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+--- Thread: Pt 1 No Holes, Screws, Clamps Antenna Mount (/thread-626.html)
Pt 1 No Holes, Screws, Clamps Antenna Mount - VK6ZFG - 10-09-2018
I am not keen on the through glass antennas. I do use these but they never seem to perform as well as “real” antennas. They are not suited to lower frequencies. One on VHF has even cost me a PA stage!
What I do use is an antenna bracket fitted directly onto the glass of the windscreen using double sided tape (preferably of the outdoor type).
This evolved from a RFI product which since seems to have disappeared. It was made of plastic and was intended for smaller antennas of the ground independent type.
It was made form plastic so had low strength and only a small
area in contact with the glass.
This was improved by an additional support but found it could be better for use with longer antennas.
This mounting approach does have certain advantages and so resulted in a number of custom made metal antenna brackets being made and used successfully.
See Continued Post.
Igor
VK6ZFG
Pt 2 No Holes, Screws, Clamps Antenna Mount - VK6ZFG - 10-09-2018
Early two piece unit still in use made from steel strip on hand.
Later single piece custom made from aluminium to cater for wiper sweep.
This was found to have some flexing with a 50MHz whip so an additional support was added (difficult when already in situ!).
Two piece aluminium bracket on other side of vehicle with dual band VHF/UHF end fed antenna.
What is important in the design is to have a large area in contact with the glass and dual support on the bracket. The simpler “U” shape was found to not work as well.
A dual support bracket can be made from one piece of metal but it is much easier to make one from two independent pieces.
The bracket needs to be customised for each vehicle using the space available on the glass after allowing for the wiper blades sweep area. Usually the LHS and RHS brackets not being not mirror images of each.
This type of antenna mount is ideally suited to VHF and UHF ground independent antennas where only a nominal ground is required. It does not suit antennas on the higher frequencies that rely on a good earth as even when an earth lead is provided it is too long to be effective. However I also always include an earth lead on principle.
50Mhz with a slightly short base loaded quarter wave whip (so as to fit in the garage) I have an additional quarter wave length of wire to provide some additional earthing aid though it does not really seem to need this on this band.
This system enables SO239 base antennas to be removed or changed as required.
Igor
VK6ZFG