Re: The LF operation from the Decca station at Puckeridge 11th April and
14/15/16 April -
Having just about recovered from the weekend's activity and travelling up
to Puckeridge again yesterday (Tuesday18th) to recover the remaining bits
of gear including tables and chairs etc and the loading coil and variometer
used by all of the operating groups involved, I thought that I would post
an initial report of the activity pending a more detailed study of the logs
and incoming reports.
Firstly, thanks to all those who participated and to all those sent in
signal reports and messages of encouragement. The exercise was arranged at
very short notice and word spead around the LF operators living within
reasonable reach of the site to invite one or two groups of operators to
take part.
Apart from the Decca mast and an RF thermo-couple ammeter , none of the
original equipment such as loading coils etc was used. For 136Khz
operation a relatively small variometer ( about 500uH max) and a tapped
toroidal auto transformer were connected to ground from the copper pipe
lead-in to the base of the mast which is supported on 4 massive ceramic
insulators. The exploratory visit earlier in the week (11th April) allowed
a purpose-built additional loading coil for 73Khz to be built by Lech G3KAU
back at base in time for the main excercise at the weekend. Three
transmitters were employed at various times, the G3GRO 300W much modified
BKE linear amplifier used for the 1W ERP tests on 73/136Khz earlier in the
week and on Friday and Saturday for running between 1 and 5W ERP plus the
well tried G0MRF 500W set-up and the G3YXM 1Kw class-D rig used previously
on many /P expeditions. During the overnight sessions on Friday in beacon
mode the ERP was 50W and 100W ERP overnight Saturday. We had a few
problems to start with in getting the variometer to handle the 500W RF and
we had a few splatts and sparks resulting in VSWR trips until we realised
that the capacitive voltage divider in the forward/reflected power meter in
the variometer was tracking over and by-passed it. Fortunately we had
another SWR meter in line. We also found that an RF sampler unit brought
along by Jim M0BMU very useful in setting up the matching and tuning in
conjunction with an oscilloscope very useful. We realised on Saturday that
the range of our RF ammeter was too small for the high power operation and
rescued the original very large 30A RF ammeter from the pile of redundant
scrap units outside in the rain and pressed it into service. During the
beacon sessions that was reading 14A into the base of the mast which looks
like 5ohms resistive in series with 3750pf ! That represents an RF power
of 1Kw into the antenna or 100W ERP allowing for an overall antenna
efficiency of 10% on 136Khz.
The receive system was a home brew up-converter with an input bandpass
filter of about 3khz bandwidth on both 73 and 136Khz followed by a
mini-circuits MAR6 preamp and MC1496 mixer IC to a 10Mhz IF feeding both a
FT990 and IC756 transceiver for most of the time. The FT990 and converter
stood up remarkably well to the very large antenna input with no sign of
cross-mod. We had a switched attenuator at the input to the converter but
for most of the time it was switched out. That attenuator was used later
for some comparative tests with a small "back-garden " type antenna nearby
which hopefully will be reported on later. We had two operator positions
side by side, one handling the 136 and 73 traffic and the second op also
monitoring 136/73Khz in parallel but also handling the HF cross-band input
mainly from 7.0Mhz.
Summary of Results : We had about 65 QSOs in total including those during
the initial setting up period on Tuesday 11th of April
already reported. Two-way contacts were made on both bands and cross-band
contacts from136Khz to 73Khz and to 7.0Mhz
There have not been any reception reports from across the pond from VE or W
which was always going to be a long shot, but the longest contact was
cross-band to 7.0Mhz with Alex, UB5WF in Loc KN58JQ about 200Km north of
Odessa on the Black Sea who gave us RST429. normal CW at a distance of
2225Km ! This was over a daylight path at 12-32 UTC on Sunday 16th. It is
not known yet what RX antenna Alex had for 136Khz but it is highly unlikely
that it was a dedicated LF antenna since there is as yet no LF activity in
Russia as far as is known. Other long distance QSOs were to Valerio, Ik5ZPV
2-way on 136 who gave us RST589 IK7HSS cross band to 7.0Mhz, and Neils
OZ8NJ (2-way136) who QSPd to us that IK5ZPV was hearing us and would call
us shortly. We also got a RST 599 on 136Khz from Christer SM6PXJ , OZ5N
and Toni HB2ASB. Two QSOs were also made on both 136 and 73Khz to Finbar
EI0CF and Ray GI3PDN. Reports on 73Khz were about 2-S points down with Ray
and Finbar by comparison with 136Khz. We also worked GJ4CBQ and GU3SQX
cross band 136Khz/7.0 Mhz which was pleasing since due to Loran QRM from
Lessay they normally have difficulty in hearing stations on 136Khz.
Perhaps one of the most unusual QSOs was with Graham G3XTZ/M operating
mobile on 136Khz CW whilst driving to the site to have a spell of operating
! I will post a full list of the QSOs made in the near future when I have
transposed the logs. We have also just had a report via E-mail from Marc
F5MAF in Toulouse, JN03PP who was hearing us at 599+ on a 2 meter diam loop
at a distance of 900Km and bemoaning the fact there is no LF activity in
his neck of the woods.
Thanks to all those who took part despite the very wet and freezing cold
weather and also to those who took the trouble to give us reports which
have yet to be analysed. At one point on Saturday as the shifts changed
over there were 12 people in the ATU shack at the base of the mast which
much represent a large slice of the active UK LF operators! They were :-
G3KAU, G3XDV , M0BMU, G0MRF, G3XYM, G3XTZ, G3YSX,, G4GVC, Kate,G4JHI, XYL
GVC, G4TSH, G3LHZ , G3GRO and not forgetting Peter G3LDO holding the fort
back home and Walter G3JKV who efforts made it all possible.
73 de Derek Atter , G3GRO ( Also licence holder of
the G3WSC Crawley Club callsign)
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