About short or long period signal level recordings
Any stable, preferably calibrated, selective rf level meter
should be useful for short period signal strength variation
checks. Or even for long time recordings, providing there
is a convenient "AGC" voltage output available as a function
of input rf voltage. In the 1970's we at the Monitoring station
attempted to use slightly modified Icom-R70 and R71 receivers
but it proved difficult to stabilize the AGC voltage picked up
from selected test points in rx AGC circuitry. Also, the lowest
indicated *S* level was excessively large, around 20..30 dBuV.
A bus controlled R&S ESH3 was used for 24h VLF/LF/MF/HF Field
strength measurements during 1989-1999, with a *CCIR* type
commecial, 1 m long active monopole placed in a open field.
Rf pick-up by long 3/4" coax cable was cut with ferrite rings.
A description of *CCIR* measuring system is on the ITU-R Docs.
I must be lucky to have an extremely useful but expensive
R&S ESH2 test receiver available now at home, while retired.
Hope that my Decca etc signal strength reports have given some
ideas of day to day variation, even with such a point checks.
At the moment I test using a small Pico (Picotechnics Ltd)
AD converter fed from ESH2 recorder voltage output into LPT1.
Below about 400..500 kHz the noise from PC is excessively high.
Pico DOS & Windows data logging, scope etc software are useful.
There have been different opinions on the use of absolute
versus relative indicated and logged input level values.
In case of real measuring receiver like ESH2 the use of
relative power level (dBm, I write it dBmW) is justifiable.
Like most measuring rx's, ESH2 meter is calibrated in dBuV.
In my case: add +20 dB for approximate LF field strength
About *SID* effect: I sent Geri some pictures of selected
SID effects on LF ground wave and/or ionospheric signals.
May suggest that in most cases *hard X-rays* produced in
a solar flare, the indicated LF levels may increase but as
shown in these examples the opposite can frequently happen.
73 de Vaino, OH2LX
At 00:00 15.2.2000 -0500, Geri, DK8KW (W1KW) wrote:
just read that Larry, VA3LK works on further improving his receiving
station after having been able to hear DCF39 33 dB above the noise last
weekend.
If we find a reliable way to find out, when solar flares occur, we have a
real good chance of crossing the Atlantic even with our small ERP signals.
I know that Peter, DF3LP, was able to observe a flare the other day when he
recorded a constant signal of an LF time signal (HBG75 on 75 kHz). The
receiving level suddenly wend up by 10 or 15 dB above the normal and then
dropped slowly down to normal within half an hour or so. If we combine a
receiver's AGC voltage output to a voltage gate switch that is connected to
a bell, we should be able to have an alarm go off to indicate, that
conditions are above normal.
I still have a spare MV61 level meter with a voltage output in the 0 to 2
Volt range and will connect it to a voltage recorder. Lets see, if we can
correlate sudden increases of signal strength to occurances on the sun.
Vaino, you are quite experienced in recording field strenght data. Any
comment on that?
Best 73 Geri
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V.K.Lehtoranta, OH2LX, POBox 50, FIN-05401 Jokela, Finland
------ Tel: +358-9-4173965 ---- Fax: +358-9-4173961 ------
E-mail: [email protected] - alias: [email protected] & [email protected]
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