials and downloads. Harry also maintains an alternate mirror server located here.

Guest Post: Backpack Shack 3.0 – Part 3

Many thanks to SWLing Post contributor, TomL, who shares the following guest post as a his Backpack Shack 3 continues to evolve:

Backpack Shack 3.0 – Part 3

by TomL

I have now gone overboard since I think bigger must be better.  The temptation was just too great and now there is an MFJ-1979 17-foot telescoping whip antenna in my car (with consequences).

MFJ Angst

I have a love/hate relationship with MFJ products because of what I think are useful ideas that are made somewhat poorly.  But I went ahead and bought the large whip since I figured they could not possibly screw up something so simple, right?

Wrong.  As I excitedly tried to screw the supposed 3/8”-24 threaded end into the nice standard Firestik K-11 magnet mount, I realized I was turning and turning it but it was not going in!!!  I even had a small steel sliver of metal sticking into my flesh to prove I was not dreaming. The previous day, it had screwed in very tightly, but it did screw in. So, there I was after a long day of work, ready to listen to some SWL-Nirvana and I could not get the blasted antenna into the mount–?  That Firestik mount is a VERY standard 3/8”-24 female thread and the other third-party antenna shafts fit perfectly and easily EVERY time I use them. I hate $60 of poor workmanship and MFJ seems to be the poster child of overpromising and underdelivering.

I was determined to make this work, by force if needed.  One of the Trucker antenna shafts by necessity had an extra coupling nut on it to allow the extra 18 inch shaft to connect, so I took it off there and tried to thread it onto the MFJ-1979.  It barely moved. Not to be thwarted, I dug out an adjustable wrench and 3/8” socket wrench with ½” socket and grunted and twisted and tightened until the coupling nut was threaded all the way “up its shaft”.  That is what I feel like telling MFJ! That coupling nut is never coming off and now that I truly have bought it and cannot return it, I might as well use it.

The stainless steel telescoping rod is extremely thin and feels like it can bend and dent with any kind of mishandling.  So it resides collapsed in a 27 inch PVC pipe with plumbing pipe foam inside to baby it when it is not being used. It remains to be seen if I can remember to “Handle With Care” when extending/collapsing it.  We’ll see.


OK, so using the 18 inch antenna shaft attached to the magnet mount, then the coupling nut on the MFJ antenna, I extended it to a total of about 13 feet.  With the DX Engineering Pre-amp turned on, and using the SDR Play RSP2, I was getting many signals booming in. All the usual names we are familiar with – RMI, CRI, Turkey, Cuba, etc.  But also the noise level was very high. I know it is summer but I may have been overloading the Pre-amp a little bit. Here is an example, Radio Progresso from Cuba with some very nice acapella music but also a noisy background (plus, a noisy laptop computer pulse!):

Click here to download MP3 audio.

So I decided to come back in the morning before my workday started and see if the static crashes would have died down.

Preamp Angst

The next morning I had everything hooked up again in the same spot at the Forest Preserve (located in a suburb of Northern Illinois).  I moved the Cross Country Preselector to be directly connected from the roof, then to the antenna switch on the “Breadboard” (see part 2) to better prevent overloading.  I turned on the Verizon battery pack and nothing. No Pre-amp light. Switched it on, off, on, off – nothing. So, I thought I must have burnt it out the previous session?

Later on, I found it was some sort of short in the switch and I will have to move the D-cell batteries to a backup battery pack. In the meantime, I had to do without the Pre-amp and was forced to extend the MFJ antenna all the way.  With the 18 inch extension attached to the magnet mount, that was a total of 18.5 feet from antenna tip to the top of my car roof.

This was actually fortuitous since I was already concerned about overloading the Pre-amp or perhaps amplifying background noise.  This forced me to test it in a more “barefoot” manner, hearing what it would natively hear without any Pre-amp. It was also lucky there was no wind to blow it over!  It seems that if one is in an RFI-quiet area with decent view of horizons, the 20+dB Pre-amp may not be needed, depending on frequency band involved.

I have read that “Norton” style 10 dB Pre-amps and custom handmade transformer baluns are used by Dr. Dallas Lankford in his Low Noise Vertical antennas.  I don’t want to get into winding baluns so I am using one Palomar Longwire Balun to simulate the “magnetic” transfer. His design uses two, one 10:1 at the antenna and a 1:1 balun at the feedline into the house.  For more reading on LNV antennas, see these references:

UNAMPed Results

I purposely monitored Voice of Korea for their news statement on the De-Nuke talks on the 25 meter band and found it came in great, just as many others have heard it.  This was encouraging. Examining carefully the Data file from the SDR, here is what I pulled from it. I am pleasantly surprised and happy with the results; some stations I had never heard before and the language and music are very exotic.  All of it was a little more than one half hour of recording time (14 June 2018, 1300 UTC). You may have to crank up the volume on the weaker recordings to hear those properly.


