MLA-30 Mod Step 1: Complete...NOT SO FAST :(

[Erik Mattson]

Oh no, no, no, no. You will not get the RSP to power that antenna. The MLA-30 ships with a 12 volt power supply and the specifications are: Power Supply: 5 volts and Current Drain: 750 mA.

The RSPdx's Bias T will only provide 4.7 volts at 100 mA and most computer USB ports only deliver 5 volts at 500 mA. The RSPdx alone requires +/- 200 mA to operate.

I saw this and was like "Great!".
https://youtu.be/1rtkClK46EE
But you're saying this won't work, right? The only reason I bothered with the MLA-30 is because I thought I could power it with the RSPdx's bias-T. I'm confused by the "5-12V 40mA" stated on the case.

[JustGreg]

The label is correct, but you need to use a USB power supply connected to the MLA-30 biasing tee USB port.  The circuit in the biasing tee converts the 5 volts input to 12 volts out of the SMA connector, labeled to Antenna.  The 12 volt powers the preamplifier in the MLA-30 antenna unit.  The preamplifier needs at least 9 volts to work.  I have tried powering the MLA-30 several ways (9 volt battery, a 12 volt wall wart with another bias tee).  The best way for me was the unit's biasing tee with the battery USB supply.  I posted a picture of the battery USB supply in this topic.  I hope this helps you.

[Erik Mattson]

Not sure how it's working for the guy on the Youtube vid, but I'm done worrying about it. This antenna isn't a necessity. Anyway, I've got a big Anker power bank. That'll do it.

Thanks again, everybody. Case closed.

[~SIGINT~]

Considering that the video never shows the circuit working and that buddy BS his mouth off for 5:18 this has zero credibility. The video is a complete waste of time.

[Erik Mattson]

Considering that the video never shows the circuit working and that buddy BS his mouth off for 5:18 this has zero credibility. The video is a complete waste of time.

Agreed. Thanks, SIGiNT.

[JustGreg]

Erik,
I tried several USB power banks and found their noise levels ranged from terrible to bad.  My suggestion to you is to keep the power bank a good distance (say 6 feet) from  both the antenna and receiver.  The FCC has no radiated emission (noise) requirements for digital devices for frequencies under 30 MHz.   No wonder listening medium wave AM and shortwave  is bad. 

[RobRich]

The inexpensive video amp in the MLA-30 might run at 5v with substantially reduced gain, though that kind of defeats the point of the small loop antenna design. ;)

About supplying USB power for preamps, short of a regulated linear PSU, I have found Apple USB wall warts tend to deliver consistently the lowest noise in my limited testing.

All that said, I suggest either modify the included bias tee to bypass the 5->12 volt step-up converter, or just outright replace the bias tee with a direct feed model.

[redhat]

I did the F connector mod to mine some time ago.  I also built a bias tee for it, running off a switch mode wall wart power supply.  With the suburban noise, and the inherent noise in the loop preamp, I noticed no difference in performance between the switching supply and batteries.

+-RH

[RobRich]

Some wall warts, even switching models, have decent filtering. Sadly, many do not.

I have added filtering caps across the internal side of the power connectors in some of my bias tees. Probably not needed, especially when using a regulated linear PSU, but they were quick and inexpensive to do.

[Erik Mattson]

The bottom line here is that it does work. Probably not as well as it should, but it works. I'm using it right now, quick-clamped to my deck railing just outside the basement window, powered with the RSPdx's bias-T. Listening to some weirdness on WBCQ (0024 UTC, 8 JAN 2022).
That said, it's just not worth the hassle.