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Author Topic: 40m Virtical Antenna Plans, need advice  (Read 3432 times)
K1BXI
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Posts: 812




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« Reply #15 on: August 18, 2007, 10:59:13 AM »

Tyler.....You said **Any advice whatsoever is REALLY appreciated** I would REALLY think about some sort of wire antenna or one that is not attached to that chimney.

I looked you up on QRZ and notice you are just starting out in ham radio. Welcome....this hobby needs young fellows like your self. I was there 50 plus years ago myself.  There is good advice in all these posts, read them carefully. Stay safe and have fun on the bands.

John........K1BXI
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W7ETA
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Posts: 2527




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« Reply #16 on: August 18, 2007, 11:36:38 AM »

One option, is to make an antenna for 20 meters, or just 17 meters.

As winter approaches, you can use your experience making the 20 meter one figuring out what you want to make for 40.

73
Bob
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N4UM
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Posts: 480




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« Reply #17 on: August 18, 2007, 11:44:16 AM »

Consider getting a used Hustler 4BTV/5BTV/or 6BTV.  Install it on the ground in as clear a spot as possible.  Put as many radials on it as possible and make them up to 30 feet long (if possible).  Their length is not critical since they'll be on the surface of the ground or just beneath it.  I've had success with this kind of setup with as few as 8 or ten radials varying between 8 and 16 feet long.  I concur with some of the previous responses you've received about the inadvisability of mounting a vertical on your chimney.  Chimney's are expensive!  The bandwidth of these antennas is only about 60 khz on 80 and about twice that on 40 meters.  They're pretty broad on the higher bands.  They're inexpensive and are extremely well built.  You can adjust for minimun swr on each band at whatever point in each band that you decide upon.  Just rememebr to start with 10 meters first then 15 etc. etc... working your way downward in frequency.  Have fun.
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N4NSS
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Posts: 6


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« Reply #18 on: August 18, 2007, 12:02:24 PM »

Try an off center Windom.  Set it up as an inverted vee Top at the chimney. One leg is 45 feet the other leg is 90 feet the center is feed with a 4:1 balun. Feed it with coax.  No tuner needed.
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KE7ENR
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Posts: 18




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« Reply #19 on: August 18, 2007, 12:07:15 PM »

Thanks for all the responses!!!!!!!!!!!

There seams to be one thing that is still unclear...
-I have to put the antenna on the roof, I guess I didn't make that very clear Smiley

Also...

-The Chimney is a double chimney, and VERY well build. Its about 2.5 feet by 5 feet, BUT I have read what you said, ***and I'm now considering buying a tripod for the roof, which is a pitched, low profile roof. I think that would be a better fit taking in to account your thoughts.

-The homebuilt plans I had seam to not mesh with your advice, so I think I'll go with something manufactured now. It would be nice to get 10 15 20 40 on a vertical. Any thoughts??? I'm also looking at the Hustler BTV's; very appealing.
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KE7ENR
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Posts: 18




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« Reply #20 on: August 18, 2007, 12:10:42 PM »

I'm now considering buying the 6BTV. It doesn't appear to come with a radial system. Any suggestions for making a simple radial system that I can attach to it on my roof???
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KC8VWM
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Posts: 3121




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« Reply #21 on: August 18, 2007, 12:20:17 PM »

The homebuilt plans I had seam to not mesh with your advice, so I think I'll go with something manufactured now. It would be nice to get 10 15 20 40 on a vertical. Any thoughts??? I'm also looking at the Hustler BTV's; very appealing.

------------------

Perhaps this antenna installation arrangement will give you some ideas on how you might construct your own antenna using the chimney as the main antenna support?

http://kc8vwm.qsl.nu/Charles%20Bushell's%20Home%20Page_files/KC8VWM%20HF%20Stealth%20Verticle.JPG

73 de Charles - KC8VWM
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KE7ENR
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Posts: 18




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« Reply #22 on: August 18, 2007, 12:24:06 PM »

I don't have that kind of chimney, it comes out of the middle of the roof Sad
Thanks anyways!!!

I think I have settled on the BTV Series. It will have to be installed elevated, with radials. But I don't know where to start with them... Any thoughts guys?
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KE3WD
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Posts: 5689




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« Reply #23 on: August 18, 2007, 01:20:13 PM »

>>***and I'm now considering buying a tripod for the roof, which is a pitched, low profile roof.<<

That is exactly the option I was about to suggest.


KE3WD
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KI4VEO
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Posts: 166




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« Reply #24 on: August 18, 2007, 02:38:23 PM »

Hustle down to Radio Shack and get some sections of aluminum tv mast (they used to carry 5 foot sections).  You'll need a litle over 30 feet total.  Drill and self tapping screws for the joints for good electrical contact.  Get a chimney strap mount while you are there.
Stop at Home Depot, or Lowes, and get a couple of PVC couplings that will fit over the mast outside diameter to cover the points on the mast where the chimney strap clamps will attach...electrically insulate the mast from the straps 'cause when it rains and the bricks get wet....well, you get the idea.  If the PVC doesn't fit tight, no problem...wrap some black electrical tape around the mast at the two points to add some thickness for a snug fit inside the PVC.

Cut your radials, attach thme with some screws to the lower chimney mount, and fan them out.

Now all you have to do is conect the coax center conductor to the bottom of the aluminum mast with a self tapping screw and the coax braid to the lower chimney mount (which already ahs your ground radials attached).

You may need to do a bit of trimming of the mast to get the antenna to resonate near your frequency of interest, but 32 1/2 feet of aluminum tubing should be pretty darn close to 7.2 Mhz.

