Topics

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

Erwin Serlé
 

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

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

Gordon Gibby
 

That was great of you to explain that!   Once you explain it it makes good sense!


On Dec 11, 2019, at 09:07, Skip Davis via Groups.Io <skipnc9o@...> wrote:

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

Erwin Serlé
 

Thank you Skip, I will add a DC-blocking capacitor. Would 100nF be good?


--
PE3ES - F4VTQ - Erwin
73

Skip Davis
 

Yes that 100nf capacitor will work fine. 

Skip Davis, NC9O

On Dec 11, 2019, at 11:52, Erwin Serlé via Groups.Io <waterwin2@...> wrote:

Thank you Skip, I will add a DC-blocking capacitor. Would 100nF be good?


--
PE3ES - F4VTQ - Erwin
73

Erwin Serlé
 

The ccircuit should have that capacitor already, I need to open that box and check

Image result for miniwhip pa0rdt
--
PE3ES - F4VTQ - Erwin
73

Skip Davis
 

Erwin by any chance did you connect up the power feed unit up in reverse with power feeding to the uBITX? 

Skip Davis, NC9O

On Dec 11, 2019, at 18:29, Erwin Serlé via Groups.Io <waterwin2@...> wrote:

The ccircuit should have that capacitor already, I need to open that box and check

Image result for miniwhip pa0rdt
--
PE3ES - F4VTQ - Erwin
73

Erwin Serlé
 

Reversing the power would not make my uBITx work I think.
And it is working (still ;-)
--
PE3ES - F4VTQ - Erwin
73

Ashhar Farhan
 

Qrp pops has some really great stuff on active antennas


On Thu 12 Dec, 2019, 4:47 PM Erwin Serlé via Groups.Io, <waterwin2=yahoo.com@groups.io> wrote:
Reversing the power would not make my uBITx work I think.
And it is working (still ;-)
--
PE3ES - F4VTQ - Erwin
73

Skip Davis
 

Erwin I was meaning the power adapter for the active antenna not the uBITX. 

Skip Davis, NC9O

On Dec 12, 2019, at 06:17, Erwin Serlé via Groups.Io <waterwin2@...> wrote:

Reversing the power would not make my uBITx work I think.
And it is working (still ;-)
--
PE3ES - F4VTQ - Erwin
73