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Author Topic: 10 Meter Antenna  (Read 14350 times)
KI4SDY
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« Reply #15 on: July 15, 2010, 06:38:07 PM »

Just to make sure that you understand; because I have never had to break the measurements down this far before for anyone, the six inches includes the four inch spring and two inches for the mount. You still end up with a 102" whip in the mount. Roll Eyes
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W8AAZ
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« Reply #16 on: July 16, 2010, 10:17:15 AM »

I once took a generic base loaded CB magnet mount antenna and retuned it for 10.  This was in the 80s when the band was hot. Left the appx. 3 foot whip intact, and took maybe 2-3? turns off the coil till it matched on 10.  Had a FT-101 with the DC power option and ran that combo in a rather compact car. Worked DX with that combo if the band was open.  But the car generated enough hash to limit my noise floor a fair bit too.  Remember they say that a medium whip in the center of the roof will have a better pattern than a full size off the bumper,  maybe partly obstructed by the body of the vehicle too.
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K0BG
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« Reply #17 on: July 16, 2010, 10:43:08 AM »

If you use a ballmount, and spring, those lengths need to be taken into account when you figure the overall length. You need to leave yourself a little leeway, to tune the antenna to the chosen resonance point. Usually, the spring account for about 6 inches (remember it is fatter than the whip), and the ballmount about 1.5 inches.

The formula is 234/f with f being in MHz. This will get you very close. For 28.4 MHz, that's 99 inches rounded off. So the actual whip length in the above example is 91.5 inches. You won't need any matching, and the input of a full 1/4 wave, plus a little ground loss, comes up to about 39 ohms input. Or, about 1.3:1 SWR.
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KI4SDY
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« Reply #18 on: July 17, 2010, 07:11:46 AM »

If you use a 102" CB whip directly installed in the mount without the spring, you won't have to cut, trim or tune anything. It will give you very broadbanded performance with a 1.2 to 1.3 SWR on most of the 10 meter band. Again, why destroy a good antenna? Try it first and if it works well for you, like it has for thousand of others, then leave it as it is. The advantage is; later if you want to use it on 10, 11 and 12 meters, you can, by just installing the spring on the antenna. You will get similar good SWR results and performance with the antenna centered on the 11 meter band. Check the eHam reviews concerning the Radio Shack stainless steel CB whip and you will see that most of the happy users (that actually used the antenna instead of working it out with a pencil or computer) were very happy with its virgin performance. They have even added antenna tuners and used it on many more bands.

By the way, as far as "eHam expert" opinion goes, you need to go the High Q Antenna site and check out the info on KOBG at the bottom of the page from a commercial antenna manufacturer, before you start taking his advice and cutting up a good antenna. It is hilarious! More ham radio manufacturers should expose some of these "eHam self-appointed experts." In many cases, their opinions do more harm than good by wasting a new ham's money and time. In this case, the guy has never even measured a 102" CB antenna and thought it was 99" long including the mount. Obviously he is talking about something he has never tried or didn't know what he was doing if he had. Notice his ego would not let him admit that he made a mistake.   
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K0BG
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« Reply #19 on: July 17, 2010, 08:43:40 AM »

If you use a full size, 102 inch whip without the spring, and ballmount, the resonant frequency will be on the low side of 27 MHz. The SWR at 28.4 MHz, when properly mounted, will be about 1.8:1. If you mount is off a trailer hitch mount, there will be enough ground losses to lower the SWR down to about 1.4:1 or so.

By the way, a standard CB whip length is 102 inches; not 9 feet (108 inches)! The 108 inch, and 120 inch ones haven't been made for over 30 years.

The formula given is correct; 234/f in MHz. You'll end up with the antenna being a little longer than what's really needed.

As for the other comments, they're lame at best.
« Last Edit: July 17, 2010, 10:52:15 AM by Alan Applegate » Logged

K0WJ
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« Reply #20 on: July 17, 2010, 10:03:40 AM »

Quote
Actually, I have proven again that another "eHam expert" does not know what he is taking about. The 9 foot whip I was referring to was with the 6" inch spring attached." Note; I told the inquirer to remove the spring for 11/10 meter use, which brings it down to 102".
Quote

No need to be so caustic.  Try explaining yourself better.  A 9 foot whip is a 9 foot whip whether there is a spring attached or not.  YOU called it a 9 foot whip.  I know what you meant, but simple math logic says that if you remove a spring from a 9 foot whip, what's left is the 9 foot whip.
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K3GM
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« Reply #21 on: July 17, 2010, 12:53:14 PM »

Slow down! slow down! ...I'm still trying to picture a 102" whip on the (I assume the front) fender of a Wrangler...  Grin
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N5EAT
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« Reply #22 on: July 17, 2010, 12:55:16 PM »

