Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Vent Pipe Mount  (Read 2525 times)
KD8SDZ
Member

Posts: 4




Ignore
« on: February 05, 2013, 01:19:17 PM »

What is the tallest antenna you would put on a vent pipe mount (3"CI) without using guy wires. I am trying to find a 2M/70cm base antenna that will work ok.

Thanks

Dave
Logged
K5LXP
Member

Posts: 4536


WWW

Ignore
« Reply #1 on: February 05, 2013, 02:02:05 PM »

PVC or steel pipe?  Can you verify it's well anchored in the roof?  I've had a Comet GP-3 with a 3' mast, and an AR-10 on steel vent pipes for about 10 years now.  But I went into the attic and verified those pipes were actually anchored to something first.


Mark K5LXP
Albuquerque, NM
Logged
AA4HA
Member

Posts: 1643




Ignore
« Reply #2 on: February 05, 2013, 02:09:41 PM »

In my first house it was about an 1 1/2" copper pipe that went alongside a roof joist on the way down and was strapped. It was pretty robust. In the house I own now it is a piece of PVC that I would not trust to keep itself on the roof.

Mounting something close to the opening of the vent pipe can be problematic. For my home that is on a septic system that is also the vent for the tank (on the roof) and hydrogen sulfide gas can be present that will quickly corrode up metals.

Maybe if I was looking for a place to mount a short 2m/70cm antenna without a mast it would be ok. I would not go putting up a mast on that pipe and expect it to not flex and potentially loosen up from the roof and create a spot for rain to leak in.
Logged

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
WB6BYU
Member

Posts: 13580




Ignore
« Reply #3 on: February 05, 2013, 02:51:33 PM »

At one time I had 10' of 1x2 sticking out the top of an ABS vent pipe that
supported my 80m dipole.  When it got stormy I could slip it further down
into the pipe to take the stress off the wire.

But I didn't own the house, so any long term damage to the seal around
the vent pipe wasn't my concern.

There are actually several issues;  the seal where the pipe comes through
the roof, possible flexing in pipe joints (which can eventually cause joints
in plastic pipe to break), how well the pipe is secured all along its length,
as well as sewer gasses and the physical strength of the pipe.  With cast
iron pipe the antenna itself isn't likely to fall over due to failure of the pipe,
but the more likely problem is leaks in the roof developing slowly over time.

To answer your question, with cast iron pipe I probably wouldn't have any
qualms about mounting a 3' to 5' antenna, and, if it is well secured internally,
an 8' antenna should be OK as long as it isn't too heavy.
Logged
KD8SDZ
Member

Posts: 4




Ignore
« Reply #4 on: February 05, 2013, 03:19:56 PM »

Great information all ! The pipe is cast iron, so I guess it's up to me to decide how much I want to stress it and the roof. Never even thought about sewer gas.

Thanks

Dave
Logged
KB4QAA
Member

Posts: 2490




Ignore
« Reply #5 on: February 05, 2013, 04:23:03 PM »

I had an AR-2 Ringo on an iron vent pipe. It was unsupported inside the structure.  That's about all I was comfortable with.  No sense ruining the roof or creating annoying leaks.
Logged
W3HKK
Member

Posts: 621




Ignore
« Reply #6 on: February 05, 2013, 05:32:35 PM »

I avoid vent pipes, chimneys, and other sources of flue gas/moisture after seeing  what happened to a tv antenna after 2 years on a vent pipe.  Corrosion was well underwayaround where the coax met the antenna hardware and phasing stub. 

SS hardware does well but not so other metals like aluminum, steel, etc.

I also prefer to avoid  potential wind damage to the house itself, and put all antennas on a separate ground supported/house braced mast rather than the house or oof itself.
Logged
KQ6Q
Member

Posts: 995




Ignore
« Reply #7 on: February 06, 2013, 08:28:22 PM »

There is a product called the Ventenna that looks like an extension of a vent pipe - designed to fit there, work, and not disrupt the vent.
Logged
K1CJS
Member

Posts: 6061




Ignore
« Reply #8 on: February 07, 2013, 06:22:31 AM »

What is the tallest antenna you would put on a vent pipe mount (3"CI) without using guy wires. I am trying to find a 2M/70cm base antenna that will work ok.

It's a toss-up.  Even though the vent pipe is iron, any joint connections will be made with either lead or with compression sleeves--neither of which will stand up to continual flexing of the pipe that may be caused by even a ten foot mast with a four foot ringo ranger on it.  If you put a five foot mast with that four foot antenna on it, the stack gasses may corrode that antenna in short order.

The best choice would be to avoid the vent stack and chimney and attach a 10 foot mast to the side of the house with house mounted stand offs made for that purpose.  You would also have the advantage of a shorter feedline to the antenna.
Logged
KA1MDA
Member

Posts: 543




Ignore
« Reply #9 on: February 07, 2013, 10:20:39 AM »

But I didn't own the house, so any long term damage to the seal around
the vent pipe wasn't my concern.

With attitudes like that, is it any wonder that many rental property owners are not "antenna friendly" to hams? Comments such as this don't really help the situation.
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!