The Martlesham Microwave Roundtable
10/11 November 2001

Martlesham 2001 - fleamarket
The annual microwave "roundtable" meeting at BT Adastral Park, Martlesham Heath, Suffolk, was, as usual, a resounding success. As in the past few years, it was a two-day event with antenna testing and an evening dinner on the Saturday (at which some 30 people attended), followed by a Sunday of further testing,a fleamarket/bring and buy and a programme of lectures.
   The photo above shows John Hazell, G8ACE (second from the right) manning a fleamarket table. The person on the far right is Allan, G8LSD.
   An antenna test range, along the lines of that used by Kent Britain, WA5VJB, at various North American microwave gatherings, was set up by Sam, G4DDK and Kent along a path near the car park.
Taking advantage of ground reflection, a 1kHz AM modulated 10GHz gunn transmitter (Marconi 6059A Signal Source)of known output and fed into a horn antenna of known gain was placed around 30 or so metres from a detector + tuned audio level meter (again a Marconi instrument). The photo to the right shows the signal source resting on an upturned plastic box.
   The "receiver" end of the range was calibrated by means of a reference horn antenna with a measured 16.5dBi gain. The level meter (see right) had a built-in calibrated attenuator. Antennas under test were connected to the detector and the audio level in respect to the standard reference was read on the indicator. Some skill is needed to locate and hold the test antenna in the region of uniform field strength of the Gunn source.
Signal source used in antenna test range

audio level meter used in antenna tests

G4DDK  setting up an 80cm dish for testing


On the left here is G4DDK attaching the detector to an 80cm prime focus dish belonging to Allan, G8LSD.  This antenna returned a gain of 34.5dBi with its penny feed.
   Some 21 antennas for 10GHz were tested, of which the best was G3PHO's 60cm offset Amstrad (ex Sat TV), fed with his version of the W2IMU dual mode horn. It topped the list at 35.2dBi
   Six antennas for the 2.4GHz band were also tested during the weekend

The photo on the right shows Mike, G3LYP, preparing the feed on his 35cm ex BSB offset dish, used on 10GHz with the modified, original dielectric feed horn, as used when this dish received satellite televison. This assembly returned a very creditable 29.5dBi gain figure, as good as or even better than several of the larger dishes with "penny feeds" that were also on test! G3LYP adjusts his 35cm dish