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 <[email protected]> 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
>>
>>
>
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