Antenna separation

[Jerry]

I want to mount an FM radio antenna at the top of my mast. Do I need to maintain any minimum distance separation from my VHF antenna?

[Joe]

I want to mount an FM radio antenna at the top of my mast. Do I need to maintain any minimum distance separation from my VHF antenna?

I suggest a VHF/FM antenna splitter available from Defender Industries for about $15. Less hassel.

Joe



tgjournal@gestalt.org

[Larry DeMers]

I want to mount an FM radio antenna at the top of my mast. Do I need to maintain any minimum distance separation from my VHF antenna?

I suggest a VHF/FM antenna splitter available from Defender Industries for about $15. Less hassel.

Joe

..I do not recommend using an antenna splitter in this application. For every convenience like this, you give up something. In this case, you give up VHF performance (due to the mismatch that the splitter allows. The antenna..if a VHF antenna to begin with..will have to be routed through the splitter, which represents a lower impedance to the VHF. This will result in an increase in SWR (Standing Wave Ratio)which means that a larger portion of your transmitted signal is reflected back to the transmitter instead of into the antenna and out into the air. Use separate antennas for this.
I would recommend that you not mount your FM antenna at the top of the mast. The VHF signal will be too close to your FM ant. and will cause some mismatch to the VHF antenna, as well as picking up some of the RF from the VHF ant.
Realize that FM antennas can be mounted on the stern rail or on the coach roof easily, and with a relatively short cable run.


Good Sailing!

Larry DeMers



demers@cray.com

[Joe]

I want to mount an FM radio antenna at the top of my mast. Do I need to maintain any minimum distance separation from my VHF antenna?

I suggest a VHF/FM antenna splitter available from Defender Industries for about $15. Less hassel.

Joe

..I do not recommend using an antenna splitter in this application. For every convenience like this, you give up something. In this case, you give up VHF performance (due to the mismatch that the splitter allows. The antenna..if a VHF antenna to begin with..will have to be routed through the splitter, which represents a lower impedance to the VHF. This will result in an increase in SWR (Standing Wave Ratio)which means that a larger portion of your transmitted signal is reflected back to the transmitter instead of into the antenna and out into the air. Use separate antennas for this.
I would recommend that you not mount your FM antenna at the top of the mast. The VHF signal will be too close to your FM ant. and will cause some mismatch to the VHF antenna, as well as picking up some of the RF from the VHF ant.
Realize that FM antennas can be mounted on the stern rail or on the coach roof easily, and with a relatively short cable run.


Good Sailing!

Larry DeMers

On our boat, a Cape Dory 330, Shakespeare's Antenna/Radio Tester actually reported an improvement in SWR after installing the splitter. Apparent (to us) VHF performance also increased. I am not recommending the passive splitter manufactured by Shakespeare, but rather the switchable unit sold by Defender. The only drawback is that you need to remember what position the switch is in lest you believe it is the VHF mode when it is actually in the FM mode.

Joe



tgjournal@gestalt.org