It was a nice day to be outside so I decided to do a little antenna experimentation. Because the only thing that counts is real world results.
An elevated ground plane with sloped radials to achieve as close to a 50 ohm resonance as possible. Constructed out of thin 22 gauge wire to make the
bandwidth as narrow as you will ever see on a real world elevated ground plane antenna.(smaller diameter the radiator elements, the narrower the SWR
(And I did not cut/stagger the radials and vertical radiator to widen out the usable bandwidth. This is a straight cut antenna. All radiators/radials
cut to the exact same frequency.)
SWR measured right at the feed point. ZERO transmission line length.
First SWR set with the antenna trimmed to 27.2mhz.
(All readings have the “to 1” truncated)
That antenna would be usable up to 29mhz which would easily cover the N/T portion of the band 28.0 to 28.5
Second set, with the antenna retrimmed to 27.4
Again, that would get you past the 29mhz mark.with les than 2 to 1 swr.
Now we change the antenna design a bit. In the third SWR set, I set it up as a ground mounted vertical. Again with a 22 gauge vertical radiator and
enough ground radials to achieve about a 20 ohm ground resistance. With the 30 some ohms resistance of the vertical radiator, it should get me right
at 50 ohms resonant impedance.
Third set ground mounted vertical trimmed to 27.0 mhz
that 27mhz tuning still gets you under 2 to 1 at the top end of the N/T portion of the band.
Fourth set, ground mounted vertical trimmed to 27.5mhz
gets you to 29.25 with 2 to 1 swr. Which is right at the bottom end of the satellite downlink band. So you can cover about the entire point to point
SSB/CW portion of the 10 meter band.
Now, for the fifth set, I changed the vertical radiator to a 1/2 copper pipe cut for 27mhz. Again, on the same ground plane. It will exhibit a wider
operational bandwidth, more along the lines of what you will see in a normal real world factory cb base antenna built on aluminum tubing construction.
Which is about what I expected. Under 2 to 1 right up to the top of the 10 meter band (29.7mhz).
It will also be usable on the 12 meter band at around 1.6 - 1.8 to 1 swr.
Experience has shown me that an elevated ground plane using 1/2 inch elements will show about the same SWR spread, so doing that would be
If I cut the pipe to 28.25mhz, I should be able to get under 1.4 to 1 SWR across the entire 10m band and the cb band. All though, it would push it out
of the range of the 12m band.
Now in the sixth set, I changed out the vertical for a center loaded whip.
in the seventh set, I changed it out to a top loaded semi truck antenna.
As you can see, the two loaded antennas show a narrower bandwidth. On those antennas, you would have to adjust them to usable SWR on 10 meters. And
real world experience has shown me that if the antenna has an adjustment, then it can usually be pulled to 10 meters without any problem.
But for the full size unloaded CB antennas, they will be perfectly usable for 10m out of the box.
As I have stated before. After you have had enough experience, results will become repeatable. I already knew about what I would see before I cut the
first wire. Sometimes you just have to put real world data in front of someone before they will come to grips with reality. Even then, they will
often try to find ways to dismiss it.
So, there is the data, right in front of your face, but you can believe what you want, if it makes everyone happy,
edit on 10-8-2013 by Mr
Tranny because: (no reason given)