That tiny signal on 500Khz

The next thing needed to get a signal on the 500KHz band is an Antenna. I removed several in my collection which I don't use much now, a WX Satellite Quadrahelix, a 10 Turn 23cm Helix, a 2.4GHz Dish and a 30m wire Dipole, in order to tidy up and dedicate a 6m mast to holding one end of my top span for 500KHz.

Even by Amateur standards my T or off centre Inverted L is small, a 6m Vertical copper wire is loaded by 10m of Horizontal. Increasing the number of wires in the Top Load would make an improvement to the signal but not to my state of embarrassment re my crowded Antenna Farm (Patch). No I think it has to stay as it is.

At the far end another 6m mast is used to support the Top Load and my 40m Doublet. In the photo the centre feed point can be seen and some high visibility beads on the wire which have all crowded toward the centre.


I measured the Antenna capacitance as 132 pF, an inductor of 751 uH is needed to tune this to resonance. This needs to be variable, Variometers are often used for this, I believe they are a bit of a lossy solution so I devised a method of 'dipping' a Ferrite Rod into the top of the coil rather like a bicycle pump arrangement. The test set up is shown here.


This turned out to be surprisingly efficient in some test arrangements but not good enough. One problem is the small wire diameter which adds losses. The other, mechanical, I mounted it too close to ground thus adding loading.

I have a large Racal glass fibre coil former, it's built like a tank and fully waterproof which has never really done an efficient job on HF. I had already re-wound it starting with 16g enamelled copper wire stepping down to 20g at the end this is 250 uH. I added a 4 turn coupling coil and SO239 Socket.

Instead of a screw in whip as is intended I added a threaded bush to my 'ferrite pump' coil to enable this to be screwed on top. This adjustable coil 41mm dia. wound using 1mm wire is 230 uH with no ferrite.

With Ferrite it can be adjusted up to as much as 900 uH. The 'pump' set up if fully waterproofed using plumbing goods.


It is a patch antenna, (cabbage patch) the Purple Sprouting Broccoli will get taller and will be gone next season.
I wonder if the closest plant does cause some loss, we will have to eat our way out of that one in the spring.

I really am that restricted for space, I shall continue to try for improvement but I think there is not a lot left to achieve judging from signal comparisons with other stations who run 5 watts.

I have definitely improved on my 40m Doublet with strapped feeders by 3dB using this antenna.

My signal has been spotted by 4 stations the most distant being G0KTN at 145Km

More results and comparisons another time.