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!
Incoming Region Produces X3 Solar Flare |
May 15, 2024 @ 14:55 UTC |
Another major solar flare, but this time from an active region just beginning to turn into view off the east limb. It is possible that the group responsible is old AR 3654 from the previous rotation. The latest flare, an X2.99 event just peaked at 14:38 UTC (May 15). Stay tuned |