inside 2m/70cm vertical...
I'm looking for a quick/easy 2m/70cm vertical antenna I can "mount" inside my house and attach to an HT for bit of improvement on the rubber duck while I'm in a single room. I've heard many people just use a mobile mag-mount on a pie pan (or filing cabinet.) Would that be better than some type of slim jim in the corner of the room (with no ground plane)?
I could even hang a wire from the ceiling... I have 8 feet from ceiling to floor, and I can use the entire 8 feet for an antenna - but I'd prefer that it has as little width as possible.
How about a mag mount stuck on a pie pan, hanging from the ceiling from the tip?
You can stick a mag mount to the top of your fridge. For a while I had a mag mount stuck on a side panel for a computer which was mounted outside of my window with a copper ground strap hanging off of the panel.
Or, you can build a quick di-pole and run it along your ceiling.
Either way rather quick to do. The key to the magmount is the RF groundplane. Read: A big long peice of wire running off of whatever metal you're mounting on.
Last edited by KC2UGV; 04-07-2009 at 03:18 PM.
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I'm reading some of the designs for slim jim's, but I don't see any plans that claim to work dual-band. Being very new to all this, I'm not sure what would be required to make a 2m antenna work well with 70cm as well.
A piece of 58" twin lead hanging in the corner of my room could be made nearly invisible... I'm even starting to wonder if I could rig something like that up and drop it INSIDE an interior wall (wood studs.)
This antenna experimenting might get to be fun. I suppose I need to invest in some meters that'll work on VHF/UHF before I actually hook anything to a radio, though.
A quarter-wave vertical (about 19.5 inches long) will work on 2-meters with unity gain and on 70 cm as a 3/4ths wave vertical with about 3 dB gain over the quarter-wave.
You can build a simple ground plane with 3 or 4 radials bent down at about a 45 degree angle (to get the feed point impedance up to around 50 ohms). The length of the radials should be about 20.5 inches. This will make for a simple, but effective, dual band antenna for the 2-meter and the 70 cm band.
The Highfields Amateur Radio Club in Wales has a very nice dual-bander made from 450 ohm window line on their "Constructors Corner" page. Their website is at Highfields ARC. Under "Technical Info" select "Constructors Corner" then "Antenna Projects" then "Dual Band J-Pole." I've made one and it works nicely. I managed to hit my local club repeater (22 miles away) with an HT standing on the front porch without too much difficulty. VSWR is low on both 2M & 440.
Find an aligator or other clamp that can reliably grasp the outer shield
of your ducks antenna connector, hook a 20" piece of flexible wire to it
and see if it suits your needs, that is the simplest performance increasing
thing you can do for an ht.
Freedom isn't free, it carries with it the highest cost known to humankind, always has, always will.
Just extending the ground plane?
Originally Posted by KC7YPJ
Wow - lots of great ideas. I really like the Highfields ARC jpole/slimjim. It doesn't really give good directions for tuning it, but dual-band, and extremely portable! It also doesn't suggest a length of the feedline, and I thought that was part of the tuning...
Would a normal slim jim designed for 2 meters work okay on 70cm without extra tuning?
More like PROVIDING a ground plane/counterpoise of the appropriate length. In theory, the body capacitance of the operator is supposed to provide this, but differences in body size, how the rig is held, whether a speaker/mike is used or not - all of these can make large differences in how well the duckie "works".
Originally Posted by KB3SOT
I don't even bother with the alligator clip. I just strip a couple inches of stranded wire (#20 or so) and wrap the bare metal around the antenna jack so the duckie holds it in place. Improves TX and RX considerably.
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That's actually very interesting, and would probably provide a huge help "in the field." I actually plan on taking the advice with some really thin wire I have laying around (would it matter if it's solid or stranded?)
However, while I'm in the "home office" (and not moving around,) it makes sense for me to plug a larger more effective overall antenna (such as a portable slim jim) I think.