Return-Path: Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by klubnl.pl (8.14.4/8.14.4/Debian-8+deb8u2) with ESMTP id wAODkOAB021648 for ; Sat, 24 Nov 2018 14:46:26 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1gQYC2-0000px-Im for rs_out_1@blacksheep.org; Sat, 24 Nov 2018 13:41:54 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1gQYC2-0000po-0E for rsgb_lf_group@blacksheep.org; Sat, 24 Nov 2018 13:41:54 +0000 Received: from sonic317-27.consmr.mail.bf2.yahoo.com ([74.6.129.82]) by relay1.thorcom.net with esmtp (Exim 4.91_59-0488984) (envelope-from ) id 1gQYC0-0004Io-3R for rsgb_lf_group@blacksheep.org; Sat, 24 Nov 2018 13:41:52 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=aol.com; s=a2048; t=1543066909; bh=yy2pnxwr4lWJaILpIgfze/XIlnh+i8uLmIdkT2h4PYw=; h=Date:From:To:Subject:References:From:Subject; b=At1OCS2fdULexXDMUy4aYw2k+axdRXFVsFkWKx699iThmRxXkJMJHkks+IH67/yabl7eqfo9DXS3q0LCkJwxZ3XHUTsoehmygvoXP29t5UI7teQim+AEUOMCIwp3QS+gZlkGIZMjNC4tk03lP3amB7lXtPG+u87TqANiqaEZVtgGfRr3EwOKtAC/CiVoXC4X0JIlr4sdJzOD9j0JY4/deqB0THL0Ah0HfuhpAOoXuUGtZI/p0P+aiB79SDr6vxTmK2XepClCS0fnuLBzI12HJqhbKtPNKVbJjutOEf7DJ63RFopPBIKDS/U1WyaWnQ8qs7Zc5VVDN+beSTXkkSrmVQ== X-YMail-OSG: ADX48gsVM1m_BGA98z9bugZpVZhuf0IMSQCTIfziSdfBuTUcoACvvplD0eWQIcf 7VoTRNEsZsxrIzrajaFCJaq8l4ralp6LQ3IfiDsSNmuekzbc6eFSBpX6yfHI_D4CrTwoUQicwUBr boeaKxvUEvdYistEUZo7fx9RxJFgvoSHZpCqTU0w8qt1ehd.R_NYtGSXedZPpRYk5E1y2972pLhG BphT3d_Jyi9_hzgHXrDmg0tY.nuOpSGu4TdLVVOLcAX8WY49hWJqTw.Wuk7_tv8RmyZSS8.IZsKM BpdAdemxdRi2r3zUnn2IMQJVDd2xW8xUe07B2TXPsQnc6zJiprEu.x9DVnpekAoq_ufwLM3nKR3F Hd7MAtaPs.SDhBJEMl5GEdtsZ2SDoXtDgHtSSQ3JTxBSLpL1wPCZ6.xd7nKUdFNavAKuU.P9CXIT x7x6Hj7Lq4jIXWnKnxVzY.gOp05JYN6LkFTnf3GZ_2w90lwAy1kQ4okq.FdY7Sc7KyXAkiylGCHk D44bXO6Ad0emlem0PyqdCuZSg2ezfBjCPU0UJfWGTA0jlbYqHpNxfnbH8vB3G6RwaUwM_gVFA1xP WffE0EBq_t4cjmFK2Wmp.6Dmswx60Ij0d9ZAB1Gm5SRh40nYd8IwVhR1m6jCJ5QVXM30YDzR6ZZn eKfS0qPyAPaf8CXcUFzeV85cIfnlzGidZrxNUOC0JJuzjGtmNv71W_vIUSXAvA.3T6xaFCi8yTMc WSLsYo3zXElzj6QcKO8qLqduYV0ZksOmVTtmKPGSJTgjh5zys9d.Z_g33pT1vT6AuL.vIvGRQErT KjN93L9pPtguk.V2X4mT9rYGcU5HtYUYUt3lMG5wvWBt5njHyFmLvtbE2PHmkIgHOHpsjo42lP3j 9q5hTF32UfJVoNFCwkYXrkyZfRToSw2tu_c2b.7AYxmsdhSiLWmaQ1U5whpt_6KyuadKct._exGf 58OkGAy55bcK7hCIboK0AjDUkzPf6h12zTelE4hCx_VPST_8RP98IIB8jnA-- Received: from sonic.gate.mail.ne1.yahoo.com by sonic317.consmr.mail.bf2.yahoo.com with HTTP; Sat, 24 Nov 2018 13:41:49 +0000 Date: Sat, 24 Nov 2018 13:41:46 +0000 (UTC) From: Markus Vester To: rsgb_lf_group@blacksheep.org Message-ID: <535225399.5427524.1543066906844@mail.yahoo.com> MIME-Version: 1.0 References: <535225399.5427524.1543066906844.ref@mail.yahoo.com> X-Mailer: WebService/1.1.12729 aolwebmail Mozilla/5.0 (Windows NT 10.0; WOW64; Trident/7.0; Touch; rv:11.0) like Gecko X-Spam-Score: 0.0 (/) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has NOT identified this incoming email as spam. The original message has been attached to this so you can view it or label similar future email. If you have any questions, see @@CONTACT_ADDRESS@@ for details. Content preview: Hi Paul, >> It's a physically small FET and maybe was not screwed down tight enough with the Sil-Pad interface,   Same thing happened here a few years ago during an attempt to melt off a thick layer of hoar f [...] Content analysis details: (0.0 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [74.6.129.82 listed in list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (markusvester[at]aol.com) 0.0 HTML_MESSAGE BODY: HTML included in message 0.0 T_DKIM_INVALID DKIM-Signature header exists but is not valid X-Scan-Signature: 92b6515a4252c45136e975e6745a1e0d Subject: Re: LF: No 2200m TX tonight Content-Type: multipart/alternative; boundary="----=_Part_5427523_711018843.1543066906842" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: *** X-Spam-Status: No, hits=3.2 required=5.0 tests=FORGED_MUA_MOZILLA,HTML_20_30, HTML_MESSAGE autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false ------=_Part_5427523_711018843.1543066906842 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Hi Paul, >> It's a physically small FET and maybe was not screwed down tight enough = with the Sil-Pad interface, =C2=A0 Same thing happened here a few years ago during an attempt to melt off a th= ick layer of hoar frost from the antenna.