How about an inverted "V", top of cab, and going down to the front fenders made from wire or fiberglass whips and shored up with fish line?
While I can't quote theory, I do know what works in trucks
With 2 loaded antennas matched for 50 ohms and even using 50 ohms coax, I would expect your feed-point impedance to be even higher around 100 ohms. This can be verified easily if you have an antenna analyzer one or know a real CB shop that has one.
This is a easy fix using a 2:1 balun. A balun is a transformer device used to balance an unbalanced feed-line for feeding a balanced antenna, Hence the name BAL-UN. At a 2:1 ratio, this means it will cut the feed-point impedance down at 100 ohms in half to 50 ohms which should give you a nice flat SWR match. 50 ohm coax cable is an unbalanced feed-line.
100 Ohms isn't going to be ideal. You won't get a big or even noticable difference in performance getting it down to 50 Ohms but the finals in your radio/linear will thank you for it.
If the mobile antenna system is measuring 100 ohms at the antenna feedpoint, then an analyzer should show a SWR at 2.1. That's why I asked the question and the responses say the impedances stay at 50 ohms using 50 ohm antennas and coax measured with an analyzer.fourstring,
I have made several 11 meter dipoles from Firestiks that seemed to work pretty well. I don't have an analyzer so I don't know their impedance. Is 100 ohms harmful to the radio? Will reducing it to 50 make a big difference in performance? I don't know how concerned I should be about it.
Thanks.
That's why I asked the question and the responses say the impedances stay at 50 ohms using 50 ohm antennas and coax measured with an analyzer.
I had the same issue with CMC when I tried it years ago on my mobile to where it wasn't worth trying to surpress it especially when running power.I had to use a choke on the antenna as it had serious CMC issue
Riverman71, here is a good link that explains a lot about VSWR and impedance matching. Actually has a tool at the bottom for calculations.
http://www.cdt21.com/resources/TechnicalTools/vswr1.asp
Hope this helps a little.
Thank you, 222.
That site is full of great info! However I was unable to find a way to compare the differences in impedance between a horizontal dipole and an inverted V dipole.
If a horizontal has an impedance of 75 ohms, what can one expect after changing it to a 90 degree inverted V? 65? 55? 35? Am guessing lots of guys have experimented with the two types and am curious what they found.
Thanks!