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Author Topic: Indoor Antenna (Magmount on Steel Plate)  (Read 4394 times)
AG6PO
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Posts: 3




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« on: February 09, 2011, 01:18:06 AM »

Hello Hams,

I'm a relatively new ham and I have a question to ask. I was gifted a Kenwood TM-V7 by a generous ham and had it mounted in my car during the summer with a magmount. When I went back to university I had to setup my radio indoors. So I grabbed a piece of scrap steel and stuck the magmount on it for a ground plane. It has worked well enough so far, but I'm looking to improve my sensitivity and range. Is my existing setup even somewhat reasonable? I'm considering getting full length 70cm and full length 2m antennas and mount them similarly.

http://www.contrib.andrew.cmu.edu/~dkozel/Images/antenna.jpg

I'd love any thoughts or comments.

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WB6BYU
Member

Posts: 13017




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« Reply #1 on: February 09, 2011, 05:52:18 AM »

That's not a bad antenna for something used indoors that can sit on top of the fridge
or other spot out of the way.

The biggest improvement you can make would be getting the antenna outdoors, or
at least as close thereto as possible.  My current 440 antenna is a ground plane with
two radials hanging against the window over my desk.  I use the suction cups with
hooks that are sold for hanging Christmas lights to attach it to the glass - the whole
thing is made of two pieces of wire soldered to the end of a short piece of coax.
A similar antenna built for 2m might work well enough on both bands, or you could
build one for each band.

I've also used loop antennas stuck to the inside of the window - there is a thread
in Antenna Restrictions at the moment on the topic.  There is also a thread on one
of the boards on operating from a dorm room that might have some useful advice
as well - especially about antennas that you can mount outside the window.
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K9YLI
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Posts: 848




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« Reply #2 on: February 09, 2011, 06:56:30 AM »

We have a disabled ham in our club.  his magmount was'nt working out very well into the repeater at about 16 miles.
I took a 4 inch square piece of Lucite, made 4 radials out of old
tv elements, hammered flat   for last 2 inches.. bolted to the lucite in the corners, SO239 in the middle..

i used a bronze brazing rod for the radiater.   cut to 20 1/4 inches, as the handbook  shows  19 1/4..
 bent the  radials down to  45 degrees,  It sits on top of clothing wardrobe just right 6 feet off the floor.  (cathedral ceiling)

SWR on 146  perfect with extra long radiater.   Dumb luck..  no trimming.   
radiator is  red fuzzy  from the original brazing flux.. 
Brought his signals way up out of the noise..

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AF6AU
Member

Posts: 38




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« Reply #3 on: February 10, 2011, 03:40:59 PM »

Where are you height wise off the ground? Got a window?

For my second floor office window, I used 2 telescoping antennas from a local electronics store (~5 in. collapsed, 22 in. extended), a 1/4 inch thick sheet of plastic 3x6", and a 10 ft. length of RG58, and a ferrite ring salvaged from a junk AT computer power supply. I made a vertical dipole that I can change the length of easily. The coax makes a loop through the ferrite then the shield feeds the bottom whip, the center the top. Using double sided tape, it sticks to the window center, and I tape the coax horizontal away from the plastic block to the window side. I borrowed a SWR meter to get the length, then marked the whip lengths with felt pen dots on the glasss. If you know Orange County Calif. I sit 6 miles west of disneyland, and can hit the Santiago Peak repeaters 30 miles east, Long Beach 15 miles west on 2m or 73cm easily and FQ with a 5 watt Alinco 580T. Can't hit Catalina Island though, it's about 40 miles. Can't complain for a portable window stick-on though. I have seen guys doing the same with buglar alarm metal window tape and a middle connection block.  If the window opens, make a dipole at the end of a length of wood dowel, and stick it out 5-6 feet or so. You would be suprised how well it works. With a simple antenna, height is everything.
73's OM
AF6AU
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K2ZS
Member

Posts: 36


WWW

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« Reply #4 on: February 19, 2011, 05:29:13 AM »

I tried J-Poles, mag mounts and even a Cushcraft AR-270 Dual band base antenna on a mount in a window but the best results came from my indoor Delta Loop on 2 meters. The Delta is suspended in a window opening that faces the city I live outside of. I suspend it using bungee cords and can change it from vertical polarization to horizontal for weak signal ssb work when I check into our local weak signal net weekly. I put a page on my website about it if your interested.

Next I am going to build a Moxon antenna for 2m. I built one for 70cm and it works great so we'll see when it's done if it works better.

Good Luck...
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Antenna restricted?
http://www.k2zs.com
KF4LXB
Member

Posts: 36




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« Reply #5 on: February 24, 2011, 08:02:29 AM »

When I first got into ham radio when I was a teenager I used a similar set-up in my parents house with some minor variations. My room was on the second floor and had two windows. Thus, I opened the windows and attached a small metal plate, like the cover of a junction box, to the ledge outside the window. Then I just mounted two mag-mount antennas on the metal plates and ran the wires in the window to my base station. I was using a two meter 5/8 wave whip antenna and a smaller 440 one. This was a pretty good set-up because it was completely reversible and not very obtrusive. I'm sure there are other issues when talking about doing something like this on campus but it may be an additional idea to draw from.
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Christian
Albemarle, NC
EM95
http://kf4lxb.blogspot.com
K1CJS
Member

Posts: 5863




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« Reply #6 on: February 26, 2011, 08:43:12 AM »

I would venture to guess that the university dorm director would look kindly on a permanently mounted antenna, but temporary probably would be OK.  How about a j-pole made out of twinlead?  Look online for the directions, and just hang it outside.

The only thing is that you may find that your present setup just as good if you put it outside the window in some manner.  One fellow I know used a cookie sheet for a base and put the magmount on that.  You just have to figure out a way to support the plate on the outside of the room window.
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