=C2=A0It almost worked and I could= see the resonance creeping=C2=A0up=C2=A0but then the PA died. At the time,= the=C2=A0four BUZ111 devices in my 300 W class-D=C2=A0were bolted to sil-p= ads using=C2=A0M3 nylon screws.=C2=A0Due to increased dissipation with=C2= =A0reactive load,=C2=A0the plastic became soft enough to release thermal co= ntact. After FET replacement, I went to metal bolts and insulation washers,= with no such problem since. This was actually the one and only FET that=C2= =A0I lost in my LF career (knock on wood). As capacitance is not a big issue at LF you could also solder=C2=A0your FET= to a copper heatspreader plate and=C2=A0use a larger=C2=A0pad to a grounde= d heatsink. Or use a configuration with grounded drains and negative supply= and take off the output from the source pin. You'll need to use an input= =C2=A0transformer=C2=A0with a gate-source secondary but that's a good idea = anyway.=20 Regarding dummy loads for LF: I've been using=C2=A0a=C2=A0coffee maker or a= toaster, with 1 kW at 230 V being close to 50 ohms, and negligible reactan= ce. Just make sure to use an=C2=A0older one containing no=C2=A0stupid and u= nnecessary=C2=A0microprocessor. Albeit=C2=A0American 120 V devices may=C2= =A0have less favourable impedances.=C2=A0 Best 73, Markus -----Urspr=C3=BCngliche Mitteilung----- Von: N1BUG An: rsgb_lf_group Verschickt: Sa, 24. Nov. 2018 12:48 Betreff: Re: LF: No 2200m TX tonight Hi Markus, That is very interesting. It changes about 25 % during the first 2-3 minutes, then it seems to settle down and not change any more. It could be moisture somewhere, but any moisture here is solid ice or frost now. I did not find any ice or frost in the transformer box or the variometer. Could be insulators or something with the antenna itself. I don't see any "fuzz" on the scomematch voltage trace so I think (hope) nothing is arcing. What worried me is this did not happen last winter so something has changed. Everything accumulates some dirt here because of blowing dust, smoke, etc. I wonder if a small amount of dirt on insulators plus moisture can combine to make funny things happen. Anyway I examined the little PA and it seems to have died due to poor thermal interface between FET and heatsink. It's a physically small FET and maybe was not screwed down tight enough with the Sil-Pad interface, which was also a previously used one. Normally I do not like to put drain voltage on the heatsink but as an experiment for this little PA (which is totally an experiment itself, but served me very well last winter) I will isolate the heat sink from the chassis/PCB and mount the little FET directly to it. The thermal resistance would be much lower! I think this is fine so long as nothing shorts the heat sink to ground. In that case some fuses die. ;-) This would add some pf of capacitance between drain and ground but it would be in parallel with the quite large C of the Class E tank, probably not much difference at 137 kHz! Parts to repair the big PA should arrive Wednesday. 73, Paul On 11/23/18 4:29 PM, Markus Vester wrote: > Hi Paul, >=20 > sorry to read that. Have pity on the poor FETs! >=20 > You mentioned that the antenna resistance is gradually decreasing > (i.e. improving) during longer transmissions. I often see that > effect here, with the current rising by say 20 % during the first > few minutes. I've put it down to moisture or dew around the coil > and insulators (tiny little polycarbomnnate pencil tubes), which > evaporates as things warm up. It is more prominent during cold > damp weather, and much more so with the very high antenna > impedance at VLF than at LF. >=20 > Good luck, Markus >=20 >=20 > -----Urspr=C3=BCngliche Mitteilung----- Von: N1BUG =20 > An: rsgb_lf_group@blacksheep.org =20 > Verschickt: Fr, 23. Nov. 2018 22:12 Betreff: LF: No 2200m TX > tonight >=20 > No transmissions from me this night. The little amplifier has > died. I think it may be related to this resistance change in the > antenna which is getting worse and worse. >=20 > I'm going back to MF for this night, sorry! >=20 > 73, Paul ------=_Part_5427523_711018843.1543066906842 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Hi Paul,

