Bruce W9OTN was recently bemoaning, correctly I think, the fact that
so few hams do any "from scratch" construction any more. I guess
I'm the "oddball", since I prefer to design and build my own equipment.
This page shows a few of the projects I've done...
Mast-Mount VHF Preamp
See the "FM Broadcast Antenna" page for the purpose of this device.
This two-stage preamp uses two high-current J310 fets, powered from 15vdc run up the coax. There's a companion DC-tee box (not shown) down in the shack that puts the power on the coax. Very stable, high-intercept, low-noise, and 18db of gain.
Not much else to say about it, other than it worked very well,
was simple to design, and cheap to build. A little ugly, but sometimes
VHF stuff works out that way; from the need to keep parasitic L and C to
an absolute minimum.
Man-size Balun:
In the course of working out the optimum way to wideband-match my rhombic antenna, this is one of the high-impedance 4:1 balun concepts I tried. Didn't work worth a damn, but it sure is purty! Kind of a Tesla-style doohickey...<g> It's 4.25" PVC pipe, 28" tall, with a 2x2 lumber frame.
Oh man, is the shop ever a mess in this picture....too many projects lately maybe!
This has a pair of xmission lines connected in series at one end, and in parallel at the other; producing 1/2 the line impedance at the parallel terminals (unbalanced end), and 2X the line imp. at the other end (balanced end). This is wound with foam-core 300 ohm twinlead, so ideally it would be working into 150 and 600 ohms at the two ends. Someday I'm going to figure out why it didn't work as expected...
Power Transformer for 14vdc/20a Supply:
Magnetics really fascinate me. Over the years, I've gotten in the habit of tearing up old "useless" transformers and making them do something useful to me. This 400va unit came out of an old typesetter power supply.
I stripped off all the secondary windings, leaving the primaries intact, and wound on a bifilar #14 winding. Sometimes, when high current is needed, it's a lot easier to wind on a pair of moderate gauge wires instead of a single real heavy wire. This winding is tapped, for use with different regulator topologies which require different amounts of "headroom".
Connector-Pin Extraction Tool:
A simple and fun little project on the lathe. This tool slips over the pins in a Molex-type connector, depressing the little locking tab and releasing the pin from the plastic housing. I already had Molex and Amp tools, but of course Icom had to use something a leeetle bit different <g>. Thus, a custom tool was required, and fabricated. From brass bar stock. If I used it alot, I'd add a nice comfy wood handle, but I've only used it once so far....
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