Yep, your reply is informative, and I agree totally with your analysis.
I think it's worth adding that the physical characteristics of his half-wave dipole, namely 4 metres off the ground and slung in an east-west direction must necessarily make it directional as a north-south RF radiator for 6 megs.
I reckon if said radiator were slung higher, it would be less directional up to a critical vertical height when it would become directional again above said critical height.
My memory ain't the best these days, but it tells me for a non-directional dipole, it should be non-sloping and about a quarter of a wavelength off the ground.
If the station were located in the UK, the op would be well advised to sling his half-wave dipole in a north-south direction were his target listenership eastern seaboard North American DXers, of course located across the pond from him.
Any thoughts on what I have added?
Over and out.
There's an interesting article about dipole height and it's affects online:
https://www.qsl.net/aa3rl/ant2.htmlJohnny Tobacco also uses a low dipole at this time... BUT with his kilowatts of power, he still gets out an impressive signal, including over the pond to the US.... just goes to show what brute RF power can achieve.... but Radio Merlin's power being a modest 20 watt, the signal is generally quite impressive too, considering it's low power.... and it also travels to the East Coast of the US.
Basically, from what I understand, a low dipole will radiate most of it's power straight up in the sky at high angles so "IF" conditions permit NVIS propagation, Radio Merlin will get most of it's power radiated straight down on the UK and surroundings, and I understand that the directionality of such a low dipole is not as great as when it is put up half a wavelength up from the ground, which for 40 meters would be a height of 20 meters above ground! Such a high dipole would be more directive east-west and the lobes of maximum radiation would be at lower angles benefiting long distance DX when and if the ionosphere allows for this.
Considering how well Radio Merlin's signal is received over Europe and in the UK when conditions allow, with only 20 watt, the relative low height of the dipole might be the most desirable, to be honest, but it should not be much lower or you get more ground losses.
A low dipole (5 meters above ground) is a "cloud warmer" at long hf wavelengths, but can be desirable if you want to try and get a strong "local" NVIS signal when conditions on the band allow for it.... when they don't you'll be sending maximum power to your local flying saucer in space or your friendly nasa astronaut on the space station or moon.
Topic: Directivity of HF dipoles (Read 4221 times)