Return-Path: Received: from mtain-dc02.r1000.mx.aol.com (mtain-dc02.r1000.mx.aol.com [172.29.64.130]) by air-ma05.mail.aol.com (v129.4) with ESMTP id MAILINMA054-b5274d88b9c42c; Tue, 22 Mar 2011 11:01:24 -0400 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-dc02.r1000.mx.aol.com (Internet Inbound) with ESMTP id 3F724380001B1; Tue, 22 Mar 2011 11:01:21 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Q233r-0001rI-0X for rs_out_1@blacksheep.org; Tue, 22 Mar 2011 14:59:55 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Q233p-0001r9-Df for rsgb_lf_group@blacksheep.org; Tue, 22 Mar 2011 14:59:53 +0000 Received: from out1.ip01ir2.opaltelecom.net ([62.24.128.237]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1Q233n-0004Rl-0Q for rsgb_lf_group@blacksheep.org; Tue, 22 Mar 2011 14:59:53 +0000 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AuMAAMdWiE1cEYdU/2dsb2JhbACCYYFkj0cDg3YOjSh3sgeRI4RxdwSBd45g X-IronPort-AV: E=Sophos;i="4.63,225,1299456000"; d="scan'208,217";a="347504173" Received: from unknown (HELO xphd97xgq27nyf) ([92.17.135.84]) by out1.ip01ir2.opaltelecom.net with SMTP; 22 Mar 2011 14:59:27 +0000 Message-ID: <002801cbe8a1$bd59f8c0$0401a8c0@xphd97xgq27nyf> From: "mal hamilton" To: References: <4D83D475.9090609@telus.net> <000b01cbe622$6a23f8d0$8d01a8c0@JAYDELL>, ,<4D86BD6F.8020006@telus.net> <4D8736CB.8040509@telus.net> <4D87E247.5020100@iup.uni-heidelberg.de> <8CDB69E4AD7AA3C-1490-33A81@webmail-m018.sysops.aol.com> Date: Tue, 22 Mar 2011 14:59:27 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2600.0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: LF: Re: Resonate the antenna, or not? Content-Type: multipart/alternative; boundary="----=_NextPart_000_0025_01CBE8A1.BD27EC40" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.1 required=5.0 tests=HTML_FONTCOLOR_UNKNOWN, 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 x-aol-global-disposition: G x-aol-sid: 3039ac1d40824d88b9c10634 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none ------=_NextPart_000_0025_01CBE8A1.BD27EC40 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Markus Have u discovered another method of resonating a vertical type antenn= a other than a large air wound water butt. I was thinking of a smaller coil with ferrite core. In my case I need= about 150 mH not too large but winding a BIG coil is still a BIG job= hi de mal/g3kev ----- Original Message -----=20 From: Markus Vester=20 To: rsgb_lf_group@blacksheep.org=20 Sent: Tuesday, March 22, 2011 11:49 AM Subject: VLF: Resonate the antenna, or not? Hi Stefan,=20 you are raising the interesting question of how important it is to= resonate the antenna. I think it boils down to a comparison of the am= plifier efficiency versus the Q factor of the matching element. Without the matching element, the amplifier (really a switchmode DC-= to-AC converter) has to transfer the reactive power back and forth bet= ween the load and the power supply capacitors. With ideal switches, in= deed nothing would be lost. But with finite efficiency, you will loose= a portion of (1 - eta), eg. 2 % per cycle if your amplifier had 98%= efficiency measured into a real load. On he other hand, if your loop= was resonated using a capacitor with Q-factor 500, you would dissipat= e only 0.2% per cycle in it. Jim's small VLF loop example (0.1 + j 2.2 ohms) had a Q of only 22,= ie. 1/Q =3D 4.5% of the energy is lost per cycle. So the total power= comparison would be 6.5% for the amplifier version versus 4.7% for th= e capacitor - really not that much difference.=20 But as Stefan says, the amplifier would have to be big enough to han= dle all the reactive power (VxA). If fed by a large enough power suppl= y, the very same amplifier could deliver 2.2 kW and raise the radiated= power by a factor of Q, ie. 13 dB. BTW There exists a similar criterion for active receive antennas: If= you have a small capacitive probe and resonate it with a coil, the co= il losses will add in some resistive noise. In a ferrite loopstick, a= (nearly lossless) capacitor is typically used to tune out the inducti= ve reactance, but this makes the antenna narrowband.