On 16 Aug 2007 at 15:38, John W Gould wrote:
> Mal et al, it will be an interesting comparison, but it will be the
> ERP (estimated or otherwise) that will be important, as well as some
> absolute measurement of the noise floor on each band.
I intend to do comparisons rather later in the year, when both 500k
and 160m will come into their own for longer distance working at
night. But my configuration using my Butternut 10m vertical on both
bands (not at the same time) will be an interesting experiment.
I have just recalculated ERPs using Reg's vertload.exe for each band,
with my 150 ohms ground loss. The antenna is identical for each band
apart from the loading coil value and the matching network.
500kHz ERP with 6W input - 5mW (.08% efficient)
160m ERP with 5W input - 50mW (1.12% efficient)
My experience with this antenna on top band (with 5W) in the past few
seasons is that it is fairly good for middle Europe and some of the
Baltic area, worked the occasional dx, but it is poor for slightly
further out and very poor for inter G and close Europe. My 'long'
wire (110ft bent) is much better for inter G. Which is what you would
expect - vertical low radiation for dx, longwire skywave for shorter
skip G.
I expect the same sort of pattern on 500 - daytime groundwave up to
150-200 miles (probably further than top band), nighttime skywave
comes in, high angle for inter G and low angle for the DXy stuff. On
many paths the skywave will be stronger than the groundwave (and we
will get the slow QSB we are already aware of on the band). Of course
at the moment until more countries get an allocation the options for
DX are a little limited....
On the subject of erp, it occurs to me that most of the formulae
assume ground wave propagation with any horizontal part acting just
as a top load. Fine if you are talking about ground wave in daylight
with little skywave, and it is over a perfect ground (if only....).
But those using quarter waves may like to consider whether this is
still a reasonable assumption after dark when the main propagation is
skywave and the ground is far from perfect. To me a quarter wave wire
will be no more than -3dB down on a dipole and your efficiency is
rather higher than what most of us are using.
73 Dave G3YMC
http://www.davesergeant.com
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