Ultra Portable Radio Design Challenge.

Started by gil, June 06, 2016, 07:16:30 AM

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March 2017: New design requirements below...

After the previous thread on UPRs (http://radiopreppers.com/index.php/topic,1022.0.html), I have laid out my requirements for the ideal survival radio. This is a challenge to RF circuit designers. I would even be willing to put some money into the project if needed. The requirements are open to discussion, but since this is my idea, I would like to have the last word. I have been thinking about this for a while and believe the idea has merit and even commercial potential (kit). A crowd funding campaign could make it a reality, assuming there is a working prototype.

Goal: To make a simple and rugged single band radio capable of being used in all weather conditions and temperatures either in SSB or CW mode, neither of which should be implemented as an afterthought. Current draw on receive should be very low for long periods of listening with occasional transmitting. Range should be global in either modes.

The radio is a single-band CW and SSB (or DSB) transceiver operating on 20, 40 or 80m. A user would build two or three for redundancy.

Requirements below will be update as needed.

  • VFO: Analog. Varactor with 10-turn potentiometer.
  • Coverage: 100kHz with high/low switch for SSB or CW band portions.
  • Display: None. Maybe frequency announcement in Morse.
  • Power: Switchable 5W-25W. SWR LED with 5W bridge, operate/tune switch.
  • Supply: 9 to 30V. 25W output at 12V and above. No batteries inside the case.
  • Current draw: As low as possible < 100mAh on receive.
  • Audio output: Two: Earphone 1000 Ohm and speaker 8 Ohm. Bluetooth?
  • Microphone: 150 Ohm (audio for H-250/U military handset).
  • Filters: SSB 3kHz. CW 400Hz.
  • CW: Iambic keyer, full QSK. Straight key mode with top key button.
  • RIT.

Whether the VFO should be analog or a DDS is debatable. The only reason for a DDS VFO would be for stability with digital modes. The design goal is small size and to make the radio somewhat watertight, at least able to survive a quick dunking or long periods in the rain. The radio should not need to be carried in a case or bag. Its case should be strong enough to be run over by a car. Simplicity is the key and adding features is not the goal. Development should be geared towards making the radio simpler, smaller and more rugged without sacrificing its mission capabilities.

I chose not to include the batteries, speaker or a tuner inside the case for the reasons cited above, but I think an SWR LED and bridge for tuning is a must. I could see this radio go into a Hammond cast aluminum case or similarly rugged enclosure.



I'll add that since it doesn't have a freq display it should have direct freq input like the MTR. However, since it can be used as a SSB radio and not need paddles there it might need a different way of entering the freq. than what the MTRs use. At any rate, I think it should have some means of doing this. Even if the VFO knob has numbers written on it finding the freq that you and you partner agreed to QSY to without a readout or direct entry might prove to be too slow and in-exact.

I know you disagree with my next thoughts but in my mind, ease and speed in setup and taredown, as well as reducing the number of wires and accessories strung all over trump the need to keep it simple. Moving the speaker and battery inside the radio's enclosure means I don't have to carry headphones whose cords a going to get tangled up with the paddles cord while I'm oppersting and I'm not going to stand up with the earbuds in and pull the radio off the stump it's sitting on. Having everything possible attached to or built into the one unit makes it easy to pick up and reposition, stuff back in to my pocket or whatever. Of course as a single band unit I think it should be able to operate without a tuner so that will help to cut down on clutter and keep the radio small. 


Gil, this was a brave post.  You know it's going to trigger a storm of discussion

I'll take vwflyer's comments a step further and say I want a little LCD display, frequency knob and direct Morse frequency entry.  This will require a digital VFO, not varactor, but as Steve Weber has shown, it can be done with very little size and power.  I also want the option of internal and external batteries.  I could live without the internal speaker.  Lastly, a built in touch-keyer with touch pads on the outside of the box, but still able to use a normal key(a la KK0G's MTR).  I like as few external wires as possible.  With the above it could be as simple as antenna and ear bud wires.


DFE on the MTR is great. That would imply a processor and DDS. I am not against it, as the processor can do the keying. It just adds complexity and coding. That said, these days it's hard to avoid. Display, no. It just puts a big rectangular hole in the case, adds cost and complexity. Not worth it. My MTR has a one digit display, I never look at it..

I'll leave the analog VFO for now, because it is simple and frequency announcement can be done in Morse. Anyone can learn the numbers..

Putting the battery and speaker inside would ultimately be up to the builder, but if a case is developed, It might be better to leave that off. I first thought of three 18650 3400mAh cells inside, but then it adds size and requires cell voltage monitoring. Remember the radio would have to run on whatever power can be found, which makes me think that power supply voltage should be extended to 9-30v with the 25W output possible at 12V and above.

