All,

?

???? I built my QMX+ as a 9V device; I frequently run field equipment from 6-packs of NiMH rechargeable batteries at 7.2V nominal.? This had me concerned about being able to also run it from my 13.8VDC home supply as I'd also like to run it from my "winter" location in the attached garage.? That fact, coupled with the fact that I got a flaky DC input jack on my QMX+, and I prefer to use Anderson Power Poles whenever possible for power connections, forced me to seek solutions. ??

???? I started out trying to switch MOSFETS using a zener diode to switch between either directly tying input to the rig when input V was below 9V, or switching that input power to a LM317 when it went higher than 9V, but that circuit didn't work very well.

??? Then I looked into LDO regulators that would regulate my input voltage to 9V whenever it exceeded 9V, and reduced it only slightly when below 9V.? As luck would have it, I had samples of Linear Technologies LT3086 LDO regulators in my junque box, so I built up a new rear plate for my rig sans the coaxial DC input and the unused QLG3 jack.? This plate has a pair of Anderson Power Poles for DC input, and acts as the heatsink for the LDO regulator.? I then whipped up a tiny PCB and mounted it (and the tab of the regulator) to the new plate.

??? As built, it outputs 7.9V as I tested it at 7.5V and fear blowing the finals in field operation.

???? I then added a 4-pin socket to the main PCB immediately behind the coaxial jack to use to insert the DC from the new regulator.? I left the Main PCB totally intact so I can revert to using the original rear plate if I need to.

???? When receiving, the LDO drops less than 50mV.? When transmitting, it drops about 250mV.? Much less than a typical diode, and enough loss for me to be satisfied.

???? Pix of the modifications are attached and schematics/PCB layouts are available on request.

?

W2EB

Bill Lazure

East Syracuse, NY USA

I found some very inexpensive voltage regulators that will reduce the higher DC voltage to what ever you want it to be. They are rated for 3 Amps.

So getting 9 or 12 volts DC from that LiFePo battery is easy.

On Amazon they are listed as:

Bill,

???? That?device runs at 150KHz.? Does it introduce any noise in your rig?? I specifically chose a linear regulator so I wouldn't add any more noise to the rig.?

?

Bill

W2EB

East Syracuse, NY

On 8/7/2024 at 11:56 PM, William Lee via groups.io <leew50@...> wrote: