From: Rob Renoud <k3rwr@md.metrocast.net>
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Date: Mon, 3 Dec 2018 11:01:03 -0500
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References: <0d2ac752-44f5-e503-e2a0-a8b4c841bcee@n1bug.com> <5C052984.8030902@posteo.de>
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To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: More on unstable antenna R
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Hi Paul,

Can you provide the values of “normal” X and R and also where and how you are measuring those values? 

73,
Rob

> On Dec 3, 2018, at 08:03, DK7FC <selberdenken@posteo.de> wrote:
> 
> Hi Paul,
> 
> How do you measure your antenna current? I know, the scope. But do you measure across a small shunt resistor or do you use a current xfmr or something else?
> 
> 73, Stefan
> 
> Am 03.12.2018 12:49, schrieb N1BUG:
>> Hi LF,
>> 
>> During past days I did some more investigating about that slow
>> antenna R change during Tx. This is making me a little crazy. I
>> don't like RF mysteries!
>> 
>> During a 2 minute Tx at 200W, antenna system R reduces about 20%
>> from beginning to end of Tx.
>> 
>> During a 2 minute Tx at 100W, antenna system R reduces about 20%
>> from beginning to end of Tx.
>> 
>> During a 2 minute Tx at 50W, antenna system R *increases* about 3%
>> from beginning to end of Tx!
>> 
>> There is almost no shift in X.
>> 
>> I went over everything I could get to (matching xfmr, loading coil,
>> connections between them, etc.) using a IR heat measuring gun. I did
>> not find anything warming up during a long Tx period. It's all cold.
>> 
>> I see a similar change happening on MF where I use a completely
>> separate xfmr and loading coil.
>> 
>> This may be a clue, but I don't know what it means. I have other
>> antennas around. All those cables come into the basement where there
>> is a disconnect point. All can be disconnected from the short cables
>> which run up into the radio rooms. If I disconnect all other cables
>> at that point, then the LF antenna R change during Tx is about 10%,
>> half what it is usually. The R at the start of a Tx period is the
>> same as always, but it does not decrease as much during the Tx period.
>> 
>> I tried connecting the coax shield to the LF antenna ground. That
>> did not make any difference.
>> 
>> Just trying to think of possible explanations...
>> 
>> Broken or bad connection somewhere up on the top hat of the antenna?
>> Seems something should fall down if so, but it hasn't yet. :)
>> 
>> Bad connection in the ground system? All above ground connections
>> are secure. Below ground connections are not accessible in winter
>> but they are heavy solid copper conductors, mostly exothermic welded
>> connections. The one exception is the heavy solid wire which runs
>> from the xfmr secondary down to the underground wire / center ground
>> rod. It is clamped, not welded. But I used three clamps, very tight
>> and with anti-oxidant paste. This connection is just one year old.
>> 
>> Ground return currents through some other path which is not stable?
>> I am sure I make RF currents in the power lines, etc.  but...???
>> 
>> Does anyone see a clue here?
>> 
>> 73,
>> Paul
>> 
>>   
>