Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-da03.r1000.mx.aol.com (Internet Inbound) with ESMTP id 1D4683800008C; Thu, 29 Sep 2011 18:35:56 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1R9PBY-0005Vb-Pk for rs_out_1@blacksheep.org; Thu, 29 Sep 2011 23:34:32 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1R9PBX-0005VS-NL for rsgb_lf_group@blacksheep.org; Thu, 29 Sep 2011 23:34:31 +0100 Received: from relay.uni-heidelberg.de ([129.206.100.212]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1R9PBV-0001A0-M3 for rsgb_lf_group@blacksheep.org; Thu, 29 Sep 2011 23:34:31 +0100 Received: from freitag.iup.uni-heidelberg.de (freitag.iup.uni-heidelberg.de [129.206.29.204]) by relay.uni-heidelberg.de (8.14.1/8.14.1) with ESMTP id p8TMYSE0000997 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Fri, 30 Sep 2011 00:34:28 +0200 Received: from [129.206.22.206] (pc206.iup.uni-heidelberg.de [129.206.22.206]) by freitag.iup.uni-heidelberg.de (8.12.11.20060308/8.11.2) with ESMTP id p8TMYRZG018410 for ; Fri, 30 Sep 2011 00:34:27 +0200 Message-ID: <4E84F253.3060204@iup.uni-heidelberg.de> Date: Fri, 30 Sep 2011 00:33:55 +0200 From: =?UTF-8?B?U3RlZmFuIFNjaMOkZmVy?= User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3 MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: <68BE37BD69E54DEE89CEBA8E30E9B94E@PcMinto> <4E484183.9090805@iup.uni-heidelberg.de> <4E494A57.90105@freenet.de> <4E4956DA.1060201@iup.uni-heidelberg.de> <4E49643E.5090708@freenet.de> <4E496FF9.4040608@iup.uni-heidelberg.de> <0A4ED65EC3B244A3BD0DAD6ACFF43793@JimPC> <4E4A5597.4070709@iup.uni-heidelberg.de> <3746D901368F4C139E414F9110153EEE@JimPC> <4E4A9A1F.2060600@iup.uni-heidelberg.de> <1B55B625C3CD4D529EC361D9C5D79D96@JimPC> <4E4AD4C8.8000509@iup.uni-heidelberg.de> <4E4AEF31.5010306@iup.uni-heidelberg.de> <1FF2FAD9854F4890A338A9F862D93FE9@JimPC> <8CE2AD319756ED7-1C20-14370@Webmail-m104.sysops.aol.com> <4E4BC177.6050902@iup.uni-heidelberg.de> <001f01cc5cf9$4b734780$0401a8c0@xphd97xgq27nyf> <4E4BF289.2070500@iup.uni-heidelberg.de> <003301cc5d07$d4e2a840$0401a8c0@xphd97xgq2! 7nyf> <4E4C24FE.8030905@iup.uni-hei! delberg.de> <002501cc5d33$a7f37f90$0401a8c0@xphd97xgq27nyf> <4E84C757.2040605@iup.! uni-heidelberg.de> <8F0D3FDDD6414BE8AC65D5D4B1CFDF1F@konda03bf4520e> In-Reply-To: <8F0D3FDDD6414BE8AC65D5D4B1CFDF1F@konda03bf4520e> X-Spam-Score: 1.4 (+) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001,RATWARE_GECKO_BUILD=1.426 Subject: Re: LF: Ferrite RX antennas Content-Type: multipart/alternative; boundary="------------070904020009050406060908" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: ** X-Spam-Status: No, hits=2.2 required=5.0 tests=CELL_PHONE_BOOST,HTML_20_30, 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-SCOLL-SCORE: 1:2:492260800:93952408 X-AOL-SCOLL-URL_COUNT: 1 x-aol-sid: 3039ac1d404b4e84f2cc5200 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none This is a multi-part message in MIME format. --------------070904020009050406060908 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable X-MIME-Autoconverted: from 8bit to quoted-printable by relay.uni-heidelberg.de id p8TMYSE0000997 Hello Joze, Nice pictures and equipment. But i've never seen you on the band :-(=20 What are you doing now with all the stuff? Do you plan a comeback? :-) 73, Stefan Am 29.09.2011 22:11, schrieb Joze Konda - S52AB: > Very good... > Here I can receive with this my primitive indor ferrite rood antena=20 > (in city) in 2004/2005: YU7AR, OK2BVG, OM2TW, S57A...Simply preamp.=20 > with BF245. > http://lea.hamradio.si/~s52ab/lf_picture/slides/indoor_fer_rood_ant_for= _137khz.html=20 > > 73, Joze s52ab > > ----- Original Message ----- > *From:* Stefan Sch=C3=A4fer > *To:* rsgb_lf_group@blacksheep.org > > *Sent:* Thursday, September 29, 2011 9:30 PM > *Subject:* Re: LF: Ferrite RX antennas > > LF, Jim, Markus, > > I finally finished my preamp for the /p ferrite antenna. It works > excellent and allows to stepless adjust the gain. The design is > very simple, just using a single BF862 like in my separated VLF E > field probe. Amp gain is a good 20 dB. The JFET is not directly > connected to the tuned winding (signal would be to large then with > this FET) but is decoupled with a second untuned winding of just 6 > to 10 turns! I found that this is optimal in my situation. > In the experimental stage i took a cardboard tube to experiment > what could be the best distance to the tuned winding but then i > found that the signal levels strongly depend on the distance of > the center of the rod. So i made the final decoupling coil > movable. Now i use a PVC ring that exactly fits on the ferrite > rod's outher PVC tube (made on a turning