Martlesham Microwave Roundtable
|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
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
|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
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.
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!