Return-Path: Received: from mtain-mp05.r1000.mx.aol.com (mtain-mp05.r1000.mx.aol.com [172.29.193.73]) by air-ma01.mail.aol.com (v129.4) with ESMTP id MAILINMA014-b4f24d88e888288; Tue, 22 Mar 2011 14:20:56 -0400 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-mp05.r1000.mx.aol.com (Internet Inbound) with ESMTP id 10F5238000093; Tue, 22 Mar 2011 14:20:50 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Q26BC-0002PL-TD for rs_out_1@blacksheep.org; Tue, 22 Mar 2011 18:19:42 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Q26BC-0002PA-0v for rsgb_lf_group@blacksheep.org; Tue, 22 Mar 2011 18:19:42 +0000 Received: from out1.ip03ir2.opaltelecom.net ([62.24.128.239]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1Q26B9-0007jv-Df for rsgb_lf_group@blacksheep.org; Tue, 22 Mar 2011 18:19:41 +0000 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Av8AAP2EiE1cEYdU/2dsb2JhbACCYYFkj0gDg3YOjSl3sm6RBoRxdwSBd45g X-IronPort-AV: E=Sophos;i="4.63,226,1299456000"; d="scan'208,217";a="341837659" Received: from unknown (HELO xphd97xgq27nyf) ([92.17.135.84]) by out1.ip03ir2.opaltelecom.net with SMTP; 22 Mar 2011 18:19:24 +0000 Message-ID: <003f01cbe8bd$ac49c5d0$0401a8c0@xphd97xgq27nyf> From: "mal hamilton" To: References: <4D83D475.9090609@telus.net> <000b01cbe622$6a23f8d0$8d01a8c0@JAYDELL>, ,<4D86BD6F.8020006@telus.net> <4D8736CB.8040509@telus.net> <4D87E247.5020100@iup.uni-heidelberg.de> <8CDB69E4AD7AA3C-1490-33A81@webmail-m018.sysops.aol.com> <002801cbe8a1$bd59f8c0$0401a8c0@xphd97xgq27nyf> <8CDB6C89A09CC8A-1490-3894C@webmail-m018.sysops.aol.com> Date: Tue, 22 Mar 2011 18:19:24 -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: Re: LF: Re: Resonate the antenna, or not? Content-Type: multipart/alternative; boundary="----=_NextPart_000_003C_01CBE8BD.AC154850" 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: 3039ac1dc1494d88e88208a3 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none ------=_NextPart_000_003C_01CBE8BD.AC154850 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Tnx info Markus I mean use a ferrite core inductor to reduce wire resistance to resona= te the vertical. I have already put 162 turns on a 0.5cm diam barell= 1mm pvc insulated wire and only get 14.5 mH=20 This could be a life time job hi de mal/g3kev =20 ----- Original Message -----=20 From: Markus Vester=20 To: rsgb_lf_group@blacksheep.org=20 Sent: Tuesday, March 22, 2011 4:52 PM Subject: Re: LF: Re: Resonate the antenna, or not? Hi Mal,=20 no, I would not recommend transmitting on a vertical without a reson= ant loading coil, it's not really efficient. A 150 mH coil would not be very difficult to make. For a straight si= ngle layer solenoid, you'd need approximately 950 turns of 0.4 mm magn= et wire on a 0.3 m diameter former. If you really want a larger one,= use about 550 turns of 1 mm wire on a 0.6 m former. Can be done in on= e afternoon ;-) Ferrite or iron can in principle be used reduce the size, but you wi= ll still need a large number of turns and a large core crosssection to= avoid saturation. As ferrites are far from perfect insulators, large= spacings from the wire to the core are required to avoid voltage brea= kdown.=20 Hope to see you soon on Dreamer's Band! Best 73, Markus (DF6NM) -----Urspr=C3=BCngliche Mitteilung-----=20 Von: mal hamilton An: rsgb_lf_group@blacksheep.org Verschickt: Di., 22. Mrz. 2011, 15:59 Thema: LF: Re: Resonate the antenna, or not? Markus Have u discovered another method of resonating a vertical type ante= nna other than a large air wound water butt. I was thinking of a smaller coil with ferrite core. In my case I nee= d 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= between the load and the power supply capacitors. With ideal switches= , indeed 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 dis= sipate 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= handle all the reactive power (VxA). If fed by a large enough power= supply, the very same amplifier could deliver 2.2 kW and raise the ra= diated 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= coil losses will add in some resistive noise. In a ferrite loopstick,= a (nearly lossless) capacitor is typically used to tune out the induc= tive reactance, but this makes the antenna narrowband.=20 If on the other hand you do not compensate the reactance, you can= still noise-match the preamp to the modulus of the source impedance,= at the penalty that it's own noise temperature will increase by a fac= tor of Q. For very low preamp noise figures (ie. Tpreamp < Tantenna /= Q), adding the tuning element brings little or no benefit for the sys= tem 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 wi= re gets disconnected from the hot end of the coil (this happened 1x),= the Z of the primary winding (unresonated) is the current limiting fa= ctor. 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).= There will be heavy reactive currents but that is no problem for the= FETs! 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,= including the driver/exciter power. I think it wouldn't be a good idea to try this with a standard aud= io amp.... My FETs are simple IRFP460, about 2.5 EUR each. There are no ferri= te parts in the whole circuit! But, unfortunately, i think there is another problem: If you try= that with your loop, who will be the next receiving station? What dis= tance? Even if you run 100A rms into that loop (BTW, what is the area?= ) you 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= loop I have would only require a 1.8uF cap and this coupled with a hi= gher Q makes for a little dicier tuning scenario. I concede this scen= ario is not as bad as I first thought when I thought about this briefl= y when Stephan enquired about a possible test from here many months ag= o. A careful review of your summary Rik was very helpful, thanks to al= l that contributed. =20 The two big , and one minor design issues to get maximum potenti= al 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= engineering 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 goes 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 goo= d old vacuum variable so some sort of other idea...=20 Hmmm, how about a special decade type box made of Polypropylene= caps? The box could be designed once the loop's characteristics afte= r 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= maybe item #3 is not a big problem after all? Anyone have a comment= here? Looking forward to more ideas as this is tweaking my interest in= to building another tuner. 73 es TU Scott VE7TIL ... ------=_NextPart_000_003C_01CBE8BD.AC154850 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Tnx info Markus
I mean use a ferrite core inductor to reduce= wire=20 resistance to resonate the vertical. I have already put 162= turns on a=20 0.5cm diam barell 1mm pvc insulated wire and only get 14.5 mH <= /DIV>
This could be a life time job hi
de mal/g3kev
 
