Mud-club

Vehicle & Technical => Discovery => Topic started by: Wireless on February 27, 2007, 01:09:23

Title: Bull Bars
Post by: Wireless on February 27, 2007, 01:09:23

Hi All,

I need a fixing point for a remotely tuned digital Screwdriver Antenna, and it needs mounting at the front of the vehicle with some protection from brush/branches etc.

I plan an NVIS antenna installation with the whip section bent over and tied to the rear of the roof, which will provide both unbroken HF coverage up to 150 miles, and be good for ducking under low trees and bushes.

So, I believe I need a Bull Bar for the 1996 Discovery (unless anyone has another solution), I've never considered one before, so has anyone a good recommendation?  Just remember I'll need to Earth it.

Title: Bull Bars
Post by: muddyman on February 27, 2007, 02:23:48

http://www.hamradio.co.uk/acatalog/Mounts.html

Any thing here any good?

Title: Bull Bars
Post by: Wireless on February 27, 2007, 13:56:15

Quote from: "muddyman"

http://www.hamradio.co.uk/acatalog/Mounts.html

Any thing here any good?

There's some good mounts on that site.  The Screwdriver usually comes with a substantial bracket to mount the antenna for DX working (other side of the planet), but I'm more interested in mounting the antenna for NVIS purposes (within a 150 mile radius), hence considering Bull Bars as a place to fix an NVIS mount.

Has to be substantial, here's an example of a Screwdriver antenna

http://www.wsplc.com/acatalog/Tarheel_HF_Mobile_Antennas.html

Any links for Bull Bars?

Title: Bull Bars
Post by: muddyman on February 27, 2007, 15:50:01

I am only a M3  :(  so still got lots to pick up. Bull Bars have a look on ebay.

Title: Bull Bars
Post by: J.D. on February 27, 2007, 16:52:01

I have a set of Disco bull bars off my Disco, they have a rust hole in one of the bars, (about 1") long and one of the brackets is twisted slightly, but other that that the are fine and nothing a hammer and a vice couldnt sort out.

Free, collected from Winchester.

Title: Bull Bars
Post by: Wireless on February 28, 2007, 14:44:21

Quote from: "J.D."

I have a set of Disco bull bars off my Disco, they have a rust hole in one of the bars, (about 1") long and one of the brackets is twisted slightly, but other that that the are fine and nothing a hammer and a vice couldnt sort out.

Free, collected from Winchester.

Thanks for the very kind offer, amazing people on this forum.

But before committing to a particular design, I'm going to have to look at a few websites showing them fitted, plus actually see a few Disco's close up with them fitted, otherwise fitting of the antenna mount/antenna might be made more difficult.

I might even have to come to a Mud Club meet and take a look around!

Title: Bull Bars
Post by: Tyke on March 01, 2007, 02:31:05

You a radio ham? . . . . most of us just bolt on anywhere suitable . . . . . certainly good enough for normal off-road coms.

Title: Bull Bars
Post by: Wireless on March 01, 2007, 09:36:46

Quote from: "muddyman"

I am only a M3  :(  so still got lots to pick up. Bull Bars have a look on ebay.

Well NVIS (Near Vertical Incidence Skywave) propagation suits low power, 10W is all that's needed for communications up to 150 mile, it relies on a take off angle for signals at between 60 to 90 degrees and is best suited on low dipoles or inverted-V wire antennas.  So not expensive either!

As you can imagine, NVIS antennas are a challenge when mobile, but the usual solution is tilted whips.

As an M3 you've access to NVIS frequencies (in UK) of 160m to 40m, so there's nothing special about it, Allied Ground Forces first used NVIS during the invasion of Normandy in 1944, so it's really old technology.

Here's a few links you might find interesting,

http://www.raynet-hf.net/tiki-index.php

Here's an explanation of NVIS Propagation;

http://www.raynet-hf.net/tiki-index.php?page=WhatisNVIS

Here's someone's 4x4 you might recognise;

http://www.raynet-hf.net/tiki-browse_gallery.php?galleryId=4

Drat, you all know my first name now...

73 de Wireless

Title: Bull Bars
Post by: Wireless on March 01, 2007, 09:57:44

Quote from: "Tyke"

You a radio ham? . . . . most of us just bolt on anywhere suitable . . . . . certainly good enough for normal off-road coms.

There's a bit of science as to where you should best mount an antenna for maximum performance, generally the centre of the roof is best for VHF/UHF & CB, but this may be impractical due to trees while off-road.

Using NVIS HF you can get a much better unbroken coverage for very little power, and although CB is on HF frequencies, it's to high a frequency to utilise NVIS Propagation, so CB at a legal 4W is a case of fingers crossed when it comes to comms over virtually any distance or topology.

Most of you have probably realised this, but found CB to be more effective over PMR446, which also a compromise because it's hand-held low power (500mW), and may have poor component and antenna design depending on the lottery of what you've bought.

The 10W VHF/UHF that muddyman is using with proper vehicle mounted antennas, is so much better that you'll always wonder why you ever opted for CB/PMR446.

For those Groups wishing to provide an Emergency 4x4 Response, getting Licensed as Radio Amateurs is not as hard as it used to be, and would immediately link you with the local RAYNET Group Control that your County Council Emergency Planning Officer relies upon to provide Emergency Communications; just ask muddyman how easy it is to get a Licence.

If anyone requires any information regarding Amateur Radio Licensing, I am quite happy to direct you to both your Local Amateur Radio Club for Training/Exam, and your Local RAYNET Group, just send me a PM with your Location.