Keep it simple! This is not the radio one would pick up for playing around, but to take to the ends of the world, on a sailboat, after the SHTF..


Jim Boswell

Gil, this is a neat idea.
My SHTF radio is a Youkits 4 bander. Now if you could put that radio is a splash-proof rugged case you could get pretty close but CW only. That radio does have wide enough bandwidth you can copy SSB real good. My other portable radio is an Icom 703 but it is not as portable as the Youkits.
My Icom 703 backpack contains: earphones, log clipboard, pencils, key, mic, extra 25ft coax, 6 mt. dipole, 20 mt. dipole, 40 mt. end-fed antenna, 24hr. clock, paracord to hoist antennas, trotline cord to hoist antennas. In a lunchpail I carry 2 12V 7 AH batteries, powerpole ex. cord, cigar plug charger wiring, multimeter. In addition I have a 30W solar panel to tag along with. I spray the backpack with Camp-Dri to give the equipment some moisture protection. I could also carry several large trash bags to cover the backpack with. Someday when I get off my lazy ass I will take a photo of this set-up and post it. This is not a SOTA station, more a picnic table portable station. I should hide all my microphones and use only CW, force myself to re-gain that skill.


Thanks Jim? Please do post photos :-)

I looked at three SSB QRP kits, but none implement CW well or at all. Those are the KD1JV Survivor, Iler 20 or 40, and MST3. There is Also the MDT from OzQRP as well, a DSB 40m rig. All those radios are fairly cheap but lack key features for a survival radio, though the "Survivor" comes close, but no keyer.. I wonder if Ray finished his..?



For the Survivor, put a picokeyer in it.  I have one of those keyers and they work well, are tiny and draw almost no power.


True. I wouldn't mind building that kit, but right now I want to monitor the maritime nets on 14300...


I have not unpacked the kit since the move from Virginia.  It's larger thanyou might think, tough certainly not large.

Before too much physical design, it's would be best to bullet-point your requirements and then let the design fill those, rather than but something then figure out how it would be useful.  har har (like the U.S. Government...)

1.  To summon help in an emergency.

2.  To gather information during an emergency.

3 ... etc.

For me, an emergency transceiver should have a'button' for a key on top.  If you want ot use a keyer - fine - but the button key is fine up to 20-22 word per minute and it is part of the rig, so it never gets lost.  I did this wil the rig I took on my long treks, helping to teach survival in some wild areas.  It was a 40m , 2W, CW only transceiver. It used a ten turn pot, into a varactor and a simply graph of turns/frequency pasted inside the lid.  It was fully enclosed in a lightweight metal box from a junk store. It was a solid sked-keeper and I still have it.  The radio was a modifier SW-40+. It had two controls:  frequency, volume. The key - as mentioned_ was a push botton on top. These days, I'd probably use a Morse 'annunciator' to let me hit a button to know my frequency on-top of the graph.

>RadioRay ..._  ._
"When we cannot do the good we would, we must be ready to do the good we can."  ~ Matthew Henry


Hello Ray,

I agree on the top button. Indeed you can lose a key but not a button part of the radio! I'll add that to the list.



I understand the reasons your not wanting a screen on the device, but if your having holes for buttons - and in theory to let the sound out of the case for a speaker.  How about something like EInk - these screens are very power efficent as they only need power when the display changes.  And they are creepy solid, you can cut them and they still work.  I have an old ereader that has dents in the display and it still works no problem.


Thanks for reading.



Thanks for the suggestion Joe. I think that ultimately adding a display should be the decision of the builder, but you have to draw the line somewhere for the initial design. The PCB would have a pin for VFO frequency output for those wanting to add a counter, but no on-pcb display.



Design Parameters Review

VFO: DDS, as wide a bandwidth as the design allows, including 40m.
Receiver: Direct conversion.
Transmitter: CW & DSB.
Display: None on the board. Frequency announcement in Morse.
Power: Switchable 5W-25W. SWR LED with 5W bridge, operate/tune switch.
Supply: 9 to 30V. 25W output at 12V and above. No batteries inside the case.
Current draw: As low as possible < 100mAh on receive.
Audio: Military handset.
Filters: CW 400Hz.
Keyer: None.

If a watertight keypad can be found it could be used to set the operating frequency. Tuning would be button-based like the Weber MTR. The lack of external controls is to improve weather resistance. DSB is to allow communication with both USB and LSB radios. Direct conversion is to simplify the design and avoid potential detection of IF, for the paranoid crowd :o