This is a updated collection of easy to build projects for radio amateurs and swl's. See all my projects in the OLDER POSTS down this blog.
Have fun.
73' John

Mutual respect is the key to global peace.....

Tuesday, September 24, 2013

End fed half wave high pass for 20m.

A common problem with qrp transceivers is a weak frontend . Most end fed antennas use low pass tuners causing high stress due  to strong signals coming from BC stations .
The High pas tuner used here helps to reduce these problems. Put 19 turns 1mm transformer wire on a T130-6 torroid to form a 4.8 uH coil. The trimmer used is a 60pF type set to about 25pF .  Put a 3.3K resistor between the antenna connector and the ground of the coax connector and tune the trimmer for resonance at 14.180 MHz.  Keep in mind that a thin antenna wire has a higher Z.
After tuning the unit connect the half Lambda wire ( 10.15m PVC covered stranded copper wire) and cut it for lowest swr. A  1:1.2 swr is easily obtained with this unit. The cabinet is a PVC type G302 made by Velleman. Every end fed / vertical needs some kind of counterpoise to push against and in this case that's the coax , so don't forget a line choke near to your transceiver.

Disclaimer:I'm not responsable for any damage due to improper reproduction of my projects.