(Station, Frequency, Language(s), Transmitter site from

Voice of Vietnam, 12020 kHz, English, Hanoi Vietnam (with local UFO noises near me)

Click here to download MP3 audio.

HCJB Beyond Australia-India, 11750 kHz, Nepali, Kununurra OZ

Click here to download MP3 audio.

Veritas, 11850 kHz, Vietnamese, Quezon City Philippines

Click here to download MP3 audio.

VOA, 11695 kHz, Cambodian, Tinang Philippines

Click here to download MP3 audio.

KCBS, 11680 kHz, Korean, Kanggye North Korea

Click here to download MP3 audio.

CRI, 11650 kHz, Esperanto (they get PAID to speak Esperanto!), Beijing China

Click here to download MP3 audio.

Taiwan International, 11640 kHz, Chinese, Kouhu Taiwan (blasting in strongly plus strong echo of broadcast at top of the hour – is a second transmitter signal going around the earth the other way and getting to me??)

Click here to download MP3 audio.

FEBA India, 11580 kHz, Malayalam scheduled but announcer says “Kannada”, Trincomalee Sri Lanka

Click here to download MP3 audio.

Radio Free Asia, 11540 kHz, Tibetan, Tinian Island signoff and transition to Kuwait (very faint)

Click here to download MP3 audio.

BBC, 12065 kHz, English, Kranji Singapore (ETWN not on air to mask this)

Click here to download MP3 audio.

Japan NHK, 11740 kHz, Thai, Kranji Singapore

Click here to download MP3 audio.

CRI, 11910 kHz, Amoy signoff transition directly to English, Beijing China

Click here to download MP3 audio.

FEBC, 12095 kHz, Hmong signoff transition directly to Khmu, Bocaue Philippines

Click here to download MP3 audio.

Radio Free Asia, 12140 kHz, Cambodian signoff transition directly to Burmese, Saipan

Click here to download MP3 audio.

Extreme Loading

Eighteen feet of whippy rod can sway in the gentlest breeze (consequences of “bigger must be better”).  The described setup has fallen over in as little as a 12 mph sustained wind when fully extended because I had the base in a plastic box.  I want plastic under the magnet(s) in order to get it off easily and put away out of sight!  Now installed is a larger QUAD magnet mount for better stability:

ProComm PCTM54 Quadruple Mag Mount

I am using the flat plastic lid from a 20 gallon tote container under the quad mount and a mover’s tie down strap to the main bar of the quad (I have room for multiple straps if needed). Ten foot fits just fine:

Erickson 34415 Black Retractable Ratchet Straps 2 Pack

A spring is attached to the base as well (strongest one I could find):

Hustler SSM-3 Super Heavy Duty Spring

Finally, the connecting stainless steel shaft at the base is a 5 inch Wilson 305-5 stainless steel shaft.

Because the backpack and quad mount can fit inside the 20 gallon tote container, this setup can be attached to a picnic table in a state park or campsite if I choose.  The Firestik single magnet mount will be recycled as a VHF antenna mount. I can go virtually anywhere now.

Instead of the 20+dB DX Engineering Pre-amp, perhaps one of those “Norton” 10 dB Pre-amps might be optimal ( broadband-preamp).  And I need to figure out why my Verizon battery pack failed as each Tenergy D cell measured fine.  Oh yeah, I have to buy an extra coupling nut, too……

Happy Listening,


Thanks so much for sharing this latest iteration of the BackPack Shack 3.0, Tom! It seems to me, as you imply, your current setup could be installed pretty much anywhere. 

I’m sorry to hear about your troubles with MFJ. I’ve only had good experiences with them in the past, but I suspect the specs on the 3/8”-24 thread were simply incorrect or perhaps metric and mislabeled.

Post readers: Read Tom’s past contributions and articles by clicking here

Click here to read Backpack Shack 3.0 – Part 1 and Part 2.

Aeronautical RDS: Ivan’s impressive collection of in-flight FM stations

Many thanks to SWLing Post contributor, Ivan Cholakov (NO2CW), who writes:

Last week I took an Eton Satellit with me on a flight from Tampa, Florida to Washington DC. The radio is very light, portable and packed with features. I have used an SDR radio before for inlight FM reception where I recorded audio, but this time I decided to only count stations with an RDS lock. With so many signals battling RDS is tricky to catch as every 10 seconds or so one station comes on top of another. The flight was just short of 2 hours and I divided my logs into three 30 minute segments. Not suprisingly looking into the technicalities I noticed RDS is commonly received from stations 50 -100 kW of power and tall towers.

Interestingly signals seem to be stronger a lower altitudes. My theory is that FM broadcast antennas heavily favor gain on the horizontal plane parallel to the terrain and send as little signal as possible out into space. I overlaid my logs onto three maps and also a video:

Click here to view on YouTube.

Impressive Ivan! I’m taking a flight later this month and might even try this with the FM radio built into my Moto G6 smart phone which also includes RDS (although I doubt reception can match that of the Satellit.

This is fascinating, Ivan! Thank you for sharing.