Return-Path: X-Spam-DCC: paranoid 1233; Body=2 Fuz1=2 Fuz2=2 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=-2.6 required=5.0 tests=BAYES_00,HTML_MESSAGE autolearn=unavailable version=3.1.3 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by paranoid.lipkowski.org (8.13.7/8.13.7) with ESMTP id tBKBBxqD016229 for ; Sun, 20 Dec 2015 12:11:59 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1aAbrK-0006Dn-1f for rs_out_1@blacksheep.org; Sun, 20 Dec 2015 11:09:02 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1aAbrJ-0006De-Ld for rsgb_lf_group@blacksheep.org; Sun, 20 Dec 2015 11:09:01 +0000 Received: from mail-wm0-f44.google.com ([74.125.82.44]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.86) (envelope-from ) id 1aAbqF-0005e2-Db for rsgb_lf_group@blacksheep.org; Sun, 20 Dec 2015 11:09:00 +0000 Received: by mail-wm0-f44.google.com with SMTP id l126so36796166wml.0 for ; Sun, 20 Dec 2015 03:07:39 -0800 (PST) X-DKIM-Result: Domain=gmail.com Result=Good and Known Domain DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; bh=LuvCRH9UqLXXI33OqfGzXoJMk8HFmWZIeyCsxSvr87g=; b=LUPhxnpwlPyjYV1B6WXGb+449FuRQ8zsdI5P1shD/zubIX6FdmVcQHyCSeXhZNRCQp CtoSnjoqJcptPA7M5aFy+eB+RZUQbdQZ0bvgf7WIoS5zVncQw1xTF5kweblnJMQKIeVZ 5E436Lf4Jcyrs5qBOtjvuE/h2W/0MB2yZD+Tg/pB5i7QxoLjXi2OZdE6u3hMmkMmt6Ge c5GlUznVl5VwnkneUhqE+jS3SJuu1RHNhMbe0CKf76Sa4IJzHT/CcjzrJqoifq99XY1W p0jHz65KNm5hSIDNPTsLZKgBkQy0XmvJvbr7ir/vuybe0MFGkbxSK3KO9f5B9EptH34+ 7WAg== MIME-Version: 1.0 X-Received: by 10.194.87.170 with SMTP id az10mr14193181wjb.144.1450609658236; Sun, 20 Dec 2015 03:07:38 -0800 (PST) Received: by 10.28.130.139 with HTTP; Sun, 20 Dec 2015 03:07:38 -0800 (PST) In-Reply-To: <56768741.3010603@posteo.de> References: <1452799271.20151208165824@chriswilson.tv> <566714E9.2040107@posteo.de> <927353708.20151219112829@chriswilson.tv> <56768741.3010603@posteo.de> Date: Sun, 20 Dec 2015 11:07:38 +0000 Message-ID: From: Andy Talbot To: rsgb_lf_group@blacksheep.org X-Scan-Signature: 860e51ceecdf98b32e8eba101d9d472d Subject: Re: LF: Variometer question Content-Type: multipart/alternative; boundary=089e010d867c63183105275261eb 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 X-Scanned-By: MIMEDefang 2.56 on 10.1.3.10 Status: RO X-Status: X-Keywords: X-UID: 5848 --089e010d867c63183105275261eb Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable There's also another issue with having a variometer in the shack, driving a length of transmission line then the loading coil / antenna. I discovered this by chance, and almost wrecked a 73kHz transmitter (back in those days) before realising the error. With a shack variometer you have the following network : Series L (the variometer) Shunt C (the feeder) In my case 12m of RG58 with around 1000pF Series L (the loading coil) Shunt C (the antenna) As with any multi element L/C network you get several poles / zeros which manifest themselves, here, as two points when reactance is zero, but with wildly different transformed impedances. In my case it was around 200 ohms (the wanted one) and also one at 6 ohms or thereabouts. Since I had been adjusting the variometer using phase angle displayed on a scope, guess which point I found first. The amp was a MOSFET audio amplifier bridge and fortunately I spotted very high drain current in time and it survived. The capacitance of a few metres of coax may seem insignificant at LF, but when introduced into part of a multi L/C network it can throw up surprises. Play with a network analysis programme and see what happens Andy G4JNT On 20 December 2015 at 10:47, DK7FC wrote: > Hi Chris, > > Am 19.12.2015 12:28, schrieb Chris Wilson: > >> Christmas last minute work and home jobs have got in the way. >> > Same here. There are always open projects :-) > > It's >> electrically and mechanically complete and working save for the >> microswitch end stops, which I rushed and in the light of day was >> relegated to the bin :) I will redo these in a more elegant manner! >> >> > Uuh, so something must have been wrong connected?! > > Is there any hope the variometer could be in the shack at the amp end >> of the co-ax feed to the loading coil? >> > Yes this is possible too and has been done by some in the past. But it is > not the best choice to match the system. There can be significantly highe= r > losses. Also the voltages across the coax cable can be very high, dependi= ng > on the reactance that you want to compensate. > We are talking about LF, don't we?! > Also you cannot use a transformer any more between coax and loading coil > because it will saturate at higher voltages... > You can use that method for a fine-fine-tuning if you want to have an SWR > of 1:1.00000000000000000000000000000000000000000 but it's not a good choi= ce > to tune a narrow band antenna from 137.7 to 136.17, for example. > > Thanks for your help Stefan, and a happy Christmas and a healthy and >> prosperous New Year, I have to say I am disappointed you haven't put >> an angel at the top of "your" tree ;) All the best I am always amazed >> at your ingenuity and courage in the woods, take care. >> > Maybe i can find an angle before xmas is starting. But we have +16 =C2=B0= C here > these days. > What i thought i could do up there in the tree is a nice breakfast with > some coffee! :-) > When is the time for teatime in UK? And do you really ALL have teatime to > that time there? ;-) Probably not. Same like here, we are not at all eati= ng > Sauerkraut all the time :-) > > 73, Stefan > > --089e010d867c63183105275261eb Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
There's also another issue with having a variometer in= the shack, driving a length of transmission line then the loading coil / a= ntenna. =C2=A0 I discovered this by chance, and almost wrecked a 73kHz tran= smitter (back in those days) =C2=A0before realising the error.