machine). Signal levels > can be reduced by > 20 dB if the output winding is moved to the > end of the rod. This will help to prevent RX overloading if the > antenna points to DCF or DLF. So, the best S/N can easily be > obtained :-) > During the construction i had some trouble with oscillations of > the FET that were not so easy to avoid but later i took a longer > cable (3m, that is necessary anyway, to get some distance to the > netbook) and all works fine now! > > BTW i can receive DLF at 153 kHz at 40 dB S/N in 1 Hz just with > that untuned loop, i.e. 6 turns of 4 cm diameter enam. Cu wire on > the FET, without the Ferrite rod! > > I will further investigate about a anti-serial winding between > ground and source, to increase the antenna bandwidth... > > A quick circuit and picture is here: > http://dl.dropbox.com/u/19882028/LF/DK7FC_LF_p_active_ferrite_anten= na.JPG > > So, looking forward to new CW skeds, probably tomorrow i will go > out and try the new RX... > > 73, Stefan/DK7FC > > > Am 18.08.2011 01:16, schrieb mal hamilton: >> Stefan >> Excellent performance for a small ferrite rx antenna. >> You mention that the loop is better than the ferrite antenna >> possibly because physically the loop has a larger signal capture >> area. >> 73 es gl >> de mal/g3kev >> >> ----- Original Message ----- >> *From:* Stefan Sch=C3=A4fer >> *To:* rsgb_lf_group@blacksheep.org >> >> *Sent:* Wednesday, August 17, 2011 9:30 PM >> *Subject:* Re: LF: Ferrite RX antennas >> >> Mal, LF, >> >> Back from /p from JN49IV75OR >> >> Mal, you are the sceptic on ferrite antennas, so pse fasten >> your seat belt before you take a look on this picture: >> http://dl.dropbox.com/u/19882028/LF/G3KEV_on_ferrite_antenna.p= ng >> >> Signal was audible as well: >> http://dl.dropbox.com/u/19882028/LF/G3KEV_audible_on_ferrite_a= ntenna.WAV >> QRB is 796 km. >> Critical for a fast CW QSO but it is evening and QRN was >> high. The ferrite antenna was just 20 cm above the >> ground/soil and 30m RG58 in between. I used the 50 Ohm preamp >> during that test. >> >> Well visible in the picture: Sferics are strongest arround >> 137.7, due to the high antenna Q. There was a frequency >> offset of about 10 Hz but never mind. Below 137.5 kHz i >> assume this is WSPR by PA0A? >> >> A comparison between the 1 m diameter single turn loop was >> done. Both antennas were adjusted to minimise DCF39. My own >> test signal out of 53.8 km was up to 55 dB S/N in 1 Hz on the >> loop without a preamp, audible of course. On the ferrite >> antenna + preamp it was 55 dB S/N too! But there must have >> been QSB due to a skywave component. Hasn't been the best >> time for that test. >> >> Both antennas can't be accurately resonated at 138.8 kHz, and >> have different Q. The ferrite antenna has about twice the Q >> of the loop. When using the loop + preamp, the ADC gets >> heavyly overloaded. Without a preamp the ferrite antenna >> performs about 15 dB worse than the loop. This should be >> solved with a single JFET amp stage. >> >> Will do further tests soon but this ferrite antenna seems to >> become a really useful alternative to any other large >> antenna. It is very well /p and /m. >> >> Looking forward to further improvements and first QSOs. Glad >> to have realised that project in a few days after starting >> the discussion :-)) >> >> If someone follows the discussion and thinks about building >> such an antenna too, just ask if you have questions that >> weren't discussed so far. Maybe this will lead us to new ideas. >> >> Ah, BTW, still no E field shield. Do the experts really think >> that this is necessary? I mean, because i will ever use it in >> a quiet location! >> >> 73, Stefan/DK7FC >> >> >> >> Am 17.08.2011 20:02, schrieb mal hamilton: >>> ok Stefan >>> Nw CQ 137.7 can u receive me >>> de mal/g3kev >>> >>> ----- Original Message ----- >>> *From:* Stefan Sch=C3=A4fer >>> >>> *To:* rsgb_lf_group@blacksheep.org >>> >>> *Sent:* Wednesday, August 17, 2011 5:55 PM >>> *Subject:* Re: LF: Ferrite RX antennas >>> >>> Mal, >>> >>> I know. But anyway one can compare the SNR levels >>> between different antennas. >>> >>> I'll set up a beacon now on 137.73 kHz, testing in QRSS-3. >>> Maybe you want to call CQ or so. If i can receive you, i >>> will send a capture. But i still cannot answer. Am in >>> Darmstadt now, not in Heidelberg. The UHF link for >>> transmitting works just in a range of 5 km and is >>> disabled now. >>> >>> I expect that i need a preamp and will not get the >>> necessary sensitivy now. Anyway i can compare the >>> antennas and check how many dBs are missed. >>> >>> RX QRV in half an hour. Beacon starting at 17:30 UTC >>> >>> 73, Stefan/DK7FC >>> >>> Am 17.08.2011 18:18, schrieb mal hamilton: >>>> Stefan >>>> But what sort of strength do you Receive weak Radio >>>> Amateur signals. That is the real test >>>> Commercial radio stations a different matter with their >>>> Megawatts >>>> de mal/g3kev >>>> >>>> ----- Original Message ----- >>>> *From:* Stefan Sch=C3=A4fer >>>> >>>> *To:* rsgb_lf_group@blacksheep.org >>>> >>>> *Sent:* Wednesday, August 17, 2011 2:26 PM >>>> *Subject:* Re: LF: Ferrite RX antennas >>>> >>>> Hello Markus, Jim, LF, >>>> >>>> Tnx for suggestions. Have to think about that >>>> later. I want to go on in small steps now. >>>> >>>> I added a 100 pF vari-cap which allows to resonate >>>> in the desired range (up to 137.8 kHz and down to >>>> 136.3). >>>> As a first test a added a small winding, just 3 >>>> turns, 3 cm far for the rods end, matched to 50 >>>> Ohm. So now it works as a passive antenna and can >>>> be fed to my RX 50 Ohm input. >>>> This is the complete LF RX arrangement, suitable to >>>> see and hear on 137 wideband: >>>> http://dl.dropbox.com/u/19882028/LF/LF-P%20RX%20RIG.= JPG >>>> >>>> The ferrite antenna is just as broad a the netbook >>>> now. Of course the distance to the netbook must be >>>> increased later. It still has no electric shield >>>> but a suitable housing to protect the Litz winding, >>>> necessary to go on with tests on various locations. >>>> >>>> The DCF-39 strength is 50 dB S/N in 1 Hz while the >>>> antenna (3 dB bandwidth =3D 280 Hz) is tuned to 137.= 0 >>>> kHz (cannot tune to 138.83). The band noise within >>>> the passband is 10 dB above the soundcards noise >>>> but this may be different in a quiet location on a >>>> quiet day. >>>> >>>> This looks all promising to me. I'll try the BF862 >>>> as a preamp soon. >>>> >>>> Will do further tests with a test signal in the >>>> passband and compare this to my 1m diameter single >>>> turn loop. And i will try my 50 Ohm preamp in front >>>> of the RX. >>>> Looking forward to the first QSOs! >>>> >>>> 73, Stefan/DK7FC >>>> >>>> Am 17.08.2011 10:59, schrieb Markus Vester: >>>>> Stefan, Jim, >>>>> you could increase the signal bandwidth without >>>>> compromising SNR by connecting a low impedance >>>>> preamplifier. This technique has been used widely >>>>> and successfully in magnetic resonance imaging >>>>> ("preamp decoupling"). The preamp is designed to >>>>> have an input impedance that differs largely from >>>>> the noise-optimum source impedance, so that you >>>>> can preserve the noise match but create an >>>>> intentional signal mismatch. >>>>> In practice, you would still want to use a >>>>> low-noise FET connected to the high impedance >>>>> point of a parallel resonant antenna. Normally the >>>>> gate input impedance (megohms) is higher than the >>>>> noise optimum (tens of kiloohms), so you would >>>>> have no preamp damping at all. The trick is then >>>>> to lower the input impedance by lossless feedback, >>>>> which has neglegible effect on the noise parameters. >>>>> One configuration is a compromise between common >>>>> source and common gate circuit configuration >>>>> ("Zwischenbasisschaltung"), which can be realised >>>>> by inserting an additional negative-feedback >>>>> winding in the source-to-ground path. This is >>>>> similar to the old regenerative audion, but with >>>>> the feedback coil polarity reversed. Another >>>>> configuration is parallel feedback from drain to >>>>> gate, by intentionally increasing the Miller >>>>> capacitance. >>>>> >>>>> Best regards, >>>>> Markus (DF6NM) >>>>> -----Urspr=C3=BCngliche Mitteilung----- >>>>> Von: James Moritz >>>>> An: rsgb_lf_group >>>>> Verschickt: Mi, 17 Aug 2011 1:13 am >>>>> Betreff: Re: LF: Ferrite RX antennas >>>>> >>>>> Dear Stefan, >>>>> >>>>> Looking good so far... >>>>> >>>>> A Q of 486 is certainly reaching the point where it= becomes inconvenient - >>>>> but remember that it is easy to reduce Q (probably = connecting a preamp, >>>>> putting it in a container, etc, will reduce Q a bit= anyway), and that the >>>>> higher Q is, the better the SNR. So I would test it= as an antenna with a >>>>> preamp - if there is more SNR than you need, you co= uld experiment with some >>>>> damping resistance. >>>>> >>>>> Cheers, Jim Moritz >>>>> 73 de M0BMU >>>>> >>>>> >>>> > -------------------------------------------------------------------= ----- > > No virus found in this message. > Checked by AVG - www.avg.com > Version: 10.0.1410 / Virus Database: 1520/3926 - Release Date: > 09/29/11 > --------------070904020009050406060908 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-MIME-Autoconverted: from 8bit to quoted-printable by relay.uni-heidelberg.de id p8TMYSE0000997 Hello Joze,

