Art, re: 204BA: wonder if they can be reconfigured as a 4-el OWA design?
Love that bandwidth!
On the 3-el 40 tip size: keep in mind that as the taper continues, the
element length has to increased due to the taper effect. The yagi design
programs will show this.
73,
Gerald K5GW
In a message dated 8/19/2011 8:47:48 A.M. Central Standard Time,
k6xt@arrl.net writes:
Pete
Someone else replied about K4JA's loss saying it was a hurricane. Our
winds don't get up there or haven't yet.
An elephant gun to Asia would be good. I'm trying to avoid a mast and
associated hardware in the tower. Another piece of R45 above the top
guys, at 75 lb, seems as light as anything else I could put up there.
The small 20 above the 40 gives me the opportunity for 3 phased 20's.
Someone suggested a 204BA, I have some of those elements but would
probably make it a 3L.
My 3L40 is an old DXE. From the factory it came with (what I consider)
huge tips. Starts out at 2 inch, ends in telescoping tubing at 0.875in.
To me that is gross overkill at the tips. I replaced the outer 16 feet
with 204BA elements to cut the weight but more important the wind load.
My neighbor K0YW has a duplicate of this ant. His element sag is
something like 3X mine. This ant is up on a hilltop 70 ft crankup
cranked down to about 50 ft for the past year with no probs so far.
Gotta wonder if K4JA's pair of 40's started twisting in opposite
directions. AB105 is stout stuff, I had some up 30 yrs ago in San Diego
area.
73 Art K6XT
Allison, Colorado
"One of the harshest lessons learned from recent disasters, especially
Katrina, is that you are your own first responder."
...LtGen Russel Honore USA
GMCC CWOps 728
NAQCC 1342 SDDXC
ARRL TA
On 2011-08-19 05:54, Pete Smith wrote:
> You're right to be concerned about twisting loads. K4JA, who is a
> pretty good back-yard engineer, lost a 200-foot AB-105 rotating tower
> with 2 40m OWAs on it in a windstorm, and from the debris it was
> obvious that it had twisted to failure. Afterward, he told me he sure
> wished he had a shear pin or other provision for breaking the
> connection between his rotator and the tower, because if it had been
> free to move it might well have survived.
>
> By the way, if you plan to phase the two 3L 20m yagis, wouldn't you be
> better off putting the top one at 100 feet? Or are you looking for an
> elephant gun to Asia?
>
> 73, Pete N4ZR
>
> The World Contest Station Database, updated daily at
> www.conteststations.com
> The Reverse Beacon Network at http://reversebeacon.net, blog at
> reversebeacon.blogspot.com,
> spots at telnet.reversebeacon.net, port 7000
>
>
>
> On 8/18/2011 8:51 PM, Art K6XT wrote:
>> I've started construction of a 150 ft Rohn 45 rotating tower using K0XG
>> base and four rings, top ring at 140 ft. Just above the top ring will be
>> a 3L40 and possibly a small 20 above that, like 3L.
>>
>> I'd be very interested in any experience or anecdotes on projects like
>> this using R45. That tower was selected because I already own it. My
>> area has the potential for icing. The ice I've seen is very light,
>> nothing like back east or in EU. But I suppose its possible. Not too
>> windy, the strongest seem to peak out around 70mph and that's rare.
>>
>> One issue I see is, there are no torque bars on the tower. All its
>> torque is transmitted to the rotator on the ground. K0XG's rings do have
>> torque bars but that doesn't help the tower.
>>
>> The general plot is to add antennas down the tower above the guy rings.
>> Second 3L20, a shorty 40 Hygain, 10 and 15M.
>>
>> Replies to k6xt at arrl dot net are FB, or here.
>>
>
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