Here is an antenna for the nineties. It's strong, computer designed, and has lots of gain.
This is a no compromise dual band antenna. Instead of using
traps, this design interlaces two separate antennas (the 10 meter band and the
15 meter band) on one boom. This is a full size, four element beam on 10, and
three elements on 15 meters!
The design uses large 1" diameter aluminum tubing to keep
ohmic losses to a minimum, to survive heavy winds and withstand ice buildups in
the winter.
The fact that it is both a 10 and 15 meter antenna allows
it to be used as the perfect antenna for anyone interested in working the RS
Satellites which have uplinks on 15 and downlinks on the 10 meter band.
The HF-SAT produces plenty of gain on both bands. The
antenna was computer optimized for maximum forward gain (hence the low front to
back). The 10 meter band has close to 9 dBd gain, (free space) and the 15 meter
band produces over 7 dBd (also free space).
Construction:
Since all elements are of 1" tubing, it's just a matter of
laying out each element end to end and cutting the last piece to the required
length for that element. Each 1" ; section is joined to the next piece via a
third piece of aluminum (.875 inch diameter) which slides into the 1" sections
(See figure 1). Drill holes on either side of the joint and use bolts to secure
each section in place. Attachment of the elements to the boom is achieved by the
use of muffler clamps.
Feeding:
Current baluns should be used at each feed point and can be
either commercial models or just loop several turns of the cable to create your
own balun. Separate cables are run to each feed point and then run to a mast
mounted switch box or straight into the shack. You can choose you own favorite
matching method but in this case a gamma match was used at each feed point, and
this worked well. If the antenna is mounted at 40 feet, the 10 meter antenna
should have an impedance near 13 ohms. The 15 meter antenna is around 27 ohms.
If you'd like, you could just use a 50 to 25 ohm balun to match the 15 meter
antenna, and skip the gamma match here.
Gain:
|
10 Meters |
10 Meters |
15 Meters |
15 Meters |
|
Free space |
Over ground |
Free space |
Over ground |
| Gain |
8.92 dBd |
13.82 dBd |
7.36 dBd |
12.22 dBd |
| F/B |
12.47 dB |
12.08 dB |
7.13 dB |
6.86 dB |
| Impedance |
13.1 + j 2.1 |
12.8 + j 1.4 |
27.4 + j 1.5 |
27.0 + j 1.3 |
Test out:
The initial tests of this antenna were performed while on a
10 foot pole. The comparison antenna was a 3 element, 10 meter mono-bander
created using standard beam formulas and was not computer designed. Local tests
showed that the HF-SAT antenna was already slightly better signal wise than the
40 foot high 3 element beam. Once the HF-SAT antenna was taken up to the 40 foot
height it proved to be 10 dB stronger than the original causally designed
antenna, an impressive and worthwhile increase in gain, to say the least. The
antenna has been excellent on both bands.
Copyright © 1996-2006 Ed Oros and Bob Cocco All Rights Reserved.
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