Steel Whips

[Wil]

No not the kind you find in those XXX stores...

I am talking 108" whips, what is the consensus here? Is there anything (steel whips) a little shorter? But taller than 4'? I have heard about them hitting spotters, so cant you cut a 108" shorter?

[wizbang]

You can always put a hook on the rollbar and keep it hooked when wheelin, you should be able to hear the crew you're with. Then you can unhook it when you are on the road to hear everything else.
:bigsmile: No headless spotters that way
:chainsaw:

[cherokeefever]

I have used 108" steel whips for several years on my Cb sets, and have had great luck with them. I do tie them down when I have to go off-road. and sometimes while I am driving down the highway as wel, and I still get pretty good reception and transmission capabilities with it tied down. I also have trimmed the tall steel whips down to make shorter ones as well and have had some success with them in other applications (like my cars and other on-road vehicles). Good luck wiht your choice on CB antennas and I hope that my $.02 here has helped you some.

[Snotty]

Radio Shack has a 60+ inch antenna. I have run mine for 4+ years now and it works great. Had the 108 and decided it was overkill. Got better reception, but I don't feel the need to talk to truckers in Kansas when I am wheeling... :D

[Wil]

What does trimming down a 108'' do to the SWR, is there any way to change the effects that it may or may not have?

[Jerry Falletta]

Trimming down an antenna will raise the resonant frequency of that antenna. The original length of 108 inches was intended to 1/4 of the wavelength of a signal at the perceived "middle" of the original (23-channel) Citizens' Band; channel 19, by the way, is the actual middle of the current 40-channel band. If you use the formula to determine a quarter wavelength (how long a basic vertical antenna should be in this case), you would arrive at a length of 103.29226 inches (234 divided by the frequency in megahertz = length of the antenna in feet). The bottom line is that these numbers are somewhat arbitrary because of other factors which affect the resonant frequency of an antenna. Using the above formula, a length of approximately 105 inches would probably be optimum, but that depends on many other factors.

A simple way to demonstrate the effects of wavelength and resonant frequency is to fill a soda bottle approx 1/3 full with water or other liquid. Blow air across the top of the bottle to make it "whistle." Next, add water to halfway up the bottle (this will reduce the length of the air space between the surface of the liquid and the top of the bottle), and blow air across the top. The resulting pitch (frequency) will be higher. As the vertical air space is lessened, the resonant frequency is raised. Conversely, if the air space is increased, the resonant frequency is lowered - this happens as you drink the soda from the bottle and blow air across the top at various intervals. Another example of this is the pipe organ... different length pipes for each pitch..... or the guitar string... shortening the distance between the bridge and the fret where you apply finger pressure will raise the pitch generated by that string.

Should you cut approximately 4.7 inches from your 108" whip? That is up to you, but once it is cut, you can't reattach it; measure (at least) twice.... cut once :D.

If you are cutting or adjusting any antenna, the use of a good SWR/wattmeter is essential. I settle for nothing less than a Bird (model 43) when I do this stuff. The cheapie units will pick up the radio signal from points other than the antenna connections and this will adversely affect the accuracy of the readings. Using a meter that is not calibrated to the frequency range being tested will also result in errors. This is why I stick with the Bird units - not cheap, but they work every time. Unless you do a reasonable amount of antenna tuning, the Bird will probably be a bit expensive, so I would recommend asking a friend who has one for some help. A number of Amateur ("Ham") Radio operators have these because we play with this stuff a lot; we are radio geeks and proud of it :D.

A good start is to find the resonant frequency of the antenna before doing anything. Record the forward and reflected power at the bottom and the top ends, as well as in the middle of the frequency range to be used. If the antenna favors the higher end of the range, then do not cut anything. If the antenna favors to lower portion of the range, then some slight adjustment in very small increments may be in order.

Keep in mind that the difference between a 1.2:1 and 1.5:1 VSWR (Voltage Standing Wave Ratio) is negligible at a power level of four watts, the difference would be approximately 0.16 watts. Always check the resonance at both ends of the frequency range before and after each adjustment. These adjustments should be made with no interference from nearby structures; this includes closing the hood, trunk, and doors of the vehicle while measuring, as well as keeping away from trees, buildings, and other structures.

Another thing to keep in mind is that "tuning" the coaxial cable is not actually worthwhile; it only occasionally appears that way. If the connectors are properly fastened to the cable, and the length of the cable is not excessive (a 50-foot run of cable for a ten foot distance between radio and antenna is excessive), then it should be OK.

[Wil]

Hmm I think I understand. Dont cut the whip to suit your needs, adjust the whip to the radio. So I need to buy a shorter whip and tune that..

[Jerry Falletta]

An "electrically shortened" antenna may be the answer if the nine-footer is just too much of a pain. Keep in mind that the shorter antennas are usually less efficient, but they usually work as well for most purposes.

One more thing to further confuse the issue.... a center-loaded (coil located somewhere up the antenna) antenna may radiate and receive signals better than a base-loaded (coil at the base), not much of a difference, but for the purist it may be noticeable. The down side of the center-loaded antenna is that it flops around more and makes for a "wavy" (varying strength on the S-meter) signal when it flops around.

The problem of efficient antennas being too long only occurs at the lower (below 50 mHz) frequencies. At the higher frequencies, antennas are naturally shorter, and can be made more efficient with the addition of adding a loading coil to effectively "electrically lengthen" and tune the antenna to a specific frequency range (i.e., an external cell phone antenna mounted on the roof or glass).

[Scorpion]

There's a place off of quebec and I-70 in denver that will "tune" your antenna for you for free (if you buy one there). If what you said is true Jerry, how do they accomplish this without messin' things up? The guy there said that the placement on the vehicle is almost as important as the length. Thoughts?

Matt

[Wil]

Ok then..thouroughly confused now. I dont think that I will be buying a whip...at least one that long. Radioshack sells one they tout as an AllTerrain steel whip. It is 66" and has what appears to be a spring at the bottom.