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Author Topic: Which is better antenna/mount for a motorhome?  (Read 7001 times)
AB1PJ
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Posts: 33




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« on: October 22, 2011, 05:29:20 PM »

I am debating which way to go:-

The motorhome is 13' tall, 43' long, there is no way to use an antenna while driving

The antenna will be used only when parked
These antennas cover 10m-80m bands
I can connect antenna ground to motorhome frame
This is a semi-monocoque frame (like an airplane frame) but the outer skin is fiberglass


1. Use a 31' vertical antenna mounted on the hitch of the motorhome
I have a icom AH-4 antenna tuner to go at the base of the antenna


OR

2. Use a 31' vertical antenna mounted on the roof (fiberglass) of the motorhome
I have a icom AH-4 antenna tuner to go at the base of the antenna

OR

3. Use a screwdriver antenna mounted on the roof (fiberglass) of the motorhome
I have a BetterRF screwdriver antenna tuner

OR

4.Use a screwdriver antenna mounted on the hitch of the motorhome
I have a BetterRF screwdriver antenna tuner


Basically, which way can i get most radiation energy out?
« Last Edit: October 22, 2011, 05:32:42 PM by AB1PJ » Logged
K0BG
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« Reply #1 on: October 23, 2011, 06:41:03 AM »

Got to my web site, and bring up the OTR&RV article. There are more photos in the Photo Gallery.
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AB1PJ
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Posts: 33




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« Reply #2 on: October 23, 2011, 06:58:19 AM »

Got to my web site, and bring up the OTR&RV article. There are more photos in the Photo Gallery.

I have been to the webpage, but my question is : which (antenna+mounting location) combo, gives the most radiation energy out assuming i want to work 10m-40m

At hitch mounted, both the vertical antenna base are approx 3 ft from ground
At roof mounted, both vertical antenna base are approx 12 ft from ground

I am inclined towards a (vertical+tuner at base) over a (screwdriver+ tuner at radio), as i hear the screwdriver is lot lossier than a vertical wire antenna. Is that true?

I am also thinking, being on the roof top the ground losses will be less (not sure how much though)  but i am only going from 3' above ground to 12' above ground ie 9' more. Is it worth
it as mounting/unmounting the antenna on the 12' high roof is a lot more work


Between
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WX7G
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« Reply #3 on: October 23, 2011, 09:42:13 AM »

Assuming the motorhome is metal or has a metal frame, roof mounting will result in higher radiation resistance.

The 31' vertical will outperform the screwdriver on 80 and 40 meters.
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K0BG
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« Reply #4 on: October 23, 2011, 09:56:48 AM »

I have a friend who drives a Provost RV. There is a two element tribander laying on the roof. Once on location, up the antenna goes. Sure beats a mobile antenna, no matter how you mount it.

In any case, RVs present a very difficult mounting situation. Adding insult, no two seemingly are built the same. Even worse, most don't have enough metal structure to them, and end up having more ground losses than a sedan. They also tend to be electrically noisy due in part to the 12 to 120 volt inverters most have. So the decision has to be yours, and part of that decision is how much work you're willing to extend. For example, that "cow catcher" on the front to K5HAB's coach shown in the Photo Gallery, cost big bucks, and a lot of labor before, and after the fact. That's about as far as I can go without knowing what the RV is.
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AB1PJ
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« Reply #5 on: October 23, 2011, 10:20:50 AM »

The motorhome i have is very similar to a Prevost bus with some differences

The MH has skeleton of semi-monocoque tubular steel frame
It has laminated gelcoat fiberglass steel framed sidewalls
It has seamless one-piece molded crowned fiberglass roof

For the prevost, it is all metal skin including sidewall and roof
but same steel frame for skeleton.

Here is a picture of the frame http://i52.tinypic.com/iqe9ep.jpg from the manufacturer....

Here is a http://i52.tinypic.com/30nf01w.jpg picture of the outside


My thinking is to put up a 31' vertical Eagle One antenna just
above the ladder and have a icom AH-4 tuner below it. I use
an icom 7000 radio for this. I don't have any amplifiers.
I could run some radials lying on the roof (43' long) connected
to AH-4 ground terminal. I would connect the antenna ground to MH frame.

