Need base station antenna for RV

[Tuno]

I had an AV-5 that worked well but fell victim to the trees
overhanging our neighborhood streets. I'm wondering if anyone has
experience using a longer antenna without a ground plane on a
fiberglass RV.

Or perhaps there's an antenna similar to the AV-5, but with a flexible
base?

~ted/2NO

[Tuno]

Absent any better ideas, I took the whip antenna I once used on my
Honda Pilot and mounted it on a 2-by-2 foot piece of sheet metal from
Ace Hardware. I attached the latter to the RV top using industrial 3M
dual lock tape at the corners, and strips of 3/16" weather seal
underneath to prevent rubbing.

I have no clue how big the ground plane is supposed to be, or if it's
needed for transmit as well as receive, but I could hear pattern
traffic at an airport 30 miles away.

2NO

[Darryl Ramm]

On Dec 27, 4:43*pm, Tuno > wrote:
> Absent any better ideas, I took the whip antenna I once used on my
> Honda Pilot and mounted it on a 2-by-2 foot piece of sheet metal from
> Ace Hardware. I attached the latter to the RV top using industrial 3M
> dual lock tape at the corners, and strips of 3/16" weather seal
> underneath to prevent rubbing.
>
> I have no clue how big the ground plane is supposed to be, or if it's
> needed for transmit as well as receive, but I could hear pattern
> traffic at an airport 30 miles away.
>
> 2NO

Saying it is' a "whip" does not tell us much. For 1/4 wave (radiator
about 2 feet long) and 5/8 wave designs (radiator about 5 feet long)
start with a ground plane at least the length of the radiating
element. A 1/2 wave (radiator about 4 feet long) antenna could still
be a whip but does not need a ground plane. If the old antenna had a
coil loaded base etc. you must use that on the new installation, e.g.
you can't just mount the whip unloaded on a threaded bolt.

An antenna transmit and receive properties are identical. A ground
plane if required works the same in both directions.

A lot depends on how much work you want to do, how large an antenna
you are willing to put up with, how you want to trade off beam shapes
(how much is the antenna beam oriented towards the horizon vs.
vertical), etc. etc.

Personally if mounting on the roof I'd use a 5/8 wave with a metal
sheet ground plane or I'd hoist a 1/2 wave antenna up on a PVC conduit
or fiberglass pole. Ham radio stores (like Ham Radio Outlet) often
have staff that can help.

Darryl

[Darryl Ramm]

On Dec 27, 9:34*pm, Darryl Ramm > wrote:
> On Dec 27, 4:43*pm, Tuno > wrote:
>
> > Absent any better ideas, I took the whip antenna I once used on my
> > Honda Pilot and mounted it on a 2-by-2 foot piece of sheet metal from
> > Ace Hardware. I attached the latter to the RV top using industrial 3M
> > dual lock tape at the corners, and strips of 3/16" weather seal
> > underneath to prevent rubbing.
>
> > I have no clue how big the ground plane is supposed to be, or if it's
> > needed for transmit as well as receive, but I could hear pattern
> > traffic at an airport 30 miles away.
>
> > 2NO
>
> Saying it is' a "whip" does not tell us much. For 1/4 wave (radiator
> about 2 feet long) and 5/8 wave designs (radiator about 5 feet long)
> start with a ground plane at least the length of the radiating
> element. A 1/2 wave (radiator about 4 feet long) antenna could still
> be a whip but does not need a ground plane. If the old antenna had a
> coil loaded base etc. you must use that on the new installation, e.g.
> you can't just mount the whip unloaded on a threaded bolt.
>
> An antenna transmit and receive properties are identical. A ground
> plane if required works the same in both directions.
>
> A lot depends on how much work you want to do, how large an antenna
> you are willing to put up with, how you want to trade off beam shapes
> (how much is the antenna beam oriented towards the horizon vs.
> vertical), etc. etc.
>
> Personally if mounting on the roof I'd use a 5/8 wave with a metal
> sheet ground plane or I'd hoist a 1/2 wave antenna up on a PVC conduit
> or fiberglass pole. Ham radio stores (like Ham Radio Outlet) often
> have staff that can help.
>
> Darryl

I meant to say ground plane *radius* at least the length of the
radiating element...

Darryl

[Tuno]

> Saying it is' a "whip" does not tell us much.

It's a 64 inch whip on a Radiall/Larson magnetic base that contains
the frequency matching coil, from Tim@W&W.

If I understand you, the ground plane *radius* has to be at least 64
inches. That's one big piece of sheet metal! I'll have to make due
with 12, unless that's going to bother my radio when I xmit.

2NO

[Andy[_1_]]

On Dec 27, 5:43*pm, Tuno > wrote:
> Absent any better ideas, I took the whip antenna I once used on my
> Honda Pilot and mounted it on a 2-by-2 foot piece of sheet metal from
> Ace Hardware. I attached the latter to the RV top using industrial 3M
> dual lock tape at the corners, and strips of 3/16" weather seal
> underneath to prevent rubbing.