Nice pictures and equipment. But i've never seen you on the band :-( What are you doing now with all the stuff? Do you plan a comeback? :-)
73, Stefan

Am 29.09.2011 22:11, schrieb Joze Konda - S52AB:
Very good...
=C2=A0
Here I can receive with this my primitive indor ferrite rood antena (in city) in 2004/2005: YU7AR, OK2BVG, OM2TW, S57A...Simply preamp. with BF245.
http://lea.hamradio.si/~s52ab/lf_picture/slides/in= door_fer_rood_ant_for_137khz.html
=C2=A0
73, Joze s52ab
=C2=A0
----- Original Message -----
Sent: Thursday, September 29, 2011 9:30 PM
Subject: Re: LF: Ferrite RX antennas

LF, Jim, Markus,

I finally finished my preamp for the /p ferrite antenna. It works excellent and allows to stepless adjust the gain. The design is very simple, just using a single BF862 like in my separated VLF E field probe. Amp gain is a good 20 dB. The JFET is not directly connected to the tuned winding (signal would be to large then with this FET) but is decoupled with a second untuned winding of just 6 to 10 turns! I found that this is optimal in my situation.
In the experimental stage i took a cardboard tube to experiment what could be the best distance to the tuned winding but then i found that the signal levels strongly depend on the distance of the center of the rod. So i made the final decoupling coil movable. Now i use a PVC ring that exactly fits on the ferrite rod's outher PVC tube (made on a turning machine). Signal levels can be reduced by > 20 dB if the output winding is moved to the end of the rod. This will help to prevent RX overloading if the antenna points to DCF or DLF. So, the best S/N can easily be obtained :-)
During the construction i had some trouble with oscillations of the FET that were not so easy to avoid but later i took a longer cable (3m, that is necessary anyway, to get some distance to the netbook) and all works fine now!

