:headbang:headbangwhat is the best mobil antenna I cant find it and is a fiberglass antenna like a Wilson silver load or a fitestick antenna better then a base load like a Wilson 1k or 5k antenna thanks
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antenna wars
- Thread starter 959
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Big and ugly will probably out-do a small and un-intrusive antenna. After that it's going to depend on the user and what he/she can put up with. A 1/4 wave is the standard for mobile antennas on 10/11 meters. Antennas much shorter than that are going to loose a little performance because of that shortness. Maybe not much, but always some.
You have to decide what's the 'best' for you.
- 'Doc
You have to decide what's the 'best' for you.
- 'Doc
When it comes to large volume commercially manufactured Mobile antennas, the best performers in the loaded 1/4 wave market came out in the following order: The A/S Big Momma, the K-40, Wilson 1000, Wilson 5000 and now the Sirio 5000. Many will claim center loading or top loading has advantages with efficiency. To some extent this is true so long as the loading to reach 1/4 wave resonance and impedance matching to 50 ohms can be handled individually.
The center and top loaded antenna supporters often forget that base loading has its advantages too. It provides us with a convenient place to ground the end of the loading coil and feed the coil at an appropriate tap point to match resonance AND impedance SIMULTANEOUSLY. Top loading would be ideal if we could bend the ground plane of the vehicle to simulate a 45 degree angle and match the 50 ohms.
Without the ability to add an inductor between the feedpoint and ground you are likely to trim the whip to get the VSWR as low as it will go but never reaching a perfect 1:1 match. This forces a compromise between best resonance and best impedance match. Base loading eliminates this issue because you have two separate inductors. One to handle impedance and one for resonance.
Having said all that, none of it really makes a big difference in performance like night and day. Without the matching inductor you'll probably have a VSWR around 1.3:1. Perfectly acceptable. What really matters is putting the longest antenna on the vehicle that you can tolerate and to place it directly on top of the largest area of metal possible.
For example, if the choice is a 4 foot whip on the roof of a pickup or a 6 foot whip on a mirror mount, always go with the slightly shorter antenna placed in the superior location. One with more metal under the antenna. Running ground wires to the antenna mount doesn't even come close to having the metal under the antenna. Remember that reflection off the metal makes up the other 50% of your mobile antenna.
The center and top loaded antenna supporters often forget that base loading has its advantages too. It provides us with a convenient place to ground the end of the loading coil and feed the coil at an appropriate tap point to match resonance AND impedance SIMULTANEOUSLY. Top loading would be ideal if we could bend the ground plane of the vehicle to simulate a 45 degree angle and match the 50 ohms.
Without the ability to add an inductor between the feedpoint and ground you are likely to trim the whip to get the VSWR as low as it will go but never reaching a perfect 1:1 match. This forces a compromise between best resonance and best impedance match. Base loading eliminates this issue because you have two separate inductors. One to handle impedance and one for resonance.
Having said all that, none of it really makes a big difference in performance like night and day. Without the matching inductor you'll probably have a VSWR around 1.3:1. Perfectly acceptable. What really matters is putting the longest antenna on the vehicle that you can tolerate and to place it directly on top of the largest area of metal possible.
For example, if the choice is a 4 foot whip on the roof of a pickup or a 6 foot whip on a mirror mount, always go with the slightly shorter antenna placed in the superior location. One with more metal under the antenna. Running ground wires to the antenna mount doesn't even come close to having the metal under the antenna. Remember that reflection off the metal makes up the other 50% of your mobile antenna.
Isn't the ground the ground plane and the vehicle the capacitor ?
But mounted high enough the ground won't affect it as much?
But mounted high enough the ground won't affect it as much?
If the vehicle is very small in terms of the wavelength or frequency being used, you are more dependant on the vehicle forming a capacitor to earth ground. This is the case on bands like 80 meters.
As you go up in frequency the ground plane relies on the metal of the vehicle itself. That is the case on 11 meters. I could park my car on the top open floor of a parking garage and get out much further than ground level. On 75 meters AM that spot sucked but ground level was good.
