[VHFcontesting] Yagis on masts

[David Pruett]

Patrick,

Sometimes it pays not to read the instructions.  I've used Rohn masts to 
hold yagis aloft, and never had any trouble.  But a little common sense 
goes a long way in this regard.

I remember a long time ago that there was an article in 73 magazine by 
some Floridian with a 1x2 call that I can't remember who took a Rohn 50 
mast, only extended it to 20' and ran it thru a thrust bearing bolted to 
the eave of his house.  With it sitting in a rotator staked to the 
ground, the entire mast rotated with a HyGain 204BA on top (four 14 MHz 
elements, 26' boom and 66 pounds).  He may have exceeded common sense 
limits, but he proclaimed the setup worked fine.

All the cautions about twisting loads, etc. mentioned by other 
respondents are certainly true, but the reality is that with most 
VHF/UHF arrays, such loads are small to miniscule.  In the miniscule 
category is the 30' Rohn mast bolted to the side of my house holding a 
2.3 GHz looper with a 6' boom.

One thing that I think would help is to follow the example of the 
Floridian, and mount the rotator at ground level with the mast sitting 
in it and let the guy rings slip so the entire mast rotates.  This gets 
the weight off the mast, and makes it easy to rotate multiple antennas 
on one mast together.

With a 40' or 50' mast, I would recommend at least one set of guys about 
half way up to keep the mast from buckling under load.

73, Dave/K8CC

On 12/27/2016 11:33 PM, Patrick Thomas wrote:
> Hey all,
>
> I've been considering augmenting the park-and-go rover setup with a push-up mast.  However, I have noticed that the Rohn H50, etc., explicitly state that they are "not recommended" for use with yagis.  And sure, physics would suggest that if you have a 15' antenna boom, you are likely to have more off-axis "arm" acting on the top of the mast, versus a vertical or even a dish.  On the other hand, I don't know if they only say that to protect themselves against people who use H50s as semi-permanent rooftop installations in 80MPH wind zones with heavy ice.
>
> So what's the verdict?  I'm sure it's "possible" but is it safe to use a large 2m yagi on an H50 when properly guyed, on a day with gentle breezes?  Or is it indeed "not recommended" under any conditions due to instability, etc?  For that matter, what about the weight of a rotor that high up?
>
> (And yes, I'm still working on the halo stack, so worst case I could always hike that up the line... but would love to have the extra gain and directionality from the yagi.)
>
> Thanks,
>
> Patrick
> KB8DGC
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