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Author Topic: 160 Meter coil for Butternut HF-2V  (Read 2248 times)
NI0C
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Posts: 2408




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« on: September 27, 2002, 11:24:30 AM »

I have just put up my HF-2V without the 160m coil, and am pleased with its performance so far on 80 and 40 meters.  The 160 meter coil kit is still in the box, and I'm trying to decide if and when to add it.  The instructions with the 160 meter kit say to limit power to 500W, and even at that level, to avoid long key-down periods.  Does this power limit apply for 80 and 40 m as well?  The antenna without the 160m coil is rated at 2KW.  I run an AL-80B amplifier with 600 to 800 watts output, and would prefer not to reduce my signal strength 2-3 dB on 80 and 40 meters to add 160m capability.  Would appreciate hearing from those who have had experience using the 160m kit with any of the Butternut verticals.
Thanks & 73,
Chuck  NI0C
   
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WB2WIK
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Posts: 20611




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« Reply #1 on: September 27, 2002, 01:55:28 PM »

No, when you add the 160m kit the power restriction does not apply to 80 & 40 meters, as no current flows through the 160m coil on the higher bands.

P.S. - Although not recommended by Butternut, I've run a kW through the 160m coil plenty of times, using CW or SSB and with the antenna mounted outdoors (obviously) in cool weather.  Probably I would not try it on RTTY...

WB2WIK/6
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NI0C
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Posts: 2408




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« Reply #2 on: September 27, 2002, 03:14:55 PM »

Thanks, Steve, for the quick reply.  Since the Butternut coils are so beefy, I think the power rating on the antenna must be based on the voltage rating of the capacitor.  If most of the (80m/40m) current is going through the cap instead of the coil, the capacitive reactance must be low enough to bring down the cap. voltage to a (hopefully) safe level.  So your reasoning makes sense.  I think I shall try the 160m coil soon, then.  What kind of ground radial system did you use with your Butternut, and what kind of 160m dx did you raise?
 
73 de NI0C

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WB2WIK
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« Reply #3 on: September 27, 2002, 03:49:35 PM »

It worked pretty well, actually.  (I no longer use, nor have it.)

Running a kW mostly on CW, I was reasonably competitive with the locals, using only the Butternut and quite a lot of radials.  If I recall correctly, I had four long radials about 130' long each, and at least 16 shorter radials about 50' long each, all on the ground, and all insulated #14 gauge wire.  The antenna, obviously, was ground-mounted.  Since I focused primarily on CW (especially since the ARRL 160 contest is CW-only), I tuned the Butternut/160 to 1.820 MHz or so and it wasn't terribly useful above 1.840.

I also tried a 165' long inverted-L with good success, and then later a 185' long center-fed doublet with 450 Ohm ladder line up about fifty feet.  They were all reasonably DX-worthy with a kW and good conditions, which of course means between November and March, during the dark hours.

73 de Steve, WB2WIK/6

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NI0C
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Posts: 2408




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« Reply #4 on: September 28, 2002, 08:02:30 AM »

Wel, I installed the coil last night, and got it all tuned up to place the resonant frequencies where I want them.  Worked a few stations on 80m and 40m with amp cranked up to 800 watts.  All is well.  Thanks, Steve!  Now to purchase more wire to add more radials.
 
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NI0C
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Posts: 2408




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« Reply #5 on: November 08, 2002, 11:26:27 AM »

Here's an update on this subject for anyone interested.  I found out last night the power limit on the Bencher/Butternut TBRS-160 kit must be respected.  (The manual says 500 watts, maximum, with short tune-up periods).  For several weeks, I got away with exceeding this limit. (My Ameritron AL-80B has an exuberant 3-500Z tube, putting out about 600-700 watts on the low bands, even with only 50 watts drive).  All was well until yesterday, when I went from 37 to 50 ground radials.  As expected, when improving the ground-system of a ground-mounted vertical, the bandwidth decreases and SWR at resonance increses.  These factors, in combination with my eagerness to go after 3XY7C, led to a blown capacitor on the 160 m kit.
I was touching up the tuning on my amplifier (off frequency, where the SWR was probably 2.5:1 or so).  The key-down period was only a second or so, but the power meter suddenly dropped from 600 watts to 200 watts, indicating a catastrophic failure.  I checked out the antenna on 40 and 80 meters, and it seemed okay.  I even had a half-hour ragchew on 80 m CW, running the amp.  However, this morning I inspected the antenna and found that one of the two 200pF 10KV caps was missing pieces of its shattered ceramic case.  I'm glad no-one was standing near the base of the antenna to absorb the shrapnel!    
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NI0C
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Posts: 2408




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« Reply #6 on: November 27, 2002, 05:43:03 PM »

It was pointed out by W3GEO in his review of the Butternut HF-2V (posted under eHam Product Reviews) that Surplus Sales of Nebraska is a source for replacement "doorknob" transmitting caps.  I looked them up on the web and ordered some HT-57 200pF 15KV caps to replace the one I destroyed several weeks ago.  Since the voltage rating on these caps is 50% higher than the caps supplied by Bencher/Butternut, I sent an e-mail to Bencher, asking if the higher voltage caps would increase the power rating of the 160 meter add-on kit.  I got a prompt reply advising that the power rating was based on the current rating, not the voltage rating, of the caps.  This is because the RF impedance at the feedpoint is very low. I'm passing this along in case anyone else is using the Butternut 160m kit with an amplifier.  My experience with this indicates that the 500 watt rating on 160 meters is not a conservative one, and that stress on the capacitors is dependent on both the SWR and the efficiency of the ground system.
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