You should always run an average gain test when you have an unusually
high or low field strength. Using EZNEC, the average gain shows as
1.227, or 0.89 dB, and this same average gain should be reported by
NEC-2. That means that the actual gain is 0.89 dB less than what NEC-2
is reporting, or just about 2.0 dBi. If you don't understand what this
test is, consult the NEC-2 manual. EZNEC users will find it indexed in
the EZNEC manual.

I suggest you also do an average gain check on your 3 dBi vertical.

Roy Lewallen, W7EL

John E. Davis wrote:
On 21 Aug 2006 17:50:21 GMT, Ed
Its all a matter of reference. I was thinking in terms of dBi.... a
vertical has 3dBi gain, a ground plane, 2 dBi.

Here is a ground plane with a free-space gain greater than 2.9 dBi and
an SWR less than 1.2 at its design frequency (as given by NEC2):

CM Groundplane antenna for MURS (151.8 Mhz)
CE
GW 1 19 0 0 0 0 0 0.444243 0.000813863
GW 2 21 0 0 0 0 0.163546 -0.4506 0.000813863
GW 3 21 0 0 0 0 -0.163546 -0.4506 0.000813863
GW 4 21 0 0 0 -0.163546 0 -0.4506 0.000813863
GW 5 21 0 0 0 0.163546 0 -0.4506 0.000813863
GE 0
FR 0 31 0 0 145 0.33
EX 0 1 1 0 1
RP 0 31 73 1001 0, 0, 3, 5, 10000, 0
EN


It uses 14 AWG wire and consists of a 17-1/2 inch vertical, and 4
18-7/8 inch radials symmetrically placed at about 20 degrees with
respect to the vertical axis:

|
|
| A A = 17-1/2 in
| B = 18-7/8 in
| T = 2*19.95 degrees
/ \ C = 12-7/8 in
/ T \ B
/ \ (only 2 radials shown)
/ \
-- C --

--John