LF: Puckeridge expedition - Interim Report

[Andre' Kesteloot]

DEREK ATTER wrote:

> 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)