Duplex Antenna

[cbehr91]

Now that I have settled into my duplex that I rent I'm looking at a more permanent setup for my radio. My main interest is rail band receiving along with occasional NOAA monitoring during skip. I live just north of a major metropolitan area and my main interest is receiving stuff to the north. My dilemma is this: which would perform better: something liked a tuned ventenna (low gain) on the roof or a commercial yagi in the attic. I really only have rail traffic directly to my north or directly to my south. Others have had good luck with a commercial yagi and homebrew half square in the attic. I am aware of the law with dishes and antennas on rentals, which for me pretty much leaves out anything outside other than something like a ventenna. In fact there is a small DirecTV dish on the roof over the garage which is separate from the main duplex thus legal.

 

[prcguy]

There was an article in a recent QST magazine about making an DirecTV dish into a VHF 2m antenna by cutting some slots in it. You can do the same thing for it to cover the rail band and 162MHz NOAA frequencies and it should work great.
prcguy

Now that I have settled into my duplex that I rent I'm looking at a more permanent setup for my radio. My main interest is rail band receiving along with occasional NOAA monitoring during skip. I live just north of a major metropolitan area and my main interest is receiving stuff to the north. My dilemma is this: which would perform better: something liked a tuned ventenna (low gain) on the roof or a commercial yagi in the attic. I really only have rail traffic directly to my north or directly to my south. Others have had good luck with a commercial yagi and homebrew half square in the attic. I am aware of the law with dishes and antennas on rentals, which for me pretty much leaves out anything outside other than something like a ventenna. In fact there is a small DirecTV dish on the roof over the garage which is separate from the main duplex thus legal.

 

[mmckenna]

One of your concerns should be what the roofing material is if you are looking at mounting an antenna inside the attic. Any metallic roofing materials, vapor barrier, etc. can effectively block RF. Before deciding to do an attic mount, make sure that won't be an issue. Simply taking your scanner into the attic and trying it with an attached antenna should show you pretty quickly if there is any major signal attenuation.

A low gain Yagi, like a 3 element, will be mostly directional in one direction, but the front/back ratio will be pretty low, so they tend to work OK in the opposite direction.

However, unless really low signal levels are a concern, a VHF omnidirectional whip will be a lot more useful.

 

[cbehr91]

One of your concerns should be what the roofing material is if you are looking at mounting an antenna inside the attic. Any metallic roofing materials, vapor barrier, etc. can effectively block RF. Before deciding to do an attic mount, make sure that won't be an issue. Simply taking your scanner into the attic and trying it with an attached antenna should show you pretty quickly if there is any major signal attenuation.

A low gain Yagi, like a 3 element, will be mostly directional in one direction, but the front/back ratio will be pretty low, so they tend to work OK in the opposite direction.

However, unless really low signal levels are a concern, a VHF omnidirectional whip will be a lot more useful.

I already have a 5/8 wave on a mag mount up there and it does pretty well, so I don't think there's a lot to block RF. The only thing that might is the vent pipe but I could mount an antenna up there and have it be clear by several feet. I had an attic mount antenna at my parents' house and the thing that killed reception the most was RFI from other household electronics. Putting ferrite beads on the internet modem and on the coax at the antenna cleared up that problem.

And yep, that's my plan with the yagi if I were to mount one up there. Point it in one direction and have the rear lobes do 'okay' in the opposite direction.

@prcguy, I've thought about doing that, but the garage is one-story and the house is two story so something in the attic or a ventenna on the vent pipe or (unused) chimney on my side of the duplex would be at a much higher elevation.