[TowerTalk] 80/40 coax trap dipole design

[Joe Subich, W4TV]

 > Now for the big question - could this antenna somehow
 > be combined, by inserting traps in the gaps? :)

Insert a shorted 1/4 wave 160 meter stub (1/4 wave x Vf
on 1.840) in the gap.  You have an open circuit on 160
and a short on 80.

73,

    ... Joe, W4TV

On 12/15/2010 4:41 PM, Rik van Riel wrote:
> 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.
>