I think to many people rely on "over engineering" of these towers to withstand
loads that never should be put on them in the first place. Years ago I bought
a HDBX48 and the gentlemen I purchased it from had a TH11DX and TX2 on top of
it. I believe he had other various antenna's on it for VHF and UHF. He got by
with it but I'm not sure how many years he had it up but regardless that was a
gross overload of that tower. I never put that beam up on that tower. The
Rohn towers are good towers but any tower has it's limits. I believe what you
are proposing as others have also pointed out is you are exceeding the limits
of the tower spec's. That's your choice but remember if something fails and
you need to file a claim with your insurance carrier you are up the proverbial
creek. More thought should have gone into that install before you put that
tower in given you knew the type of antenna you wanted to put on it. Either
way good luck with whatever you decide to do.
Brian KB0IXM
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 21 Aug 2013 11:32:37 -0400
> From: <RShirbroun@newportlabs.com>
> To: <n6sj@earthlink.net>, <towertalk@contesting.com>
> Subject: Re: [TowerTalk] Question on mast height above tower
> Message-ID:
>
> <FD1AE75DECD6114FA082EBFECDE1D48F01661DF7C7@AM-USA58-EXC103.corp.merial.net>
>
> Content-Type: text/plain; charset="us-ascii"
>
> Thanks Steve. According to the calculator the guys at Texas Towers use, the
> mast (2" diameter, 0.25" wall) should easily handle it. My concern is just
> if the ratio of 13' above and 2' below the top plate is excessive and would
> potentially put too much stress on the tower itself.
>
> 73,
> Randy, ND0C
>
>
>
> -----Original Message-----
> From: Steve Jones [mailto:n6sj@earthlink.net]
> Sent: Wednesday, August 21, 2013 10:13 AM
> To: Shirbroun, Randy AH/US; towertalk@contesting.com
> Subject: RE: [TowerTalk] Question on mast height above tower
>
> Randy-
>
> If you can find a copy of Dave Leeson's "Physical Design of Yagi Antennas"
> (out of print) he explains how to calculate all the moments created by your
> combination of wind speed, boom/mast lengths and material types. Then you
> select the proper material, length and wall thickness to withstand those
> forces. That stack sounds like a big load on the base of the 2" mast, but
> whether it will hold depends on the yield strength of the chrome moly mast
> you use.
>
> 73,
> Steve
> N6SJ
>
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
> RShirbroun@newportlabs.com
> Sent: Wednesday, August 21, 2013 7:51 AM
> To: towertalk@contesting.com
> Subject: [TowerTalk] Question on mast height above tower
>
> I didn't get any comments or suggestions to my previous post, so I'll try
> again.
> If this is a dumb question, feel free to tell me!
>
> I have just erected a new HDBX 40 in place of my 30 year old HBX 48,
> sacrificing 8' of height to gain some strength and load capacity (and peace
> of mind!). The stock rotator plate allows 2' of mast below the top plate and
> I will be using the heavy duty Yaesu thrust bearing (along with the Yaesu
> heavy
> duty 2800 rotator plus the absorber plate). I have added steel angle
> braces
> to reinforce the rotator plate.
>
> I'm looking at using a 15' chrome/steel 2" mast (in place of my previous 9'
> mast), so 13' of the mast would extend above the tower. The mast would
> support a TX38 tribander just above the top plate, a 6 m beam half-way up,
> and a 40m rotatable dipole near the top, 12' above the top tower plate and
> the thrust bearing. The mast, of course, is very heavy, weighing around
> 75lbs. The tribander weighs 40lbs and with 5 ft2 surface area; the 6 m.
> beam weighs 10lbs with 1.5 ft2; the dipole weighs 10lbs and is 0.5 ft2.
>
> Is this too much mast for this tower? (BTW - I'm aware the boom length
> exceeds the 10' maximum for this tower, but the HBX 48 handled a similar
> tribander for 30 years, with occasional severe ice-loading, without any
> problems.)
>
> Thanks and 73,
> Randy, ND0C
>
>
>
> ________________________________
> This e-mail and any files transmitted with it are confidential and intended
> solely for the use of the individual or entity to whom they are addressed.