=20 If on the other hand you do not compensate the reactance, you can st= ill noise-match the preamp to the modulus of the source impedance, at= the penalty that it's own noise temperature will increase by a factor= of Q. For very low preamp noise figures (ie. Tpreamp < Tantenna / Q),= adding the tuning element brings little or no benefit for the system= noise figure. Best wishes, Markus (DF6NM) -----Urspr=C3=BCngliche Mitteilung-----=20 Von: Stefan Sch=C3=A4fer An: rsgb_lf_group@blacksheep.org Verschickt: Di., 22. Mrz. 2011, 0:41 Thema: Re: LF: Loop TX antennas at VLF... Hi Scott,=20 I have some comments, yes.=20 I would try not to resonate the PA but drive it with a H bridge PA= that can handle pretty much reactive power. If you think about Rik's= and Jim's calculation and assume 70 V across the loop, while taking= 32 A, you ( ah, you have 115 V mains?) you may directly rectify the= mains and drive a H bride with it and feed the loop with that switche= d rectified voltage. So you would get about 75 A. That's not a problem= for some well choosen FETs and caps (on the DC side!). Jim and Wolf= already suggested to try that.=20 I know it from my kite antenna: When the wind is poor or if the wire= gets disconnected from the hot end of the coil (this happened 1x), th= e Z of the primary winding (unresonated) is the current limiting facto= r. I am still switching at 300 VDC and 8970 Hz to a bundle of wire of= 50 turns on a water barrel (say 70 cm diameter on the lower side). Th= ere will be heavy reactive currents but that is no problem for the FET= s! The resistive losses in the whole circuit (measured on the 230V AC= side by a true rms multimeter) are below 25 W in such a situation, in= cluding the driver/exciter power. I think it wouldn't be a good idea to try this with a standard audio= amp.... My FETs are simple IRFP460, about 2.5 EUR each. There are no ferrite= parts in the whole circuit! But, unfortunately, i think there is another problem: If you try tha= t with your loop, who will be the next receiving station? What distanc= e? Even if you run 100A rms into that loop (BTW, what is the area?) yo= u will radiate probably below 1 mW ERP...=20 Now reading the above comments from the others ;-) Best 73, Stefan EI/DK7FC, currently in IO62SI41IS Am 21.03.2011 12:30, schrieb Scott Tilley:=20 Hi Rik Thanks for this! I may be comparing apples to oranges alittle (maybe alot). The lo= op I have would only require a 1.8uF cap and this coupled with a highe= r Q makes for a little dicier tuning scenario. I concede this scenari= o is not as bad as I first thought when I thought about this briefly= when Stephan enquired about a possible test from here many months ago= . A careful review of your summary Rik was very helpful, thanks to all= that contributed. =20 The two big , and one minor design issues to get maximum potential= from a loop down at 9KHz will be: 1) Current handling capability of the caps. 2) Tuning capability. 3) Ferrite saturation for the matching xfmr... Or should we use= ferrite? #1 can be resolved, I think, as you have suggested with the use of= LOTS of polypropylene caps... However, #2 will likely be the difficult one and be abit of an eng= ineering challenge as the small loop proposed below may just get away= with course tuning but as you get larger and reduce the Rac the Q goe= s up and so does the tuning criteria. This is where I got stuck with= my original glimpses of thought on this. We can't rely on a good old= vacuum variable so some sort of other idea...=20 Hmmm, how about a special decade type box made of Polypropylene ca= ps? The box could be designed once the loop's characteristics after= installation have been bracketed in... The other downside of polypropylene caps will be there tendency to= drift once you put alot of current into them, so you'll need lots! = This drifting issue could be very problematic as I discovered on 137= with anything other than good transmitting micas with high current ra= tings at the operating frequency. =20 Based on the results of others using mains transformers on 9KHz ma= ybe item #3 is not a big problem after all? Anyone have a comment her= e? Looking forward to more ideas as this is tweaking my interest into= building another tuner. 73 es TU Scott VE7TIL ... ------=_NextPart_000_0025_01CBE8A1.BD27EC40 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Markus
Have u discovered  another method of reso= nating a=20 vertical type antenna other than a large air wound water butt.<= /DIV>
I was thinking of a smaller coil with ferrite= core. In my=20 case I need about 150 mH not too large but winding a BIG coil is still= a BIG job=20 hi
de mal/g3kev
 
