The following doesn't always get brought up in discussions of the venerable 102" stainless steel whip for use as a high reliability, broad-banded, good working antenna for 10-11-12 meters.
Very common for CB
. This antenna will be a full 1/4 wave ground plane.
What is commonly found on many vehicle installations is that you put this whip on by itself and find find that the SWR is not flat in the CB
area, say in the middle at channel 20.
Common to find again that with testing it is discovered that the center resonance point is further up the band. The math will show that the center resonance point on 102" is right about at 27.520 mhz or "Channel 52" for you sophisticated raydideo operators. Checkout and save the 1/4 ground plane calculator below. Amateur Quarter Wave Ground Plane Antenna Calculator
So why is this? Why do they make and market the 102" whip as a ready-for-CB
antenna when actually it is not ready for CB
(many installations) and has to be lengthened to be resonant square in the CB
band, commonly accomplished by adding a 4 inch heavy barrel spring, or by using a solid Shaft Extender?
I don't know. I just know that on my pickup and every vehicle I have ever run one on, and as most of the locals around here find....you must do something to lengthen the 102 to make it flat line the SWRs in the CB
band....which is critical when running an amplifier....which is always best run with no or very little SWR.
This is a good lesson for newbies in particular as one might expect to simply go to a CB
antenna seller, purchase a made-for-CB
antenna, slap it on the car and expect it to work with no tuning or adjustments....and particularly so for the 102 whip that appears to be complete and there isn't anything to adjust anyway.
So most installations require the addition of the 4 inch spring which has a wire running up inside it, which effectively lengthens the whip another 4 inches.
Even that is insufficient on some installations and even more lengthening is required. This was so on my pickup and I had to add 6 more inches to achieve at flat SWR across the CB
area. I used a 6 inch Shaft Extender from Monkey Made Antennas for this.
There is another handy solution. MFJ still makes a 108" Stainless Whip which should be just what the doctor ordered and should give excellent resonance on CB
by itself. Their part number is MFJ-1966 and they are $26.95 which is a reasonable price. (Their) problem here is - because it is so long it is an oversize package for shipping and the shipping on these costs more than the antenna does....unfortunate.
But still is less than what you would pay for something like a new Wilson 5000 magnet mount.....so cost is relative.
Just something to think about when considering the 102
Again it makes me wonder why all the manufacturers didn't just offer a 108" all along.