View Single Post
  #16   Report Post  
Old July 3rd 07, 01:52 AM posted to rec.radio.amateur.antenna
J. Mc Laughlin J. Mc Laughlin is offline
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 172
Default Rohn 25G without guys, how high?

Dear Rick: Sorry to have received the call-sign incorrectly. Your
Father's call does not ring any bells.

The main reason for two sections above a house bracket is because of the
significantly greater probability of greater wind pressure on the two
sections compared to three sections that start at ground level. You also
expect to have more effective area for the greater wind pressure to work on.

I have become convinced that the reason few urban TV/FM antennas and
Rohn 20 (no cross braces) towers fail is because of a dramatic reduction in
wind pressure up to about 35 feet above ground in a typical urban
environment.

The real limitation (for you) may turn out to be due to the building
code used in your area. When the time comes to have a serious antenna tower
for HF, do find a professional engineer licensed in your State who's advice
about how to satisfy the building code and 222G will be worth every penny
you pay to him or her.

Warm regards, Mac N8TT

P.S. My neighbor K8DO still does things that give me the willies. Even
when I was young, I sure would not climb 50 feet of un-guyed Rohn 25.
Medical school instills rather more "confidence" than engineering schools
do.
--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Rick (W-A-one-R-K-T)" wrote in message
news
On Sun, 01 Jul 2007 16:39:37 -0500, J. Mc Laughlin wrote:

Two sections above guys next to the house is pushing prudence. With a
clear area next to the proposed tower in the back, three sections with
just a VHF antenna seems reasonable in view of your description.


I'm curious why two sections above the guys, next to the house, is
marginal but three sections self-supporting out in the open seems OK.

Actually the three sections self-supporting would be as close to the house
on one end as the guyed tower is on the other end.

Perhaps the tribander on the guyed tower makes the difference, but in
truth I think the chances are fairly slim that I'll end up doing that. I
have two inverted vees and two NVIS dipoles, which together cover 160
through 40, which these days are the only HF bands that really hold my
interest... I never was much of a DX hound and with the Internet and
satellite phones, it doesn't seem like hardly anybody wants to pass any
traffic or run phone patches anymore. Perhaps when the sunspots get more
favorable I'll re-think the notion of the tribander but until then it's
probably pretty low on the priority list.