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Author Topic: Antenna Questions  (Read 1305 times)

Posts: 3

« on: August 03, 2012, 07:30:02 AM »

I  am totally new to installing an antenna. I have had my tech ticket for a few months and have been using a 5W HT, but am itching to make further contacts than it would allow by upgrading to a base unit and associated antenna.
MTC has a deal on a Kenwood TM-281A, and although the radio is not feature-rich -- and that may be a good thing -- I'm happy with what it can do. Included in this deal is an MJF-1740 2m/220/440 1/4wave Ground Plane Base Antenna.
I live in Las Vegas, and although we don't get alot of rain -- being facetious here -- we do have a sort of 'Monsoon Season' that brings lots of storms with the associated lightening. As I don't want to go thru all the grounding steps necessary to mount the antenna on the outside of the house I was thinking I could mount it in the attic. Although I know this would cut down on the range/usefulness of the antenna a bit, I'm a little unsure if I can do this with this antenna due to the radials. I think that radials are used as grounding lines, but I'm a little confused in that ARRL states that they can improve the efficiency of an antenna.
I guess my only real question is if I can install this antenna in my attic like a simple J-pole, or should this only be installed on a long mast outside?

Posts: 530

« Reply #1 on: August 03, 2012, 08:13:25 AM »

If you can only install in the attic - do it.

This antenna is a 1/4wave 2m ground plane & the main vertical element and radials can be cut to work on 220 or 440.

Height is the most important item here - if it can be outside & higher or same height - set it up that way.

Use good vhf/uhf coax like 9913 - make 1 loop about 6-8 inched below feedpoint - use as little total length of coax, to get job done.

The radials are the 2nd part of the antenna - needs to work best.

Was in Las Vegas last month.....Do not remember most of it.............. Grin

73 K1WJ David Cool

Posts: 17273

« Reply #2 on: August 03, 2012, 08:28:11 AM »

Sure, you can put it in the attic.

The radials provide the "other half" of the antenna, connected to the coax shield.  Without
them it is like trying to use a lamp with only one wire connected to the socket.  They
don't have to be grounded to anything - they do their job all on their own.

Performance will depend to a large extent on your roof material.  Wood shingles aren't too
bad, metal roofs are poor.  Tile can become lossy when it gets wet if it isn't glazed. 
Foil-lined insulation doesn't help much, either.  Stucco has a layer of chicken wire inside,
which isn't very transparent at RF.
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