>> It's a physically s= mall FET and maybe was not screwed down tight enough with the Sil-Pad inter= face,
 
Same thing happened here a few years ago during an attem= pt to melt off a thick layer of hoar frost from the antenna. It almost= worked and I could see the resonance creeping up but then the PA= died. At the time, the four BUZ111 devices in my 300 W class-D w= ere bolted to sil-pads using M3 nylon screws. Due to increased di= ssipation with reactive load, the plastic became soft enough to r= elease thermal contact. After FET replacement, I went to metal bolts and in= sulation washers, with no such problem since. This was actually the one and= only FET that I lost in my LF career (knock on wood).

As capac= itance is not a big issue at LF you could also solder your FET to a co= pper heatspreader plate and use a larger pad to a grounded heatsi= nk. Or use a configuration with grounded drains and negative supply and tak= e off the output from the source pin. You'll need to use an input tran= sformer with a gate-source secondary but that's a good idea anyway.
Regarding dummy loads for LF: I've been using a coffee make= r or a toaster, with 1 kW at 230 V being close to 50 ohms, and negligible r= eactance. Just make sure to use an older one containing no stupid= and unnecessary microprocessor. Albeit American 120 V devices ma= y have less favourable impedances. 

Best 73,
Markus

-----Urspr=C3=BCngliche Mitteilung-= ----
Von: N1BUG <paul@n1bug.com>
An: rs= gb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt:= Sa, 24. Nov. 2018 12:48
Betreff: Re: LF: No 2200m TX tonigh= t

Hi Mark= us,

That is ve= ry interesting. It changes about 25 % during the first 2-3
minutes, then it seems to settle down and not change any more= . It
could be moisture somewhere, but any moi= sture here is solid ice or
frost now. I did n= ot find any ice or frost in the transformer box or
the variometer. Could be insulators or something with the antenna
itself. I don't see any "fuzz" on the scomematch= voltage trace so I
think (hope) nothing is a= rcing.

What wo= rried me is this did not happen last winter so something has
changed. Everything accumulates some dirt here because of b= lowing
dust, smoke, etc. I wonder if a small = amount of dirt on insulators
plus moisture ca= n combine to make funny things happen.

Anyway I examined the little PA and it seems to ha= ve died due to
poor thermal interface between= FET and heatsink. It's a physically
small FE= T and maybe was not screwed down tight enough with the
Sil-Pad interface, which was also a previously used one.

Normally I do not like= to put drain voltage on the heatsink but as
= an experiment for this little PA (which is totally an experiment
itself, but served me very well last winter) I will i= solate the heat
sink from the chassis/PCB and= mount the little FET directly to it.
The the= rmal resistance would be much lower! I think this is fine so
long as nothing shorts the heat sink to ground. In that cas= e some
fuses die. ;-) This would add some pf = of capacitance between drain
and ground but i= t would be in parallel with the quite large C of the
Class E tank, probably not much difference at 137 kHz!

Parts to repair the big P= A should arrive Wednesday.

73,
Paul


On 11/23/18 4:29 PM,= Markus Vester wrote:
> Hi Paul,
>
> sorry to rea= d that. Have pity on the poor FETs!
>
> You mentioned that the antenna resistance i= s gradually decreasing
> (i.e. improving) = during longer transmissions. I often see that
> effect here, with the current rising by say 20 % during the first
> few minutes. I've put it down to moisture o= r dew around the coil
> and insulators (ti= ny little polycarbomnnate pencil tubes), which
> evaporates as things warm up. It is more prominent during cold
> damp weather, and much more so with the very = high antenna
> impedance at VLF than at LF= .
>
> Go= od luck, Markus
>
>
> -----Urspr=C3=BCngliche M= itteilung----- Von: N1BUG <paul@n1bug.com>
> An: rsgb_= lf_group@blacksheep.org <rsgb_lf_group@blacksheep.org>
> Verschickt: Fr, 23. Nov. 2018 22:12 Betreff:= LF: No 2200m TX
> tonight
>
> No transmissions fr= om me this night. The little amplifier has
&g= t; died. I think it may be related to this resistance change in the
> antenna which is getting worse and worse.
>
> I'm going= back to MF for this night, sorry!
>
> 73, Paul

------=_Part_5427523_711018843.1543066906842--