> If you have received this e-mail in error please notify the system manager:
> postmaster@merial.com This e-mail and its attachments have been scanned for
> the presence of computer viruses, however it is always advisable to run a
> virus check on e-mails and attachments before opening them.
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>
> This e-mail and any files transmitted with it are confidential and intended
> solely for the use of the individual or entity to whom they are addressed. If
> you have received this e-mail in error please notify the system manager:
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> the presence of computer viruses, however it is always advisable to run a
> virus check on e-mails and attachments before opening them.
>
>
> ------------------------------
>
> Message: 2
> Date: Wed, 21 Aug 2013 11:46:49 -0400
> From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk@tm.net>
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] Question on mast height above tower
> Message-ID: <5214E0E9.9030307@tm.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> On 8/21/2013 10:51 AM, RShirbroun@newportlabs.com wrote:
> > I didn't get any comments or suggestions to my previous post, so I'll try
> > again.
> > If this is a dumb question, feel free to tell me!
> >
> > I have just erected a new HDBX 40 in place of my 30 year old HBX 48,
> > sacrificing 8' of height to gain some strength and load capacity (and peace
> > of
> > mind!). The stock rotator plate allows 2' of mast below the top plate and I
> > will be using the heavy duty Yaesu thrust bearing (along with the Yaesu
> > heavy
> > duty 2800 rotator plus the absorber plate). I have added steel angle
> > braces
> > to reinforce the rotator plate.
>
> My opinion...The mast is plenty strong, (far more than needed) but I
> have my doubts about thr tower to reliably stand that much load. That
> series of towers are designed for relatively light loads and low torque
> conditions. They are stamped metal that is riveted and I believe the
> load plus leverage of the mast exceeds the tower ratings by a
> substantial margin.
>
> The 10' boom limitation is to limit the torque.
>
> 73 and good luck,
>
> Roger (K8RI)
> > I'm looking at using a 15' chrome/steel 2" mast (in place of my previous 9'
> > mast), so 13' of the mast would extend above the tower. The mast would
> > support
> > a TX38 tribander just above the top plate, a 6 m beam half-way up, and a 40m
> > rotatable dipole near the top, 12' above the top tower plate and the thrust
> > bearing. The mast, of course, is very heavy, weighing around 75lbs. The
> > tribander weighs 40lbs and with 5 ft2 surface area; the 6 m. beam weighs
> > 10lbs
> > with 1.5 ft2; the dipole weighs 10lbs and is 0.5 ft2.
> >
> > Is this too much mast for this tower? (BTW - I'm aware the boom length
> > exceeds the 10' maximum for this tower, but the HBX 48 handled a similar
> > tribander for 30 years, with occasional severe ice-loading, without any
> > problems.)
> >
> > Thanks and 73,
> > Randy, ND0C
> >
> >
> >
> > ________________________________
> > This e-mail and any files transmitted with it are confidential and intended
> > solely for the use of the individual or entity to whom they are addressed.
> > If you have received this e-mail in error please notify the system manager:
> > postmaster@merial.com This e-mail and its attachments have been scanned for
> > the presence of computer viruses, however it is always advisable to run a
> > virus check on e-mails and attachments before opening them.
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
>
>
>
>
> ------------------------------
>
> Message: 3
> Date: Wed, 21 Aug 2013 11:51:46 -0400
> From: "Doug Scribner" <dscribner@myfairpoint.net>
> To: "Towertalk" <towertalk@contesting.com>
> Subject: Re: [TowerTalk] Question on mast height above tower
> Message-ID: <78A0051C877848BBA9D4138625423187@HP3400>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
>
> Randy,
>
> I think that I would be more concerned with the tower holding up vs the
> mast.
>
> Rohn rates the HDBX-40 for 18 sq ft @ 70 mph wind speed. This assumes 2
> things:
>
> 1) The load is no more than 3 feet above the top
> 2) The boom length does not exceed 10 feet
>
> You've exceeded those 2 specs already. In addition, your County is listed @
> 85 mph in the County Windspeed Data so the 18 sq ft is no longer valid.
>
> I would seriously re-think that install...
