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Author Topic: Comet CHA250B vs Jetstream 680  (Read 15039 times)
NA0AA
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Posts: 1042




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« Reply #15 on: March 10, 2012, 07:15:37 AM »

An all-band antenna is similar to a racecar/pickuptruck/limo/minivan/economy car....


If you must buy an antenna and get on the air NOW, go with a BTV, put down what radials you can and get on the air.  Then, for your NEXT antenna, buy an Antenna book and have at some book learning on how to better meet your needs in your available space.

Antenna farms in limited space tend to be really individual designs due to the wide variety of limitation imposed - for example - if you had supports or could put them up at the 'corners' a loop comes to mind - a full wavelength 80 meter loop is roughly a 66' square - it can be less than a 1:1 aspect ratio but the flatter the rectange the less effective...

So read a bit, look at your site and then start planning your 'improvements'.
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KG4RUL
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« Reply #16 on: March 10, 2012, 08:55:39 AM »

I have actually done an A/B/C comparison between: Diamond BB-7V; Comet CHA250B; 41' vertical with minimal radial field.  Both the Comet and Diamond antennas were an S4-S5 with the vertical at S9+ when contacting the same station over a 15 minute time interval.  They do work but only marginally.
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G4AON
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Posts: 542




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« Reply #17 on: March 10, 2012, 12:01:45 PM »

You could do a whole lot worse than use a fibreglass fishing pole around 33 foot long, over here in the UK there are several for sale at good prices on ebay. Run a 1/4 wave wire up it for 40m and tape each section, tie it to a wooden fence post and feed it against at least 16 x 22 foot radials laid on the ground or buried (radials laid on the ground are de-tuned and so do not need to be as long as a radial raised above ground). It will knock the socks off those wide band compromise antennas.

I am using one in the Commonwealth (BERU) contest this weekend on 40m and working any VK I can hear, often first call.

No need to spend money on fancy antennas to get good results from a small plot.

73 Dave
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WA8FOZ
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Posts: 192




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« Reply #18 on: March 10, 2012, 05:01:32 PM »

Quote
You could do a whole lot worse than use a fibreglass fishing pole around 33 foot long,...

What he said.

I took the liberty of Googling your QTH, You have trees, I believe. You could have parallel vertical wire radiators running from a common feedpoint at ground (32 feet for 40m, 16 feet for 20m, 11 feet for 15m, and so forth) for as many bands as you like. The top of the 40m radiator could be bent parallel to ground if your tree isn't high enough. Put in as many radials in your grass as you reasonably can(this has been explained here and elsewhere before: close cut lawn in spring/wire in thatch held down with lawn staples/wire of any type and length as your lot allows, etc). This could be done in a few hours and would work MUCH better than the Comet or similar alternatives - costs almost nothing, too.

Have fun!
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W2JD
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Posts: 2




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« Reply #19 on: March 11, 2012, 08:27:02 PM »

I believe that in addition to the Gap Titan, you could look at the Cushcraft R-8 or R-6000, and the Hy-Gain Liberty AV-620 or 640. They have a counterpoise made of 8 ft. whips. I used an R-8 for one year, and it worked quite well. The bandwidth on 40M is about 150 kHz. but on 20 and above is almost full band. Both the AV-640 and the R-8 cover 40,30,20,17,15,10, and 6. On 6M I never had too much luck with it.

73,

Jose
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AC4RD
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Posts: 1235




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« Reply #20 on: March 12, 2012, 04:05:51 AM »

 I looked at the reviews for the Gap Titan here on Eham and they are all very glowing.   There is some counter Poise to the Gap Titan, that I can only think will be an asset.  But it doesnt get into big Radial fields that I just dont have the space for.  

Greg, those traditional verticals, the ones that need radials, are a quarter-wave above a radial field.  The Gap antennas are a bit different--they're actually vertical dipoles, with the feedpoint halfway up the antenna.  (Disclaimer: the Gap antennas I've seen are vertical dipoles; maybe they have new models now that I don't know about.)  The vertical dipoles don't need radials because both halves of the antenna system are there--one above and one below the feedpoint in the center.

I had a Gap "Eagle" years ago, and it worked pretty well, considering.  In my setup, the Eagle wasn't as good as a full-sized dipole at 40 feet or so, but it did work, and I was overall pretty pleased with it.  If space is an issue for your antenna installation, a Gap may be worth looking at.  GL and 73!  --ken ac4rd
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AB7X
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Posts: 1




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« Reply #21 on: April 06, 2012, 07:15:57 PM »

Thanks to all who have contributed to this thread.  There seems to be some very good viewpoints to the CHA-250/Jetstream 680 issue.

