Masts

[Steven.M.London at att.com]

I used an 18 foot section of 1/4" thick chrome-molybdnum alloy
pipe for 13 years (similar to what K5RC is selling).  It is strong stuff.
I had a KLM 3 el 40 meter beam mounted 15 feet above the top of the tower.  The
tower was guyed 3 feet from the top.  Guess what - the top tower section bent,
but the mast stayed straight.

Steve London, N2IC/0
n2ic at longs.att.com

>From Stankiewicz, Warren" <wstankiewi at arrl.org  Wed Jun 22 15:57:00 1994
From: Stankiewicz, Warren" <wstankiewi at arrl.org (Stankiewicz, Warren)
Date: Wed, 22 Jun 94 10:57:00 EDT
Subject: Masts
Message-ID: <2E08513B at arrl.org>


If you're looking for some really good mast material, and money is no 
object, I strongly recommend using solid titanium rod. I have a piece that 
works really well, is lightweight, and holds up to just about anything 
Nature (or antennas) can throw at it. It was really expensive, though--the 
35-foot, 1 /14 OD piece I have probably runs close to a kilobuck or more 
these days..

Warren, NF1J (wstankiewi at arrl.org)

>From Trey Garlough <GARLOUGH at TGV.COM>  Wed Jun 22 16:00:26 1994
From: Trey Garlough <GARLOUGH at TGV.COM> (Trey Garlough)
Date: Wed, 22 Jun 1994 08:00:26 -0700 (PDT)
Subject: Mast question
Message-ID: <772297226.688341.GARLOUGH at TGV.COM>

> I have purchased a 20' mast from Texas Towers.  It has withstood my 
> requirements for 7 years now.  It came galvanized.

Yep.  Same here, but as I recall the mast I got from Texas Towers was
2" before being galvanized, so don't plan to use a Rohn 2" thrust bearing
with it.

--Trey, WN4KKN/6

>From Tony Brock-Fisher <fisher at hp-and.an.hp.com>  Wed Jun 22 16:35:55 1994
From: Tony Brock-Fisher <fisher at hp-and.an.hp.com> (Tony Brock-Fisher)
Date: Wed, 22 Jun 1994 11:35:55 -0400
Subject: Masts
Message-ID: <9406221535.AA09242 at hp-and.an.hp.com>

I have refrained from making my most urgent mast reccomendation until now
because it solves one set of problems at the expense of causing another
set of problems. But now that Trey has us all into 3" thrust bearings,
here goes...

The most inexpensive way of increasing strength of masts is to increase
the section modulus. The easiest way to increase the section modulus
is to increase the OD. So instead of staying below 2" OD, and using
some super-expensive super-hard-to-saw alloy to increase yield strength
to 100K+ PSI, just go to 2 1/2 or 3 inch OD pipe. The strength goes way
up, but the cost is low because any old steel (almost) is strong enough.
Now go get a 3" thrust bearing, redesign the boom-mast clamp, and 
use a pipe reducer at the rotator end, and you're in business.

-Tony (not a MEch-ie) K1KP, fisher at hp-and.an.hp.com

>From Bruce Herrick <bdh at mixcom.mixcom.com>  Wed Jun 22 17:12:20 1994
From: Bruce Herrick <bdh at mixcom.mixcom.com> (Bruce Herrick)
Date: Wed, 22 Jun 94 11:12:20 CDT
Subject: Antenna Switches
Message-ID: <199406221612.LAA03966 at mixcom.mixcom.com>

As usual, we waited until the last minute...We need a non-shorting 3
position coax switch for Field Day.  Looking at the AES catalog, I have a
choice of B&W, Alpha Delta, and MFJ.  Although the descriptions do not
specifically state shorting or non-shorting, it appears the B&W and A/D are
shorting types.  The MFJ may not be.  I called a friend at AES who's going
to grab an ohmmeter and check when he gets a chance, but does anyone on the
reflector have any input?

Please email me direct; I'll summarize to the net.  Thanks.

73, Bruce WW1M
-- 
Bruce D. Herrick               bdh at mixcom.com      Home:   414.462.1270
Pryon Corporation                                  Office: 414.253.5678
N93 W14575 Whittaker Way                           Fax:    414.253.2772
Menomonee Falls, WI  53051                         PacketCluster: WW1M > NB9C

>From barry at w2up.wells.com (Barry Kutner)  Wed Jun 22 16:47:37 1994
From: barry at w2up.wells.com (Barry Kutner) (Barry Kutner)
Date: Wed, 22 Jun 94 15:47:37 GMT
Subject: Mast strength
Message-ID: <3LTBoc1w165w at w2up.wells.com>

There is a way to calculate the EXACT mast requirements for your station. 
I believe there were some formulas published in NCJ several years ago 
that shows how to do it.

As an example, the bending stress of a TH7 one foot above the thrust 
bearing, with a 40-2CD 12 feet above the TH7 is as follows:
58,590 psi at 100 mph
47,460 psi at 90 mph
28,710 psi at 70 mph

This is why Randy's Texas Tower mast has held up well, being rated at 
about 80 Kpsi. 

My calculations came with the help of a friend who is mechanical 
engineer. Posting the fomulas and calculations would be difficult due to 
subscripts, greek letters, etc. If anyone would like to see sample 
calculations, send me SASE and I'll send copies to you (2 pages).

P.S. Please don't make any mention of Reunion Island on the envelope. You 
know what happens to those... (couldn't resist)



--=====================================================================
Barry N. Kutner, W2UP       Usenet/Internet: barry at w2up.wells.com
Newtown, PA                 Packet Radio: W2UP @ WB3JOE.#EPA.PA.USA.NA
                            Packet Cluster: W2UP >K2TW (FRC)
.......................................................................


>From drs at ccd.harris.com (Doug Snowden)  Wed Jun 22 18:12:54 1994
From: drs at ccd.harris.com (Doug Snowden) (Doug Snowden)
Date: Wed, 22 Jun 1994 13:12:54 -0400
Subject: Masts, More Questions
Message-ID: <9406221712.AA60192 at rs2>

Ok, now we have a good idea of what people are using, or recommend
for use as mast material. Now, what is the typical scenario in
getting the mast to the top of the tower, installed, with antennas?
I think we are talking about over 300 lbs (???) of mast if we were
using 3 inch stuff of 20 foot length. My main concern is the
manipulation of the mast while it is on/in the tower and antennas 
are being added.  You can guess that I have never had more than one
antenna on my mast, and never had a big mast.

Doug, N4IJ drs at ccd.harris.com