While evaluating HF multiband vertical antenna I found this interesting review about the CHA250B by Comet.
I saved for further reference, author is K3DAV whose site is gone qrt.
Comet CHA250B HF Vertical
By David – K3DAV (2/7/2012)
There are a few compromise HF vertical antennas within the same class as the Comet CHA250B on the market.
“BUTTERNUT” makes the HF6VX, but you need to buy extra kits to add some of the bands. That
doesn’t make much sense.
“DIAMOND” has one similar to the Comet called the BB7V. It has a cheap design with a separate
add-on load coil with a flimsy wire that connects the coil to the main element. That doesn’t
make much sense either.
“GAP ANTENNA” makes the TITAN-DX. But in reality, it is a center fed vertical dipole. Only the
top half is a main radiator. And this thing has way too many ugly radials sticking out in all
directions that can break off in the wind. This thing is an eye-sore.
“HUSTLER” has the 6-BTV. Not a bad antenna, but it is loaded with several power robbing
band traps. Again this makes no sense.
“HY-GAIN” has the AV-18AVQII, but again with all of those power thieving traps for certain
bands, and a separate add-on load coil for 80 meters. What’s up with that?
“JETSTREAM” makes a real look-a-like, copycat version of the CHA250B called the JTV680. But
the JTV680 is made of thinner lower grade aluminum that will break easier in the wind, and
the coil is basically a fat 50 ohm resistor type that sucks power away.
And every one of those antennas have high SWR throughout the HF band that requires you to have or purchase an antenna tuner. That means they all have a poor impeadence match which robs even MORE of your power. (Except the JTV680 which just uses a big fat resistor to rob your power.)
Then there is my favorite.
The little antenna that could.
Just to reassure you, I do not work for NCG Company, (the parent company of Comet antennas), and they do not pay me for this review. I am just so impressed by the performance of the CHA250B, that I thought it was worth a page on my website. So take every word I say here as pure and quite honest. And I never exaggerate.
The Comet CHA250B HF Vertical.
I fondly call it my 24 foot dummy load. The design of this antenna is so simple it is almost stupid. At first glance, it is pleasing to the eye. Nice shiney aluminum standing tall, and that’s it. No big ugly radials anywhere from head to toe. More importantly, there are NO FREQUENCY TRAP COILS to suck away your power. The entire length is one continuous piece of aluminum tubing, and the whole element radiates RF at all times. Actually, it kinda looks like an old style CB antenna. My first thought was, how can this thing work? It’s just a balun with aluminum tubing far too short for frequencies below 15 meters. But after my experiences using this antenna, I can tell you, IT WORKS pretty damn good. At least much better than I ever expected it would.
A diagram of the matching transformer built-into the big round black housing within the mounting bracket.
Before you decide to purchase one, keep in mind that this antenna is a compromise antenna. It will not give you top performance like a monster yagi or a perfectly cut dipole up high. But if you are space restricted like me, and want a good HF vertical to get you talking on HF, this is the one antenna to own. As I have told many hams who laugh at this antenna, “You may not give the guy in Australia a big 20 or 30dB signal, but I gave them an S-9 signal, and we had a very nice QSO.” And isn’t that the whole point of ham radio? Making the contact, and possibly a new friend? Also keep in mind that you can NEVER use a linear on this antenna. It can handle a maximum of 250 watts SSB, but only 125 watts on AM & FM. This antenna is for the space restricted ham who only uses the 100 watts of power out the back of the radio.
These are quotes from the NCG website about their own product….
- “If you have the space, budget and desire to erect a full size antenna system we suggest you do so… bigger IS better. However…if you live in an antenna restricted area and must manage with antenna or space restrictions, or you simply wish to operate incognito, you will be forced to make significant antenna compromises. The CHA-250B will make the most of these circumstances!”
- “The Comet CHA-250B is a newly design broadband vertical with NO GROUND RADIALS. This antenna is EXTREMELY easy to assemble, requires no tuning or adjustments and VSWR is under 1.6:1 from 3.5MHz – 57MHz!”
And for you guys who already have yagis or dipoles on huge towers, the CHA250B is a good standby, or can be used as just a good omnidirectional monitoring antenna to see what’s on the bands. This antenna is quiet with great ears. And it covers the entire HF spectrum, so it makes a fantastic general coverage antenna. It also covers TX on the MARS/CAP frequencies.
The CHA250B comes in 5 pieces. Assembly took me 20 minutes. The entire antenna is 6068 aircraft aluminum, and fits together easily. Each section going up fits inside the one below it. Two of the sections are pre measured with pre tapped holes for inserting a small sheet metal screw. The other two sections must be measured to set them correctly. They too slide inside the lower section, but are held in place with a hose clamp. You only need to measure the element a few inches from the bottom end that slides into the other section. The instructions give you the exact measurements to use. Mark the measurement with a marker or a scratch, then insert the element exactly to the mark, then tighten the clamp. Then you are ready to raise the antenna into it’s new home. From opening the box to complete installation took about an hour.
The specifications for the CHA250B are very simple. Here is how the NCG website list them.
Broadband: TX 3.5 – 57MHz RX 2.0 – 90MHz
VSWR: 1.6:1 or less
Max Power: 250W SSB, 125W AM-FM
Impedance: 50 Ohm
Weight: 7 lbs 1 oz
Mast Size Required: 1″-2″ diameter
Max Wind Speed: 67MPH
The following is the measured wavelengths on particular bands for the CHA250B. No tuner is needed except for 160M as this antenna is not designed for use on 160 meters.