Keeping in mind that everything is a compromise, I am seriously considering one of these antennas for use on my Fifth Wheel, mounted on the ladder on a mast about 15 feet long.  I am considering antennas that don't need a ground counterpoise and the choices seem rather limited.  That said, it appears that one of these could be easily stored and erected in the matter of a few minutes.  KE5DFR mentioned that he is using the Jetstream 680 on his Fifth Wheel and gave it a rating of '4'.

So does anyone have a better idea for an antenna that could be used on a Fifth Wheel?  I am not an avid DX-er and not a fan of contests, so a compromise antenna would probably suit me fine.  Incidentally, I have an R-7 at my home QTH.  Again, I am not looking for a technical analysis of these antennas, just a recommendation of something that might perform better.
Thanks
Ken  (AB7X)
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K5LXP
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« Reply #22 on: April 06, 2012, 08:56:17 PM »

If compromise is what you want, save the expense of the Comet by installing a long whip and feeding it with a 10dB inline power attenuator.  Great SWR across the bands, same crappy performance but a lot simpler and less expensive.


Mark K5LXP
Albuquerque, NM
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N5XED
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Posts: 1




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« Reply #23 on: June 11, 2012, 01:46:20 PM »

If you have purchased the Comet or Jetstream vertical.....put a few radials down with it.....shorten the overall length to 22 feet.....and use it on 15m.....then it won't be a total waste.

Gary
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K8SSB
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Posts: 1




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« Reply #24 on: July 02, 2012, 05:47:25 PM »

One of our club members has installed the Comet.  He's quite pleased with its performance working several states and countries in just a few short weeks.  He lives in a mobile home park and is severely restricted.  I have not heard any reports on the Jetstream 680 but was hoping to get some good info on your thread... I need an antenna that is portable, fast to put up and take down, with no radials or counterpoise... though something like an r5 or r7's little counterpoise could work. As far as a compromise goes, though it's true that it will not be as efficient as a vert with a nice radial field, it still works.  I have a dipole on 40, a shortened dipole on 75/80, and an R5 covering 20/15/10.  With that limited system, and the 75/80 is pretty much a dummy load, I worked a clean sweep on the phone sweeps... Operator finesse can make up for lower radiated power.  So, that being said, I'm going to go the eham product revuews for the jetstream info... 73
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KL7IPV
Member

Posts: 984




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« Reply #25 on: July 02, 2012, 08:22:55 PM »

I said this on eHam on March 1, 2006 and since then the antenna has not changed:
"Until I moved into this CC&R location, I used a 5BTV or a 6BTV for over 30 years. They work well and most of the time I used it I had no radials. Compared to using a dummy load with a pipe sticking out of it, I would go with the BTV series of antennas. Good luck.
73,
Frank
KL7IPV
"
I also remember a VK5 station took one apart to show us just how it was made. Spend your money on a 5BTV and run at least one ground radial. I also used a 4BTV on my 5th wheel mounted on my ladder and it worked well.  Here is another reply: http://vk1od.net/antenna/misc/CHA250.htm

Here is a PDF of the antenna breakdown: http://www.kl7ipv.com/sirdrakejr/CHA250BXII.pdf that came from this thread: http://www.eham.net/reviews/detail/5175


Good luck
Frank - KL7IPV
« Last Edit: July 02, 2012, 08:46:00 PM by KL7IPV » Logged
KG4RUL
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Posts: 2734


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« Reply #26 on: July 02, 2012, 08:42:52 PM »

I had the opportunity to an A-B-C comparison between the Comet CHA-250B, the Diamond BB-7V and a 21' Flagpole with twelve 20' radials laid on the ground.  Based on the S-Meter in my Kenwood TS2000, the Comet and Diamond antennas were consistently 3-4 S units less the the flagpole, on 40 & 20 meter bands, compared to the flagpole.  Attaching the radials to the Comet and Diamond antennas did not make any appreciable difference.  On another occasion, I was able to test the Comet antenna mounted at the top of a 30' Penninger mast.  In that configuration, on 20 meters, the Comet compared favorably to a G5RV at 30'.  If the Comet or Diamond antennas are all you can get away with, they will work, to some extent.
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