CB Antenna Length

[Tic Wilson]

The CB antenna broke off, leaving the spring mount unscathed, (probably low tree limb) and is only a stubby now.  I have ordered a replacement, and it is standardized at 48".  I no longer carry a standing wave meter, so does anyone know  approximately how long the antenna should be? Quarter wave of a CB antenna is 108", So I would 1/2 that until I arrive at best (shorter than 48") length, or approximately 27"??  No rush, and thank you!

[Keith Moffett Co-Admin]

Doesnt it have to be fine tuned with a meter regardless? 

[Tic Wilson]

that would be ideal.

[Jerald Cate]

1/4 wavelength for CB is approximately 102 inches so 1/2 that should be around 51 inches.  If you just bought a new antenna I would just put it in the base and use it as receive only until I could find a CB shop around a truck stop somewhere.  Have them tune the antenna to the frequency you use the most to transmit on probably Ch 19.

[Tic Wilson]

Thanks, that is what I will do.  I usually only turn it on and listen when the traffic is backed up and I'm wondering why.  I very rarely use it for transmit.  I only asked the question because it seemed that the original was not that high.  On the other hand, every source I checked show a 48" replacement.  Thanks again.

[Gerald Farris]

Tic,
From my experiences with C/B antennas on the roof of coaches over the years, I never use one longer than 24 inches because you will break it off if it is any longer, and I have even broken several 24 inch ones. The C/B antenna on my coach now is a factory tuned 24 inch stainless steel whip that is tilted back at about 45 degrees, and I was hitting it on underpasses often enough to break off a fiberglass antenna last summer in Michigan.

Gerald   

[Larry Moore]

Gerald

Same here, I have broken three fiberglass antennas so far.  Now have a 18" "rubber duckie", working fine.  No SWR adjustment required, just works.

[Bill Lampkin]

Broke of the fiberglass 'Firestick' antenna first trip. Replaced with a 24" whip and spring mount. I have a Radio Shack SWR meter and used it to try to tune the antenna. I found that a very small adj of the antenna in the mount made a big difference in the SWR. I couldn't get the SWR down all the way, I think I settled on the best freq is about CH 20. There is a CB shop over in Corning I'd like to take the MH there and see what they say. We have a 14'1" RR underpass not far and we don't hit the antenna when we pass under. Remember 'curb' feelers?? Factory tuned antennas I have not heard of that before, I thought each CB antenna requires tuning. I Might learn something here.

[Larry Moore]

Bill

SWR (standing wave ratio) is a measure of the power that is transmitted then reflected back to the unit because of an antenna that is out of "tune".  The old metal and base load antennas required trimming the mast length to get the best SWR and the most transmission power out of the antenna.  None of this really makes much difference in the reception of the signal. Fiberglass and Rubber Duckie antennas are just set to work unless you mount them too close to a reflection source (metal).  They would  require a 'match' box to tune further. Again, reception is not greatly affected. Mounting location (side, top, back, etc) makes a difference in the transmission pattern of the antenna. Metal close to the antenna is always problematic. I always check the SWR just to be sure that it is in a reasonable range so as not to damage the transmitter in the radio.

[Keith Moffett Co-Admin]

Used to have a CB in the P U truck back in the day.  I recall the transmit failing when the antenna was found to be bad.  When the antenna failed, the first time I hit the key to transmit it blew the output transistors.  This is how the shop explained it as I recall.  I only mention it because someone might wonder why theirs still isn't working after a new antenna.

[Bill Lampkin]

Larry, Sounds like you know your RF propagation! Its always seemed to me to be much more art than science!