[TowerTalk] Looking for a Short Rotatable Dipole or...

[Roger (K8RI) on TT]

Just another thought:

  30' pole on the roof supporting 5 center fed, half wave sloping 
dipoles. I have used a couple, but if you have the room, use the 5 
switched dipoles.  I believe it's in either the ARRL handbook, or the 
Antenna handbook..  They are simple, seem to work stateside and DX.  
Switched as in the handbook, the have a little gain and a bit of a F/B 
that really helps.

Even 2 or three will give a bit of directivity.    I'm thinking of 
switching to 75/40 fan dipoles and experiment with the 5 antennas 
instead of just a single monoband on 75 and one on 40 at present. Wire 
is cheap and easy to experiment with.  I've worked all continents with 
just two 40 meter slopers and an AV640 (on 40) at 25 feet.

73

Roger (K8RI)



On 4/28/2016 Thursday 5:01 PM, jimlux wrote:
> On 4/28/16 9:31 AM, john at kk9a.com wrote:
>> Unless your roof is very high, a rotatable dipole will have little
>> directivity. The simplest and least expensive antenna is a wire 
>> dipole. If
>> you want something better try a 33' vertical with a good ground system.
>>
>
> or two dipoles roughly crossing, and a switch or goniometer to select 
> between them.
>
>  Dipoles (short dipoles in particular) do not have a "narrow" beam in 
> any sense of the word (HPBW is 120 degrees).  What they have is a null 
> that can be placed on an interfering signal.
>
> The null *is* fairly narrow
>
> at about 9-10 dB down, it's about 45-50 degrees wide
> at 20 dB down it's about 15 degrees wide
>
> So if you want to knock down that big gun in the next city (who you're 
> hearing from the sidelobes) so you can hear the other folks you're 
> both trying to work, a rotatable dipole (or the electronic equivalent) 
> would be useful.
>
>
>
>
>> John KK9A
>>
>> I''m looking for a 40m rotatable dipole (preferably a F12 EF-140S) to 
>> add
>> to the C3-SS on my roof.
>> The "S"is shortened version. Sadly, nothing larger will fit.
>>
>
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-- 

73

Roger (K8RI)


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