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G0FTD > BEACON 05.12.03 01:21l 96 Lines 4073 Bytes #999 (0) @ WW
BID : 940142G0FTD
Read: DB0FHN DM1CG GUEST
Subj: Re: History of the amateur beacon
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0RES<ON0AR<GB7FCR<GB7WIG
Sent: 031203/2010Z @:GB7WIG.#34.GBR.EU #:32225 XFBB7.03 Bid:940142G0FTD
From: G0FTD@GB7WIG.#34.GBR.EU
To : BEACON@WW
One thing I have noticed over the years is that:
1) Hearing a beacon from a given country does not mean that you'll ever hear
anyone to make QSO's with.
And more importantly -
2) You may hear signals from a certain country but not the beacons also
in the same country even when using an approximation of erp etc.
(Which is usually lower for the beacon than the average operators erp).
Now why is this ?
Is it:-
1) The angle of take off with respect to the radiation pattern being
of HIGHLY critical importance once MUF/OWF's etc have been accounted for ?
Or..
2) Highly localised areas of ionospheric charging that forms the refractive
path between two points ?
At 28Mhz I suspect that both play key roles, but at more median or more
predictable frequencies such as 14Mhz for example I suggest that it's more
to do with the angle of take off.
My reasons for this are that at higher frequencies the ionospheric charging
and it's relationship to refracting higher frequencies is more critical.
Ion density is not a constant. The sun spews out it's matter in a non
consistent way a bit like a 12 bore gun and when it arrives at our ionosphere
it arrives in inconsistent density across a given area above us. Higher
frequencies are more critical of this ion density and minor angles of
radiation
elevation from a given antenna can make a big difference as energy arrives at
slightly different areas of lesser or greater ion density.
At lower freqs it's not as critical and so two or three stations using
dissimilar antennas in a given area will have only minor variations
in received signal strength at a mutual receiving point.
This is especially true at much lower frequencies such as those at approx
(less than) <8 Mhz were the amount of wavelength above a dielectric (earth)
is of smaller amounts compared in percentage units to that of antennas used
at higher frequencies.
The best rule of thumb then at higher frequencies such as 28Mhz is that
one cannot expect consistency of received signals at a mutual receiving
point even when there are minor differences in antennas, their associated
maximum power radiation elevation and their relative distances betwen the
mutual receiving point.
Something else although slightly off topic has been remembered by me and
may be of interest in observing field strengths and that is one of
polarization losses. If I remember correctly the higher the frequency the
more likely that the incident signal can be transposed in it's E field
orientation by it's refracting medium. It is usual to observe signal strength
variation as being key to the amount of polarization transposition than
that of ion density in the refracting medium in median freqs - but of
more or less equal importance at higher freqs such as 28Mhz.
A method of observing incoming polarization is to have two receivers,
each receiver being connected to a proper balanced linearly polarized antenna.
One being of vertical and the other of being horizontal polarization relative
to the E field. Care MUST be taken to ensure that each antenna's response
is of sufficient linearity in relation to the E field.
Once this is confirmed - each reciever's AGC feedback or recieved signal
strength indicator (RSSI) can be connected to a 'scopes X and Y plates
accordingly - and the resultant trace will indicate the incoming polarization.
It is of the UTMOST importance that the AGC response is in effect ZERO for
realtime results otherwise you'll get incorrect results. This normally means
that if you tap into the receivers AGC loop you will need to ensure that the
T = CR response is exactly the same on each receiver for a correct but
slightly
delayed correlation of ion density or of zero T = CR response for instant
correlation to ion density between the to points forming a path.
Have fun...especially those in spinifex plagued areas prone to occasional
rain (Bob - we love you really ! - honest !!)
(I promise our year long leg pull is now at an end).
Regards - Andy
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