The Survival Podcast Forum

Survivalism & Self Sufficiency Topics => Communications => Topic started by: firetoad on January 12, 2009, 10:53:46 PM

Title: 2 Meter Ground Plane Antenna
Post by: firetoad on January 12, 2009, 10:53:46 PM
I thought I would pass along some information on my 2 Meter base antennas for all here.  I was extremely pleased with the results of my recent antenna "upgrade" and felt I needed to share. 

I started out my 2 Meter base rig with a simple horizontal, 1/2 wave dipole antenna for several reasons.  It is an extremely economical design and easy to build.  I actually purchased my first antenna, a 1/2 wave dipole, since I didn't know much, if anything, about building my own antenna at the time.  Also, since I have restrictions in my subdivision, I had to install the antenna in my attic and the dipole takes up very little room.  Once it was installed, I could hit local repeaters without too much issue but noticed some deficiences in coverage and somewhat lacking longer range performance.  So, I did a little research and found that the horizontal dipole is not a very efficient design for 2 Meter.

During my "dipole" research, I found a number of recommendations for a simple ground plane antenna (single vertical 1/4 wave radiator with four ground radials, at 45 degrees to the ground and 90 degrees from each other).  I also found that these antennas were a piece of cake to build.  It seems that if you can solder, you can build one of these 1/4 wave, ground plane antennas.  So, I set out to build one of these antennas but needed a few parts first. 

What I needed: 

The only item from the list above that I had to purchase was a $3 SO-239 Chassis Mount Connector.


Below is the set of instructions that I used for the build:

After a little soldering, some rosin splattered on the kitchen table and scraps of romex on the linoleum, I had one ground plane antenna.  A few minutes later, I was up in the attic replacing the dipole with this unit. 

The antenna is actually suspended with 550 cord through a loop that I put into the end of the radiator/vertical mast.  Remember, your overall radiator length is from the insulator of the SO-239 up to the end of the loop if utilized.

The antenna was held vertical by a horizontal piece of cord wrapped around the SO-239.

Also, take note that although this installation is mainly protected from the weather in the attic, it can get very humid up there.  So, I used some liquid electrical tape to seal the coax and connector interface to prevent water from getting into the coax.  Water intrusion is the number one enemy of coax.

OK, so the antenna is installed, but would the performance of the antenna be any better than the dipole?  A short answer to this question...  YES, YES, YES!  I was able to hit repeaters up to 60+ miles away this evening!  The 1/2 wave dipole didn't even come close to this!  Reception has also increased!

While tuning the antenna, I just made one trip to the attic and called it good.  I started with an SWR of ~1.5:1 at 144 MHz and got down to ~1:1 at 145.075 MHz.  Wow, I was really impressed!  At 148 MHz, I found that the antenna had an SWR of ~1.3:1.  The highest SWR I had was 1.5:1.  With those results from a single tuning, I figured that I would call it good.  While I could bring the 1:1 closer to my op frequencies right around 146 MHz, I felt that what I got was just fine for now since I also work some repeaters down around 145 MHz.  Besides, I had very little time to get this project completed and was lucky to even get it done! 

SWR Chart

It all can't be peaches & cream, so what are the problems?  Well, I have found that I am getting some TVI on my upstairs main TV.  It seems that the antenna is so good that I am "overloading" this TV system!  I think I have actually tracked it down to a piece of cheap, quick connect coax that I will be replacing tomorrow in the morning.

EDIT:  I did some further SWR testing and found that the SWR was better than I had found last night.  So, I updated the post as well as the SWR chart for the antenna.  Call it sleep deprivation from the newest baby!
Title: Re: 2 Meter Ground Plane Antenna
Post by: DeltaEchoVictor on January 12, 2009, 11:25:18 PM
Nice antenna FT.

Nice radio too. ;D
Title: Re: 2 Meter Ground Plane Antenna
Post by: firetoad on January 12, 2009, 11:34:13 PM
Thanks man!

It was a piece of cake to make and definitely performs well for the $3 price!   ;D

I do like that radio!  Thanks man!
Title: Re: 2 Meter Ground Plane Antenna
Post by: Tactical Badger on January 14, 2009, 03:47:52 AM
Excellent post!!

Awesome setup.

I was going to build a Desk Buddy and put it in my attic.  I like this setup MUCH better.
Title: Re: 2 Meter Ground Plane Antenna
Post by: firetoad on January 14, 2009, 11:48:11 PM
Well, I haven't been able to cure the TVI.  So, I decided to run some "higher quality" coax and move the antenna above the garage as far from the living room TV that I could.  While it is not perfect, I am now down to just a small amount of background noise that is barely noticeable.

Also, at low power, I was measuring a SWR of 1:1 across the entire 2m band.  At 65W, the highest SWR I measured was 1.3:1!  I tried a couple of distant repeaters and actually heard a courtesy tone from one that was 70+ miles away!!!