BTW i can receive DLF at 153 kHz at 40 dB S/N in 1 Hz just with that untuned loop, i.e. 6 turns of 4 cm diameter enam. Cu wire on the FET, without the Ferrite rod!

I will further investigate about a anti-serial winding between ground and source, to increase the antenna bandwidth...

A quick circuit and picture is here: http://dl.dropbox.com/u/19882028/LF/DK7FC_LF_p_active_ferrite_= antenna.JPG

So, looking forward to new CW skeds, probably tomorrow i will go out and try the new RX...

73, Stefan/DK7FC


Am 18.08.2011 01:16, schrieb mal hamilton:
Stefan
Excellent performance for a small ferrite rx antenna.
You mention that the loop is better than the ferrite antenna possibly because physically the loop has a larger signal capture area.
73 es gl
de mal/g3kev
=C2=A0
----- Original Message -----
Sent: Wednesday, August 17, 2011 9:30 PM
Subject: Re: LF: Ferrite RX antennas

Mal, LF,

Back from /p from JN49IV75OR
Mal, you are the sceptic on ferrite antennas, so pse fasten your seat belt before you take a look on this picture: http://dl.dropbox.com/u/19882028/LF/G3KEV_on_fe= rrite_antenna.png

Signal was audible as well: http://dl.dropbox.com/u/19882028/LF/G3KEV_audib= le_on_ferrite_antenna.WAV
QRB is 796 km.
Critical for a fast CW QSO but it is evening and QRN was high. The ferrite antenna was just 20 cm above the ground/soil and 30m RG58 in between. I used the 50 Ohm preamp during that test.

Well visible in the picture: Sferics are strongest arround 137.7, due to the high antenna Q. There was a frequency offset of about 10 Hz but never mind. Below 137.5 kHz i assume this is WSPR by PA0A?

A comparison between the 1 m diameter single turn loop was done. Both antennas were adjusted to minimise DCF39. My own test signal out of 53.8 km was up to 55 dB S/N in 1 Hz on the loop without a preamp, audible of course. On the ferrite antenna + preamp it was 55 dB S/N too! But there must have been QSB due to a skywave component. Hasn't been the best time for that test.

Both antennas can't be accurately resonated at 138.8 kHz, and have different Q. The ferrite antenna has about twice the Q of the loop. When using the loop + preamp, the ADC gets heavyly overloaded. Without a preamp the ferrite antenna performs about 15 dB worse than the loop. This should be solved with a single JFET amp stage.

Will do further tests soon but this ferrite antenna seems to become a really useful alternative to any other large antenna. It is very well /p and /m.

Looking forward to further improvements and first QSOs. Glad to have realised that project in a few days after starting the discussion :-))
If someone follows the discussion and thinks about building such an antenna too, just ask if you have questions that weren't discussed so far. Maybe this will lead us to new ideas.

Ah, BTW, still no E field shield. Do the experts really think that this is necessary? I mean, because i will ever use it in a quiet location!

73, Stefan/DK7FC



Am 17.08.2011 20:02, schrieb mal hamilton:
ok Stefan
Nw CQ 137.7 can u receive me <= /div>
de mal/g3kev
=C2=A0
----- Original Message -----
Sent: Wednesday, August 17, 2011 5:55 PM
Subject: Re: LF: Ferrite RX antennas

Mal,

I know. But anyway one can compare the SNR levels between different antennas.

I'll set up a beacon now on 137.73 kHz, testing in QRSS-3.
Maybe you want to call CQ or so. If i can receive you, i will send a capture. But i still cannot answer. Am in Darmstadt now, not in Heidelberg. The UHF link for transmitting works just in a range of 5 km and is disabled now.

I expect that i need a preamp and will not get the necessary sensitivy now. Anyway i can compare the antennas and check how many dBs are missed.