----- Original Message -----
Sent: Tuesday, March 22, 2011= 4:52=20 PM
Subject: Re: LF: Re: Resonate= the=20 antenna, or not?

Hi Mal,
 
no, I would not recommend transmitting on a vertical witho= ut a=20 resonant loading coil, it's not really efficient.
 
A 150 mH coil would not be very difficult to make. Fo= r a=20 straight single layer solenoid, you'd need approximately 950 turns= of 0.4 mm=20 magnet wire on a 0.3 m diameter former. If you really want a la= rger=20 one, use about 550 turns of 1 mm wire on a 0.6= m former.=20 Can be done in one afternoon ;-)
 
Ferrite or iron can in principle be used reduce the size, but= you will=20 still need a large number of turns and a large core crosssection to= avoid=20 saturation. As ferrites are far from perfect insulators, l= arge=20 spacings from the wire to the core are required to avoid voltag= e=20 breakdown. 

Hope to see you soon on Dreamer's Band!
 
Best 73,
Markus (DF6NM)


-----Urspr=C3=BCngliche=20 Mitteilung-----
Von: mal hamilton <g3kevmal@talktalk.net><= BR>An:=20 rsgb_lf_group@blacksheep.org
Verschickt: Di., 22. Mrz. 2011,=20 15:59
Thema: LF: Re: Resonate the antenna, or not?