With a shack variometer you have the following network :
<= br>
Series L (the variometer)=C2=A0
Shunt C (the feeder= ) =C2=A0 In my case 12m of RG58 with around 1000pF
Series L (the = loading coil)
Shunt C (the antenna)

As w= ith any multi element L/C network you get several poles / zeros which manif= est themselves, here, as two points when reactance is zero, but with wildly= different transformed impedances.=C2=A0 In my case it was around 200 ohms = (the wanted one) and also one at 6 ohms or thereabouts. =C2=A0 Since I had = been adjusting the variometer using phase angle displayed on a scope, guess= which point I found first. =C2=A0 The amp was a MOSFET audio amplifier bri= dge =C2=A0and fortunately I spotted very high drain current in time and it = survived.

The capacitance of a few metres of coax = may seem insignificant at LF, but when introduced into part of a multi L/C = network it can throw up surprises.=C2=A0 Play with a network analysis progr= amme and see what happens

Andy =C2=A0G4JNT


On 2= 0 December 2015 at 10:47, DK7FC <selberdenken@posteo.de> wrote:
Hi Chris,

Am 19.12.2015 12:28, schrieb Chris Wilson:
Christmas last minute work and home jobs have got in the way.
Same here. There are always open projects :-)

=C2=A0 It's
electrically and mechanically complete and working save for the
microswitch end stops, which I rushed and in the light of day was
relegated to the bin :) I will redo these in a more elegant manner!
=C2=A0 =C2=A0
Uuh, so something must have been wrong connected?!

Is there any hope the variometer could be in the shack at the amp end
of the co-ax feed to the loading coil?
Yes this is possible too and has been done by some in the past. But it is n= ot the best choice to match the system. There can be significantly higher l= osses. Also the voltages across the coax cable can be very high, depending = on the reactance that you want to compensate.
We are talking about LF, don't we?!
Also you cannot use a transformer any more between coax and loading coil be= cause it will saturate at higher voltages...
You can use that method for a fine-fine-tuning if you want to have an SWR o= f 1:1.00000000000000000000000000000000000000000 but it's not a good cho= ice to tune a narrow band antenna from 137.7 to 136.17, for example.

Thanks for your help Stefan, and a happy Christmas and a healthy and
prosperous New Year, I have to say I am disappointed you haven't put an angel at the top of "your" tree ;) All the best I am always am= azed
at your ingenuity and courage in the woods, take care.
Maybe i can find an angle before xmas is starting. But we have +16 =C2=B0C = here these days.
What i thought i could do up there in the tree is a nice breakfast with som= e coffee! :-)
When is the time for teatime in UK? And do you really ALL have teatime to t= hat time there? ;-) Probably not. Same like here, we are not at all eating = Sauerkraut all the time :-)

73, Stefan


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