Crawley Amateur Radio Club

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23cm VHF NFD (2006) Report

G5LK/P makes a big score on the 23cm band from a new field day site in Suffolk from locator JO02RF

The combined Crawley/ Reigate team of operators on 23cm G5LK/P made our best ever claimed score this year of over 50,000 points from 142 QSOs which compares very favourably with the 22000 points made last year from 74 QSOs.

The best distance worked this year was SM7DTE at 912km with an average distance per QSO being close to 360km - a high scoring rate for 23cm.

A total of two SMs and seven OZs were worked plus two GMs and an EI In addition, quite a few DLs were worked at distances over 700km.

A number of factors probably contributed to the big increase in score. The conditions were good in patches without any evidence of any great tropo lift. However, the combination of a 100ft tower this year and a site locatied on a 60ft local high spot looking out over very flat terrain close to the Suffolk coast would be expected to contribute significantly to the increased score. The site was tree lined but the 100ft tower allowed us to look over the tops of the local trees.

Another factor this year was that despite some technical troubles at the start we were able to rapidly overcome these and start within about 10 minutes of the nominal kick-off time of 14-00 UTC. We were also able to maintain a fully manned station with experienced operators right throughout the night thus able to take advantage of the early morning tropo “lift” which was in evidence between 04.00 and 07.00 UTC.

The equipment used this year was similar to last year with the primary system comprising of a 200W solid state PA and low noise preamp (0.7dB NF) mounted above the rotator feeding four M2 22element yagis stacked vertically with a 4-way splitter.

Mounting the PA and LNA up at the masthead means that the feeder loss up the 100ft mast is relatively unimportant since the PA unit only needs 0.5W maximum drive.

The DC power supply was provided by two very compact Melcher 26V DC-DC inverter modules working in parallel supplying 20A DC peak, mounted in the lid of the polycarbonate O-ring sealed box. The 26V DC inverters are fed with 65V DC from the shack up the mast via relatively light cable since a moderate amount of voltage drop in the cable does not matter.

Soaring ambient temperatures during the day in excess of +30 deg. C caused us to keep a close eye on the temperature of the masthead PA heat-sink since it is fully exposed to the sun. The indication on remote temperature monitor on the PA control unit in the operating caravan gradually climbed to over +45deg C but stayed within the rated maximum of +55 deg. C . It was fortunate that as a design precaution, a flat, clip-on fan, of the type used on CPU heat-sinks, is mounted externally on the heat sink fins to assist the cooling. The fan is protected by a hood to channel the air flow past the fins

One disappointment was that during the testing phase in the hour or so before the start time, it was discovered just as the 100ft mast was being wound up, that the secondary masthead system with a 60W PA and independent rotator was clearly not working properly so we hade to make an executive decision to continue with just the primary system only.

This was a pity after all the hard work that went into it. This secondary system would have allowed an independently steered antenna system with the aim of possibly increasing the scoring rate still further.

It turned out after examination at the end of the contest that the “N” connector on the EcoFlex RF cable at the antenna port of the PA/LNA masthead unit had not been screwed home properly. Moral …double check all RF connectors before winding up the tower!

One other minor problem discovered right at the start was some RF feedback via the operator's boom mike into the operator/logger audio control box. A quick fix was to revert to a fist mike

However, despite the heat and hard work, everyone seemed to enjoy the congenial weekend – especially the excellent food produced by the support staff in the rest tent – and in particular the excellent heavy-duty cooked breakfasts!

Thanks are also due to Bob Carpenter G4BAH who offered the use of his 12 acre site in Suffolk just a few weeks before NFD - prompting a rapid QSY from JO01OC at Folkestone to JO02RF !

73 , de Derek G3GRO

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