On Sunday, February 16, 2014 4:36:32 AM UTC-6, Brian Reay wrote:


What band or bands are you trying to work?



80m to 10m on this antenna, inc. 60m



I have antennas on the vehicle for VHF/UHF



--

73

Brian

G8OSN/W8OSN

www.g8osn.net

That makes it harder trying to do all bands.
It's often easier to pick only the bands one uses the most,
and compromise on the others.

In your case, I'd prefer string dipoles up between trees,
but it seems you lack the room for that.

My next choice would be mounting a mobile antenna on top
of the RV. You don't have to drive with it on, but if you
had an antenna mount on the roof to use, it would sure make
it easier to mount an antenna. You wouldn't have to worry
about a counterpoise, etc.. The RV would be it, assuming it
has a metal skin.
But I'd prefer using a normal coil loaded mobile antenna than
the auto tuned whip. I think the larger loading coil would
be more efficient, and better current distribution if center
loaded.

But I suppose you could improve the current distribution of
your 7m whip by adding some type of top hat, or top hat wires
or spokes.

The only drawback to a mobile antenna like say a bug catcher is
you have to be able to adjust the coil tap to change bands.
It may well be too high to reach on top of an RV.

So you'd probably have to yank it off the roof to change bands.
I have this on my mobile antennas, but I use a Hustler quick
disconnect, which makes it fast and easy.
I suppose a screwdriver antenna would be an easy route to
changing bands, but they are heavy and fairly expensive for
anything decent.

Myself, I camp a lot, and my usual setup 98% of the time
are 40 and 80 dipoles strung up in, or between trees.
Sometimes I run the two dipoles with one coax feed, sometimes
I make a single dipole, and use insulators with wire jumpers
to shorten a 80m dipole to 40m. Just depends what I have laying
around and how many trees are involved.
I don't worry about any of the higher bands. I can still use
them to a degree by using a tuner on the dipoles. Or tack on
an extra dipole if really needed. A 40 dipole works 15m as is
pretty well.
But I talk on 80 and 40 most of the time. 40 in the day, 80 at
night. And 160 if I have enough wire in the air.

wrote:
On Sunday, February 16, 2014 4:36:32 AM UTC-6, Brian Reay wrote:

What band or bands are you trying to work?

80m to 10m on this antenna, inc. 60m

I have antennas on the vehicle for VHF/UHF


That makes it harder trying to do all bands.
It's often easier to pick only the bands one uses the most,
and compromise on the others.


snipped for brevity

Thank you for your considered response, none of which I disagree with.

However, I am trying to avoid the need for trees etc. and having wires
crossing other peoples' pitches. We tend to have fewer trees on European
campsites.

The vertical is something I have experimented with prior to buying the RV
during club mini-field week sessions and had good results with. I
previously I ran out a number of radials but this are too much of a trip
hazard on a campsite. I can reduce it to one, about 5% longer than the
vertical but I was looking for something 'out of the box'.

The antenna is on a tripod.

On Sunday, February 16, 2014 7:55:35 AM UTC-6, Brian Reay wrote:


The vertical is something I have experimented with prior to buying the RV

during club mini-field week sessions and had good results with. I

previously I ran out a number of radials but this are too much of a trip

hazard on a campsite. I can reduce it to one, about 5% longer than the

vertical but I was looking for something 'out of the box'.



The antenna is on a tripod.

If you have to use the tripod, I would probably try to keep
the metal under the tripod as dense as possible, as that is
where a lot of ground loss is. A lot of short radials are better
than a few long ones for the same amount of wire.
Some type of screen or mesh that you could lay down might help a bit.

I found on mobile whips, the metal under the antenna is really
critical. I once ran a length of angle iron across the back of
my truck bed behind the rear cab window. It was well grounded,
and even had strap that ran from the bed sides to the base of
the antenna to make double sure it was well grounded.

It was horrible.

I finally came to the conclusion there just wasn't enough metal
under the whip, and just being well grounded by a strap was not
enough.
I moved the antenna over on to the top of the side tool boxes,
which are part of the truck, and gave more metal under the whip,
and the antenna came alive in it's normal fashion.
It was this experience which leads me to believe that trying
some kind of bumper hitch mount is basically a waste of time.
It may work, but nothing like it normally does on good metal.

