Efficient grounding to your mobile HF antenna
|Flat braided copper ground strap(Left:Tinned - Right:Plain)|
Lately ,and actually after i bought the Albrecht 2990 ,the first thing that came into my mind was to install a 10m band antenna to my car. Searching for an antenna i came across a cheap but well constructed 11m to 10m band antenna, tunable from 25Mhz to 30Mhz. The Alan S9. This antenna is a standard 1.5m vertical antenna commonly used for CB ,but with tuning you can easily make it for the 10m band. First thing to do because this is a tall antenna(but not heavy at all, bottom load) was to install a mount. For that application i used the same mount that i have used for my V-U antenna installation, which fits perfectly to my car. All ok till the procedure of tuning the antenna is necessary. I noticed that even following the instructions i could not achieve SWR less than 1.6 ,which is not bad for my qrp mobile station, but why not try and make it as perfect as possible.
In general ,one key element to make an HF antenna work on your car is good and multiple grounding to the chassis ,and some times ,if needed, to the exhaust system. Starting measuring for my grounding efficiency to the antenna, i noticed that it was very poor and in some cases non existent.
And now the major question!how can i achieve efficient ground from my antenna to the car's chassis? using off course copper wire to connect the antenna mount to the chassis. Well ,yeah easy to say, but not so much. This grounding cable must be very very good conductor, and by saying that ,must have around 10 times the standard copper wire(used for electric appliances)conductivity.
Here comes the answer...copper braided strap,used for grounding only! these straps ,comes to various lengths and widths. In your car use the smaller from factor strap because you do not want to have a "copper belt" hanging from anywhere. There are two kinds, the first one is the just a copper strap(cheaper), and the second one tinned copper braided strap(more expensive).
Plain copper strap
Pros: cheaper, lighter, more flexible
Cons: can bend easily, easily oxidized in humid environments
Tinned copper strap
Pros: Does not rust!!!, harder in general
Cons: approx. 40% more expensive, heavier, does not bend easily
For my car I've chosen the plain copper strap ,because the ground connection is inside the cabin, so does not come in contact with the elements, that can oxidized it. In other cases use the tinned strap ,because after a while you will end up with a green strap...except if you live in Nevada or Africa(places with no humidity, or very low humidity).In case you hear any engine noise you might want to consider to ground the exhaust as well.
Now the antenna is tuned to 1.2 to 1 SWR ,on 28.450Mhz!I've already have a couple qso's with only 4 watts!
73 de SV1JRF