VHF/CB antenna

[dpslusser]

Whats the purpose of VHF/CB antenna's?

 

[Reel Poor]

Re: VHF/CB antenna

They are for receiving and transmitting radio wave signals from and through the air. VHF and Citizen Band (CB) radios transmit on different frequencies, so the antennas cannot be interchanged.

 

[dpslusser]

Re: VHF/CB antenna

They are for receiving and transmitting radio wave signals from and through the air. VHF and Citizen Band (CB) radios transmit on different frequencies, so the antennas cannot be interchanged.

What I mean is...why do they sell combination CB and VHF antennas?

 

[tashasdaddy]

Re: VHF/CB antenna

so you can have both types of radio on the boat. cb is for short distance to gab with another boat, vhf is official marine radio, combo antenna's are not very effective, compared to separate antenna's.

 

[dpslusser]

Re: VHF/CB antenna

so you can have both types of radio on the boat. cb is for short distance to gab with another boat, vhf is official marine radio, combo antenna's are not very effective, compared to separate antenna's.

What I don't understand is that, these antennas, they must have two seperate leads coming off of them correct? One for a VHF Radio, the other for CB? Plus, what happens when you have to trim the CB antenna for minimum SWR? Unless its already pre trimmed with a preset length of cable. THAT, I didn't look into

 

[tashasdaddy]

Re: VHF/CB antenna

combo antenna's are not very effective

 

[Gary H NC]

Re: VHF/CB antenna

On those combo antennas what ever your SWR reading is is what you get.Unless its a steel whip antenna and thats not worth a flip with a VHF radio..2 antennas is the only affective way to go.

 

[Texasmark]

Re: VHF/CB antenna

CB is around 27 MHz and VHF is up in the 200 MHz range. The wavelength (time to emit .....electrical length of......a single 360 degree cycle of energy) for the two is roughly 8-12 to 1 sort of thing with the length the reciprocal of the frequency (higher the freq, shorter the wave/antenna). Antennas are cut to 1/4 or 1/2 wavelength and matched to the transmitter/receiver.....(sandy beach vs bulkhead thing I discussed awhile back).

I guess if you have a combo, and using a single wire, your VHF antenna is going to be roughly 10 wavelengths long. Never messed with something like that so I am not familiar with the feed impedance, nor the gains/losses. But on length, usually, the longer the antenna, the higher the gain because of the longer signal path exposed for radiation/reception.......as long as you don't loose all that gain by a bad match at the radio.

Mark