On 12/15/2010 04:09 PM, Jim Brown wrote:
> On 12/15/2010 6:15 AM, Jim Thomson wrote:
>> This just amounts to a midpoint placement of a loading coil
>> in each leg.
>
> No, it's not. Re-read my description. It's also not new -- these designs
> have been around in one form or another for years, but most hams, me
> included, are lazy about doing the engineering to build them ourselves,
> so we buy another guy's work. Now that I'm retired, I AM doing more of
> my own design work, rather than buying another guy's work.
I have a crazy idea for a compact 160/80/60 antenna that works
reasonably well even over poor ground and has gain on 80 and 60.
The idea is to have a 160m double L (aka lazy U) antenna, which
also acts like a 2 element bruce array on 80m. I suspect it
might require crazy traps and it might not even be possible,
but lets throw it out there as a pre-holiday-break challenge.
First, the basic antenna designs, where X is the feedpoint.
160m double L, with the ends folded over a little:
+------------------------------------------+
| |
| |
X
| |
| |
+------------------------------------------+
80m bruce array:
+------------------------------------------+
| |
| |
X |
| |
| |
+------------------- ----------------------+
The size of both antennas is similar, about 100' long
and 70' high (low wire 10' off the ground, top wire 70').
The feedpoint is also in the same position.
The wire lengths are not exactly the same though, the
80m antenna is a little longer to get a good match.
Incidentally, both types of antenna radiate decently
on 60m, because the amount of wire is close to 3 half
wavelengths on 60 meters. The gain on 60 is off the
broad side of the antenna.
Over very poor ground (New Hampshire), the antenna gain looks
like this:
160m: -1.5dBi at a 30 degree takeoff angle
80m: 2 dBi off the broadside, 90-100 degree beamwidth
60m: 3-4dBi off the broadside, depending on the antenna shape
Gain can be improved a dB or so by adding minimal radials,
and more by adding more radials. Performance on good ground
will be significantly better than the numbers above.
Most important is that the antenna does not perform
catastrophically bad without radials (or a poor radial
system), like eg. a 1/4 wave vertical would.
Now for the big question - could this antenna somehow
be combined, by inserting traps in the gaps? :)
Having one of these antennas do it all would give me the
ability to mount two of them, and get 4 directions on 80m
and 60m...
I suspect it would make many other hams in wooded areas
with rocky soil quite happy.
--
All rights reversed.
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