I am not connecting the antenna electrically to the aluminum ladder
The ladder will be used to hoist the antenna up and mechanically secure it.
The ladder is also not connected to the MH frame or ground.

My thinking is, this might help in reducing some of the ground losses, but
is 9ft more such a big deal?




« Last Edit: October 23, 2011, 10:56:23 AM by AB1PJ » Logged
WX7G
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« Reply #6 on: October 23, 2011, 12:33:32 PM »

The reason to mount the antenna above the motor home metal frame is to avoid magnetic field cancellation. With the antenna mounted low on the vehicle there will be charge flow upwards in the antenna and downwards in the motor home frame causing some cancellation of radiation from the portion of the vertical that is adjacent to the frame.

With the screwdriver antenna this is quite important because much of the screwdriver antenna would run adjacent to the frame.

I'm studying this same issue in anticipation of mounting a screwdriver antenna on a truck camper. I would like to remove the antenna while driving and mount it easily from the ground when camped. I don't want to have to climb the ladder each time. Perhaps an electric lift-and-lay mount at the top of the ladder is the solution.
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AB1PJ
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« Reply #7 on: October 24, 2011, 04:04:43 AM »

http://www.flagpolebuddy.com/

Could this the answer to hoist the antenna up/dn the roofline?
At least no more reactive field coupling.
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WX7G
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« Reply #8 on: October 24, 2011, 05:20:34 AM »

The flagpole buddy looks great for antenna mounting. You got me thinking about antennas other than a screwdriver. Maybe a Hustler 6BTV will be the antenna.

I'm planning to live full time in the truck camper and want decent antenna performance for contesting and DXing.
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AB1PJ
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Posts: 33




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« Reply #9 on: October 24, 2011, 05:41:42 AM »

I'm not sure if you plan on using the antenna while in motion or at rest

If you plan to be in motion, and this being a truck camper, your choices of antenna
mount is just one place - the hitch or the front grille guard area, which is the worst place on the entire truck camper assuming you have no access to the roof of your truck or to you bed due to camper already mounted there.  Both the hitch area and front grille guard area will incur heavy H field coupling and radiation loss.

If you plan to use this when parked, i think the ladder mounted flagpole vertical antenna with 10 or so radials on the top of the roof OR maybe a metal painted roof (maybe a diamond aluminum plate would work too) and antenna in the center of the roof is the best you can do.

There is also a dipole option - inverted V dipole, using a tall 50' pole on your hitch.

I will be interested in knowing which way you made out successfully?

Please keep us posted
thanks
jim
 
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WA8FOZ
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« Reply #10 on: November 05, 2011, 09:49:59 PM »

Quote
There is also a dipole option - inverted V dipole, using a tall 50' pole on your hitch.
This would be the best option from a standpoint of radiation efficiency. Consider a heavy-duty telescoping fiberglass pole mounted on the rear hitch. This supports an inverted-v, used when attachment points for the legs are available. When they are not, use it to support a vertical wire, and use the body of your vehicle was an image plane, supplemented by wire radials when possible.

Sounds like fun to me!
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N6DMR
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« Reply #11 on: November 16, 2011, 12:25:10 AM »

I think the downside of roof mounted verticals or screwdriver antennas on a glass or rubber roofed MH is the ground losses that are inherent in a raised vertical.  Probably a good roof mount option is the Scorpion 680 with their radials kit and a topcap.  The best tilt mount for the roof is probably a Tarheel Lift and Lay, and using quick disconnects for the radials.  This setup would be pretty efficient and durable but is a more expensive option, probably right arount $1500.00.

I have a 40ft National Tropical, Class A Diesel.  I use a Flagpole Buddy mount with their 22 ft fiberglass telescoping flagpole.  Below the flag, I attach the end of a Miracle Antenna MMD as a sloper to the front of the motor home.  I tie the antenna BNC connector to a topside accessory junction box which runs the coax down through the ceiling into the overhead TV/Entertainment area.  I ran the coax to the drivers left console with female PL259's.  I currently use a 17M Miracle MMD, and could also use the longer 20M version.  On 40M with a tuner, matching is no problem.  Very quiet receive and I get good signal reports as well.

