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Author Topic: mfj antenna  (Read 366 times)
AF4OB
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Posts: 37




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« on: October 20, 2004, 05:21:09 AM »

has anybody used an mfj 1661 or 1664 antenna?
there say they will take 200 watts,but they have the same size coil as there antenna that will take 1.2 kw.
 73 af4ob
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AD5X
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Posts: 1432




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« Reply #1 on: October 20, 2004, 06:18:33 AM »

I have an MFJ-1664.  Works fine and easy to adjust.  But you have a PVC coil form on this antenna.  I haven't made measurements, but you probably have around 6 ohms of coil loss (assumed 20 uhy and coil Q ~ 150 on 40 meters), 10 ohms ground losses, and maybe 1-1.5 ohms radiation resistance (base loaded antenna).  So probably 1/3rd of your power is being dissipated in the coil.  At 1.2 kw, that is 400 watts of heat!  Bet that PVC coil will melt in no time.

Phil - AD5X
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AF4OB
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Posts: 37




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« Reply #2 on: October 20, 2004, 07:27:33 AM »

thanks for the reply,i am not going to run 1.2 kw  just telling you what mfj said. i was looking into running 400 watts   think it will take that af4ob
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AD5X
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Posts: 1432




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« Reply #3 on: October 20, 2004, 08:34:02 AM »

I think you're asking for trouble.  You'll still be dissipating over 100 watts in the coil (probably more like 130-150 watts).  Not sure the PVC can handle that without softening. I realize that you're talking intermittant operation, but I'd still abide by the max power rating spec'd by MFJ.  But obviously, it's up to you.

Phil - AD5X
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WA4JM
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Posts: 19




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« Reply #4 on: February 01, 2005, 12:07:06 PM »

I have a 1664 antenna that is mounted on a heavy duty trunk lip mount.  I also dumped the supplied matching coil and replaced it with the matching coil sold by hamstick.  Next I found that trimmimg a stainless steel CB whip to about 6 feet would get me down to 3900 KHZ.  You measurements may vary.

I also had to guy the antenna with some fishing line.

It works great on 75 meters and super on 40 with these mods.
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