More Indoor UHF Experiments

Continuing on from my earlier UHF exploits, my next 70cm antenna was made from brass tubing with the same Mix 61 bead balun.

Brass tubing 70cm dipole with its bead balun inside of a PVC pipe

However, I eventually cut it too short as I worked on getting its resonant frequency up.

Each leg is now around 10.3cm long

NanoVNA: SWR of 2.2 @ 436 MHz, 23.41+j7.66Ω

DD8SF and I thought that the issue was the feed point design, so I switched to something much simpler: brass tubing soldered onto knurled nuts that could easily be screwed onto and off studs at the feed point.

Brass tubing soldered onto knurled nuts

Brass tubing mounted to the feed point

NanoVNA: SWR of 1.357 @ 435 MHz, 36.85+j548mΩ

This design also was my first real foray into telescoping legs.

Same brass leg antenna, but with an additional level of telescoping legs and mounted in the window

NanoVNA: SWR of 1.816 @ 450 MHz, 47.89+j29.56Ω

Same brass leg antenna, but with an a third level of telescoping legs and mounted in the window

NanoVNA: SWR of 1.281 @ 432.6 MHz, 42.87+j9.035Ω

I also did some experimentation with traps and a fan dipole, neither of which really panned out.

Antenna trap on a telescoping brass tubing section

Fan dipole mounted on the same feed as above

NanoVNA for fan dipole: SWR of 1.499 @ 429.6 MHz, 74.89-j1.61Ω

The last thing I tried was a super chunky pair of aluminum tubes, targeting maximum bandwidth. DD8SF said that it was far too large for what the NanoVNA was showing, but we later determined that the issue had to do with a metallic coating on the windowpane.

Off-center dipole made of thick aluminum tubing, mounted to the same feed as above

NanoVNA: SWR of 1.792 @ 420 MHz, 28.07+j3.136Ω

#AmateurRadio #HamRadio