Proud Mary wrote ...

In favourable conditions, 7W CW will give you a reach of hundreds of miles and sometimes further at 3.5Mhz, with even a mediocre, makeshift antenna, such as a long wire thrown up into a tree.

The choice of antenna will be governed by local variables, the space and height availlable, limitations on height imposed by planning permission and proximity to aerodromes, accessible 'free' high points such as roofs and trees, signal 'shadows' caused by mountains and buildings, proximity to large metal structures, local EMI that can be reduced by a particular antenna orientation, ground conductivity, and last - but by no means least - money.

So if you'd like to tell us a bit more about the proposed antenna location, you'll get more helpful replies.

Proud Mary wrote ...

If you haven't got any dogbone antenna insulators, buy these:



(I have dealt with this seller several times, and he seems honest.)

Obtain some nylon or polypropylene cord/thin rope strong enough to to take the strain when the antenna and trees are flexing in the wind.

Pace out the distance between the trees. You have to bridge this gap as follows: cord - insulator - antenna wire - insulator - cord. Make sure the cord is long enough at either end so that the insulators are clear of the branches.

Now before cutting any of your cord, you can make your life easier if you thread the cord through one eye of the dogbone like a pulley, so you can raise and lower the antenna from the ground.

You also have to make a decision about the feeder. You can either (A) take the coax directly to one end of the antenna, making it fast to the dogbone to relieve strain on the electrical connection, OR (B) you can use the antenna in an "L" configuration, continuing the antenna wire downward from the dogbone directly to the back of the sender, or to a coaxial cable at some point in between.

How to choose? Well, if the "L" configuration (whose geometry is not very important) would take the antenna downlead close to domestic cables, other coaxial cables etc, I would choose to take the coaxial feeder all the way out to the first dogbone.

What wire to use? There are quite a few 'antenna wires' aimed at the amateur market, but green//yellow single 6mm Earth bonding wire as used in domestic installations will do just as good a job, and will not be hard to find.

Solder the connection of the coaxial inner to the antenna wire, and coat liberally with a flexible non-conductive sealant, or self-almagamating tape.

Don't put too much tension on the antenna. A dead straight line is not necessary. A slight curve will allow for flexing of the trees in heavy weather.

Don't fall out of the tree!


PS: I've just glanced at the power oscillator circuit with the EL84 that you've linked to. The unfiltered output will radiate every harmonic under the sun, right up into the VHF, so you may become a star of your neighbour's radio and TV sooner than you'd ever have dreamed possible. Strictly speaking, you should do all this setting up and reduction of harmonics with a dummy load, but get the thing off the ground, Alf, and then you can worry about attenuating unwanted emissions with a basic C-L-C pi filter next.

Proud Mary wrote ...

I'd call it "a long wire" or "end-fed long wire".

Quartz crystals: The crystals used in the heyday of single valve power oscillator transmitters like yours - the 1930s and 40s - were very much more robust and were designed to handle much higher power levels than one would expect today. So you may have overdriven your crystal, which may now be fractured, and continuing to resonate, but without its original enthusiasm.

To use modern crystals to their best advantage with a valve oscillator, it is best to generate the signal at the lowest level at which the circuit will still oscillate reliably and then amplify the signal by means of a buffer amplifier, which isolates the oscillator, and stop it being 'pulled' by changes in the power amplifier. This configuration uses three valves - oscillator, buffer amplifier, and power amplifier - but you can get away with two in one envelope - for example, a triode output pentode - with some some sacrifice of quality.

If you put up the circuit of your superregen, we can think about why it isn't working properly.

Proud Mary wrote ...

My encouragement has been directed at the so-called random wire antenna as I think this will be easiest for you to get started with, and can usually produce very satisfactory results for a small outlay. There's a useful blurb about random lengths to avoid here: You'll find out lots more if you Google for random wire antenna. I'm sure that not all of it will agree with what I have suggested, but that is often the way with antennas - everybody insists their own recipe is the best.

You can use a superregen to receive CW, but you will need to set the regeneration so that the detector is just oscillating. This oscillation mixes with the incoming signal to produce a beat note in the audio range. You can also demodulate FM with a superegen.

Signs that the superregenerative detector is working: a loud rushing, hissing sound which goes down almost to nothing when a strong signal is detected.

As for more crystals in series or parallel combinations, I think you would be throwing good money after bad, and only whet the oscillator's appetite for more! I realize that this advice may leave you without any oscillator at all, so I will have a think and see what can be done.