----- Original Message -----
Sent: Tuesday, March 22, 2011= 11:49=20 AM
Subject: VLF: Resonate the an= tenna, or=20 not?

Hi Stefan,
 
you are raising the interesting question of how important it is=  to=20 resonate the antenna. I think it boils down to a comparison of the= amplifier=20 efficiency versus the Q factor of the matching element.

Witho= ut the=20 matching element, the amplifier (really a switchmode DC-to-AC conver= ter) has=20 to transfer the reactive power back and forth between the load and= the power=20 supply capacitors. With ideal switches, indeed nothing would be lost= . But with=20 finite efficiency, you will loose a portion of (1 - eta), eg. 2 % pe= r cycle if=20 your amplifier had 98% efficiency measured into a real load. On= he other=20 hand, if your loop was resonated using a capacitor wi= th=20 Q-factor 500, you would dissipate only 0.2% per cycle in it.
 
Jim's small VLF loop example (0.1 + j 2.2 ohms) had a Q of only= 22, ie.=20 1/Q =3D 4.5% of the energy is lost per cycle. So the total power com= parison=20 would be 6.5% for the amplifier version versus 4.7% for the capacito= r - really=20 not that much difference.
 
But as Stefan says, the amplifier would have to be big enough&n= bsp;to=20 handle all the reactive power (VxA). If fed by a large enough power= supply,=20 the very same amplifier could deliver 2.2 kW and raise the radiated= power by a=20 factor of Q, ie. 13 dB.
 
 
BTW There exists a similar criterion for active receive an= tennas: If=20 you have a small capacitive probe and resonate it with a= coil, the=20 coil losses will add in some resistive noise. In a ferrite loop= stick, a=20 (nearly lossless) capacitor is typically used to tune out the induct= ive=20 reactance, but this makes the antenna narrowband.
 
If on the other hand you do not compensate the reacta= nce, you=20 can still noise-match the preamp to the modulus of the source= =20 impedance, at the penalty that it's own noise temperature= will=20 increase by a factor of Q. For very low preamp noise figures (i= e. Tpreamp=20 < Tantenna / Q), adding the tuning element brings littl= e or no=20 benefit for the system noise figure.
 
Best wishes,
Markus (DF6NM)
 
 
 
-----Urspr=C3=BCngliche=20 Mitteilung-----
Von: Stefan Sch=C3=A4fer=20 <schaefer@iup.uni-heidelberg.de>
An:=20 rsgb_lf_group@blacksheep.org
Verschickt: Di., 22. Mrz. 2011, 0:41=
Thema:=20 Re: LF: Loop TX antennas at VLF...

Hi Scott,

I have some comments, yes.
I would try not to resonate the PA but drive it with a H bridge= PA that=20 can handle pretty much reactive power. If  you think about Rik'= s and=20 Jim's calculation and assume 70 V across the loop, while taking 32= A, you (=20 ah, you have 115 V mains?) you may directly rectify the mains and dr= ive a H=20 bride with it and feed the loop with that switched rectified voltage= . So you=20 would get about 75 A. That's not a problem for some well choosen FET= s and caps=20 (on the DC side!). Jim and Wolf already suggested to try that.
<= /DIV>
I know it from my kite antenna: When the wind is poor or if the= wire gets=20 disconnected from the hot end of the coil (this happened 1x), the Z= of the=20 primary winding (unresonated) is the current limiting factor. I am= still=20 switching at 300 VDC and 8970 Hz to a bundle of wire of 50 turns on= a water=20 barrel (say 70 cm diameter on the lower side). There will be heavy= reactive=20 currents but that is no problem for the FETs! The resistive losses= in the=20 whole circuit (measured on the 230V AC side by a true rms multimeter= ) are=20 below 25 W in such a situation, including the driver/exciter power.<= BR>I think=20 it wouldn't be a good idea to try this with a standard audio amp....=
My FETs are simple IRFP460, about 2.5 EUR each. There are no fe= rrite=20 parts in the whole circuit!

But, unfortunately, i think there= is=20 another problem: If you try that with your loop, who will be the nex= t=20 receiving station? What distance? Even if you run 100A rms into that= loop=20 (BTW, what is the area?) you will radiate probably below 1 mW ERP...= =20

Now reading the above comments from the others ;-)

Be= st 73,=20 Stefan EI/DK7FC, currently in IO62SI41IS


Am 21.03.2011 12:30, schrieb Scott=20 Tilley:
Hi Rik

Thanks for this!

I ma= y be=20 comparing apples to oranges alittle (maybe alot).  The loop= I have=20 would only require a 1.8uF cap and this coupled with a higher Q ma= kes for a=20 little dicier tuning scenario.  I concede this scenario is no= t as bad=20 as I first thought when I thought about this briefly when Stephan= enquired=20 about a possible test from here many months ago. A careful review= of your=20 summary Rik was very helpful, thanks to all that contributed. = ;=20

The two big , and one minor design issues to get maximum= potential=20 from a loop down at 9KHz will be:
1) Current handling capabilit= y of the=20 caps.
2) Tuning capability.
3) Ferrite saturation for the ma= tching=20 xfmr...  Or should we use ferrite?

#1 can be resolved,= I think,=20 as you have suggested with the use of LOTS of polypropylene=20 caps...

However, #2 will likely be the difficult one and be= abit of=20 an engineering challenge as the small loop proposed below may just= get away=20 with course tuning but as you get larger and reduce the Rac the Q= goes up=20 and so does the tuning criteria.  This is where I got stuck= with my=20 original glimpses of thought on this.  We can't rely on a goo= d old=20 vacuum variable so some sort of other idea...

Hmmm, how ab= out a=20 special decade type box made of Polypropylene caps?  The box= could be=20 designed once the loop's characteristics after installation have= been=20 bracketed in...

The other downside of polypropylene caps wi= ll be=20 there tendency to drift once you put alot of current into them, so= you'll=20 need lots!  This drifting issue could be very problematic as= I=20 discovered on 137 with anything other than good transmitting micas= with high=20 current ratings at the operating frequency. 

Based on= the=20 results of others using mains transformers on 9KHz maybe item #3= is not a=20 big problem after all?  Anyone have a comment here?

Lo= oking=20 forward to more ideas as this is tweaking my interest into buildin= g another=20 tuner.

73 es TU
Scott
VE7TIL
...
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