Comet CAA-500MarkII Antenna Analyzer
Reviewed by Phil Salas, AD5X
ad5x@arrl.net
Comet recently introduced their nextgeneration antenna analyzer — the
CAA-500MarkII. Like the original
CAA-500, reviewed in the March
2012 issue of QST, the
MarkII has a large analog cross-needle
meter for displaying SWR and impedance magnitude.1 The MarkII, however, adds a 1.4 ×1.15 inch full-color
TFT LCD (see Figure 1) that displays
the operating frequency, fixed frequency SWR and impedance data, and
swept frequency SWR data.
Overview
The CAA-500MarkII is a fairly large
instrument — almost as big as a classic Bird 43 wattmeter. Connectors are
an SO-239 for 1.8 – 300 MHz, and a
Type N for 300 – 500 MHz. Power requirements are six AA-size alkaline or
NiMH cells (not included) or external
8 – 16 V dc, 250 mA power source (dc
cable included). The CAA-500MarkII
also includes an internal trickle charger
for NiMH batteries, an upgrade from
the original CAA-500. Typical charging time is 15 hours, and typical battery
operating time is up to 9 hours (there is
a battery indicator on the LCD). An autopower-off timer helps conserve battery
life. It’s adjustable from 1 to 9 minutes (default is 5 minutes) and can be turned off.
The CAA-500MarkII provides a single frequency measurement mode and two sweptfrequency modes. The single frequency
mode displays SWR and impedance (Z)
on the cross-needle meter, and digital and
bar graph SWR readings across the full
frequency range. Digital readings of resistance (R) and reactance (X, unsigned) are
displayed below 190 MHz, while only a
bar graph display of Z is available above
190 MHz.
The two swept frequency modes display
SWR in graphical form.
graphs SWR using preset amateur band
frequency ranges.
selection of the center frequency and sweep
bandwidth.
Table 2 summarizes the specifications and
performance of the CAA-500MarkII.
MANUAL SWEEP
CAA
-500
AUTO SWEEP
permits
Test Results
The CAA-500MarkII output level is quite
constant over the full frequency range as
shown in Table 3. The frequency can be
set to within 1 kHz, but this is a tricky adjustment especially at the higher frequencies. Additionally, the signal is noisy and
“warbly.” Further, initial frequency drift
takes about 15 minutes to stabilize when
the CAA-500MarkII is powered from an
While limited in measuring capability and performance compared
to other antenna analyzers in its
price range, the CAA-500MarkII
covers all amateur bands from
1.8 to 500 MHz, making it a single
“all-band” instrument.
Bottom Line
external dc supply but continues after
that period when used with the inter-
nal batteries. Also, just touching the
case or dc power cable caused some
frequency change. For these reasons,
the CAA-500MarkII would probably
not be the best tool for precise receiver
measurements.
Next I checked SWR accuracy, starting with a precision 50 Ω load. Then
I tested the CAA-500MarkII with
shorted microwave attenuators of
5 dB (1.92:1 SWR), 3 dB (3.01:1
SWR) and 2 dB (4.42:1 SWR). I
also used loads made from Caddock
thick-film resistors — a 7.5 Ω load
(theoretically 6.67:1 SWR), a 200 Ω
load (theoretically 4:1 SWR), and a
400 Ω load (theoretically 8:1 SWR).
As Caddock resistors are specified for
high frequency applications, I used
these tests to not only compare the
CAA-500MarkII against a high quality Array Solutions AIMuhf vector
impedance analyzer, but also to see
how good the Caddock resistors really
are.2 As you can see in Table 4, the
CAA-500MarkII SWR readings
compare favorably to the AIMuhf
readings, especially for the lower im-
pedance measurements.
Because the Caddock resistive loads are
not perfect, I used 150, 200, and 400 Ω
Caddock loads to check impedance measurement accuracy at 50, 146, 222, and
440 MHz. As Table 5 shows, the impedance measurement capability of the
CAA-500MarkII is better at lower frequencies and lower impedances.
For my final tests, I built lower impedance complex loads with an SWR of approximately 2:1 for 50 MHz, 146 MHz,
and 222 MHz. Table 6 displays the
CAA-500MarkII resistance (R) and
reactance (X) measurements on 6 and
2 meters, and an impedance measurement at 222 MHz compared to the Array
Solutions AIMuhf. As you can see, the
CAA-500MarkII provides reasonable
impedance measurements at 50 MHz,
but the accuracy degrades as you go
higher in frequency. Again, the sign of
the reactance is not displayed on the
CAA-500MarkII.
