Hello Tom,
Tom Rauch <w8ji@contesting.com> wrote:
But you would have to know and record the absolute signal
level changes referenced to some starting point for a long
period of time every night for many nights. I would guess at
least a year.
I already said that. In order to appreciate the variation of the signal
(especially during a long period of time) on should refer to a calibrated
source. This could be a signal stable generator. Also, the receiver thermal
amplification drift should be known. Than this could be monitored by a
thermometer then subtracted from the overall variation.
Having in mind that the event which we are looking for have a significant
amplitude variation from the average, if will be true than should be evident.
If so, one could organize much more precisely measurements to determine the
precisely amounts.
The receiving antenna could not change, the receiver
calibration could not change, it would have to have enough
signal to noise during measurement periods to know the real
signal level (and not S+N level), the transmitter ERP in
your direction could not change.
Well, at the antenna port of the receiver you'll have an 20dB coupler say.
Attached on that, on the 20dB port you'll have the reference signal (a XO for
example) and on the direct port the antenna. You will have to measure two
signals (carrier). One is the XO and the other the beacon. The best is to use
1Hz filter for each of theme. The RX have its Nf. What we have is:
1. XO signal atenuated with 20dB + RX Nf
2. beacon's signal + antenna noise+cable noise+coupler noise
1. is as stable as possible depending of the stability of theNf and
amplification of the RX and amplitude of the XO's signal.
2. will have the noises as a unknown factor. If one will use a 1Hz filter than
from the Nyquist P= KTB well eliminate B and remain only the temperature
meaning only the signal power+ 1Hz of noise which means much more less than a
normal SSB receiver (2400 times less)!
One cannot control the amount of noise coming from the antenna but could
minimize it having as less bandwidth as possible!
When you are all done with
that, someone has to average the signal levels and even
perhaps compare peaks if that is what you want to know.
This will be done after the measurements in the analyzing process.
A few spot checks would never produce anything useful.
If those spots could be correlated with a particular event than could produce
alot!
In the USA, we are not allowed to have unattended beacons
except on specific bands. 160 meter and 80 meter beacons
must have a control operator present. I don't know anyone
who would follow that rule for a single night, let alone a
year of nights.
Thanks for this information. I didn't know about that.
The antenna would have to be gain stable under all weather
conditions. That would rule out most receiving antennas
people use on 160.
Yes, should be but it didn't in the reality due to several factors. In the
parabola case, its temperature (I'm talking about noise power temperature)
stability is very high because its side lobes. In the case of a wire antenna,
this parameter is very bad! The ideal case is when the antenna have only the
main lobe and that lobe is illuminated only by the source of the signal!
Two case:
1. Imagine a broad band noise coming together with the signal. This will
increase the antenna noise than its noise temperature.
2. the physical length of the antenna will vary due to the hot cold elongation
of it wire. This will modifies its impedance increasing/decreasing the loss. We
know that a noise temperature of a "loss" (say a piece of coaxial) is
(1-loss)*T where loss is expressed linearly and T is its physical temperature
in Kelvin. For example, let take a loss of 3dB and see what will be the noise
temperature for typically winter/summer temperature (-15/+45 degree C or
258/318 Kelvin).
(1-0.5)*258 = 129K [1]
(1-0.5)*318 = 159K [2]
overall variation is 30K or about 0.9dB.
>From the above examples one could see that the main unknown factor as a
>magnitude is the perturbation (natural or man made) in terms of broad band
>noise.
The determined errors can be assumed!
Tom, you are right about such measurements. If one want to produce relevant
result than should take care of a lot of factors. I remember when I did
radioastronomical observation with a commercial gear (11GHz). Instead of small
Sun burst I saw the thermal deviation of the gear used:)!
73 de YO3FFF
Cristi
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