>
> Doug - K1ZO
>
> ----- Original Message -----
> From: <RShirbroun@newportlabs.com>
> To: <n6sj@earthlink.net>; <towertalk@contesting.com>
> Sent: Wednesday, August 21, 2013 11:32 AM
> Subject: Re: [TowerTalk] Question on mast height above tower
>
>
> > Thanks Steve. According to the calculator the guys at Texas Towers use,
> > the mast (2" diameter, 0.25" wall) should easily handle it. My concern is
> > just if the ratio of 13' above and 2' below the top plate is excessive and
> > would potentially put too much stress on the tower itself.
> >
> > 73,
> > Randy, ND0C
> >
> >
> >
> > -----Original Message-----
> > From: Steve Jones [mailto:n6sj@earthlink.net]
> > Sent: Wednesday, August 21, 2013 10:13 AM
> > To: Shirbroun, Randy AH/US; towertalk@contesting.com
> > Subject: RE: [TowerTalk] Question on mast height above tower
> >
> > Randy-
> >
> > If you can find a copy of Dave Leeson's "Physical Design of Yagi Antennas"
> > (out of print) he explains how to calculate all the moments created by
> > your combination of wind speed, boom/mast lengths and material types.
> > Then you select the proper material, length and wall thickness to
> > withstand those forces. That stack sounds like a big load on the base of
> > the 2" mast, but whether it will hold depends on the yield strength of the
> > chrome moly mast you use.
> >
> > 73,
> > Steve
> > N6SJ
> >
> >
> > -----Original Message-----
> > From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
> > RShirbroun@newportlabs.com
> > Sent: Wednesday, August 21, 2013 7:51 AM
> > To: towertalk@contesting.com
> > Subject: [TowerTalk] Question on mast height above tower
> >
> > I didn't get any comments or suggestions to my previous post, so I'll try
> > again.
> > If this is a dumb question, feel free to tell me!
> >
> > I have just erected a new HDBX 40 in place of my 30 year old HBX 48,
> > sacrificing 8' of height to gain some strength and load capacity (and
> > peace of mind!). The stock rotator plate allows 2' of mast below the top
> > plate and I will be using the heavy duty Yaesu thrust bearing (along with
> > the Yaesu heavy
> > duty 2800 rotator plus the absorber plate). I have added steel angle
> > braces
> > to reinforce the rotator plate.
> >
> > I'm looking at using a 15' chrome/steel 2" mast (in place of my previous
> > 9'
> > mast), so 13' of the mast would extend above the tower. The mast would
> > support a TX38 tribander just above the top plate, a 6 m beam half-way up,
> > and a 40m rotatable dipole near the top, 12' above the top tower plate and
> > the thrust bearing. The mast, of course, is very heavy, weighing around
> > 75lbs. The tribander weighs 40lbs and with 5 ft2 surface area; the 6 m.
> > beam weighs 10lbs with 1.5 ft2; the dipole weighs 10lbs and is 0.5 ft2.
> >
> > Is this too much mast for this tower? (BTW - I'm aware the boom length
> > exceeds the 10' maximum for this tower, but the HBX 48 handled a similar
> > tribander for 30 years, with occasional severe ice-loading, without any
> > problems.)
> >
> > Thanks and 73,
> > Randy, ND0C
> >
> >
> >
> > ________________________________
> > This e-mail and any files transmitted with it are confidential and
> > intended solely for the use of the individual or entity to whom they are
> > addressed.
> > If you have received this e-mail in error please notify the system
> > manager:
> > postmaster@merial.com This e-mail and its attachments have been scanned
> > for the presence of computer viruses, however it is always advisable to
> > run a virus check on e-mails and attachments before opening them.
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
> >
> > This e-mail and any files transmitted with it are confidential and
> > intended solely for the use of the individual or entity to whom they are
> > addressed. If you have received this e-mail in error please notify the
> > system manager: postmaster@merial.com This e-mail and its attachments have
> > been scanned for the presence of computer viruses, however it is always
> > advisable to run a virus check on e-mails and attachments before opening
> > them.
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
> >
> >
> > -----
> > No virus found in this message.
> > Checked by AVG - www.avg.com
> > Version: 2013.0.3392 / Virus Database: 3211/6595 - Release Date: 08/21/13
> >
>
>
>
> ------------------------------
>
> Subject: Digest Footer
>
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> ------------------------------
>
> End of TowerTalk Digest, Vol 128, Issue 78
> ******************************************
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