At 1.900MHz this antenna equals a 0.045 wave. (Ant. Tuner Required)
At 3.600MHz = 0.084 wave.
At 60 meters = 0.120 1/8) wave.
At 7.100MHz = 0.166 wave.
At 10.130MHz = 0.236 (1/4) wave.
At 14.200MHz = 0.331 (1/3) wave.
At 18.170MHz = 0.424 wave.
At 21.200MHz = 0.495 (1/2) wave.
At 24.950MHz = 0.582 (5/8) wave.
At 28.500MHz = 0.665 (2/3) wave.
And finally at 50.000MHz = 1.165 wave. Too long for 6M, but still works.
NO TUNER REQUIRED FOR HF. NO KIDDING!
The entire antenna is just over 24 feet tall including the base load coil and mounting bracket. The coil is built into the bracket, and is the most important part of the antenna. The coil is built like a transformer, and provides a nice 50 ohm load on all bands. NO JOKING! I put my MFJ-269 analyzer on this antenna including the 60 feet of coax into the shack. I can spin the tune dial on the analyzer from 3.5MHz continuously scanning the entire HF spectrum through 54 MHz, and the SWR never goes above a 1.6. It is usually near flat except for a few band edges. When I checked below 3.5MHz or above 54MHz, the SWR starts to climb fast. But between those two frequencies, it is great. Even on 60 meters. I am not exaggerating. It really is that good. You do not need a tuner with this antenna on any HF band. As I said, the load coil is a transformer, but it acts sort of like a dummy load. They take a tap from the coil through capacitance to feed the main element.
There is only one exception, and that is on 160 meters. The CHA250B is not designed to cover 160M, so a tuner is necessary. See down below for more details about this antenna and 160 meters.
No counterpoise or radials required. REALLY!
But they can help.
Because of the load coil design which uses the coax or metal mounting pole as a counterpoise, you do not need ground radials or counterpoise wires with the CHA250B. It works quite well without them. I can tell you this from my experience. My first contact on this antenna was a ham in Scotland on 20 meters. I only use the 100 watts from my Icom 746PRO. We talked for about 15 minutes and he gave me a signal report of S-9 to 10dB. I had about the same on him. He never seemed to have any problems hearing what I said, as he always responded to the points or questions I made. I knew at that point that this antenna was pretty good. By the way, I only use LMR-400 coax with all of my antennas including the CHA250B.
I used to talk with a few guys in a free-for-all QSO just before sundown every night on 75 meters. 3805kc to be exact. I am in central PA near Harrisburg. The others were all around PA with one guy in upstate NY. He would get an S-5 or S-6 from my little antenna over 120 miles away. But after the sun went down, I talked up and down the eastern seaboard. A friend close by to me suggested I install a couple of counterpoise wires. So we cut 2 wires, one at a 1/4 wave on 75 meters, and the other to a 1/4 wave on 40 meters. My friend in upstate NY said my signal went up to an S-9, bordering on 10dB. So it made an improvement. This is something to note about the CHA250B. It can run without the counterpoise wires, but it helps to add them.
BUT! There’s A Bonus Feature I didn’t Count On.
The CHA250B antenna is not designed to work below 80 meters. At least according to the manufacturer. But just out of curiosity, I tried it on 160 meters. Keep in mind that my CHA250B is only 20 feet from it’s mounting bracket to the ground, and I use LMR-400 coax. So as they say, “your milage may vary”. The SWR on 160M is right on a 3.0. I hit the button for the auto-tuner in my 746PRO, and in 5 seconds it tuned it to flat. So far on 160 meters, I have worked NY, NJ, IA,OH, IN, VA, and NC. Not too shaby for a 23.8 foot dummy load. I know it is nothing compared to a good 160M dipole, but it works and I made contacts.
As for performance the CHA250B actually covers the frequencies as advertised, but it has it’s limits. I have found the CHA250B to work very well on 75/80, 60, 40, and 20 meters. I have now worked all continents (Except Antartica) on those bands with it. Usually with good reports. I have even broken through pile-ups with just 100 watts. But as you go above in frequency, the performance slightly drops off, but not so bad that you can’t still make good DX contacts. I find 17 and 15 meters to be pretty good. 12 and 10 meters is fair to OK, but it could be better. But even though the manufacturer says it works on 6 meters, it is fair to poor on 6 meter performance. It is over a full wave on 6M, so I didn’t expect too much up there. My old GP-15 was 200% better on 6 meters. But it does work there.
So I have come to certain conclusions on my antennas. The CHA250B works very well for me on 160 through 20 meters. So they are the bands I use this antenna for. I have a Solarcon I-MAX 2000 for 17 through 10 meters. The I-MAX 2000 is the best vertical antenna for these bands. It performs better on 17 and 15 meters, but a whole lot better on 12 and 10 meters than the CHA250B. And I already have a Comet GP-9 for 2M/440, and a Dominator 6M for 6 meters.
I know of several hams that have purchased the other brand name verticals I mentioned at the beginning of this article, and they were not all that happy. I talked them into trying the CHA250B, and they were very surprised at how well it works for what it is. They all agreed it was an improvement over their original HF vertical purchases. All of us so far believe that it works at least better than we thought it would for a compromise antenna with such a simple design.If you have any questions about the CHA250B contact me at firstname.lastname@example.org