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.

Brian,

Here is an idea to try... an off-center-feed L-dipole. It works this way: calculate the resonant length for the frequency of interest plus 3%; make your vertical arm 2/3 long. Make a second arm 1/3 long and mount it 15 to 30 degrees above horizontal Connect inner coax to the long vertical arm. Connect braid to the shorter arm then adjust its length and angle to lowest SWR. A telescoping antenna is useful at this point. You will find that there is one point where the impedance is exactly 50 ohms.

This antenna is directional. There will be gain towards the side arm direction and stronger gain horizontally from the side arm. Signals on the back side will be weak. Take some care which way you set up. Get the arms as high off the ground as possible to get lower angle of radiation and less power adsorbed by the ground and the hot side arm out of reach when transmitting.

Dick, KK4OBI