Satgen 594 Doppler 5 (HF SATS)  by GM4IHJ  (BID SGEN594)   2000-08-12

In Satgen 593 , two of the doppler signal patterns seen from RS13 HF
satellite passes near the north polar auroral region, were described.
There is another pattern, seen less frequently, but none the less
repeated faithfully, particularly when the satellite is over the high
Arctic to the east of Scotland, in the late morning just before or
just after midday.

Auroral Zone Multipath signals - A typical example occured on 23rd
February 2000, between 1154 and 1159z, when the satellite was sub
horizon , tracking from 73N 264W  down to 57N 252W. Up to 1154z the
signal had been T1, 60Hz wide. Then at 1154z that signal narrowed in
bandwidth to about 20Hz sounding T4, and a second T4 20Hz wide signal
appeared at a frequency 100Hz below the first original signal. The
two signals then continued running parallel 100Hz apart each
dopplering down about 40 Hz in 5 minutes as the satellite continued
to drop further subhorizon , ( -9 to -20 degrees elevation). With the
satellite dropping down in latitude over Asiatic Russia , towards
Lake Baykal. Then at 1159z the second signal disappeared suddenly,
while the now even stronger original signal continued to be received
for a further 10 minutes by which time the satellite was overflying
22N 247W.

Double signals of this type have occured on satellite overflights of
the auroral zone at least once a month this year. 

Intertwined Signals - Much less frequent than the above doublet is a
fourth type of subhorizon signal from an HF satellite sub horizon
over the northern auroral zone. In this case the signal does not
separate into two distinct units some tens of Hz apart. But, instead 
of separating the second signal appears to intertwine with the
original creating a doublet on the FFT display looking like two ropes
twisted together forming a broad 50 Hz wide band of signal response.
A good instance of this type of signal was recorded on 9th October
1999.

South polar signals . At various times during this solar cycle peak ,
signals received in Scotland from RS13 passes near the south pole,
have shown example of the same characteristics described in the
previous satgen 593 and, the paragraphs above in this bulletin. These
south polar records rarely have the clarity of the equivalent north
polar records , but they do reveal that the same types of ionospheric
anomalies are common to both poles.

RIP Comet Linear. The midsummer Scottish post midnight twilight
totally defeated any attempt to see this visitor in early or mid
July. Although it was seen by observers using good binoculars or
small telescopes at station further south, when it was reported as
reaching magnitude 6. Unfortunately it did not last . As Linear
approached its perihelion closes approach to the Sun, it
disintegrated. Suggesting that it was at best much more fragile than
the hardy regular comets we are used to. Although there are records
of other comets breaking apart near the Sun.