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The other day I was rigging a bag for a job and noticed something odd I wanted to share with you.

In the bag: 788t, 3x Sennie EK100G2 with DC-2 battery eliminators on a Hawkwoods VLR-SQN4S. The 788t was connected to the VLRs fixed cable.

One of the Sennies showed one bar of reception, although all TX were off, and my RF-Explorer one meter away on the table showed an empty spectrum.

I took the RF-Explorer in the bag, and the noise foor was around 9db higher, with a slight sawtooth pattern. I plugged the 788t off the Hawkwood power source and the noisefloor went down. I powered the 788t from the last Hirose connector, but the noise went up again.

I suspected some correlation with the VLRs internal regulators and luckily, I had a Hawkwoods PC-7 with a 2xM Hirose Cable around, that fits with the Twist D-Tap of the Bebob battery. When I connected the 788t directly to the battery, no noise offset was noticable, bingo! Nice side effect: I can now see the batteries current voltage (and therefore if its running low) in the 788t lcd.

 

With the Bebobs Twist D-Tap, I found a workaround for me. If I'd be stuck with other battery types, I'd try to modify, the VLR and bypass the regulator.

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That's what happens when two switching regulators that aren't isolated 'beat' against each other - it creates harmonics and all sorts of other nasties. Most, if not all of our modern sound gear can handle wide input ranges so I don't see battery regulators as that necessary. If you have a special case voltage needed, I would get a regulator specifically for that thing, and isolate it from everything else.

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Thanks, any recommendations on capacitor values? I imagine it varies from device to device?

I made a filtered power cable for my old Zax stereoline but at 3200 uF the cap is very bulky.

Thanks!

It depends per device. The cap needs to be able to handle the voltage and current of the device, without 'choking' it. I think Glen Trew spoke about this in another thread, but I can't remember which one.
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