I am not trying to do calcs for a permit. The towers are already up :-).
Trying to do a "safe" matching of antenna to tower.
You hit the nail on where the confusion lies. I am trying to reconcile
the vendor numbers which use a different wind load spec.
Tashjian is using the most recent EIA-232-G. SteppIR appears to be a bit
behind using EIA-232-A.
I mentioned the wind zones only as they seemed to relate to the spec the
vendors chose and the resultant wind load ratings. The station location
is in Zone A.
I have the same sense the Tashjian LM-470 is quite a bit stronger than
before. Thicker leg walls and 65K PSI vs 50K PSI metal.
The base also has considerably more concrete than required.
On 8/2/2012 10:34 PM, Grant Saviers wrote:
> I looked at my permit submission for an HDX589, a tower series much
> beefier than the LM's (I have a 354 also). The calcs are now
> EIA-222-F and mine were 85mph 3 sec gust and 71mph fastest mile per
> county code, exposure B.
> That allowed a 13.7 sq ft (round) antenna, the 4L SteppIR (no
> trombones) 32' boom plus a 2m 11L. My second HDX589 has the W6NL
> design 40m Moxon (110mph version) which I scratch built, and an 80m
> F12-180C dipole, which push the limits a bit, but historic winds at my
> Redmond QTH are way below the calc requirements. Check for historical
> peak wind data on wunderground.com. You might find a station nearby
> your QTH that has credible history.
> So, if you were doing calcs for a permit, I doubt you would get
> anywhere near 17 sq ft in a 100mph zone (I give up on reconciling all
> the EIA numbers though) for an LM470. QRZ.com says San Mateo for your
> address, but for 100mph you must be on a ridge line.
> I still have my former QTH on the east side of the valley on a 1550'
> ASL ridge east of San Jose.
> Also, I'm pretty sure the newer LM's are more reinforced, and that
> older wind load calcs were "easier" in looking a older UST catalogs.
> Clearly true for base designs which are now significantly bigger than
> in the old catalogs.
> Grant KZ1W
> On 8/2/2012 6:23 PM, Steve Dyer W1SRD wrote:
>> I tried to get an answer from SteppIR to no avail so I thought I would
>> reach out to the TT community. Searched TT archives and googled for
>> answers. I've read K7NV's and W6NL's writeup as well about this subject.
>> Would like to be confident my LM-470 can handle a DB36 (17.5 sq ft using
>> 100 MPH EIA-222-C) .
>> I believe the 4 El SteppIR (9.7 sq ft) is fine on the WT51
>> Usual caveats about crank it down in the wind already noted. Also, the
>> Tashjian specs are for a *new* tower. I don't know the vintage or
>> history of the LM-470 I have. It came with the property.
>> Thanks es 73,
>> Here is my original email to SteppIR:
>> I am sure I am not the first to ask to understand the difference between
>> wind load ratings.
>> SteppIR calculates wind load using EIA-222-C at 100 mph (wind zone B)
>> which is equivalent to 120 mph for a 3 second average used by
>> EIA-222-G. See Leeson, W6NL (
>> http://www.kkn.net/dayton2007/w6nl_ant.pdf )!
>> Tashjian uses TIA-222-G 85 mph 3 sec average which maps to a 70 mph
>> fastest mile (222-A wind zone A).
>> This leads me to to the questions:
>> 1. Is a tower rated at 13 sq ft/85 mph using 222-G is OK for the 4 El?
>> Tower is a WT-51.
>> 2. Is a tower rated at 18 sq ft/85 mph using 222-G is OK for the DB36?
>> Tower is a LM-470D.
>> I understand you cannot commit to the safety of the tower, but I need to
>> reconcile and understand the differences between the two measurement
>> systems before I go forward.
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