Comet CHA-250B - The Inside Story - AntennaRestrictions Forum at eHam.net

$\'\'$

$\'\'$

$\'\'$

eHam.net Forum : AntennaRestrictions : Comet CHA-250B - The Inside Story

Forum Help

1-10 of 21 messages

Page 1 of 3 Next

Comet CHA-250B - The Inside Story	Reply
by KG4RUL on January 24, 2008	Mail this to a friend!
I was reading the reviews for this antenna and found the post by Iain VK5ZDB. He had actually disassembled the "matching network" on the antenna. Contrary to popular myth, he found that it is an elaborately constructed balun, NOT a "dummy load"!!! Here are the results of his investigation, an interesting read: http://www.vk5zdb.com/cha250bxii.pdf

RE: Comet CHA-250B - The Inside Story	Reply
by W3LK on January 24, 2008	Mail this to a friend!
The net effect is the same - just like the "matching network" inside the MAX-COMM "tuner" upon which this antenna (and its Diamond clone) appear to be based. The majority of the power is lost in heat and not radiated as RF. 73, Lon - W3LK Naugatuck, Connecticut

RE: Comet CHA-250B - The Inside Story	Reply
by WB2WIK on January 24, 2008	Mail this to a friend!
Not sure what to make of the results. The test indicates 5 to 7 dB loss (varying with frequency) when terminated in a 50 Ohm load, but the actual load impedance will be all over the place, and without radials it's still half an antenna.

RE: Comet CHA-250B - The Inside Story	Reply
by N3OX on January 24, 2008	Mail this to a friend!
See my comments in TowerTalk forum but consider that the matching network enclosure, which appears to have a larger surface area than a hundred watt light bulb, needs heat sink fins for an antenna rated 125W CW. 73, Dan

RE: Comet CHA-250B - The Inside Story	Reply
by AA4PB on January 24, 2008	Mail this to a friend!
Dan, those big fins tell the story about where all the RF energy is going - heat. Seems like many these days are trying find the magic antenna that will radiate a big signal on all bands from a very small size - often from the deck or attic. There will always be someone claiming to have just such an antenna for sale :-)

RE: Comet CHA-250B - The Inside Story	Reply
by W3LK on January 25, 2008	Mail this to a friend!
<< There will always be someone claiming to have just such an antenna for sale :-) >> And there's a sucker born every minute to just dying buy it! <g> 73, Lon - W3LK Naugatuck, Connecticut

RE: Comet CHA-250B - The Inside Story	Reply
by TF2JB on January 27, 2008	Mail this to a friend!
I met a ham down in Germany in November of las year. He was very angry at the amateur radio dealer who had sold this antenna to him, for not accepting to take back (in his own words): "...this "dummy-load" of an antenna". I think there is a limit to what dealers should agree to put on the market. When the experience is as bad as with this product, it will simply be to the benefit of all (including the dealers) to pull this off the market. Of course the factory should also realize that it will make a bad name for itself - not only for this product - but for all other products which could very well be good performers... 73 de TF2JB.

RE: Comet CHA-250B - The Inside Story	Reply
by KL7IPV on February 7, 2008	Mail this to a friend!
They are now advertising a "NEW" model. I wonder what part of it is upgraded? Frank

RE: Comet CHA-250B - The Inside Story	Reply
by N3OX on February 10, 2008	Mail this to a friend!
"I wonder what part of it is upgraded? " Epoxy encapsulation so it's harder to open?

RE: Comet CHA-250B - The Inside Story	Reply
by AA9OC on February 17, 2008	Mail this to a friend!
When attempting to transmit on a nonresonant antenna there are two ways one can accomplish it. First, you can build a matching network to cancel out the reactive components and bring the feedpoint closer to 50 ohms. Second, you can build a broad band transformer or terminating resistor that will absorb the reflected wave by converting it into heat. I personally don't see anything wrong with companies selling broad banded antennas such as the B&W broadbanded folded dipole or the Comet antenna which use the later approach. Since HAM radio is a technical hobby, it is important for HAMs to be educated enough to know the pros and cons of such a vital component of the station. Just like reduced antenna size will compromise performance, so too will such a broad banded impedence transformer. I'm sure there is a unique set of circumstances where this antenna would be a great choice over other options. I can't think of any at the moment though. Anthony

Page 1 of 3 Next

Next Topic: Hustler 5BTV
Previous Topic: Help with CCR antenna

Email Subscription
You are not subscribed to this topic.

Check our help page for help using Forum, or send questions, comments, or suggestions to the Forum Manager.

$\'\'$