VK4ZXI

Homebrew cavity resonator/duplexer for 2m repeater There has been some interest in the club establishing another 2m repeater, but lacked a duplexer. A couple of old cavity resonators were discovered in the back shed. We were able to tune these very quickly and easily using the new Chinese KC901H network analyser (more about that in another post). Why and how they work: an antenna in a box! Up to that point I had heard of cavity resonators but had little idea of how they worked or how they were made. Similarly, so was my knowledge of repeater. However, as I started to learn about them, I became quite intrigued with the technical finesse of being able to transmit and receive with the same antenna simultaneously, albeit on different frequencies. Further, as desirable repeater sites are restricted in number, many repeaters share the same site, again on different frequencies and bands. The solution to the repeater problems is in using very selective band-pass and/o...

Multi-band squid-pole dipoles and Yagi antenna: Feasibility? One source of thin fibreglass for use with the loading coils on the TET-Emtron antenna I have been working on is telescopic "squid" poles (used for catching squid). A 7m squid pole is in seven sections, a metre long, from 45mm to 8mm for the heavy-duty version. The poles only cost about $30 each. They are available from http://haverford.com.au/telescopic-poles.html . Given that I was thinking of the TET Yagi elements using the tricks of vertical antenna to reduce length, I thought, why not go the other way and use telescopic squid-poles as rotatable dipoles or Yagi elements? Telescopic elements are quite useful for me as my tilting mast tilts to the short end of a trapezoid, with only 3 to 4m for a boom, compared to 10m at the other end. With the mast right down, I can mount the boom and one side of a Yagi horizontally, rotate the boom 90 degrees to its correct orientation, then extend the elements on the othe...

Small multiband HF beams- TET-Emtron revisited While I haven't posted much recently I have been chasing a few wild ideas. I bought a few antenna from a deceased estate, including bits of a couple of TET and TET-Emtron HF beams. TET 2 element 20/15/10 beam TET 2 element 20/15/10 beams are quite innovative, especially considering they were first made pre-1985 with: capacitive hats to physically shorten the element length dual-drive, driving the radiator and reflector, 180 degrees or more out of phase. This doesn't increase the gain much, but does increase the front to back ratio, which is just as good. close-coupling of radiator and reflector to shorten the boom length. I had just the radiator of a version of the HB-23M, which is enough to use an antenna analyser to see what it does, albeit at ground level (which messes up capacitive hats and low frequencies). I have to make up the rest. The traps, the rectangles on the elements, are two parallel R/C circuit...