Re: Active antenna into uBITx V5 gives some smoke on the coax #ubitx #antennas #v5


Skip Davis
 

Erwin there is a good reason for what you experienced with the active antenna the uBITX antenna input looks like a short for DC. This is because the antenna input is connected via a low pass filter to T2 of the mixer. If you measured the uBITX antenna input with a ohmmeter you will see zero ohms. 
If you install a capacitor in series with the input to isolate DC on the active antenna on the uBITX side you should be fine. 

Skip Davis, NC9O

On Dec 11, 2019, at 07:29, Erwin Serlé via Groups.Io <waterwin2@...> wrote:

I have a loosely soldered uBITx on my work area connected to a 12V power supply and a headphone. Nothing properly mounted , shielded etc.
Just to hear some RF coming in as the kit arrived just some hours ago.

I works, with hum, other sounds etc. As expected. Power supply shows 166 mA current at 12V.

Then I changed the coax coming from one of my normal antenna's into a coax coming from my active antenna. A design by PE0RDT also known as mini-whip.
The electronics receive their power via the coax going out and connected to another 12V power supply.

This is a BAD idea.
I saw strange flickering on the uBITx display, going on and off, and also the same on the first 12V power supply powering the uBITx board. And I noticed smoke coming from the coax, at both sides, into the uBITx and at the power/connector box to the active antenna.
I pulled the 12V from the active antenna, pulled the (warm and melted) coax from both sides, switched of the 12V powering the uBITx board.

After connecting a normal antenna all is well again.

Possibly there is (quite) some difference between the 2 ground potentials of the 2 different supplies. I will need to measure this ;-)
Later...
When I have grounded all things great and small, and have a good metal enclosure etc.

--
PE3ES - F4VTQ - Erwin
73

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