If the antenna apprears a bit too short, electrically speaking, you can add a foot or so of length to it with a bit of #10 or #12 solid electrical wire - just strip off some insulation from one end, form an EYE loop, and use a self tapping screw to attach it to the top of the mast...or, if easier, do it at the bottom and move your coax center conductor attachment point to the end of the short piece of wire.

When you are satisfied everything is working OK, use some silicone sealant to seal the exposed braid and center conductor.  OH how water LOVES to wick up into coax via the braid........
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N3JBH
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Posts: 2358




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« Reply #25 on: August 18, 2007, 03:35:20 PM »

the hustler 6 bvt mounted on your tripod should work fairly well. add 3 or 4 25 foot long radials to it placed on your roof and you should be good to go.

i do recomend you find a buddy that has antenna anylizer to help you adjust the antenna. othere wise you sure get tired of climbing up and down the roof.
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N5YPJ
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Posts: 642




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« Reply #26 on: August 18, 2007, 03:54:58 PM »

 Read This -  Don't attach a vertical to a modern day chimney and expect your chimney to last or your antenna. Todays, and many of the older chimneys were not designed to support an antenna whipping around in the wind. The chimney can "snap off", I've seen a few poorly built ones that have come off without anything mounted on them. Only a wire antenna or radial should be attached to a chimeny and kept a safe enough distance that the heat and smoke don't cause the wire to corrode.

You've got the best possible idea for mounting a vertical, mount it up high where all antennas should be mounted if you expect them to perform. Problem - 1/8 wave radials will not work on a 40 meter ground plane, but will radiate will on 20 meters of course there your element won't come close to loading, 1/8 wave radials will only work on the ground and be a compromise at that. Get a 5BTV or 4BTV Hustler, a roof tripod and some copper wire for 1/4 wave length resonant radials.

Sometimes you have to be inventive, deceitful and even sweat a bit or even bust your butt to get what you want. If you install a vertical properly you will be well satisfied on all but local radio work. If you cut corners, you will get exactly what you paid for.

73

Richard
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K5LXP
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Posts: 4522


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« Reply #27 on: August 19, 2007, 06:43:25 AM »

This is a pretty simple installation.  If you have the surface area available on your roof, a 5BTV or equivalent vertical mounted on a tripod in the center with resonant radials spread out will work great (I have a similar arrangement on my roof with a Butternut vertical).  Alternatively, a Cushcraft R8 mounted on a tripod on the roof will also work well, and you won't have to mess with the radials (more $ though).

Mark K5LXP
Albuquerque, NM
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WB6BYU
Member

Posts: 13486




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« Reply #28 on: August 19, 2007, 08:47:27 AM »

Radials are simply wire (or any other conductor you have handy.)  Since
you are using an elevated mount (rather than on the ground) the radials
need to be of resonant length for each band, but fewer radials are needed
for efficient operation.

First, go back in the eHam article archives and look for the article on
roof-mounted verticals by Steve WB2WIK.  It tells you everything you
need to know, and says it better than I can.  Perhaps someone can post
a link to the article.

For roof mounting, two radials for each band will work (or even one if
that is all you can manage), but up to 4 may be better in some cases.
The radial wires connect to the mounting base of the vertical close to
the coax connection - NOT to the base of the tower.  For roof mounting
the lengths of the radials affect the resonant frequency of the antenna -
you can actually tune the antenna by trimming the lengths of the wires.
They should all be the same lenth, and trimmed equally if you do this.
Most verticals also have adjustment range on the antenna itself - usually
by sliding pieces of tubing together or apart.  Note that each band has
to be adjusted individually. With a trap antenna, start by adjusting 10m
then work up the antenna (down in frequency) from there.  The radial
adjustments are (generally) independent from one band to the next,
however, so you can trim the 10m resonance by adjusting the radial
lengths without throwing off the settings for the other bands.  (The
lengths of the 40m radials may affect 15m.)

Practically, I'd get a spool of #14 to #22 insulated wire (perhaps in a
dark color, or one that matches the roof, if you don't want it to be too
noticable.)  If you are going to run significant power output, it may be
better to keep the radials off the roof and put insulators on the ends
of the wires.  In that case, put some screw eyes around the perimeter
of the roof, run the radials out in the desired direction, put an insulator
on the end of the wire, and run Dacron rope from there to the screw
eye.  Generally the longer radials are the most difficult ones to fit, so they
will go out to the corners (and bend around to follow the edge of the
roof if they don't fit - often the case on 80m.)  The shorter radials can
run in directions where you have less distance to the edge of the roof.
Ideally the radials for each band would be symmetric, but if your roof
doesn't allow that just do the best you can.  For lower power levels
(including 100 watts) I might angle the radials down to the roof level
at some distance out from the tower then tuck the remainder under the
shingles from there to the ends of the wire.  Or you may use some
combination thereof - if the top of the roof tower needs to be guyed,
you can make some of the radials from copperweld wire (strong!) and
use them as the guys, then run the remainder from light wire down
and lay them on the roof.

(The vertical may need to be guyed with Dacron rope in the middle
as well to keep it from bending too much in the wind.)

If you need insulators for the ends of your radials, check a Farm Supply
store for the plastic ones used on electric fences.
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G0GQK
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Posts: 634




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« Reply #29 on: August 19, 2007, 12:46:06 PM »

Amazing isn't it !  He says he doesn't have any trees and the first one to respond writes about having a tree !

G0GQK
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