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30 mag 2018

Strong Signal on Transceiver while tuning

1 commento

Hello, I have my baby loop for a while know and if the atu tunes the loop i see an signal with 9+60db on my transceiver depanding on the band.

in the lower bands like 40m it is 9+20. The higher i geht the stronger the signal is.

My question is, if this is normal and all others have this too or do i need to worry about my transceiver with a maybe to strong input signal?



31 mag 2018

Hi, Arne,

The short answer is, this is normal. The beauty of the C-M antenna, unlike the MFJ loop for example, is that the loop controller contains its own frequency synthesiser and uses this as the tuning signal. Inside the loop controller is a changeover relay, and when you request the controller to tune the loop the microcontroller commands the synthesiser to produce a tuning signal and this is sent to the loop at a power of approximately 10mW. The changeover relay operates and disconnects the tranceiver from the antenna and connects it to the RF output of the synthesiser. The VSWR is constantly being measured as the actuator motor is driven searching for a null point. When the minimum VSWR is found this stops, and the relay switches the transceiver back to the antenna. Unfortunately the relay is only a single-pole single-throw relay and a certain amount of the tuning signal leaks across into the transceiver, this is what you are seeing. If they had used a double-pole double-throw relay the design could then have shorted the transceiver port to ground, which would have reduced the feedthrough signal. However, the signal leaking through, although quite high, is not damaging, and although it captures the AGC, the transceiver soon recovers. So, not to worry. Hope this helps.

Adrian, 5B4AIY

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