I have another truck, and it's mount is on the side of the cab
with a big GE ball mount.
It's the best of the two. That antenna really cooks on that truck.

Most times I see true intelligence on this forum, but lately it makes me wonder...
An educated person wouldn't need tuners or multiple dipole antenna's to operate.
If you understood antenna's as well as you think you understand antenna's, you would realize that there are antenna's out there that does a little bit of everything - very well thank you - and that antenna tuners do not make your antenna resonant - just makes the transmitter happy.

There is a antenna out there that I know of that will work everything from 70 CM to 80 meters - with the exception of 15 and 30 meters - without a antenna tuner - it is called an off-center fed dipole...

Please - before you attack my post - look at this web site....
HY Power Antenna's - http://www.hypowerantenna.com/produc...er-fed-antenna

Before anyone talks any crap - please let me explain..........

I know the man that designed this antenna... He holds 27 US Patents.
K3CC

I used this antenna a couple of years ago for Field Days and I made hundreds of contacts - 100 contacts an hour on phone - with no amplifier and with the antenna just 30' off the ground.

While others were sitting on their hands doing nothing, I was busy in a pile up on 20 / 40 / 80 meters phone...

Yes the Kenwood TS 590 also had a lot to do with this, but the kicker was that there was an idiot there that was free-banding - hopping from one band to the next working digital that was causing a lot of interference to the other participants. I chose to just tune the bugger out. Others with lesser equipment were forced to wait until he was done before they attempted to work their bands while I just kept going.

There is a real neat video included with the web site that shows the operator using this antenna as low as 6' off the ground....
A man has got to do what a man has got to do!

"Channel Jumper" wrote in message
...
gareth;815654 Wrote:

[b]Then run a "shortish" earth braid from the vehicle's chassis to the
antenna.[b]

You are confusing earth ground with a counter poise..

No, I'm not.

To establish a counter-poise, the counter-poise needs to be directly
beneath the antenna.

No, it does not. You are providing the second half of a pendulum

Just hooking some braid to the antenna won't do anything.

Yes it will, taken together with the mass of the vehicle, as I suggested.

On Monday, March 3, 2014 2:28:21 AM UTC-6, gareth wrote:

Just hooking some braid to the antenna won't do anything.



Yes it will, taken together with the mass of the vehicle, as I suggested.

It's possible that connecting to the RV may improve performance
due to the antenna becoming a perverted dipole of sorts.
But as a means of lowering ground losses under a vertical, your
solution will prove to be quite poor.
But that it would actually act like a dipole seems fairly remote
to me.

And there is something that seems to confuse people about
short verticals used on vehicles and such. And I think could
also be applied to short verticals on tripods.
I've fairly much proven to myself that varying the length of the
metal on the ground side of the vertical usually does not convert
it to a different length dipole. Per say..

If this were the case, I would have to modify and re-tune my
mobile whips every time I changed to a different size vehicle,
or added other metal to the vehicle.
If the antenna acted as a dipole, I would expect to need to re-tune
in every change of vehicle or mount.
This does not happen.
These short verticals are still acting like verticals on the ground,
with varying numbers of radials, or metal mass, not perverted dipoles
slightly above the ground.

My mobile antennas are still resonant at the same frequency no matter
what vehicle they are on, big or small, and no change if I add extra
radial wires to the vehicle, or even connect directly to the ocean,
which I have done in the real world when parked next to the Gulf of
Mexico.

What does this tell me? That the metal under a mobile whip is
acting a lot more like a radial system, or even the ground itself,
than the other half of a physical dipole.

So what else does that tell me? That connecting a braid from
a tripod mounted short vertical to an RV is likely to not pan
out too well as far as reducing ground loss under the vertical.
In fact, I predict it to be fairly useless.

On Monday, March 3, 2014 10:51:14 AM UTC-6, wrote:
That the metal under a mobile whip is
acting a lot more like a radial system, or even the ground itself,
than the other half of a physical dipole.

