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17 Meter End Fed Halfwave Antenna

This antenna is for a new rig I acquired, a QRP Labs QCX-mini 5 watt CW transceiver. I wanted it lightweight, on a female BNC connector, and be self-contained.  (For a full rundown on how these transformers are built, see: HERE)  

I started with a SMD mount BNC-F, but the pins didn't align with the holes on the board, so I snapped off 3 of them.  Then, I took a piece of circuit board and rounded it to the best of my ability with a Dremel sander:

IMG 2757  

Knowing I wanted for the radiating element to exit the top nearest to the center, I took a piece of 28ga Poly Stealth wire and soldered it onto the board.  It would later be connected to the toroid:

IMG 2758

 

Here we see the BNC ground, center, and radiating element soldered into place:

IMG 2759  

I then shunted the connector's center pin to ground with a 100 pF capacitor and cleaned-up my solder joints:

IMG 2761

 

A T50-43 toroid was wound with 26ga magnet wire.  Three primary and 26 secondary turns were made to create the transformer.  Once everything was soldered in place, the little LC circuit was ready to test:

IMG 2794

 

I cut a piece of Poly Stealth wire a bit longer than 17m and trimmed it to length.  I arrived at a good SWR, inductance and impedance on the circuit.  Happy with the resonance, I potted the toroid with 5-minute epoxy to the board, and the board to the connector:

IMG 2796

 

It was finished with a piece of heat shrink:

IMG 2797

 

All finished and connected to the radiating element:

IMG 2799

 

The wire was still a little long when this shot was taken, but the SWR got even better once trimmed:

IMG 2800

 

All wrapped-up and ready to go.  I want to start cutting my own end insulators with Bakelite, Delrin, or some other material:

IMG 2804

 

Field testing in the yard on the SOTABeams Tactical Mini:

IMG 2802  

 

It was a fun little project that yielded me a great EFHW for 17 meter QRP on a budget.  Thanks for stopping by!

73,
Chris