[TowerTalk] Rotating a dipole on a side-arm

[Roger (K8RI)]

Gene Smar wrote:
> Scott:
>
>      I have a Cushcraft D40 (compact) rotatable dipole at the top of my 
> tower's mast at 78 feet.  I find that it is pretty much non-directional, 
> that is, I can't seem to find a null or even a measureable drop in RX levels 
> when I rotate it.
>
>      My point being is that on 40 and probably 60 meters, the SteppIR dipole 
> will probably not have to be rotated at all.  If you intend to operate on 
> the higher freqs during an emergency, then you might see some directionality 
> that will have to be overcome by turning the antenna.  But under what 
> circumstances would you be using freqs above 7.3 MHz during an EOC 
> activation? 

Emergencies covering wide areas, and/or direct communications with 
headquarters of participating agencies at a distance. We run all bands 
up through SHF with maybe the exception of 160

73

Roger (K8RI)
>  The EOC's mission should have a major influence on your choice 
> of frequencies and hence antennas.
>
>
> 73 de
> Gene Smar  AD3F
>
>
> ----- Original Message ----- 
> From: "Scott Honaker" <scotthon at pilchuckvet.com>
> To: <towertalk at contesting.com>
> Sent: Tuesday, November 24, 2009 6:15 PM
> Subject: [TowerTalk] Rotating a dipole on a side-arm
>
>
>   
>> Our county is building a new Emergency Operations Center and tower.  We
>> have had notoriously bad luck with our roof-mounted wire HF antennas.  I
>> have been considering using an HF multiband dipole (like a SteppIR) on the
>> tower.  There will be a microwave video downlink at the top so I am left
>> with a side-arm mount.  I see the Tessco catalog lists 72" side-arms.
>>
>> The next question is how to I rotate it and not whack the tower.  I need a
>> rotor or controller with adjustable stops.  Does such a thing exist?  I
>> can't trust simply marking the display with a "don't turn here sign".  The
>> rotor needs to not go there.
>>
>> We expect to use a free-standing 3-legged tower so I anticipate I can get
>> at least 90 degrees of rotation.  That should let me cover any bearing and
>> hopefully let me reduce the effect of local noise.
>>
>> What should I be considering?
>>
>> Thanks,
>>
>> Scott N7SS
>>
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>>
>>
>>
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