Wednesday, August 30, 2017

Mag Loop Tuning Aid

Since the HF transceiver I use doesn't have an SWR meter, I went in search for a way to ensure my mag loop antenna is tuned properly without any extra equipment. So, I built this little tuning aid.

I remember seeing somewhere online recently a user posted a picture of a LED soldered to a loop of wire and then run through a snap-on ferrite core. They then clipped it onto an antenna wire and when they would tune for best SWR, the LED would get brighter. I thought that the idea looked perfect for my STL antenna.
Tuning Aid Getting brighter when transmitting.
I use LMR-400 for my loops main element and I didn't have any snap-on cores big enough for that. I did happen to have a regular solid core that was big enough to slip on over the coax connector. I also wound up using an incandescent bulb instead of an LED, but it works the same. I wound the wire only two turns through the core and wired them to the light. When transmitting on my lowest power setting and turning the tuning knob back and forth slowly, you can see the light get brighter and dim out depending on how much power is being emitted by the loop. This also corresponds to how good the SWR match is at the transmitter. 

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