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Re: [TowerTalk] Wind Load Spec Differences Between Tower and Antenna

To: Grant Saviers <>,
Subject: Re: [TowerTalk] Wind Load Spec Differences Between Tower and Antenna
From: Steve Dyer W1SRD <>
Date: Fri, 03 Aug 2012 10:05:22 -0700
List-post: <">>
Thanks Grant.

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.

Steve W1SRD

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  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. 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,
>> Steve
>> W1SRD
>> 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 (
>>  )!
>> 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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