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Author Topic: Long wire antenna suggestions for Yaesu FC-40  (Read 3292 times)
WB4VET
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Posts: 7




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« on: January 25, 2006, 06:47:57 AM »

I am getting ready to install a long wire antenna coupled to a Yaesu FC-40 tuner.  I am looking for suggestions from anyone who can recommend a long wire length which the FC-40 can tune for 160, 80, and 40 meters.  Any suggestions would be greatly appreciated.

Thanks, Jack
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K0BG
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Posts: 10248


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« Reply #1 on: January 25, 2006, 07:01:28 AM »

You might want to do a search here on Elmers, as this question has been asked many times, and there isn't a simple answer. Further, the manual is of help here as it lists the lengths to stay away from. It doesn't cover the requisite ground plane (counter poise if you please). Hence the search suggestion.

Alan, KØBG
www.k0bg.com
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AA4PB
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Posts: 14329




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« Reply #2 on: January 25, 2006, 08:12:57 AM »

Stay away from exact multiples of 1/2 wavelength (high impedance) and be sure to have a good RF ground connected to the tuner.
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Bob  AA4PB
Garrisonville, VA
WA7NCL
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Posts: 625




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« Reply #3 on: January 25, 2006, 08:26:27 AM »

Try 130ft (halfwave on 80m).  Sometimes the autotuners have trouble with exact half wave since the end is very high impedance.  If that length is a problem adjust the length to be more tword odd multiple of 1/4 which is low impedance.  You want the end feed to be as high impedance as possible to minimize ground return current and maximize efficiency but you still need to keep the autotuner happy.

You will find the bigest problem with FC40 and other autotuners is getting an appropriate ground.  Many guys will have you laying out 1/4wave tuned radials and driving ground rods.  I would suggest you mount the tuner remotely near an outside water faucet and connect the tuner to it with a short heavy wire.  Run the antenna wire up and out from the tuner to a tree or other supports.

If you want short range communication via high angle radiation, maximize the horizontal part of the wire.  If you want more low ange, maximize the vertical part.

Don't be too analytical when using a random wire antenna.  You will probably need to fiddle with it for length and layout.  Just remember for the autotuner, the grounding is critical.

Other things I have used for makeshift grounds are: metal heat ducts in houses, the re-bar in a foundation.  I have used the power mains ground that is at a power entry panel for the house mains but its really not recommended because of RFI to and from the radio.  Lastly, if you are willing to expend the effort, you can put a wire on the ground for a so-called counterpoise.

I hope you find this helpful.  Just remember to experiment until you get something that works.
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K3AN
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Posts: 787




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« Reply #4 on: January 25, 2006, 06:31:25 PM »

Cut the antenna wire to just over an exact multiple of a half wavelength on the lowest frequency. The resulting high feedpoint impedance results in less power lost in the grounding system. That means more of your signal gets radiated. If you're skeptical, check out Figure 5 in the article "Optimum Radial Ground Systems" in the August 2003 QST.

Yes, your tuner will have to be capable of matching a high impedance load. If you find it doesn't, then you'll have to trim the antenna length until it does. But as you shorten the antenna and lower its impedance, the proportion of the power lost in the ground system will increase.

Unfortunately, a half wavelength on 160 is around 250 feet of wire.
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