Some of the things I am currently working on (playing with).

For some time I have been studying, building and testing antenna traps with a view to cramming the maximum number of bands into my 125ft back garden without hanging up umpteen separate dipoles. I quickly lost interest in most of those traps found in the various radio manuals. Mostly they are too big, too heavy and look crap. I have never been very keen on the straightforward open wound trap with a high voltage ceramic capacitor hung inside it. I have yet to find a reasonably priced ceramic cap that was not affected by temperature and humidity. There are, of course zero temperature coefficient ceramic caps available, but they are becoming harder to find and they are not cheap. I also quickly lost interest in co-ax traps. Apart from their size and weight they look crap. So, I decided to try to produce a trap that had sufficient self capacity not to require an external capacitor. Had sufficiently high Q to operate effectively and produce a simple antenna that would operate on the bands I choose without serious bandwidth limits. These traps are bifilar wound with twin 3mm fig of 8 cable rated at about 1.2kV and 5amps, and are wound with two layers. You finish up with 8 ends so you need to make sure that you connect them correctly otherwise everything cancels itself out. There is sufficient self capacity in the windings to resonate these traps on any band without an external capacitor.
   Of course, the simplest and probably most effective general purpose multi-band antenna would be a doublet fed with open wire line, but this necessitates a tuner at the bottom of the feeder, which in my case would be about 90 feet away from the shack. That would mean building a remote controlled ATU in a water-tight enclosure which would not be cheap to produce. Plus, I don't like spending money.
I do not claim to have invented anything here. I have simply used several techniques that are freely available on t'internet, and combined them to produce what I think is an effective trap that does not limit me to a few kHz of any band and hopefully does not require a big, heavy, expensive ATU at the bottom of the feeder.
I am currently working on a four band system fed with RG58 and you will be able to judge the results for yourself if you hear me on 30/40/80 or 160. You may need to check the cw end though. These traps were not intended for high power use and are currently being run at 200watts max, although the voltage/current rating of the cable suggests that they should be ok at much higher levels. This antenna is now fully operational and I have a pulley at the top of each mast to hoist the wire up and down. It is now functional on 30, 40, 80 and 160 at 35ft, The hanging down end sections are made from a Slinky, cut in half with solder tags attached at each end. I can shift the top band resonance anywhere within the band by simply stretching/slackening the Slinky.

Click on the Ant Projects link at the bottom to see some constructional pics of the traps.
A Hi voltage motorized variable capacitor, pictured on the Shack page. This is/was an attempt to make a remote tuned capacitor for use with a mag loop. Unfortunately, and I should have known better, you can't put hi-voltage RF components in Black plastic boxes unless you fit nylon or similarly insulated input/output terminals. I first found this out with my remote L match at the bottom of my inverted L. The vacuum capacitor is mounted in a black plastic box and did not seem to tune very well when I installed it. Upon examination I found that the brass bolt connection terminals, through the side of the box, were hanging loosely in charred, over-sized holes. The RF (50w max) had burnt the box away. I fitted a section of perspex to the side and fed the connecting bolts through that. It has now been working fine for over 3 years. The current capacitor appears to be the same. No bonfires yet but I only fired it up with 5 watts for a few minutes while scanning the frequency range. It seemed to work fine on receive but the moment I applied RF power to it the SWR became infinity and it no longer tuned, not even on receive. I intend to fit a perspex plate to this cap now and try again. The capacitor has two fixed 1mm x 75mm x 80mm brass plates with two layers of Teflon in between and a moving brass plate between the Teflon sheets. The upper copper plate visible in the photo is a piece of fibre-glass pcb purely to support the motor etc. This project is currently on hold while I play traps.