Other SOTA sites: SOTAwatch | SOTA Home | Database | Video | Photos | Shop | Mapping | FAQs | Facebook | Contact SOTA

Cable for USB power banks with KD1JV rigs (ATS / MTR models)


I’ve seen lots of postings about designing/building your own power sources using 18650 cells. Being lazy (and not terribly mechanically gifted), I was looking for an easier way, one that would allow me to use the ubiquitous inexpensive off-the-shelf 5V powerbanks.

There was a previous post by Tommy SA2CLC, who was kind enough to even send me some blank PC boards for a power booster. But again, I’m not terribly gifted in such projects, so I kept looking.

I have found a first solution with the Adafruit Model 2778. I love the idea of being able to pick up a cheap powerbank to use with my MTR-5b with the help of this very cheap ($US 6.50) cable. There is also a 9V version available (Model 2777).

The cable is rated for 500 mA, but the factory got 700 mA out, and I’ve been getting 960 mA out during initial tests using an MTR-5 and a dummy load.

Note: when I used the powerbank/booster cable with my KX2, the rig shut down the second I started to transmit due to insufficient current.

One key thing to be aware of is that the cable/MTR setup does not work with every powerbank. Some of them switch off if the load draws too little current. On receive, the MTR5b from LNR is spec’d to draw 30 ma @ 6V and 20 ma @ 12V. On my tests with a KD1JV 5b kit, the rig/12V converter cable setup was drawing an average of 60 mA from my powerbank. This was adequate to keep my Varta powerbank turned on during receive, but my larger Voltcraft powerbank turned off after just a few seconds of receive. Note that one workaround is to add a device such as the Sotabeams “USB battery pack keep-alive load” – but it’s not really practical for outdoor use.

Here is a photo of my test setup with a dummy load; field trials to follow shortly. I have the MTR5b in Tune mode (continually sending a carrier into the dummy load). You can see that the MTR is detecting an input voltage of 11.6V (lower right display). The current draw in Tune mode was 0.96A (as measured with a LogiLink Model PA0067 1-Port USB power meter). I left it running for a good 15 seconds continuous.

I was wondering if I would get QRM from the converter module, but there was no discernable difference in noise from the powerbank and a LiFe battery. I was also concerned about chirps in my signal, but I monitored transmission into the dummy load from my desktop xcvr and heard no difference from the powerbank to the battery.

Thus far the results are encouraging, next are the field tests. If you hear me on the air in the near future, please give me accurate signal reports (I won’t be offended if you give me a 595C).



Instead of running a radio directly, these boost converter cables look like they would be useful for charging small 12V lithium packs, such as those we use in the KX2 and similar radios.

Based on Adafruit’s testing, it would take 6-8 hours to charge a 12V battery in the 2500-3000 mAH capacity range, using the boost converter cable running from a 5V power bank.

It’s not really a plug-and-play charging device, although it might work. It would be good to add metering and current limiting, so it would be a small project to make a reliable, safe charger. The voltage output looks to be just about right for a 3S lithium ion or LiPO battery. Limiting the current to 500 MA or less would be smart. With charging there’s no problem about the auto-shutoff of the 5V power bank. It would be a good feature and would terminate the charge before the battery was topped off. This is probably a good idea when charging overnight, camping, etc.

Most of the larger 5V power banks have two or more USB outputs, so it seems that you might be able to run TWO of these boost cables as chargers simultaneously, so you could charge two KX2 batteries at one sitting. The larger banks have enough energy to do this, based on the numbers available. The 5V bank would shut off once the energy is down too low - they offer self-protection from over-discharge.

Has anyone tried these boost cables for this? Or similar?



i have a similar setup for the smaller MTR3b … i have 2x powerbank that gives out 1A max from the USB port. i originally just wired them both serially, but the powerbank turns off after a few minutes. same as your observation. MTR3b RX power draw is a measly 30mA, according to specs.

on a trip to Akihabara i bougth some DC boost boards based on the X​L​6​0​0​9 chip [Japanese warning DCDC-XL6009]. works like a charm for me. the board has an accesible VR so i adjusted the Vout to about 9.4V (this is a magic number since i have a number of Mizuho pico TRX that also want <10V). the converter also seems to be quiet in my case (i had the luxury of using cable lengths as short as possible).