Markus
Have u discovered  another method of re= sonating a=20 vertical type antenna other than a large air wound water butt.
I was thinking of a smaller coil with ferrit= e core. In=20 my case I need about 150 mH not too large but winding a BIG coil is= still a=20 BIG job hi
de mal/g3kev
 
----- Original Message -----
Sent: Tuesday, March 22, 20= 11 11:49=20 AM
Subject: VLF: Resonate the= antenna, 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.

Wit= hout the=20 matching element, the amplifier (really a switchmode DC-to-AC conv= erter) 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 lo= st. But=20 with finite efficiency, you will loose a portion of (1 - eta), eg.= 2 % per=20 cycle if your amplifier had 98% efficiency measured into a real=20 load. On he other hand, if your loop was resonated= using a=20 capacitor with Q-factor 500, you would dissipate only 0.2% pe= r cycle in=20 it.
 
Jim's small VLF loop example (0.1 + j 2.2 ohms) had a Q of on= ly 22, ie.=20 1/Q =3D 4.5% of the energy is lost per cycle. So the total power= comparison=20 would be 6.5% for the amplifier version versus 4.7% for the capaci= tor -=20 really not that much difference.
 
But as Stefan says, the amplifier would have to be big enough=  to=20 handle all the reactive power (VxA). If fed by a large enough powe= r supply,=20 the very same amplifier could deliver 2.2 kW and raise the radiate= d power by=20 a factor of Q, ie. 13 dB.
 
 
BTW There exists a similar criterion for active receive= antennas:=20 If you have a small capacitive probe and resonate it wit= h a coil,=20 the coil losses will add in some resistive noise. In a ferrit= e=20 loopstick, a (nearly lossless) capacitor is typically used to tune= out the=20 inductive reactance, but this makes the antenna narrowband.
 
If on the other hand you do not compensate the reac= tance, you=20 can still noise-match the preamp to the modulus of the source= =20 impedance, at the penalty that it's own noise temperatur= e will=20 increase by a factor of Q. For very low preamp noise figures= (ie.=20 Tpreamp < Tantenna / Q), adding the tuning element br= ings=20 little or no benefit for the system noise figure.
 
Best wishes,
Markus (DF6NM)
 
 
 
-----Urspr=C3=BCngliche=20 Mitteilung-----
Von: Stefan Sch=C3=A4fer <schaefer@iup.uni-heidelberg.de<= /A>>
An:=20 rsgb_lf_grou= p@blacksheep.org
Verschickt:=20 Di., 22. Mrz. 2011, 0:41
Thema: Re: LF: Loop TX antennas at=20 VLF...

Hi Scott,

I have some comments, yes.
I would try not to resonate the PA but drive it with a H brid= ge PA that=20 can handle pretty much reactive power. If  you think about Ri= k'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= drive a H=20 bride with it and feed the loop with that switched rectified volta= ge. So you=20 would get about 75 A. That's not a problem for some well choosen= FETs and=20 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=20 gets disconnected from the hot end of the coil (this happened 1x),= the Z of=20 the 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 multimet= er) are=20 below 25 W in such a situation, including the driver/exciter power= .
I=20 think it wouldn't be a good idea to try this with a standard audio= =20 amp....
My FETs are simple IRFP460, about 2.5 EUR each. There are no= ferrite=20 parts in the whole circuit!

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

Now reading the above comments from the others ;-)

= Best 73,=20 Stefan EI/DK7FC, currently in IO62SI41IS
<= BR>

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

Thanks for this!

I= may 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= makes for=20 a little dicier tuning scenario.  I concede this scenario= is not as=20 bad as I first thought when I thought about this briefly when St= ephan=20 enquired about a possible test from here many months ago. A care= ful review=20 of your summary Rik was very helpful, thanks to all that=20 contributed. 

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

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

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

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

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

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

Looking forw= ard to=20 more ideas as this is tweaking my interest into building another= =20 tuner.

73 es=20 TU
Scott
VE7TIL
...
<= /DIV>=
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