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From: <jrusgrove@comcast.net>
To: <rsgb_lf_group@blacksheep.org>
References: <1505616786.3121832.1542660969942.ref@mail.yahoo.com> <1505616786.3121832.1542660969942@mail.yahoo.com> <9661df0f-67e4-41c6-169c-6b947906af64@n1bug.com> <5BF342AB.2060309@posteo.de> <464d4413-511d-6d10-3f9a-cc4c59b12a0d@n1bug.com> <5BF3BA16.5010008@posteo.de> <7600cf68-d27b-62ba-684b-ae6b95faa3d0@n1bug.com> <5BF3F4F0.9020802@posteo.de> <9ff24448-997b-6d1f-5fe4-5b24948d6687@n1bug.com> <BBFBDD1106944C22804920DEDCC454AC@DELL4> <99803338-0335-7e76-b3cb-3f0aa1447972@n1bug.com>
Date: Tue, 20 Nov 2018 09:53:23 -0500
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Subject: Re: LF: WSPR-15 last night
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Paul

Okay on no frost ... at the moment ;~) .

Water in coax / connectors? Dummy load at far end would prove / disprove that. Running out of ideas 
...

Jay


----- Original Message ----- 
From: "N1BUG" <paul@n1bug.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Tuesday, November 20, 2018 9:01 AM
Subject: Re: LF: WSPR-15 last night


> Thanks Jay,
>
> Yes, I shamelessly copied your transformer design. it is a stack of
> three 2.4" cores, 77 material. The cores are Fair-Rite parts
> purchased from Mouser. Each core was wrapped individually, then they
> were stacked and the whole thing wrapped to bind them together.
>
> Good suggestion about moisture in the box. I just now went out and
> pulled the cover off for a look. I see no evidence of frost or
> moisture. I also checked inside the 50 gallon plastic drum
> containing the coil with similar findings.
>
> My present theory is that something common to both LF and MF changes
> resistance as RF warms it. Assuming the change is happening at the
> antenna end of the line, I think it is natural that on MF the
> scopematch would show a reactance change even though it is really
> resistance that is changing. I freely admit to being not too clever
> with a Smith chart, but I believe such is expected with a 1/8
> electrical length feed line.
>
> But if that theory is correct, that leaves the coax itself
> (doubtful), the antenna (not including coil), ground system or some
> environmental factor.
>
> 73,
> Paul
>
>
> On 11/20/18 8:30 AM, jrusgrove@comcast.net wrote:
>> Paul
>>
>> On your website the pix of the transformer looks to be a stack of 3) FT240 cores ... assume 
>> you're
>> using 77 material? If so, this same setup handled a kW of rf at WD2XNS with no problem ... with 
>> one
>> exception.
>>
>> Your pix also shows that you used the same sealed enclosure that I used. On more than one 
>> ocassion
>> the core and inside of the box became heavily 'frosted' causing various impedance matching 
>> problems.
>> Bringing the unit indoors and allowing it to dry out restored normal operation when installed 
>> back
>> out at the antenna. Apparently, the sealed box allowed it to develop it's own internal 
>> 'atmosphere'
>> and the problem occured during periods of wildly changing temperature and humidity. The cure was 
>> to
>> drill a number of holes in the bottom of the enclosure to equalize the 'atmosphere' inside and
>> outside the box. Alternatively, a small 'breather' could be fitted to the case. Don't know that 
>> this
>> is what's going on in your case but it's easy enough to check.
>>
>> One other thought ... did you wrap the 3 cores with tape individually before assembling the 
>> stack?
>> Have seen unexpected problems at HF when not doing that so I now do it as a matter of course.
>>
>> Jay W1VD
>>
>>
>> ----- Original Message ----- 
>> From: "N1BUG" <paul@n1bug.com>
>> To: <rsgb_lf_group@blacksheep.org>
>> Sent: Tuesday, November 20, 2018 7:44 AM
>> Subject: Re: LF: WSPR-15 last night
>>
>>
>>> Hi Stefan,
>>>
>>> On 11/20/18 6:50 AM, DK7FC wrote:
>>>> Don't waste to much time, it is now the best time in the season! Do you
>>>> have a second PA, maybe a QRP version? Still worth to try!
>>>
>>> No, because I had an attack of stupidity. ;-) Instead of saving my
>>> old PA, which would be 3 or 4 dB down from the new one, I took it
>>> apart to experiment with the design. My idea was to upgrade and
>>> modify it to create a spare PA that could be almost equal to the big
>>> one. Seems the idea was OK. :-) But for many reasons I did not
>>> continue that project. I will look around for the box which contains
>>> that project, maybe I can easily put it back to its original form...
>>> if the cat didn't find the box and take too many parts!
>>>
>>>> Maybe you can run a permanent carrier and reach negative R values then?
>>>> The world's energy problems will be finally solved! ;-)
>>>
>>> Hmm, then I will be rich and famous or just famous?
>>> Or neither and remain infamous? ;-)
>>>
>>>> Depends on how you measure the current. A saturating current transformer
>>>> will become warm or hot. Should be easy to check.
>>>> Or it is an iron dust core thermally drifting away. It is useful to
>>>> measure the voltage behind the LPF.
>>>> Just some spontan thoughts.
>>>
>>> OK, thanks for the ideas. I did notice last night something
>>> interesting on MF. The phase was changing slightly during each TX
>>> period. Something to note is that on MF, the coax to the antenna is
>>> almost exactly 1/8 lambda electrical length. So any change in
>>> antenna R shows up mainly as a change in phase at the transmitter.
>>>
>>> So it may be that something in the antenna is changing R on MF also
>>> (with only ~75 watts RF). It's a completely different coil and
>>> transformer so what could it be. I don't know.
>>>
>>> Maybe I am cooking trees? Just joking. It will be some engineering
>>> defect in my RF systems. Good news is there is plenty of snow now,
>>> so any fires around the antenna should be slow to spread. :-)
>>>
>>> 73,
>>> Paul
>