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| Bluest Member Since: 23 Apr 2016 Location: Lancashire Posts: 3996   
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Madtom, thanks for the information although this just makes things more complicated than ever!
I do have the option to mount the antenna above the rear door, there is an unused grommet there that I could pass the coax through although it's not my first choice as I would need to find some sort of gland to properly waterproof it. I could potentially mount it on the bull bar at the front (Aussie style!) too, which I would prefer, but is the lack of height not a problem? In either case I don't see it being easy to run the antenna cable away from the metal body of the car. If all I have to wire an earth from the mount to the car chassis is auto electrical wire, is that a waste of time then? 2007 110 TDCi Station Wagon XS |
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7th Aug 2019 5:47pm |
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| MadTom Member Since: 10 Sep 2013 Location: Olomouc Posts: 572  
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I may not it wrote right - problem is not the coaxial cable, just not place it directly next to other cables, like cables to injector. Antenna wire is the 1,5m long wire on the top of the antenna base - the antenna itself.
Aussie style - you are right, or just look on military car - Hummer with long antennas od bullbar, old Series with antenna boxes on top of front fenders. Military have already solved the right place for antennas. "Drobek" = The Small One - Discovery 2, "Blufínek" = The Blue Thing - Defender 130, and for me at least Ford Mondeo  |
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7th Aug 2019 5:57pm |
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| landy andy Member Since: 15 Feb 2009 Location: Ware, Herts Posts: 5416 
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The base as in where you mount it, so was roof bar, now gutter mount.
A magmount aerial works, and that is only earthed via the coax cable. |
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7th Aug 2019 6:20pm |
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| MadTom Member Since: 10 Sep 2013 Location: Olomouc Posts: 572
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Mag mount is also earthed over capacitance between roof and mag mount itself. But on CB they are not good, compared to some sort of clip.
But on Defender they are no usable, they don't hold on alu. There is a large difference between earthing (= connecting to car body) for lights (= DC) and for CB antenna (= 27 MHz). The earth connection must be the right for the working frequenci. For light it is just DC, and you have to car for resistance, for CB antenna, if has to have very low inductance at frequency 27 MHz, and it is not easy to make a measure. Best way is to use antenna holder and place, that does not need any extra earthing. "Drobek" = The Small One - Discovery 2, "Blufínek" = The Blue Thing - Defender 130, and for me at least Ford Mondeo |
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8th Aug 2019 6:34am |
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| gilarion Member Since: 05 Dec 2013 Location: Wales Posts: 5084  
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I found an SWR meter great for tuning the Arial
SWR meter The SWR meter or VSWR (voltage standing wave ratio) meter measures the standing wave ratio in a transmission line. The meter can be used to indicate the degree of mismatch between a transmission line and its load (usually a radio antenna), or evaluate the effectiveness of impedance matching efforts  Click image to enlarge For those who like Welsh Mountains and narrow boats have a look at my videos and photos at.. http://www.youtube.com/user/conwy1 |
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8th Aug 2019 12:15pm |
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| ianmacd Member Since: 02 Mar 2018 Location: Sussex Posts: 2 
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A few observations here.
I have a dual band (2m/70cm) antenna on a gutter mount above the rear door and it works fine. It is a decent diamond mount though. No 'ground' needed for mine as I picked a half wave antenna but by ground what you actually mean by ground is the other leg of what is effectively a dipole antenna. It doesn't need to be connected to the body or chassis at all, it just has to be an effective counterpoise to the vertical section. This is easiest done by connecting to the body though especially at HF wavelengths like cb were it was pointed out, any mobile antenna is a compromise. A quarter wave ground plane antenna at 27MHz would be almost 3m long. If you don't have an effective counterpoise at the feed point of the antenna then the likely result is the outside of the coax braid will become the counterpoise and start radiating. In some antennas this is a desired effect but not for any mobile mounted CB antenna for sure. Lucky at only 4W you are unlikely to do any real harm to people. What you could do (and this is where measuring the reflected power is important and usually expressed as a ratio using a VSWR meter) is blow the 'final'/PA transistors in the radio so making sure your antenna system is well matched isn't just about achieving better range, its about making sure your radio survives when you 'key up'. Current: 2012 L322 Autobiography 4.4 TDV8 & 2016 Defender 90 XS both in Black. Past: RR L322 2008 & 2004, 2011D4, a few Disco2s, P38, RR Classic, couple of Disco1's, SIII SWB |
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8th Aug 2019 1:54pm |
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