MARTLESHAM MICROWAVE
ROUND TABLE NOVEMBER 2002
PAGE
4
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The Sunday activities also included the now well-established
antenna test range. A standard low power, 1kHz AM modulated Gunn
source on 10GHz was set up at ground level some 100 metres from where you
see this group. By taking advantage of ground reflection, the receiving
end was calibrated with a standard horn antenna driving a detector which
is turn feeds a surplus HP VSWR indicator. The latter reads the gain difference
between the standard horn and any 10GHz antenna connected to the detector,
so enabling the actual gain of the antenna system to be calculated very
easily. A source for any other microwave band maybe connected of course.
By carefully moving the antenna under test around
at approximately head and shoulder height, an area is found where there
are no obvious variations in meter reading. The difference between the
horn and the antenna under test is read at this point. The system is surprisingly
repeatable and accurate. It has been used across the USA by that travelling
microwave man Kent, WA5VJB, who introduced the method over here at Martlesham
a few years ago. Nowadays Sam, G4DDK, sets it up at UK microwave events.
This year, only four antennas were brought along by
various folk, three of them being offset fed types. |
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This close up shows G4DDK holding up G8AGN's
60cm offset fed dish while Jim, G4WYJ holds the HP VSWR indicator. G8AGN's
antenna uses a home made, milled dual mode horn to dimensions scaled down
from an 11GHz Amstrad SatTV type. Barry, G8AGN, was pleased that the system
produced a gain of around 36dB at 10GHz, indicating very good efficiency
for this size of antenna. |
| The only prime focus antenna system of the day
is shown here, with Peter Blair, G3LTF, on the left being watched by Andy
Talbot, G4JNT, on the right. The novel method of getting RF to the feed
horn certainly helps to explain why some non-microwave folk think we all
have to develop plumbing skills before we take up this branch of amateur
radio! |
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| Well, that was Martlesham 2002. Many thanks to
the Martlesham Amateur Radio Society for putting on such a great weekend.
We all enjoyed it immensely. Here's to next year! |
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