I have been using the DVB-T’s magmount whip antenna after trimming its removeable part to 67mm length as shown in the image 1.
Recently I opened the base of the magmount antenna (images 2, 3 & 4). I noted that there is about 15 mm of vertical metal part between screwable whip and feed coax.
This hidden vertical metal is part of antenna, and hence antenna length should be measured from the bottom of this part where coax is soldered to it. Since this part is 15 mm long in my antenna, my magmount’s length was actually 67 mm + 15 mm = 82 mm. I therefore chopped off another 15 mm from the whip, making the length of removeable part 52 mm instead of 67 mm. See image 5. I noticed about 5% to 10% improvement.
Things to be tried:
Remove black plastic circular adhessive cover from bottom of antenna, and check electrical continuity between exposed metal base plate & the outer metallic part of MCX connector at other end of antenna’s coax.
Place exposed base on a metallic can and check if direct contact gives any improvement.