I don't think aluminium will bend the earth's magnetic field by any noticeable amount, but it will keep out RF. The reference to 'soft metals' is almost meaningless; could it really mean soft iron?

The extra wire is just adding a bit of end-loading capacitance. It doesn't matter too much exactly how it is connected, because the potential is almost the same (and the current fairly low) at the end of the antenna. It is adding capacitance where previously there was already some capacitance from the main wire.

Putting the extra wire as an extension in line with the antenna (i.e. lengthening the antenna) is different because it makes the antenna effective length longer. It is adding capacitance where previously there was nothing.

Anyone standing next to the antenna is in the near field, so exposure depends to some extent on the antenna Q. Narrow bandwidth antennas, as typically used by amateurs, have stronger local induction fields than a genuine wideband antenna for the same radiated power.

You can estimate the voltage experienced by someone touching the antenna. An ideal resonant grounded quarter-wave would have an impedance of about 35 ohms. At 100W this is a peak voltage of 83.66V. Even DC at this level would be enough to make someone jump. AC and RF would be worse. A real antenna would be worse, as any reactance seen at the base would increase the feed voltage. Lets make a wild guess that at one of your operating frequencies the antenna looks like 20+100j. 100W then means peak voltage of 322.5V. My guess is a nasty slow-to-heal RF burn.

If the joints in the main loop are not yet soldered, then maybe all you are seeing is the joint resistance. Small loops can only work if all sources of loss are reduced as far as possible, as the radiation resistance is so small. A bit of joint resistance won't disturb the inductance, so it will tune up OK but will have very low efficiency.

I think most 0A2s don't have any deliberate radioactivity in them. For those that do, once the activity declines due to age you will just have to rely on ambient light or natural radiation to help them fire - just like those which never had any help to start with. The firing voltage may be a little higher and a bit variable but in most circuits they should still be OK.

The J-pole is essentially a narrow-band end-fed half-wave dipole, with a matching section. It is easily detuned by nearby objects, so not ideal for indoor use. A folded dipole with a suitable balun may work much better in a loft.

Some use of feeder radiation? No sign of a balun in the pictures.

See discussion http://forums.qrz.com/showthread.php?217136-Chameleon-Antenna&highlight=Chameleon? Interesting comment on eHam vs. Chameleon reviews.

Is the BFO near the power supply? If so, two possible problems are:
- power transformer magnetic field affecting the valve
- BFO RF energy getting into the HT rectifier, called 'modulation hum' - capacitors across the rectifier can help

Remember that some older receivers were not designed for SSB, and a bit of hum on CW was accepted as normal.

Yes, I should have noted that. My main point is that the forward power has voltage and current exactly in phase because the line impedance is pure resistance 50 ohms. Same for reverse power, because that also sees a 50ohm line. At any point on the line we see the superposition of forward and reverse waves. If they are equal, then as you say we get just a standing wave which is the net result of two travelling waves.

On the contrary, this exercise demonstrates that the inline power meters correctly distinguish between forward and reflected power. 30W out and 30W back means net power transfer of zero, and net system efficiency of zero.

Forward current and voltage are combined to give forward power. Similarly for reverse power. As the line has 50 ohm impedance (i.e. pure resistance) the forward current and voltage will be perfectly in phase with each other, irrespective of termination. Similarly for reverse power; but forward and reverse will differ. The net voltage (sum) and net current (difference) will not necessarily be in phase everywhere except when the line is properly terminated.

I'm glad I'm not the only one who forgets what things are called! I sometimes do it with people too.

Something which bothers me about the Pullen mixer is that the second triode is deliberately biased so that it has a limited dynamic range. It needs to do this to get the curvature for mixing, but it is difficult to get the required second-order curve without some unwanted third too. The Pullen is almost an unbalanced differential pair; if you want even-order, why start with odd-order and unbalance it? Yet it has good reports. Maybe it is just a bit better than its rivals.

Measure the diameter and spacing of the wires. Plug values into the formula for twin wire transmission line. If necessary, correct for insulation permittivity.

Alternatively, measure using an RF impedance meter.

I don't wish to take part in the debate about loading coils. If I had realised that the 'brainteaser' was related to that issue I would have kept well away.

Going back briefly to virtual photons, it is a long time since I seriously studied EM and QM but I seem to remember that static and quasi-static fields, when quantised, give rise to virtual photons (i.e. off mass-shell). Only radiation fields have real photons. Note that a virtual photon is just as real as a real photon, but it can temporarily misbehave (as far as it is allowed to by the Heisenberg uncertainty principle). In any case, invoking photons to explain low frequency phenomena (anything much below infra-red) is daft, and can be a sign that someone is either confused or desperate.

He never said it was a two-terminal network. He said it was a real component. Real components have stray capacitance to the box etc.

Last time I studied EM, fields were allowed to go off to infinity. It is true that a diverging electric field must come from a charge, but it can go either to another charge at a finite distance or off to infinity. Otherwise you could not calculate the Coulomb field from a single charge in an otherwise empty universe. A time-varying field will have curling components too and they just go round in circles, never landing anywhere. Bringing in photons to explain low frequency phenomena is generally a bad idea, as most of the photons around components are virtual; only in the radiation field do you get real photons.

I was wondering where you could buy 1930 ohm coax cable! A big coil will of course have a high inductance and a relatively low capacitance (when compared to coax) so at some frequencies can behave like a section of transmission line.

My initial guess, before I carefully read the question, was a pi network as that has impedance inverting properties but then I saw that only one component was present. A pi network is of course a lumped approximation to a transmission line.