RX QRV in half an hour. Beacon starting at 17:30 UTC

73, Stefan/DK7FC

Am 17.08.2011 18:18, schrieb mal hamilton:
Stefan
But what sort of strength do you Receive weak Radio Amateur signals. That is the real test
Commercial radio stations a different matter with their Megawatts
de mal/g3kev
=C2=A0
----- Original Message -----
Sent: Wednesday, August 17, 2011 2:26 PM
Subject: Re: LF: Ferrite RX antennas

Hello Markus, Jim, LF,

Tnx for suggestions. Have to think about that later. I want to go on in small steps now.

I added a 100 pF vari-cap which allows to resonate in the desired range (up to 137.8 kHz and down to 136.3).
As a first test a added a small winding, just 3 turns, 3 cm far for the rods end, matched to 50 Ohm. So now it works as a passive antenna and can be fed to my RX 50 Ohm input.
This is the complete LF RX arrangement, suitable to see and hear on 137 wideband: http://dl.dropbox.com/u/19882028/LF/LF-P%20RX%2= 0RIG.JPG

The ferrite antenna is just as broad a the netbook now. Of course the distance to the netbook must be increased later. It still has no electric shield but a suitable housing to protect the Litz winding, necessary to go on with tests on various locations.

The DCF-39 strength is 50 dB S/N in 1 Hz while the antenna (3 dB bandwidth =3D 280 Hz) is tuned to 137.0 kHz (cannot tune to 138.83). The band noise within the passband is 10 dB above the soundcards noise but this may be different in a quiet location on a quiet day.

This looks all promising to me. I'll try the BF862 as a preamp soon.

Will do further tests with a test signal in the passband and compare this to my 1m diameter single turn loop. And i will try my 50 Ohm preamp in front of the RX.
Looking forward to the first QSOs!

73, Stefan/DK7FC

Am 17.08.2011 10:59, schrieb Markus Vester:
Stefan, Jim,
=C2=A0
you could increase the signal bandwidth without compromising SNR by connecting a low impedance preamplifier.=C2=A0This technique has been used widely and successfully in magnetic resonance imaging ("preamp decoupling").=C2=A0The preamp is designed to have an inp= ut impedance that differs largely from the noise-optimum source impedance, so that you can preserve the noise match but create an intentional signal mismatch.
=C2=A0
In practice, you would=C2=A0still=C2=A0want to=C2=A0= use a low-noise FET connected to the high impedance point of a parallel resonant antenna. Normally the gate input impedance (megohms) is=C2=A0hig= her than the noise optimum (tens of kiloohms), so you would have no preamp damping at all. The trick is=C2=A0then to lower the input impedance by lossless feedback, which has neglegible effect on the noise=C2=A0paramete= rs.
=C2=A0
One configuration is a compromise between common source and common gate circuit configuration ("Zwischenbasisschaltung"), which=C2=A0can be realised by inserting an additional negative-feedback winding in the source-to-ground path.=C2=A0T= his is similar to=C2=A0the old=C2=A0regenerative audion, but with the feedbac= k coil polarity reversed. Another configuration is parallel feedback from drain to gate, by intentionally increasing the Miller capacitance.

Best regards,
Markus (DF6NM)
-= ----Urspr=C3=BCngliche Mitteilung-----
Von: James Moritz &l= t;james.moritz@btopenworld.com>
An: rsgb_lf_group &l= t;rsgb_lf_group@blacksheep.org>
Verschickt: Mi, 17 Aug 2011 1:13 am
Betreff: Re: LF: Ferrite RX antennas

Dear Stefan,

Looking good so far...

A Q of 486 is certainly reaching the point where it becomes inconvenient =
-=20
but remember that it is easy to reduce Q (probably connecting a preamp,=20
putting it in a container, etc, will reduce Q a bit anyway), and that the=
=20
higher Q is, the better the SNR. So I would test it as an antenna with a=20
preamp - if there is more SNR than you need, you could experiment with so=
me=20
damping resistance.

Cheers, Jim Moritz
73 de M0BMU=20

No virus found = in this message.
Checked by AVG - = www.avg.com
Version: 10.0.1410 / Virus Database: 1520/3926 - Release Date: 09/29/11

--------------070904020009050406060908--