Please consider how the people driving behind you will feel when that
unzips or unsticks at 75 mph.

Andy

[Tim Mara[_2_]]

ground planes (radiation surface)really can never be too big but often there
are times when the "ideal" ground plane just simply cannot be used...as a
simple rule of thumb the ground plane radius can be equal to the radius of
the length of the conducting mast...with this as a ROT you'll find the
typical ground plane for a 5/8 wave antenna tuned to 118-136 MHz is going to
be quite large. A car, van or SUV roof top though is getting pretty close to
the ideal even for a long mast like this...also keep in mind the ground
plane may not always be the center of the mast, in these cases the signal
sent may be better from the area or direction with the most ground plane...
Even when it isn't possible to have a single large metal ground plane you
can use simple foil tapes (Home depot) "metal" duct tape or even copper or
metal wires in a radial "X" Pattern (like the whiskers (ground plane)you see
on many base antennas...
also ideal...not always available...in the case of your handheld radio the
radio itself is the ground plane.........certainly not anywhere near the
"ideal" but it works....with some necessary compromise (BTW, your handheld
antenna isn't really 6" long but is a coiled 1/4 Wave mast equal to about
22"-24" for airband... even many glider manufacturers have installed simple
rubber duck antennas in gliders for ELT antennas using little more then the
coax cable running back to the ELT.....certainly not ideal...but a
compromise that will still work....with limitations.
Best to try the antenna/radio combination with a SWR meter..try adding and
removing mast and ground plane where possible and get the best signals
output you can for your situation...it may be a compromise but all things
considered may be the best you can possibly get..and likely, quite good
enough
tim

Please visit the Wings & Wheels website at www.wingsandwheels.com


"Tuno" > wrote in message
...
>> Saying it is' a "whip" does not tell us much.
>
> It's a 64 inch whip on a Radiall/Larson magnetic base that contains
> the frequency matching coil, from Tim@W&W.
>
> If I understand you, the ground plane *radius* has to be at least 64
> inches. That's one big piece of sheet metal! I'll have to make due
> with 12, unless that's going to bother my radio when I xmit.
>
> 2NO

[Tuno]

I rarely drive it faster than 62 and it's in a wind shadow, but good
point, I've added a safety lanyard.

[Eric Greenwell]

Tim Mara wrote:

> Best to try the antenna/radio combination with a SWR meter..try adding and
> removing mast and ground plane where possible and get the best signals
> output you can for your situation...it may be a compromise but all things
> considered may be the best you can possibly get..and likely, quite good
> enough

If you can get the SWR under 3, good enough. You probably know a pilot
or ham with a meter, or you can buy an adequate one from Radio Shack. A
CB meter is fine, even though it's frequency rating is lower than we use.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[Andy[_1_]]

On Dec 28, 10:27*am, Tuno > wrote:
> I rarely drive it faster than 62 and it's in a wind shadow, but good
> point, I've added a safety lanyard.

If you decide to go to a bigger ground plane I have a suggestion.
Years ago I needed a quick and cheerful ground plane for a magnetic
base antenna and I found that auto drip trays made of galvalized steel
were available at quite low prices (Checker, Pep Boys, Autozone) and
work quite well. Mine resided on the patio roof on the El Tiro club
house for a while. Pehaps it's still there.

Andy

[Tuno]

Andy,

I decided to go with a bigger ground plane and followed your
suggestion.

There is now a patio on top of my RV <g>. It's a little top heavy (a
hot tub and 5-burner grill will do that), but wtf, there will be
killer stargazing at Parowan, where applicants outnumber the 18M
nationals 42 to 1, 182 days out.

~tuno (really ... not counting the days)

[Alan[_6_]]

In article > Tuno > writes:
>> Saying it is' a "whip" does not tell us much.
>
>It's a 64 inch whip on a Radiall/Larson magnetic base that contains
>the frequency matching coil, from Tim@W&W.

What frequency are you planning on operating on?

If it is around 123 MHz, and a 1/4 wave, it should be about 23 inches
long. For a 5/8 wave, I calculate 59 inches in length.

>If I understand you, the ground plane *radius* has to be at least 64
>inches. That's one big piece of sheet metal! I'll have to make due
>with 12, unless that's going to bother my radio when I xmit.

The ground plane radius should be about 1/4 wavelength plus about 5%
(these figures from radials such as wire). The wavelength at 123 MHz is
about 96 inches, so 1/4 wavelength would be 24 inches. Add 5 % and you
would build with radials of 25.2 inches. Planting the magmount somewhere
near the middle of the roof should do just fine.

Note: this is for a 1/4 wave antenna. For a 5/8 wave antenna, the
ground current should be lower due to the higher base impedance, so the
ground plane will have less impact. I suspect that the 64 inch whip was
added to a 5/8 wave base transformer, and may be just a bit long for the
aircraft band.

On top of a motor home, a 64 inch whip will hit a lot of things as you
drive.

Alan
wa6azp