2/2/06
Comparing some commercially available antennas
Antenna marketing is a racket
in that the less honest you are, the more antennas you sell. (Nobody goes to court over a TV
antenna.) Gain figures published by
antenna makers are mostly useless, except maybe for comparing antennas by the
same maker. The data for all of the charts
in this section came from computer simulations of the antennas. The author performed the simulations.
Why computer
simulations? (non-essential reading)
A few years ago QST, which
is the principal publication of the HAM radio community, announced that they
would no longer accept advertising for antennas if the ads contained gain
figures that were measured experimentally.
Henceforth any such gain figures would have to be the result of computer
simulations. There were two big
problems with the experimental data:
1. The experimental antenna is affected by its
surroundings. Computers can do true
“free space” modeling.
2. The process of choosing the surroundings
encouraged overly favorable choices.
Most of us would call it cheating, but they justified it to themselves
by the belief that their competitors were doing it.
The program used for these
simulations was NEC-4/EZNEC4 by Lewallen (W7EL), which is one of the programs
approved by QST. Data points were
produced every 12 MHz (UHF) or 2 MHz (VHF).
Some problems were encountered which necessitated approximations, so the
data is not highly accurate. But the
author stands behind the principal features of the graphs and resulting
conclusions. The antenna model files
are available for viewing.
(The files are at http://hometown.aol.com/kq6qv/SIMS
. This is an anonymous FTP site. Go first to the file README.TXT.)
Raw Gain for some common UHF antennas
A Channel Master 4228 8-Bay
B Channel Master 4221 4-Bay
C Channel Master 4248 Yagi/Corner-Reflector
D Televes DAT-75 Yagi/Corner-Reflector
E Winegard
PR-8800 8-Bay
F
Winegard PR-4400 4-Bay
G Channel Master 4242 VHF/UHF Combo
H Channel Master 3018 VHF/UHF Combo
I Zenith Silver Sensor indoor LPDA
J Small
indoor loops
K Double-Bow
L
AntennasDirect DB-2
M Winegard Square Shooter
N
Winegard PR-9032
Yagi/Corner-Reflector
O Channel Master 3671B VHF/UHF Combo
P MegaWave Wideband Indoor Antenna
Q
Winegard SharpShooter
Indoor Directional Antenna
R
AntennasDirect DB-4 4-Bay
S
AntennasDirect DB-8 8-Bay
T
AntennasDirect XG91
Yagi/Corner-Reflector
Raw gain is the true gain, as gain is
defined. But a fraction of the power is
going to be rejected by the transmission line because of an impedance
mismatch. This rejected power gets
retransmitted. What is left is the net
gain. The following graph is the
one you should pay the most attention to.
Net Gain for some common UHF antennas
B Channel Master 4221 4-Bay
(3021)
C Channel Master 4248 Yagi/Corner-Reflector (3023)
D Televes DAT-75 Yagi/Corner-Reflector
G Channel Master 4242 VHF/UHF Combo
H Channel Master 3018 VHF/UHF Combo
I Zenith Silver Sensor
indoor LPDA
N Winegard PR-9032 Yagi/Corner-Reflector
O Channel Master 3671B VHF/UHF Combo
P MegaWave Wideband Indoor Antenna
Q
Winegard SharpShooter
Indoor Directional Antenna
T AntennasDirect XG91 Yagi/Corner-Reflector
Click on the antennas above to
see more data about each antenna. Some
of these antennas are UHF-only. While
you might not need VHF presently, you probably will after 2008.
The 4242 and 3018 represent
typical Yagi/Corner-Reflector UHF antennas that are part of a VHF/UHF
combo. You can estimate any other
unknown such antenna from these two.
Just find the length of the UHF part of the boom of the unknown antenna
(measured from the intersection of the corner planes to the front-most
director). Comparing this length to the
4242 and 3018 will let you estimate where the plot for the unknown lies in the
above graph.
The 4242 has a 87“ boom (UHF
part).
The 3018 has a 57“ boom (UHF
part).
Raw gain for some common VHF antennas
A
Radio Shack VU-75XR VHF/UHF combo
B Radio Shack VU-90XR VHF/UHF combo
C Radio Shack VU-120XR VHF/UHF combo
D Radio Shack VU-190XR VHF/UHF combo
E Winegard
YA-1026 Wideband Yagi for VHF 2-6
F Winegard
YA-1713 Wideband Yagi for VHF 7-13
G Rabbit ears – 40” 45°
H Channel Master 3671B VHF/UHF combo
I
Wade single channel Yagis
Explanation (non-essential reading)
Why show
raw gain when net gain is what is important?
1. If atmospheric noise exceeds receiver noise
then the raw gain is what counts. (This
is rare for VHF or UHF but does occur in some neighborhoods.)
2. To determine which of two antennas has a
narrower beam on a given channel, just compare their gains at that
channel. But in this case you use the
raw gain, not the net gain.
3. There are cable-matching methods that make
the net gain as good as the raw gain for any channel. But while these methods make some channels better, they make
other channels worse, and there is seldom an overall improvement. There is presently no hardware available
that lets consumers improve the match, except for some indoor antennas.
4. The program that predicts net gain is not
very accurate. Net gain is affected by
minor details in the way the cable attaches to the antenna. The raw gains are very accurate.
Net gain for some common VHF antennas
A
Radio
Shack VU-75XR VHF/UHF combo
B Radio Shack VU-90XR
VHF/UHF combo
C Radio Shack VU-120XR
VHF/UHF combo
D Radio Shack VU-190XR
VHF/UHF combo
E Winegard YA-1026 Wideband Yagi for VHF 2-6
F Winegard YA-1713 Wideband Yagi for VHF 7-13
H Channel Master 3671B
VHF/UHF combo
If all the elements are parallel (as in a straight-type LPDA) then there will be nulls at +90° and –90° that might be useful for eliminating ghosts and interfering signals.
Getting the
most out of rabbit ears
Using a UHF antenna for VHF
Some UHF antennas are advertised as working for VHF also. As the following net gain graph shows, there
is not much truth in that. For channels
7-13, the MegaWave and the Winegard PR-8800 perform about as well as rabbit
ears. The Square Shooter is terrible
for all VHF channels. All of these antennas
are useless for channels 2-6.
The surprise here is the Channel Master 4228, which has a lot of
gain for VHF-high, especially channels 9-13.
What makes it different is the screen that is continuous across all 8
dipoles. Other 8-bays, like the 8800
and the DB-8, have a reflector that is not continuous across the right and left
halves, and thus they have no useful gain for VHF.
Related topics
Stores and
websites supplying antenna equipment
This page is part of “An HDTV Primer”, which starts at www.hdtvprimer.com