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Author Topic: Tuning a Butternut HF6  (Read 1660 times)
G0DJA
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Posts: 4




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« on: July 28, 2006, 01:35:46 AM »

I wonder if anyone, who has experience of tuning a Butternut HF6V , can help me please?

The situation is that I have a second hand HF6V, with the 160/17/12M coils fitted, which I have just put together.

I can tune up almost all of the bands, with expected results such as very sharp tuning on 160/80M and wider bandwidths on the higher bands.  However I cannot get any tuning point on 20M.

I'm using a Palstar ZM-30 antenna analyser to adjust the antenna, so it's not the usual problem of the average VSWR meter not being a reliable indicator, and the results on most bands for VSWR, Impedance and Reactance are as expected for a ground mounted vertical over a not very good radial system.  However, as I said before, most bands are behaving as expected.

The readings across the 20M band, which I would expect to be broad given the way that the HF6V is designed, are as follows:

Frequency   VSWR   Resistance  Reactance
14.000MHz   1.8:1  79          -j25
14.100MHz   1.8:1  82          +j22
14.200MHz   1.9:1  84          +j26
14.300MHz   1.9:1  88          +j23

Scanning between 10MHz, where the match is OK at 1.1:1 55+j0 across the Amateur band, and 18MHz shows that the above figures are the best in that range.  This suggests, to me, a bad connection but given the description of how the antenna is designed to operate on 20M, and the readings for 80/40/30M which are all controlled by the settings of the same coils as for the 20M band, I am at a loss as to what might be wrong.  I have tried the suggestion in the instructions of moving the 30M coil to a different point on the 40M coil, but that did not seem to make any difference.

Anyone any ideas?

Thanks - Dave (G0DJA)
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AD5X
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Posts: 1425




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« Reply #1 on: July 28, 2006, 04:13:07 AM »

Hi Dave - Do you have the 20-meter 1/4-wave 75 ohm matching line at the base?  The 20 meter impedance is high, and the 1/4-wave 75 ohm line generally takes care of this.  It is not really necessary on the other bands.  However, a 1.8:1 SWR isn't really a problem unless your radio is turning down power.

Phil - AD5X
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G0DJA
Member

Posts: 4




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« Reply #2 on: July 28, 2006, 06:08:32 AM »

Hi Phil,

Thanks for the reply.

Yes, I have the 75 ohm coax matching section in line.

I've even tried adding 4 radials of 5 metres length to see if that made any difference, but am afrain not.

I could just use the AT-11MP to tune it dwn a bit, but is seems strange that the match is so far off what I would have expected...
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AD5X
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Posts: 1425




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« Reply #3 on: July 28, 2006, 11:50:17 AM »

Hi Dave - Actually, mine is about 1.5:1 on 20M, so not that different.  20M is really the only band where I don't get a 1:1, but I haven't really worried about it since it doesn't really impact anything.  I always have a tuner in-line (MFJ-994B) that I use if necessary, mostly for extending operation on 160 and 80 meters.  You might try posing your question on the Butternnut Antennas Yahoo user's group (http://groups.yahoo.com/group/Butternut-antennas/).  Maybe someone there will have more insight.  

Incidentally, check my website to see how I added 60 meters to my Buttenut.

Phil - AD5X
www.ad5x.com
ad5x@arrl.net
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G0DJA
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Posts: 4




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« Reply #4 on: July 31, 2006, 09:24:04 AM »

Thanks for the additional information.

I've subscribed to the Butternut group, as you suggested, so it will be interesting to see what other people come up with.

I'm using an AT-11MP to tune the vertical, so we'll see if that works out OK and I was interested to see your modification for 60M as I've just sent off to have my Notice of Variation (which expires today) for that band extended to 2010.
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KY7F
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Posts: 2




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« Reply #5 on: August 06, 2006, 08:24:09 PM »

Hi Dave,

I've pretty-much used verticals over the years, and have had excellent luck with my HF6V. One thing in your original post throws a "flag" with me, and that is your ground radial system. My HF6V is ground-mounted, and I have twelve 26' ground radials buried down about 3" as symmetrical as I could get them. This makes a big difference in the tuning, at least at my qth. My soil condx are "average". On 20m, my swr is about 1.1-1.2:1. On 80m, the bandwidth is very narrow at about 20khz. (Note: mine is tuned for the cw parts of the bands.)On the other bands, it'll tune for about 2:1 or less. (I don't have the 160m kit for mine, nor plan to put it on.)

First of all, make sure you have ALL of the original equipment for the antenna, as another poster mentioned. If you have an antenna analyzer, this will be a big help in the tuning process. Personally, I would tune it in sequence like it says in the manual. I might also call Butternut and ask them about any extra tuning requirements if you've added-on several other bands. It sounds like you're making this one into an "HF9V+". I'm sure this is nothing they haven't helped other hams with before.

Another thing, make sure your feedline coax (assuming you're running that) is good. I once had some "spare coax" that I tried to use. My antenna wouldn't tune worth a darn. Replacing it with new cured the problem.

Again, you need to have a good rf ground system with this vertical. If it's "marginal", it's not good enough. Good luck!

Doug KY7F
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K8TDJ
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Posts: 24




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« Reply #6 on: December 11, 2006, 03:11:34 PM »

Hi Dave, The other posters had good suggestions, but my question is, why worry? My roof-mounted HF-6V with a few radials had an swr of 1:5 to 1. That meant I was reflecting a ratio  of 4% ( at 100 watts, thats 4 watts) before the tuner. You'll be fine at 1.8 :1.  73, Jim K8TDJ
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