It depends on where it is connected to the vehicle. If connected near the center, the vehicle acts like two opposing radials and radiates mostly omnidirectional. If connected on the rear bumper, it can act like one radial. On my S10 with a rear bumper-mounted 17m hamstick, my signal was quite directional beaming toward the front of the vehicle. I would sit in the parking lot at Intel and aim my S10 mobile antenna system. I often gained an S-unit by aligning the vehicle with my contact. The fact that the S10 was a quarter wavelength long on 17m probably helped.
--
73, Cecil, w5dxp.com

On Monday, March 3, 2014 12:52:37 PM UTC-6, W5DXP wrote:
On Monday, March 3, 2014 10:51:14 AM UTC-6, wrote:

That the metal under a mobile whip is

acting a lot more like a radial system, or even the ground itself,

than the other half of a physical dipole.



It depends on where it is connected to the vehicle. If connected near the center, the vehicle acts like two opposing radials and radiates mostly omnidirectional. If connected on the rear bumper, it can act like one radial. On my S10 with a rear bumper-mounted 17m hamstick, my signal was quite directional beaming toward the front of the vehicle. I would sit in the parking lot at Intel and aim my S10 mobile antenna system. I often gained an S-unit by aligning the vehicle with my contact. The fact that the S10 was a quarter wavelength long on 17m probably helped.

--

73, Cecil, w5dxp.com

I bet it still acted like a vertical near the ground though, instead
of a dipole low to the ground. For instance, I bet the hamstick
did not require a drastic re-tuning when mounted near the rear vs
mounted in the center.

So I still think in your case, it was acting more like a near
ground mount vertical with a fat radial to the front, rather than a
whip at the rear with the car being the other half of a dipole.

And strictly speaking, I suppose it is. Sorta.. Kinda..

But it's not acting like one in operation. It's acting like any
other short vertical that is near the ground.

I saw a bit of directivity when I had the antenna on the rear trunk
lid of a Monte Carlo in much the same way as your S10. It favored
the forward direction a tad. I don't notice too much directivity
on the trucks, but both have the antenna near the center.

Anyway, as it applies to the tripod vertical, I wouldn't expect
running a braid to an RV as a very effective way to reduce ground
losses below the antenna. And the chances of it pairing up with
the RV to produce a usable "dipole" of sorts are not likely to
pan out. Ground losses will still be high below the whip, and
I bet the RV will more likely resemble a big pile of earth a few
feet away, than a viable radiating element. :/
Unfortunately, the big pile of pseudo earth will be in the wrong
location to be of much help to the tripod mounted whip.

On Tuesday, March 4, 2014 5:22:18 AM UTC-6, Jeff wrote:
Also do not neglect the (considerable) capacitance of the vehicle body
ground to the the real ground.

I was on the top uncovered story of a three-story parking garage made of concrete and steel and the weather was dry.
--
73, Cecil, w5dxp.com

On Tuesday, March 4, 2014 10:19:49 AM UTC-6, W5DXP wrote:
On Tuesday, March 4, 2014 5:22:18 AM UTC-6, Jeff wrote:

Also do not neglect the (considerable) capacitance of the vehicle body

ground to the the real ground.



I was on the top uncovered story of a three-story parking garage made of concrete and steel and the weather was dry.

--

73, Cecil, w5dxp.com

Makes sense to me. You had a 4 ft wide solid metal appx 1/4 wave
radial system in the forward direction. So what was below the truck
shouldn't have really mattered much. Or at least in that direction.
Which is the whole point of having a dense "radial" system below
a low vertical. And even more critical with a low short vertical.

His is a 7m fishing pole fed with a auto tuner. Would be short on
40 and 80. I bet adding a few top loading wires would help on those
bands, but that's probably out of the question if he can't string up
dipoles and such. Maybe make some "L" spokes to clamp on the top with
a hose clamp. A wire connecting the outer ends of the spokes would be
even better. Would improve the current distribution. Or could add a
center loading coil for 40 and 80. That would help if no top loading.