I also have a Butternut HF6V (10M-80M) vertical that I put up outside when I have the space. It is ground mounted on a round wooden tilt base I built that has 16 tape measures (25ft) attached aroung the edge.  I pull the tapes out as quick and easy ground radials. Gets up on 80M, but is not the most efficient at that frequency............

The third option I use is a Transworld Antennas TW-2010 5 band (10M thru 20M) ground mounted antenna.  I can put this up in minutes and is a great DX antenna.  I have worked many Field Day contests with this antenna and usually if I can hear them, I can make the contact.

A really good website to check out is www.K0BG.com, Alan has a lot of really good information there.

73's

Duane
K3AL
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AB1PJ
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« Reply #12 on: November 16, 2011, 03:01:49 AM »

Has anyone tried a SteppIR vertical such as BigIR?

A vertical is more efficient than a screwdriver, so i am still
thinking of verticals

thanks
jim

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N6AJR
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« Reply #13 on: November 16, 2011, 03:27:12 PM »

just a couple of thoughts here of mounts I have seen in the past.  one option was an ATAS 120 mounted on a motorized diamond  mount on the roof.  when driving the antenna laid down on the roof and when stopped  he raised the antenna.  It also worked nicely as his radio was an FT 857 which autotuned the antenna.

another idea I saw was  a mount for a 20 or 30 foot push up mast.  it had a pivoting mount on the rear bumper and colapsed down the side of the coach and rested in a u shaped bracket with a keeper on it just below the drivers side window.  when parked, he put the antenna on the end and rotated it up vertically  to a clamp gizmo attached to the rear ladder so it was upright when up.  he stood on the ladder and mounted his antenna ( I think it was a 2 element tribander of some sort)  and he added a set of 2 17 neter and 2 40 meter "guys" and a second coax to feed them.  lots of ways to go , you could make a nice mount that you park on and run a mast up from that, or even try something like a hustler  multi tipped  mobile antenna or just a long fiberglass mast with a wire on it you could extend when parked  into a SGC 237 or such.  good luck and let us know what way you went.
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N6DMR
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« Reply #14 on: November 18, 2011, 11:12:02 AM »

Jim,

Do some homework on these antenna suggestions you are considering.  The Steppir Verticals ALL require extensive ground radial systems.  I snapped this from the Steppir site:

SPECS                   Biggir          Biggir with 80M coil    Smallir    
Element Length    32 feet                    same                   18 feet    
Minimum Radials    12 x 16 foot    12 x 46 foot    12 x 9 foot

ALL of these verticals need a minimum of 12 radials and the length of the Biggir radials for 40M is 16 Ft. If you try to roof mount these the radials need to be right under the base.

These are all designed as GROUND mounted antennas, with a built in match tuner at the base.  If you try to raise these up off the ground the efficiency will suffer badly.  The MAIN issue you face with a fiberglass roof mount or RV hitch mount, etc. for a vertical will be ground losses. On 40M, I would think a raised vertical would be less that 20-30% efficient as a radiator.
 
You could pick up a Flagpole Buddy mount and mast and field a Miracle Antenna Multiband MMD Dipole for 40M for less that $300 and you would end up with an antenna efficiency above 80% with no need for any ground radials.  This setup could be put up in less that 15 minutes and will always be in your "space" avoiding conflicts with RV neighbors and with a flag on the pole must folks would never even know it was an antenna.

Again, I highly recommend spending some time on Alan's ( www.K0BG.com ) website and check his comments on Antenna Matching, Shunt Coil Adjustment and such.

An AS-120 or Tarheel screwdriver will get you on the air and you'll make contacts.  ANY antenna is better than nothing.  But putting up a ground mount vertical (which is what a screwdriver is) needs to be evaluated based on where you will be mounting it.  These do best when mounted on the metal BODY of the vehicle, with the fiberglass body panels of the RV it becomes a big issue for ground losses and will end up killing antenna efficiency unless you have a plan for effective ground radials.

Respectfully,

Duane
K3AL
   
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