Topic: VHF antenna

I am replacing my old VHF with a new unit. The plan is to use the old unit as a station in my place in Tobermory which has an old style TV antenna atop a 30+ foot tower. Question: Can the old TV antenna (VHF?) be used to receive marine VHF signals in the frequency range that we use?

Re: VHF antenna

Tobermory? I'll stop there this summer on my way from Midland to Montreal in my new C32. Any good anchoring/mooring spot you recommend (Little Tub Hbr./Big Tub Hbr.)?
From there I'll go straight across Lake Huron to Sarnia.

Re: VHF antenna

The TV antenna won't work well as the frequencies are different even though they're both in the VHF range of the spectrum...

Channels 2-6 (VHF-low) range from 55-85 mHz
Channels 7-13 (VHF - High) range from 175mHz to 211 mHz
Marine VHF is around 162 mHz

You might be able to receive very strong signals (like Wx broadcasts), but it won't transmit worth beans.

While the antenna won't be much good, the tower will be great and you might even be able to use the existing co-ax cable too, depending on its size and condition.

Just put a properly tuned marine VHF antenna on top and you'll be all set.

Re: VHF antenna

not a bad idea, but it's a bit illegal..........

Re: VHF antenna

I would not try to transmit with that set up. The antenna is tuned as a combination of wire/coax and antenna. If the tuning is way off, which it could be in this setup you get a high SWR (standing wave refection) and a high percent of the transmitters power is reflected back to the radio rather than off the antenna. This can burn out the radio. Wire is not just wire. The old flat TV wire has an impedance of 200 ohms and VHF coax is 50 ohm (I think). The radio is made to match the connector and the coax and the antenna.  If you are only receiving then any length of wire will work to some degree. The longer and higher the better.

Re: VHF antenna

Wire is not just wire, but I said "existing COAX".  Coax is coax and different types will all work to some degree.  You'll get more or less loss with different types (say RG58 vs RG8X), but many boats' radios are rigged with the smaller, higher loss coax. 

Marine VHF radios are not made to match any particular length or kind of coax.  Marine VHF antennas are tuned with a loading coil in the base of the antenna, not in the radio or in a separate tuner (as in a backstay SSB antenna).  Perhaps you're thinking of CB antennas, where the coax IS part of the tuned system and shouldn't be cut or changed. 

The length of the coax to a 30 foot tower shouldn't be a problem either.  In fact, its probably similar in length to a masthead antenna cable. 

As Stefan pointed out, you'll have to square away your licensing issues with the local authorities if you plan to transmit!

Re: VHF antenna

as long as all you want to do is listen....... or should i say "listen to the mail...."