Homebrew Ground Plane

[doctordave]

I have a home-made ground plane antenna, 1/4-wave, cut precisely for a 1 MHZ segment (39-40 MHZ) in which I need the greatest range. I only used 3 ground radials and, of course, the vertical element....all are 6' in length. Would I likely benefit from additional ground radials? Some plans suggest using 4-5....thoughts on this?

Also, the elements are all copper piping w/ 1/2" diameter....any significant benefit associated w/ utilizing greater diameter piping for the frequencies involved? Some antenna design specs suggest that 1" is preferred.

Thanks much.

Dave

 

[N_Jay]

I have a home-made ground plane antenna, 1/4-wave, cut precisely for a 1 MHZ segment (39-40 MHZ) in which I need the greatest range. I only used 3 ground radials and, of course, the vertical element....all are 6' in length. Would I likely benefit from additional ground radials? Some plans suggest using 4-5....thoughts on this?

Also, the elements are all copper piping w/ 1/2" diameter....any significant benefit associated w/ utilizing greater diameter piping for the frequencies involved? Some antenna design specs suggest that 1" is preferred.

Thanks much.

Dave

The larger the diameter the elements the wider the bandwidth of the antenna. The ground radials are usually about 105% of the radiator.

The cut length also gets slightly shorter as the elements get larger in diameter, but I forget the rule of thumb.

 

[pro92b]

There is a graph in the ARRL VHF Handbook that shows length factor vs. element diameter. At 39.5 MHz a 0.5 Inch diameter element should be shortened by 3%. A 1 inch diameter element should be shortened by 3.5%.

 

[loumaag]

doctordave,

When adding elements to homemade antennas, remember to factor in the weight of such things. Based on your description of the antenna you have up there right now, I would guess that it weighs just over 6.5 lbs (I don't know how you assembled them, but the weight of the tubes would be just at 6.5 lbs). If you left the dimensions the same (6 ft elements) and built it the same with 1" copper tubing, the tubing alone would weigh 17 3/4 lbs. Not trying to discourage antenna builders, just remember to be safe.

 

[doctordave]

Thanks for the responses....and yes, it is a weighty beast of an antenna....nicely suspended high in my attic. Actually works nicely - even better than my scantenna or big RS ground plane for 39-40 MHZ. The mere $20 total cost in parts was another plus.

 

[ROY_PICKETT]

ALUMINUM ?

COULD A PERSON USE ALLUMINUM CONDUIT INSTEAD OF COPPER PIPE? WOULD THAT MAKE IT ANY LIGHTER? I AM NEW HERE AND THOUGHT I WOULD THROW THAT IN. ALL I HAVE IS WHAT LOOKS LIKE A TINY GROUND PLANE NOT WEIGHING ANYMORW THEN 2 POUNDS,MABY LESS,AND I AM NOT SURE IF I AM RECIEVING AS GOOD AS I COULD.. I LIVE ON A HILL,AND NO BIG TREES WITHIN 100 FEET OF ME. I AM NOT EVEN SURE THE BAND WITH OF THE ANTENNA I HAVE. THE ELIMANTS R NO BIGGER ARROUND THEN A CLOTHES HANGER.THEY R ALSO NO LONGER THEN 1 FOOT. IT IS A STORE BOUGHT ONE,BUT I WANT TO INPROVE IF I CAN.....THANKS

 

[merlin-7]

one favor

turn off the caps lock....

Thanks

 

[loumaag]

ROY_PICKETT
Please take a look at this Topic posted by the Webmaster of the site.

 

[ROY_PICKETT]

SORRY

I apploigize for the mistake. i am new to this. my username and password
are in caps,and after entering them,didn't realize i had left them on. i do appolagize..i been a mamber for only 3 days now....i wont do it again...

