The Usual Uninteresting Solution
There are a couple of issues one reads about related to the topic of this article. One is that AC powered USB supplies introduce noise, and that battery USB supplies will sometimes automatically shut off because of the low current draw — the battery supply decides noting is connected and shuts down.
The first is solved by using a battery supply, and the second is solved by selecting a supply that stays on under the low-powered load. I personally use a 10000 Bscame BS-1 battery bank that I like a lot.
First World Problems
But what if you don’t have a battery pack handy? Where else can one get power for an MLA-30+? Let’s start by asking what the Biasing Tee needs in terms of power. That’s easily measured.
Rounded off it’s 75 mA. In this case the voltage was 5.17, so the power requirement is 75 mA * 5.17 V = 388 mW. Now what else might you have around the house that consumes a similar amount of current? It turns out that a quiescent USB flash drive might consume 50 mA, and one from which data is being read consumes between 100 and 200 mA .
So what might one have around the house that reads from a flash drive?
How About a Radio?
There are a number of emergency radios that are designed to power external devices, but there is another class of radios designed to play MP3 files from flash drives like:
The EVCHE EC-2110BTS has to be turned on and switched to the MP3 position to power the antenna, but it works great. The radio is powered by an 18650 battery. A very good 18650 battery capacity is 3500 mAh or 2500 * 3.7 = 12900 mWh. It should be able to power the antenna for about 33 hours (less whatever current us used by the radio for other things. One can’t use the EVCHE EC-2110BTS as a radio during this time because it has to be set for MP3 for there to be power to the USB jack.
And if that weren’t enough, this radio can be alternately powered by two D cells. That should do in a pinch.
These numbers are rough approximations. Battery supplies often don’t live up to their specifications. Your mileage may vary.