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« on: January 26, 2024, 2356 UTC »
Yep. I figured on picking up an used Acopian, Allen-Bradley, or similar power supply anyway. Lambda works for me. Supposedly NOS as well. Thanks for the link.
The DC blocks arrived. Did a quick test on a SDR. No immediately noticeable insertion loss on MW/HF.
There appears to be a little loss down in lower LW under probably 100KHz, though I did not care enough break out the NanoVNA to measure.
Hardly surprising IMO, as they are inexpensive DC blocks for CATV. Anyway.
Here is an interesting one. My nightstand receiver is basically a small WinARM notebook, an inexpensive MSI SDR, and an active miniwhip.
IIRC, the bias tee probably already has an internal isolation choke. though I did not bother testing it. Instead I added a mix 73 binoc ferrrite with like 3-4 bifilar turns on the antenna side just in case.
Not bad but still some weak evenly spaced lines in the waterfall. Likely from the notebook and/or SDR. Dropped the PSU, which I already know is somewhat noisy at low frequencies, yet they were still there. Touched the metal case of the SDR, and they mostly disappear. Now I am getting somewhere.
Tried adding a mix 73 binoc ferrite wound as an 1:1 isolation transformer near the SDR. No real help there, so it is not coming from upstream, which is not too surprising if the bias tee likely already has a choke.
Okay, what if it is actually a ground loop or similar causing the issue? I grounded the SDR back to the power strip ground. The issue is now mitigated.
A some point I should get around to moving the feedline to a passive antenna as well, but the nightstand SDR is mostly for background noise, so "whatever" for now.
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