Cecil Moore wrote:
Try the ARRL Antenna Book. In general, symetrical elevated
radials don't radiate. In general, ground mounted radials
are lossy.
jawod wrote:
I second this. ARRL Antenna Book:
Check pages 2-16 to 2-18 and "The Effects of Ground' which is Chapter 3.
All the answers you need are there.
Newsgroups can be helpful but sometimes only partly. A good text is
your best friend.
Learning this stuff can be a lot of fun. It can be frustrating, too.

Just last month, with four elevated 40 meter radials 6 feet high, the
antenna was about 5 dB weaker than the very same antenna with 16
radials laid directly against soil.

This basic result repeated at three different soil locations on three
different bands, 160, 80, and 40, so it is not a fluke.

In my last quick measurement on 7MHz:

16 long radials directly on the earth (no attempt to make resonant
since they have very low Q) 0dB reference

8 long radials on the ground -1.3dB reference

4 long radials on the ground -3dB reference

4 resonant elevated radials at six feet -5.6dB reference

73 Tom

Sometimes the more I learn the less I know.

I have dabbled a lot along these lines in the last few months. I have
determined my methods are faulty.

When I compare two or more antennas for gain I have no means to
measure the actual gain because I really don't know what the radiation
pattern is in real life.

However, comparing measured gains with calculated gains has given me
more confidence in the EZNEC calculations.

I have limited my test antenna to a 30 foot vertical with radials
consisting of electrical extent ion cords connected in parallel
stretched out on the ground. I seem to be manipulating the take off
angle and the impedance of the feed by adding and subtracting these
radials. The vertical seems to be more quiet (fewer signals) than a
dipole but pretty much the same strength on those it hears. The
reference dipole is the 40M section of my CushCraft A3S Beam at about
40 feet.

The only certain conclusions I have made are that getting high
confidence numbers about radials is a lot of work and probably beyond
my resources. The ARRL Antenna Handbook and EZNEC are usually right.

Usually right...
If you lie to EZNEC it will lie right back to you with an even bigger
lie. Be very careful with assumptions!

The Antenna Handbook...
There is still the unresolved issue of conjugate matching. I noted
last week or so that a copy of Walter Maxwell's book that retailed for
$19.95 went for about $75 on EBAY.

John W8CCW

On 10 Jul 2006 04:01:01 -0700, wrote:



Cecil Moore wrote:
Try the ARRL Antenna Book. In general, symetrical elevated
radials don't radiate. In general, ground mounted radials
are lossy.
jawod wrote:
I second this. ARRL Antenna Book:
Check pages 2-16 to 2-18 and "The Effects of Ground' which is Chapter 3.
All the answers you need are there.
Newsgroups can be helpful but sometimes only partly. A good text is
your best friend.
Learning this stuff can be a lot of fun. It can be frustrating, too.

Just last month, with four elevated 40 meter radials 6 feet high, the
antenna was about 5 dB weaker than the very same antenna with 16
radials laid directly against soil.

This basic result repeated at three different soil locations on three
different bands, 160, 80, and 40, so it is not a fluke.

In my last quick measurement on 7MHz:

16 long radials directly on the earth (no attempt to make resonant
since they have very low Q) 0dB reference

8 long radials on the ground -1.3dB reference

4 long radials on the ground -3dB reference

4 resonant elevated radials at six feet -5.6dB reference

73 Tom
John Ferrell W8CCW