 

[loumaag]

Roy, (I guess that is your name. )
Don't feel embarresed and don't feel we were picking on you. It is just one of those quirks about reading hundreds of posts a day that makes looking at all CAPS (or for that matter all small letters) pretty tough. In any case welcome to the boards, look around, feel free to ask questions (answer some if you know the answer) and have fun. 8)

 

[K5MAR]

Re: ALUMINUM ?

COULD A PERSON USE ALLUMINUM CONDUIT INSTEAD OF COPPER PIPE? WOULD THAT MAKE IT ANY LIGHTER? I AM NEW HERE AND THOUGHT I WOULD THROW THAT IN. ALL I HAVE IS WHAT LOOKS LIKE A TINY GROUND PLANE NOT WEIGHING ANYMORW THEN 2 POUNDS,MABY LESS,AND I AM NOT SURE IF I AM RECIEVING AS GOOD AS I COULD.. I LIVE ON A HILL,AND NO BIG TREES WITHIN 100 FEET OF ME. I AM NOT EVEN SURE THE BAND WITH OF THE ANTENNA I HAVE. THE ELIMANTS R NO BIGGER ARROUND THEN A CLOTHES HANGER.THEY R ALSO NO LONGER THEN 1 FOOT. IT IS A STORE BOUGHT ONE,BUT I WANT TO INPROVE IF I CAN.....THANKS

As is mentioned in another topic, when you start mixing metals, you end up with corrosion, which kills your reception. It's best to use tha same material throughout.

What is the length of the elements on your antenna, something a little more precise than "no longer than 1 foot", please. Then somebody can calculate the resonant frequency of your antenna. If it's a Radio Shack antenna, then the elements are longer than that, and it's a VHF-high antenna.

And what freqs are you trying to receive?

Mark S.

 

[ROY_PICKETT]

ANTENNA

The antenna is alittle to high for me to measure,and i can't take it down right now because of a medical problem... i was wrong though,sence i went to look at it,it is more 16 inch radials ,three of them,at the bottom comeing out at a slight angle,one comeing streight out the top about 18 inches long , and two more comeing out the top at angles and about 3 inches long...i will have to get it down later or get someone else to do it,the i will post again...i was trying to get the police band like 155.835 better.... i am sure it would help to raise the antenna,,right now it does ok,,and it is only 12 feet off the ground.i just have trouble recieving the mobile units sometime because where i live there alot of peeks and valleys......i will post again with a better discription later.....really i was also wondering if it sounds like a scanner antenna,and not a fm antenna,i got it from someone else........thanks

 

[loumaag]

You are describing the Radio Shack Outdoor VHF-HI/UHF Scanner Antenna (RS# 20-176). This is one of my favorite antennas, but it does require being up in the air and most importanatly, away from other objects. It works very well in the 155MHz band and if you are getting poor performance, I would check the feed line for problems first.

 

[K5MAR]

Yes, that's the Radio Shack antenna, P/N 20-176, and it's a VHF-high/UHF antenna. Here's the link to the RS description:
http://www.radioshack.com/product.a...me=CTLG_008_009_010_001&product_id=20-176

Features:
• Covers 108-1300MHz with peak performance in 152-470MHz range

This is basically a VHF-high ground plane antenna, so your best bet is more height. Also, the best coax you can afford.

Mark S.

 

[loumaag]

Hey Mark, now you have to learn to type faster! :lol:

 

[K5MAR]

Hey Mark, now you have to learn to type faster! :lol:

Had to stop to listen to my scanner! :lol:

Mark S.

 

[ROY_PICKETT]

thanks

I checked the link guys,and that is the antenna i have. as for the feed line,that could be some of the problem. i had to splice a coax end from a car stereo coax and used a adapter to hook up my antenna. even that part is in the house,,i could imagine that still can cause some problems.. like i said,it is only 12 feet off the ground,,but i have no real trees besides some persimmon saplings within 100 feet of the trailor. i also live on a good hill,so when i get this setup right, it souldn't be a problem at all.... thanks all...