Duct 20th to 22nd April 2005

Some interesting tropo about this evening Wednesday 20.04.05, but mainly
down south from here, been windy to 40 Km/h this way.

For the first time in at least 4 years, maybe longer, some VK7 stations have
been able to access the Canberra VK1RGI 146.950 repeater on Mt Ginini.

10.20 pm - VK7LCW, Peter, in Penguin, north coast Tasmania (663 Km) made it
to Canberra repeater. Worked VK3HV, VK2ZPB and VK2PDW. VK2KRR was just

11.00 pm - Phil VK7JJ from Weymouth, north coast Tasmania (625 Km) made it
to Canberra repeater. Worked VK3HV, VK2KRR, VK1ZQR, 2ZPB.

VK7JJ also worked VK1ZQR on simplex, but I am unsure if it was on FM or SSB
at this stage.

Also VK5PO near Barossa Valley I think may have worked VK7JG at Launceston
on 144.150 SSB but I am unsure if they made it. This would be 900 to 1000

Leigh VK2KRR

Today (Thursday) into the Canberra 146.950 repeater I heard John VK5PO at Eden Valley
getting into the repeater a bit noisy, BUT!! this was at about 11.30 AM till
around 12 Midday... amazing and in excess of 900 Km.

Later at about 3 PM I heard a station from Newcastle getting into the
repeater. Only about 400 Km I think, but a mountainous path.

Just now, at 6.45 PM I just heard John VK5NJ getting into Canberra from
Mount Gambier, which is around 756 Km.

Who knows who else may come through........

Leigh VK2KRR

After some amazing tropo conditions last week into the Canberra repeater, I
decided to look further into what was going on.

On Wednesday evening 20.4.05, tropo conditions were there but not there for
me so to speak. From memory the Adelaide 144.450 beacon was up to about a 4
with QSB and it eventually faded away off the S meter totally. The only
repeater heard was Crafers 147.000, but was very eratic with QSB only weak
to about 5/4.

The Mt Lofty Adelaide beacon is about 680 m ASL. The Crafers repeater is
around 610 m ASL.

I worked on SSB 144.100 -

VK5PO - 5/5
VK5USB - 5/5
VK5ZLX - 5/7
VK5UBC - 5/3
VK5DK - 5/3

Most of the signals were poor with QSB, the signals noted were peak signals.

Some VK7s worked the Canberra repeater. As did some VK3s. Canberra repeater
is at 1770m ASL.

No DX was noted above 144 MHz.

On simplex, weak DX was only noted on SSB. On repeaters most DX was on
Canberra (VK1RGI) or Grampians (VK3RWZ) 146.950. Note that Grampians
repeater is 1170m ASL.

The weather here was quite windy, but I am not sure about other areas, but I
think it wa much calmer in VK3 areas.

I checked the Duct graphs through AREPS to find the duct height appearing at
around the level of these higher repeaters. The base of the duct was
indicated as being 1400 m ASL over Adelaide and 1100 m ASL over Melbourne. I
could not get a reading from Wagga but would assume duct height over
Canberra being similar to the repeater height at 1700m ASL. A reading from
Wagga the next morning confirmed this and indicated duct base at 1500 m ASL
with top in the 16 to 1700 m area. Pressumed to be similar or higher at

Thursday evening, Adelaide was out, but John VK5NJ in Mt Gambier was into
Canberra repeater, as were many VK3s. On the graphs, there was no indication
of activity at Adelaide, but a weak DPL (duct potential layer) was present
at 1550m ASL; at Melbourne, duct base height was
1350m ASL. Again pressumed to be at around repeater height at Canberra.

I found these observations of duct height around the Canberra area
interesting, but not unexpected. Usually, if the duct is too low ie 500 m
ASL, nothing is heard at Canberra as the duct is blocked by hills. This is
normally the case.

Though, what I do find unexpected and puzzling for me is the height of the
duct at the out lying areas away from Canberra. 1100+ m ASL around VK3/VK7
and stations getting into a pulling signals from the duct to Canberra on FM.
Even worse is VK5NJ getting to the Canberra repeater using 100 W to a 5/8
vertical when the duct at Melbourne was apparantly at 1350m ASL and DPL at
Adelaide 1550m ASL. Mt Gambier airport height is only 69m ASL.

On limited studies I have done of ducts across the Bight for example, the
duct height at Mount Gambier is usually at ground level or slightly above,
at worst case, at least below 900m. So you can see that with duct heights in
excess of 1000m ASL and stations still getting in is a little weird. OK at
the Canberra repeater end as its probably in are area of the duct.
Also, stations like VK3IDL at Ballarat, who is apparantly located in the 700
m ASL zone should have a better chance in this situation due to his height,
which did seem to be the case as he was the last and one of the only more
distant stations that called in on Friday evening.

Due to the height difference, I guess this why any transmissions above 2m
were useless.

Something else interesting to note is that on the Hawaii to California duct
path, as indicated in Wally VK6KZ's tropo paper, is that at the Hawaiian end
the duct height is usually between 1500 and 2600m ASL and gradually drops to
around the 450m ASL area at the California end. Both ends, stations are
located around the height of the duct. Just another example of why I found
our latest duct a little strange.

Leigh VK2KRR