QST® – Devoted entirely to Amateur Radio www.arrl.org Reprinted with permission from September 2016 QST
Table 2
Comet CAA-500MarkII, serial number AA15E0763-1
Manufacturer’s Specification Measured Performance
Frequency range: 1.8 – 500 MHz As specified.
(35 range segments).
Frequency settability: 1 kHz. As specified.
Frequency accuracy: Not specified. Actual frequency is within the 1 kHz
display range.
RF output level: 0 dBm HF/VHF, –1 dBm UHF. See Table 3.
SWR range: Analog meter 6:1; LCD, 9.9:1 As specified.
SWR graphical display: 6:1 As specified.
SWR accuracy: Not specified. See Table 4.
Impedance range: 12.5 – 300 Ω, 190 – 500 MHz. See Tables 5 and 6.
Resistance range: 10 – 500 Ω, 1.8 – 190 MHz. See Tables 5 and 6.
Reactance range: 0 – 500 Ω, 1.8 – 190 MHz. See Tables 5 and 6.
Size (height, width, depth): 3.5 × 7.75 × 2.65 inches. Weight: 2.1 lbs with batteries.
Price: $400.
Table 3
Output Power (dBm) vs Frequency
Power measured with a NIST-traceable MiniCircuits PWR-6GHS+ power sensor.
Specified power output is 0 dBm at HF and VHF, and –1 dBm at UHF.
--------------------- Measured Power (dBm) at Frequency (MHz) ------------------------------
1.8 3.5 7 14 28 50 144 222 440
0 0 0 0 –0.1 –0.3 –0.2 –0.5 0
Figure 1 — The color LCD is a new feature on
the CAA-500MarkII. It displays battery life, frequency, SWR, and impedance data.
Table 4
SWR Accuracy Measurements
Loads measured with the CAA-500MarkII compared to the AIMuhf. See text.
Freq 1:1 SWR 1.9:1 SWR 3:1 SWR 4.4:1 SWR 7.5 Ω Load 200 Ω Load 400 Ω Load
(MHz) CAA CAA/AIM CAA/AIM CAA/AIM CAA/AIM CAA/AIM CAA/AIM
1.8 1.0 2.1/2.01 3.2/3.17 4.6/4.62 6.7/6.76 3.9/3.97 7.9/7.93
3.5 1.0 2.1/2.01 3.2/3.16 4.8/4.61 7.0/6.72 3.9/3.96 7.8/7.93
7 1.0 2.1/2.01 3.2/3.17 4.8/4.61 7.1/6.73 3.9/3.96 7.8/7.93
14 1.0 2.1/2.00 3.2/3.15 4.7/4.59 6.9/6.70 3.9/3.97 7.8/7.95
28 1.0 2.2/2.00 3.3/3.15 5.2/4.59 7.6/6.71 3.9/3.97 7.7/7.93
50 1.0 2.2/2.00 3.2/3.17 5.1/4.60 7.7/6.73 3.8/3.95 7.4/7.92
146 1.0 1.9/1.97 3.2/3.19 5.0/4.75 9.4/7.05 4.0/3.84 7.7/7.59
222 1.1 1.8/1.92 3.2/3.15 5.2/4.76 7.8/7.25 3.8/3.74 7.3/7.18
440 1.0 2.2/2.03 3.1/3.07 6.8/4.81 8.0/8.73 4.2/3.40 >9.9/6.13
Figure 2 — Fixed frequency measurement of
a 160 meter antenna.
Table 5
Resistive Load Measurements
SWR and impedance measurements of 150, 200, and 400 Ω Caddock resistive loads with the CAA-500MarkII compared to the AIMuhf.
The CAA-500MarkII reactive readings are unsigned. See text.
Freq ------------- 150 Ω Load ---------- ----------- 200 Ω Load ----------- ------------ 400 Ω Load -----------(MHz) CAA AIM CAA AIM CAA AIM
SWR/R/X/Z SWR/R/X/Z SWR/R/X/Z SWR/R/X/Z SWR/R/X/Z SWR/R/X/Z
50 2.9/123/50/– 2.9/134/–39/140 3.8/176/49/– 4.0/186/–45/192 7.4/266/165/– 7.9/317/–156/353
146 3.1/50/61/– 2.9/81/–63/103 4.0/74/85/ – 3.8/127/–86/154 7.7/61/132/– 7.6/129/–175/218
222 3.4/–/–/50 2.8/54/–56/78 3.8/–/–/70 3.7/90/–86/124 6.9/–/–/80 7.2/72/–138/156
440 3.0/–/–/18 3.1/21/–25/33 4.2/–/–/25 3.4/38/–57/68 >9.9/–/–/25 6.1/23/–70/74
– = not measured.
Reprinted with permission from September 2016 QST ARRL, the national association for Amateur Radio
®
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