View Single Post
  #4   Report Post  
Old September 27th 06, 05:43 AM posted to rec.radio.amateur.antenna
Owen Duffy Owen Duffy is offline
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 168
Default First homebrew antenna and a question

On Tue, 26 Sep 2006 23:57:56 -0400, jawod wrote:

I spent the day lowering the folded dipole that I BOUGHT. I was unable
until recently to find how bad the SWR was on most bands. The only
reasonable SWR was on 17 meters.

So, I replaced it with a homemade G5RV, measured appropiately for each
leg of the dipole (14AWG) and for the 300 ohm window line to R/G8U.

I now find reasonable SWR on most bands (WARC, not so much). Here's the
deal: min SWR comes in right at 3.5 MHz, 6.75, 13.43, 18.07 and 29.06.
It appears that I made the classic newbie mistake...antenna too short.


Have a look at Fig 4 at http://www.vk1od.net/G5RV/index.htm . Though
the graph doesn't show VSWR on the RG213, the loss is lowest where the
VSWR is lowest. You should be using an ATU, and it is the line loss
that is more important than the VSWR of itself.

Your antenna sytem appears a little long rather than short, did you
measure the length of the radiator conductors, did you measure the 300
ohm line, did you allow for the velocity factor of the 300 ohm line?

Owen


Now, since I am using an ATU, I think this should be close enough for
acceptable efficiency (at least for 80, 40, 20, 17 and 10 meters).

What do you think?

John
AB8O

PS, When I get the time, I'll try EZNEC but for now, I just want to work
what I hear for a change (!)

--