I agree with cutting down a Wilson CB antenna.  They are fantastic performers and stay very securely mounted.
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KC7NFF
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« Reply #23 on: July 17, 2010, 11:07:33 PM »

     All of this information is great, but the bickering is confusing the hell out of me and probably others as well who are trying to learn something here.  Can we please re-focus I am pretty much still at a loss.  I completely understand that antennas are everything but I am still not sure which antenna to buy for 10 meters.   Screwdrivers are out as I am a full time student so my budget is pretty tight.  I have almost $400 saved and out of that I need to get two antennas, Heavy duty fender mounts, a duplexer or triplexer and last but not least pay for the install as I do not have any experience or equipment for tuning.  This is the type of mount I am looking at    http://www.rightchannelradios.com/hood-roof-cb-mounts-83/jeep-wrangler-hood-mount-243.html   but there is a place up here that I can get ones that are made for taller antennas.  The ones in the link can only handle up to four foot antennas. 
         I do not mean to put a damper on anyone's opinion as it is all excellent information but I am down to just a few more things before I get everything installed and the antennas are really working me over.  I am still wondering if a 10 meter hamstick at seven feet will work for me or if I should just stick to a dual band antenna and a 6 meter antenna.  If I go this route and having an ft-8900r will I damage the radio if I do not have an antenna for 10 meters?  I do not want to ruin my new mobile because I have the wrong set up.  So please help as there is no one here in Coeur D' Alene, Idaho that I can really talk to about this.  Thanks for your patience and help
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K0BG
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« Reply #24 on: July 18, 2010, 06:26:00 AM »

Quite obviously, the hood mount you refer to isn't all that stout. You could mount a CB whip on it I suppose, but I wouldn't. A Hamstick is a bit shorter, and a bit lighter, and may be all the antenna you need. However, Diamond makes an antenna specifically for this radio (CR8900A), which covers all four bands. It isn't very sturdy in my opinion, and it's about 3 dB down from a hamstick on 10 meters. This way, you'll have only one antenna to mount, and I don't believe you need a diplexer with this antenna.
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KI4SDY
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« Reply #25 on: July 18, 2010, 07:02:31 AM »

The mount you are planning to use will restrict your options and the diamond antennas are not that rugged. They also are tunable, so your going to need to invest in at least a SWR meter for best performance unless your going to chance it with the "factory settings." I am not a big fan of triple or quadruple band antennas for performance and durability reasons, but if you this type of antenna would be best for your situation, its your money.

$400 is more than enough to to set up a good performing antenna array of antennas dedicated for HF, VHF and UHF. If you want an inexpensive good performing antenna for 10 meters, just add an inexpensive flat bar rear bumper mount that bolts on with the stud mount attached and screw in a 102" CB whip, without the spring. Again, you won't have to tune or cut anything, but you need to check the SWR on any antenna you install to make sure it is installed properly, for best performance and to protect your equipment. If the SWR is high you could burn up your transmitter. Protection circuits do not always work!   

Check out the MFJ 864 SWR meter. I think it will fit your needs. Borrow a meter from someone else if you have to, but definitely you need to learn how to use one if you are going to stay in this hobby. Wink
     
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KI4SDY
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« Reply #26 on: July 18, 2010, 08:01:07 AM »

I guess my best inexpensive versus performance suggestion would be a magnetic MFJ VHF/UHF power gain magnetic antenna, a 6 meter ham stick for the mount you were going to use and a 102" CB whip for 10 meters mounted on the rear bumper. That will leave you plenty of money for a SWR meter and hundreds left in your pocket! Grin
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WX7G
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« Reply #27 on: July 18, 2010, 09:53:56 AM »

A 10 meter Hamstick will work well enough, costs $31, has low wind loading, and looks good.
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KC7NFF
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« Reply #28 on: July 18, 2010, 09:25:17 PM »

Thanks gentlemen for the wonderful information, I do know of plenty of people who have an swr meter and the place I am having it installed will tune them correctly for me.  I believe that I am going to go with the triband 2m/6m/70cm and a 7 1/2 foot hamstick for 10meters.  For this I will need a duplexer for two separate antennas which I will purchase from HRO.  When the install is complete I will post pics.  But in the mean time keep the information coming.  The more informed I am the better off I will be. Also I am not going with the mounts that I referred to.  I will be using bigger flat bars for the antennas mounted on the hood channel of my 99 tj (Soft Top Only).
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KC7NFF
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« Reply #29 on: July 18, 2010, 10:20:35 PM »

What are your thoughts on the Outbacker Perth Plus? Because then I could mount a dual band antenna (2m/70cm) on one side of the hood and maybe the Perth Plus on the other. Of course if I go this route I will need to save up more moneys and these antennas run between $200-$350.  Oh and just for a reminder I am going to be using an FT-8900r.
« Last Edit: July 18, 2010, 11:24:37 PM by Adam Brown » Logged
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